Western tiger salamander (Ambystoma mavortium): COSEWIC assessment and status report 2012

• Southern Mountain population
• Prairie / Boreal population

Southern Mountain population – Endangered
Prairie / Boreal population – Special Concern
2012

Table of Contents

Document Information

• COSEWIC Assessment Summary
• COSEWIC Executive Summary
• Technical Summary - Southern Mountain population
• Technical Summary - Prairie / Boreal population
• Wildlife Species Description and Significance
  • Name and Classification
  • Morphological Description
  • Population Spatial Structure and Variability
  • Designatable Units
  • Special Significance
• Distribution
  • Global Range
  • Canadian Range
  • Extent of Occurrence and Area of Occupancy
  • Search Effort
• Habitat
  • Habitat Requirements
  • Habitat Trends
• Biology
  • Life Cycle and Reproduction
  • Survivorship and Generation Time
  • Physiology and Adaptability
  • Dispersal and Migration
  • Interspecific Interactions
• Population Sizes and Trends
  • Sampling Effort and Methods
  • Abundance
  • Population Trends
  • Population Fluctuations
  • Fragmentation of Populations
  • Rescue Effect
• Threats and Limiting Factors
  • Habitat Loss, Conversion and Fragmentation
  • Road Mortality
  • Introduced Species: Fish
  • Introduced Species: Bullfrogs
  • Agriculture and Chemical Contaminants
  • Disease
  • Number of Locations
• Protection, Status, and Ranks
  • Legal Protection and Status
  • Non-Legal Status and Ranks
  • Habitat Protection and Ownership
• Acknowledgements and Authorities Contacted
  • Authorities contacted
• Information Sources
• Biographical Summary of Report Writer
• Collections Examined

List of Figures

• Figure 1. North American distribution of the Western Tiger Salamander (Ambystoma mavortium) with its subspecies, and the Eastern Tiger Salamander (Ambystoma tigrinum). Figure adapted from Schock (2001) and Petranka (1998).
• Figure 2. Gray Tiger Salamander, Ambystoma mavortium diaboli; typical colouration of adult salamanders: older salamanders may show regression of dark markings (right) compared to younger individuals (left) (photos by A. Didiuk).
• Figure 3. Blotched Tiger Salamander, Ambystoma mavortium melanostictum, from Alberta; typical colouration. Upper left – recently metamorphosed juvenile (with slight evidence of gills lower left). Upper right - Mottling on belly of a terrestrial adult from Alberta; Lower right: large pedomorphic (neotenic) individual from Tyrell Lake compared to smaller larvae. Photos by A. Whiting.
• Figure 4. Distribution of Western Tiger Salamander occurrences in British Columbia. Shown are the extent of occurrence and index of area of occupancy (for breeding sites alone; 58 cells = 232 km²). Map prepared by A. Whiting.
• Figure 5. Canadian distribution of all occurrences of Western Tiger Salamander, showing the Southern Mountain DU in the west and Prairie DU in the east. Green shading indicates the total extent of occurrence (572,490 km²). Map prepared by A. Whiting.
• Figure 6. Distribution of water bodies that have been stocked with game fish in Alberta since 1920 (blue) and known Western Tiger Salamander records from central and southern Alberta (red). Fish stocking is similarly prevalent in British Columbia, Saskatchewan, and Manitoba, but data were not available for detailed mapping. Map prepared by A. Whiting.

List of Appendices

• Appendix 1: Threats Calculator results for the Southern Mountain population of the Western Tiger Salamander in British Columbia (February 2012).
• Appendix 2: Threats Calculator results for the Prairie / Boreal population of the Western Tiger Salamander (September 2012).

Document Information

COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows:

COSEWIC. 2012. COSEWIC assessment and status report on the Western Tiger SalamanderAmbystoma mavortium in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xv + 63 pp.

Previous report(s):

COSEWIC. 2001. COSEWIC assessment and status report on the tiger salamander Ambystoma tigrinum in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 33 pp.

Schock, D.M. 2001. COSEWIC assessment and status report on the tiger salamander Ambystoma tigrinum in Canada, in COSEWIC assessment and status report on the tiger salamander Ambystoma tigrinum in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. 1-33 pp.

Production note:
COSEWIC would like to acknowledge Arthur Whiting for writing the status report on the Western Tiger Salamander, Ambystoma mavortium, in Canada, prepared under contract with Environment Canada. This report was overseen and edited by Kristiina Ovaska, Co-chair of the COSEWIC Amphibians and Reptiles Specialist Subcommittee.

For additional copies contact:

COSEWIC Secretariat
c/o Canadian Wildlife Service
Environment Canada
Ottawa, ON
K1A 0H3

Tel.: 819-953-3215
Fax: 819-994-3684
COSEWIC E-mail
COSEWIC Website

Également disponible en français sous le titre Évaluation et Rapport de situation du COSEPAC sur la Salamandre tigrée de l’Ouest (Ambystoma mavortium) au Canada.

Cover illustration/photo:
Western Tiger Salamander -- Photo by A. Whiting.

© Her Majesty the Queen in Right of Canada, 2011.
Catalogue No. CW69-14/658-2013E-PDF
ISBN 978-1-100-22005-5

COSEWIC
Assessment Summary

COSEWIC
Executive Summary

Western Tiger Salamander
Ambystoma mavortium

Southern Mountain population
Prairie / Boreal population

Wildlife Species Description and Significance

Western Tiger Salamanders are among the largest salamanders in North America and are top predators in the largely fishless ponds and lakes where they occur. Terrestrial adults have a blotched, barred or reticulate pattern of yellow or off-white on a dark background. Genetic and morphological evidence indicates that the Western Tiger Salamander, consisting of several subspecies, is a separate species from the Eastern Tiger Salamander, Ambystoma tigrinum, with which it was previously combined as a single species. Much of the older literature does not necessarily distinguish the Western Tiger Salamander from the Eastern Tiger Salamander, as currently recognized.

Distribution

Western Tiger Salamanders have a wide distribution in arid interior regions of western North America. They occur along the border of the Prairie ecozone in Alberta, east to the Red River in Manitoba, south into western Minnesota and down to Texas, west along the border of Mexico and then north through Arizona and along the eastern slopes of the Rocky Mountains north to Alberta. There is a disjunct distribution in northern Oregon, Idaho and through Washington into the southern Okanagan region of British Columbia. Tiger salamanders in British Columbia are disjunct from populations in the remainder of Canada and occur in the Southern Mountain ecozone, whereas the remainder of the Canadian distribution occurs in the Prairie ecozone in Alberta, Saskatchewan and Manitoba. This distribution is likely the result of post-glacial expansion into Canada from at least two points on either side of the Rocky Mountains.

Habitat

Western Tiger Salamanders occupy a variety of open habitats, including grasslands, parkland, subalpine meadows, and semi-deserts. Key habitat features include sandy or friable (crumbly) soils surrounding semi-permanent to permanent water bodies lacking predatory fish. Terrestrial Western Tiger Salamanders burrow actively into soil or utilize small mammal burrows for refuges and over-wintering. Breeding habitats must hold water for the 3 to 7 months required to complete larval development. Populations of completely aquatic neotenic adults (animals that retain larval form after sexual maturity) are occasionally found in cool, fishless lakes.

Biology

Western Tiger Salamanders migrate to breeding sites in wetlands or lakes following spring rains soon after ice-off. Females lay eggs singly or in small clusters attached to twigs or stems of emergent plants below the water’s surface. Juveniles migrate en mass from breeding sites into terrestrial habitats in late summer. Males may reach sexual maturity in their second year, while females mature a year or two later. Generation time is approximately 5 - 6 years.

Both larvae and adults are carnivorous and feed on a wide range of small prey. Western Tiger Salamanders do not fare well where predaceous fish have been introduced, or are naturally occurring, as all life stages are preyed upon.

Population Sizes and Trends

Population sizes and trends are poorly known, and numbers of adults may vary considerably among sites and years. There is an inferred decline in the number and size of populations in the Southern Mountain region in British Columbia, where continued habitat loss, habitat alteration, and introduced species threaten the persistence of populations.

Outside of British Columbia, little is known about the occurrences of Western Tiger Salamanders. Anecdotal reports suggest that the species persists over relatively wide areas of the prairie provinces. Mass mortalities, primarily due to disease and road kill, are reported sporadically in localized areas.

Threats and Limiting Factors

Tiger salamanders face the same pressures and threats as other amphibian species with separate requirements for terrestrial adults and aquatic larvae. Over much of the species’ Canadian range, there are immense pressures from loss, degradation and fragmentation of habitat. In the Prairies, a change has occurred in land use from grazing and low-scale agriculture to large-scale farming and conversion of habitat to accommodate growing urban populations and expansion of oil and gas developments. Within the core area of the species’ distribution in British Columbia, in the Okanagan Valley, there has been rapid habitat loss due to housing and vineyard developments with associated pollutant run-off. The introduced American Bullfrog poses an additional threat in this region. Increasing human populations and road densities have greatly increased the potential for road mortality during seasonal migrations between breeding sites and terrestrial overwintering and foraging habitats. Fish stocking for recreational fishing, aquaculture, and mosquito-control can have severe impacts on tiger salamander populations and continue to occur throughout the species’ Canadian range.  The emergence of infectious diseases, specifically the widespread Ambystoma tigrinum virus, can decimate local populations.

Protection, Status, and Ranks

The Southern Mountain population of the Western Tiger Salamander in British Columbia is listed federally as Endangered and is on Schedule 1 under the Species at Risk Act. Approximately 16% of breeding sites of this population are within protected areas, and an additional 27% receive some protection through voluntary stewardship efforts; the majority of the sites, however, are on unprotected private lands.

Tiger salamanders in Alberta, Saskatchewan and Manitoba, as the Prairie / Boreal population, were previously assessed by COSEWIC as Not at Risk, but this assessment included Eastern Tiger Salamanders in Manitoba. There is no specific protection for tiger salamander habitat, but there are records of tiger salamanders from various parks and protected areas.

Technical Summary - Southern Mountain population

Ambystoma mavortium
Western Tiger Salamander
Southern Mountain population
Range of occurrence in Canada: British Columbia

Demographic Information

Extent and Occupancy Information

Quantitative Analysis

Threats (actual or imminent, to populations or habitats)

Rescue Effect (immigration from outside Canada)

Status History

Status and Reasons for Designation

Applicability of Criteria

Technical Summary - Prairie / Boreal population

Ambystoma mavortium
Western Tiger Salamander
Prairie / Boreal population
Range of occurrence in Canada: Alberta, Saskatchewan, Manitoba

Demographic Information

Extent and Occupancy Information

Quantitative Analysis

Threats (actual or imminent, to populations or habitats)

Rescue Effect (immigration from outside Canada)

Status History

Status and Reasons for Designation

Applicability of Criteria

Preface

Technically this is a new report as it considers the Western (formerly Barred) Tiger Salamander, Ambystoma mavortium, alone for the first time. The species was previously assessed by COSEWIC (2001) as a subspecies within a polytypic species formerly known as the Tiger Salamander, Ambystoma tigrinum. Of the subspecies formerly recognized as Tiger Salamanders within Canada, the Eastern Tiger Salamander and the Western Tiger Salamander (which includes the subspecies Gray Tiger Salamander and Blotched Tiger Salamander) are now recognized as distinct species (Crother 2012).

A recovery strategy for the Southern Mountain population has been prepared (Southern Interior Reptile and Amphibian Recovery Team. 2008). This strategy describes strategies for protecting habitat, filling in data gaps on population processes, habitat use, and life history, and building support for habitat protection among stakeholders and the public. Steps towards protecting habitat according to the recovery strategy targets have been initiated.

COSEWIC History
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership
COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (2012)

Wildlife Species
A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)
A wildlife species that no longer exists.

Extirpated (XT)
A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)
A wildlife species facing imminent extirpation or extinction.

Threatened (T)
A wildlife species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)*
A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)**
A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)***
A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
** Formerly described as “Not In Any Category”, or “No Designation Required.”
*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006.

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.

COSEWIC Status Report on the Western Tiger Salamander Ambystoma mavortium in Canada - 2012

• Southern Mountain population
• Prairie / Boreal population

Wildlife Species Description and Significance

Name and Classification

The Western (formerly Barred) Tiger Salamander, Ambystoma mavortium (Family Ambystomatidae or Mole Salamanders) was first described by Baird in 1850 (Gehlbach 1967). Subsequently, it was considered part of the taxon A. tigrinum, a polytypic species with a geographic range spanning much of North America (Bishop 1943; Gehlbach 1967). Based on molecular, phylogenetic (Shaffer and McKnight 1996), and morphological evidence (Irschick and Shaffer 1997), the western form was recently elevated to a species status and is now known as A. mavortium (Crother 2012). It is separated from the eastern form,now known as the Eastern Tiger Salamander,Ambystoma tigrinum. The Red River in Manitoba acts as an approximate dividing line between the two species in Canada. Older literature does not generally distinguish between the Western Tiger Salamander, A. mavortium, and the Eastern Tiger Salamander, A. tigrinum.

The Western Tiger Salamander currently includes 5 subspecies (Crother 2012).The validity of these subspecies has been questioned (Jones and Collins 1992; Shaffer and McKnight 1996; Storfer et al. 2004) and requires a detailed, range-wide analysis. Much of the range of the two northern subspecies is recently colonized (< 18,000 years) (Shaffer and McKnight 1996). The Gray Tiger Salamander, A. m. diaboli, occurs in the prairies of Manitoba and Saskatchewan (Figure 1, 2) and according to distribution maps in Stebbins (1985) might also occur in east-central Alberta, but this has not been confirmed (Russell and Bauer 2000). The other subspecies in Canada is the Blotched Tiger Salamander, A. m. melanostictum (Figure 3), which occurs in south-central Saskatchewan and westward in central and southern Alberta and as a disjunct population in the Southern Mountain region of British Columbia (Figure 1).

Figure 1. North American distribution of the Western Tiger Salamander (Ambystoma mavortium) with its subspecies, and the Eastern Tiger Salamander (Ambystoma tigrinum).

Figure adapted from Schock (2001) and Petranka (1998).

Figure 2. Gray Tiger Salamander, Ambystoma mavortium diaboli; typical colouration of adult salamanders: older salamanders may show regression of dark markings (right) compared to younger individuals (left).

Photos by A. Didiuk.

Figure 3. Blotched Tiger Salamander, Ambystoma mavortium melanostictum, from Alberta; typical colouration.

Upper left – recently metamorphosed juvenile (with slight evidence of gills lower left). Upper right - Mottling on belly of a terrestrial adult from Alberta; Lower right: large pedomorphic (neotenic) individual from Tyrell Lake compared to smaller larvae. Photos by A. Whiting.

The English common name Barred Tiger Salamander for A. mavortium has been replaced recently by Western Tiger Salamander, so avoiding confusion arising from using Barred Tiger Salamander for both the species and one of its subspecies (Crother 2012). The French common name is salamandre tigrée de l’Ouest (Green 2012).

Morphological Description

Western Tiger Salamanders are large, robust mole salamanders that are among the largest terrestrial salamanders in North America. Males reach a total length of about 200 mm, while females are generally smaller (Sarell 1996; Petranka 1998; Hammerson 1999). Some salamanders reach over 300 mm in length, but these are generally neotenic, permanently aquatic forms that fail to transform and retain larval characters including gills and a tail fin in sexually mature adults (Figure 3; Cormie 1975). The largest reported body size is 385 mm for A. m. diaboli from Devils Lake, North Dakota (Larson 1968). The salamander has 11-14 costal grooves on each side of its body. Sexual dimorphism is subtle, with males having a longer tail, which is more laterally compressed than the tail of females, and a swollen vent during the breeding season (Schock 2001).

The colouration of terrestrial forms, though somewhat variable, has been used to discriminate subspecies of the Western Tiger Salamander from each other and from the Eastern Tiger Salamander. Metamorphosed adults have a blotched, barred or reticulate pattern of yellow (cream or white) on black (or grey, dark brown or olive green) background; the boundaries of blotches are not always sharp. The underside is sooty grey. In contrast to western forms, Eastern Tiger Salamanders have spots and lack blotches or bars. Distinguishing between the subspecies of Western Tiger Salamanders is more difficult. The distributions of the two subspecies found in Canada (Ambystoma m. diaboli and Ambystoma m. melanostictum) overlap extensively throughout Saskatchewan, and colour variations may exist even within subspecies or regions. Ambystoma m. diaboli typically have dark spotting on a light background (especially typical of large aquatic adults). Individual Ambystoma m. melanostictum transform into terrestrial stages with light markings on a dark background, and the background gradually reduces to spots with the former light spots and bars becoming a light background colour (Figure 2; Cook, unpubl. field observations in western provinces 1959-1970; Brunton 1998). Recently metamorphosed juveniles can be irregularly mottled or spotted without distinct blotches and often have a thin, dark line along the middle of the dorsum where the dorsal fin membrane was resorbed (Schock 2001).

Larvae hatch at about 15 mm in total length and have three long gill stalks and a broad dorsal fin membrane. Gill stalks are longer than the head and are swept back along the body. Tiger salamanders lack true balancers, but the lower pair of gills may act in their place. Larvae in June-July are translucent yellow-green. Toward the end of September the smallest larvae are 100-150 mm long and show some loss of the transparent quality of the tail fin and skin (Cormie 1975). Older individuals are grey and similar to younger larvae except for size and scarring. Permanently aquatic neotenes are large (often in excess of 300 mm long) and often heavily scarred, but otherwise similar to larvae. In spring, aquatic adults are easily distinguished from larvae based on their large size.

Cannibal morphs tend to occur in the southern subspecies Ambystoma m. nebulosum and Ambystoma m. mavortium (Lannoo and Bachmann 1984) but have not been reported for the subspecies found in Canada. Cannibal morphs of both larvae and neotenic adults are larger and have wider, flatter heads and an enlarged vomerine tooth ridge when compared to non-cannibal morphs (Collins et al. 1993). Large neotenic salamanders may occur in some Canadian localities and may cannibalize smaller larvae, without displaying morphological specializations.

Neoteny occurs throughout the range of the Western Tiger Salamander and has been reported from at least 5 sites in British Columbia (Sarell pers. comm. 2011), and occasionally from Alberta (e.g., Tyrrell Lake and Crooked Valley Reservoir near Calgary; Goater pers. comm. 2011) and Saskatchewan (e.g., near Saskatoon, Didiuk pers. comm. 2011). Neoteny is more common where terrestrial habitat is unsuitable or where water is permanent. Rarely, larvae may prolong metamorphosis until the following spring or summer provided they can overwinter in water. Prolonged metamorphosis may be more common in montane populations as a result of extended hydroperiods, lower temperatures, and associated slower growth and development rates, compared to prairie populations (Wissinger et al. 2010).

There is little chance for confusion between Western Tiger Salamanders and other salamanders as they are generally the only salamander present throughout their range. The exception is the Rocky Mountain ranges in Alberta and the Southern Mountain regions of British Columbia where their distribution overlaps with that of the Long-toed Salamander, Ambystoma macrodactylum. Terrestrial forms are easily distinguished by the greater size of the Western Tiger Salamander and their distinctive colouration.

Population Spatial Structure and Variability

Little is known about the spatial structure of Western Tiger Salamander populations in Canada. One study on landscape genetic structure of A. m. melanostictum examined 8 microsatellite loci from 10 sites across the northern range in Yellowstone National Park, Wyoming and Montana (Spear et al. 2005). The study revealed restricted gene flow among populations from different sites (FST = 0.24) and further isolation by distance and elevation (mean of 21.8 ± 15.2 km SD; range 0.5 to 53 km). River crossings and open shrub habitat were associated with greater gene exchange among populations, but movements appeared to be restricted due to topographical features. These results may apply to montane populations in British Columbia and Alberta but not to prairie populations. The only other study describing movements between populations is of marked individuals of A. m. nebulosum in Colorado (Denoel et al. 2007). The maximum distance between 8 study ponds was 100 m where up to 40% of individuals moved between ponds in a given year, and individuals visited up to 5 ponds within their life time (mean 1.6 ±0.1, n = 90 salamanders). Movement rates between ponds such as these may be more characteristic in the prairie pothole region of Manitoba, Saskatchewan and Alberta where terrestrial habitat is more suitable to dispersal. Movement among wetlands is less likely in British Columbia where populations are often separated by roads, xeric terrestrial habitat and wetlands occupied by introduced fish. However, movement patterns among wetlands have not been investigated in Canadian populations. Likewise, site philopatry, the propensity to return to a natal pond, has not been adequately explored, but could have strong effects on population spatial structure. Eastern Tiger Salamanders, A. tigrinum,have shown philopatric behaviour, whereby salamanders returned to their natal ponds despite other wetlands being available (Semlitsch 1983). Schock (unpubl. data) has observed similar philopatric behaviour for individually marked salamanders from a population of A. m. diabolinear Edenwold, Saskatchewan. Given the potential for philopatry in Western Tiger Salamanders, the destruction of a single breeding site could eliminate an entire population.

Structuring within populations may occur at sites where there is neoteny. Neotenic adults remain within the pond year-round and are thus capable of breeding in spring before metamorphic adults appear. Metamorphic adults are also the only individuals that might disperse and enter nearby populations across upland habitat. Furthermore, morphological differences between metamorphic and neotenic morphs may result in divergence of feeding habits (Denoel et al. 2006, 2007) during the breeding period, leading to spatial segregation within a pond.

Regionally, populations in the Southern Mountain region of British Columbia are geographically separated by the Rocky Mountains and are disjunct from the rest of the Canadian populations of Western Tiger Salamanders (Figure 1). The distribution of Western Tiger Salamanders in British Columbia is restricted to the South Okanagan, Lower Similkameen and Kettle River watersheds (Figure 4). There are no suitable habitats nearby, although there are apparently suitable wetlands and upland habitat further north (Ashpole pers. comm. 2011; Sarell pers. comm. 2011). Movement of salamanders between breeding ponds is unlikely as distance increases, and may be rare in general due to the arid sagebrush-bunchgrass plant community, which predominates in upland habitats in this area.

Figure 4. Distribution of Western Tiger Salamander occurrences in British Columbia

Shown are the extent of occurrence and index of area of occupancy (for breeding sites alone; 58 cells = 232 km²). Map prepared by A. Whiting.

The remainder of the Canadian distribution consists of both the Blotched Tiger Salamander (A. m. melanostictum) in Alberta and Saskatchewan and the Gray Tiger Salamander (A. m. diaboli) in Saskatchewan and Manitoba. Though recognized as two separate subspecies, there has been no genetic work across the distribution to delineate clear genetic boundaries or barriers to dispersal. Subspecific designations are based only upon colour pattern variation between populations (Irschick and Shaffer 1997). Genetic differences in the genome of ranaviruses (FV3 and ATV) that commonly infect tiger salamanders could be used to identify host-pathogen differences that may be related to genetic barriers to the host populations. To date, there appears to be little genetic difference in ATV that might identify barriers to gene flow among salamander populations (Schock et al. 2009).

Designatable Units

The Western Tiger Salamander is considered to consist of two designatable units (DUs): Southern Mountain population in B.C. and Prairie / Boreal population in Alberta, Saskatchewan, and Manitoba. Western Tiger Salamanders in British Columbia and in the Prairie provinces occur in the Southern Mountain and Prairie ecological areas (or Intermountain and Prairie faunal provinces), respectively. They represent separate postglacial range expansions into Canada and are separated by the Rocky Mountains. It is unknown whether there are morphological or ecological adaptations to the different environments that the two populations occupy. However, there are differences in land uses and threats to which the salamanders are exposed. The Southern Mountain population was previously recognized as a DU, based on the disjunct distribution of these salamanders from the remainder of the species’ distribution in Canada (Figure 1). The Prairie / Boreal population includes two subspecies, Gray and Blotched tiger salamanders. The two subspecies are not easily distinguishable, and further evidence to support their validity is required. Therefore, they are considered a single DU in this report. The Prairie / Boreal population, as had been described in the previous status report (Schock 2001), no longer includes tiger salamanders east of the Red River in Manitoba, as they are now recognized as Eastern Tiger Salamanders.

Special Significance

The Western Tiger Salamander is one of the largest terrestrial salamanders in North America and the only salamander species in Saskatchewan and one of two salamander species in Alberta. Tiger Salamanders have received little public attention in Canada; however, the interpretive centre in St. Leon, Manitoba, focuses on their life cycle. The Western Tiger Salamander was designated the state amphibian of Colorado in March 2012 (Colorado State 2012).

Tiger salamanders are generally the top predator in naturally fishless systems. In the Prairie Pothole regions, tiger salamanders may occupy the fish niche (Zaret 1980; Benoy 2008) and control macroinvertebrate abundance (Benoy et al. 2002; Benoy 2005, 2008), which in turn influences nutrient cycles and regulates phytoplankton biomass (Holomuzki et al. 1994). Salamander larvae transport energy from aquatic production to terrestrial uplands after metamorphosis; these exports may be significant in large populations (Gibbons et al. 2006; Regester et al. 2006a, b).

Tiger salamanders are frequently used as model species to develop and test evolutionary, ecological and physiological hypotheses, owing to their large size, phenotypic plasticity, wide geographic distribution, and ease with which they can be reared in laboratory settings. These same characteristics also make them common in the pet trade.

Distribution

Global Range

The Western Tiger Salamander is widely distributed in the arid and semi-arid interior of western North America (Figure 1). Its range is bordered to the north by the mixed-wood and boreal forests in Alberta and Saskatchewan and the boreal plains in Manitoba. The eastern extent of the distribution appears to be Red River in Manitoba from where it extends south into Minnesota and Iowa, where subspecies of the Western Tiger Salamander (A. m. diaboli withA. m. melanostictum, and A. m. mavortium) overlap with the Eastern Tiger Salamander (Routman 1993). The exact distributions of the subspecies (Shaffer and McKnight 1996) remain unclear, and the distribution map created by Petranka (1998) is likely to change with continued research within contact zones in the east (Routman 1993; LeClere pers. comm. 2011). The eastern distribution extends through Nebraska, Kansas, Oklahoma and Texas, west along the border of Mexico and then north through Arizona along the eastern slopes of the Rocky Mountains north to Alberta. There is a disjunct distribution in Northern Oregon, Idaho and through Washington into the southern Okanagan region of British Columbia. The indistinct range boundary between subspecies complicates the mapping of distributions (Shaffer and McKnight 1996). Several subspecies of Western Tiger Salamander (usually A. m. mavortium) have been introduced into California and other western US states as a result of the practice of using salamander larvae as fish bait, thus complicating attempts to delineate subspecies boundaries (Fitzpatrick and Shaffer 2004, 2007; Johnson et al. 2010, 2011).

Canadian Range

In British Columbia, the Western Tiger Salamander occurs in the dry southern interior region of the province, south of Peachland. It is restricted to scattered, isolated populations in the South Okanagan, Lower Similkameen, and Kettle River watersheds (Figure 4) with the range extending south to the U.S. border.

The remainder of the species’ distribution is relatively continuous and extends to the northern edge of the prairie ecozone up to the beginning of continuous coniferous forest (Cook 1960), covering a wide area in central and southern portions of Alberta, Saskatchewan and Manitoba within the aspen parkland and short grass prairie (Figure 5). Populations occur within the montane region of Alberta east of the Rocky Mountains up to elevations of 2,800 m in the Bow Valley area near Banff (Clevenger et al. 2001; Alberta FWMIS 2011) and at a number of sites within Waterton Lakes National Park (WLNP Wildlife Observations 2011). One population from the Wagner Natural Area, west of Edmonton, was previously incorrectly placed on maps near Slave Lake (Schock 2001). The distribution in Manitoba is south of the boreal plain ecozone from Riding Mountain National Park and the southern edge of Lake Manitoba east to Red River near Winnipeg and then south, west of Red River, to the US border. Red River appears to act as a dividing line between the Eastern Tiger Salamander and the Western Tiger Salamander, but the exact boundary is unclear and requires verification (Ngo et al. 2009). Recent efforts have identified populations of Eastern Tiger Salamanders from Tolstoi, Rosseau River, and Gardenton, all east of Red River (Collicutt pers. comm. 2011; Manitoba Herp Atlas 2011).

Figure 5. Canadian distribution of all occurrences of Western Tiger Salamander, showing the Southern Mountain DU in the west and Prairie DU in the east.

Green shading indicates the total extent of occurrence (572 490 km²). Map prepared by A. Whiting.

Extent of Occurrence and Area of Occupancy

Calculations of the extent of occurrence and index of area of occupancy were completed using ArcGIS 10 by A. Whiting with the help of C. Nielsen at the University of Alberta.

Southern Mountain Population:

In British Columbia, declines in the area of occupancy and extent of occurrence reported in the previous status report (Schock 2001) were inferred from apparent extirpations at historical breeding sites, combined with extensive habitat loss (Southern Interior Reptile and Amphibian Recovery Team 2008). Since then, knowledge of the number of sites and number of populations has increased; there are now 86 known breeding sites of Western Tiger Salamanders (BC SPI 2011; BC CDC 2012), an increase from 41 sites (formerly listed as 41 locations; Schock 2001). Including the number of non-breeding detections, there are 331 occurrence records from the past 10 years (2001-2011). Using the most recent data available, and utilizing a buffer of 500 m around each occurrence point and joining points with overlapping buffers (referred to as sites) there are up to 68 sites that have had at least one life stage present in the past 10 years (since 2001). The increase in the number of sites represents greater survey effort (Noble and Spendlow 2006; Crosby unpubl. data) rather than an increase in occupied sites.

The extent of occurrence (EO) for British Columbia, using all detections, with the minimum convex polygon method is 5054 km² (Figure 4). B.C. Conservation Data Centre (Stipec pers. comm. 2012) calculated the EO as 2208 km² using an alpha hull that excluded the northwestern mountainous area, which is unsuitable habitat. Both estimates are greater than the EO of 1,500 km² reported in the previous status report (Schock 2001); the increase is a result of increased surveys in neighbouring watersheds. Utilizing a point in the centre of each breeding site, the index of area of occupancy (IAO) using a 2x2 km grid and ignoring the total area of the water body is 232 km² (58 cells); IAO is  464 km² (116 cells) if all detections of individuals are included, even where breeding populations are unlikely. B.C. Conservation Data Centre (Stipec pers. comm. 2012) calculated an IAO of 248 km² given 62 occupied cells within the Southern Mountain area. AO was reported as 150 km² in the previous status report (Schock 2001); IAO was not calculated.

Prairie / Boreal Population:

Based on occurrence records with a buffer of 500 m placed around each point or group of points, there are over 597 known sites throughout the Prairie / Boreal population. However, some of these observations are over 40 years old and may not represent extant populations. Within the Prairie Provinces, there are no reports of changes in the distribution of the species through time, but systematic surveys are lacking. However, in the past 10 years since Schock’s (2001) report, incidental reports of the presence of Tiger Salamanders leave the impression that the salamanders remain relatively widely distributed in Saskatchewan and Manitoba, although some populations are spatially isolated. A herpetological atlas currently under way in Manitoba has added 16 new sites in the past year (Manitoba Herp Atlas 2011). Efforts to conduct a herpetological atlas in Saskatchewan have been ongoing since 2001 (Schock 2001), but results are as yet unavailable. In Saskatchewan, Western Tiger Salamanders persist within the expected range (Didiuk pers. comm. 2011), but without systematic surveys it is unclear if there has been a change in EO or IAO. In Alberta, there are a number of new records, but data gaps remain, especially in the east (Alberta FWMIS 2011).

The EO for the Prairie Provinces is 567,437 km² based on data from recent surveys and historical records. This represents an increase of more than 67,000 km² since the last status report (Schock 2001). Based on available data, there are 597 cells with detections or occurrences resulting in an IAO of 2388 km². This estimate is much lower than the AO of 50,000 km² previously reported (Schock 2001), which may have been inferred based on habitat availability. The lack of reporting from Saskatchewan and Manitoba and lack of dedicated tiger salamander surveys in Alberta probably greatly underestimate the IAO.

Search Effort

Systematic surveys for Western Tiger Salamanders have been conducted only in British Columbia (Tarrangle and Yelland 2005; Noble and Spendlow 2006). These surveys included historical sites as well as new sites in potentially suitable habitats. Regional surveys for amphibians in the Okanagan are ongoing, and include those by Sara Ashpole and Christine Bishop and their students (e.g., Ashpole et al. 2011; de Jong 2008); currently Jonquil Crosby is documenting road mortality of Western Tiger Salamanders (Ashpole pers. comm. 2011). Ashpole et al. (2011) found the Western Tiger Salamander at 8 of 96 ponds surveyed from 2003 – 2006 in lowland valley and agricultural areas of the South Okanagan Valley. Tarrangle and Yelland (2005) found the species at 7 of 52 wetlands surveyed in South Okanagan. Tarrangle and Yelland (2005) found the species at 7 of 84 wetlands surveyed in the Okanagan, Similkameen, and Kettle Valley areas. Amphibian surveys by Mike Sarell (Ophiuchus Consulting) and by members of BCFrogwatch have resulted in additional tiger salamander records. Additional surveys in surrounding areas have supported the absence of tiger salamanders outside of their known B.C. range (Deguise and Richardson 2009; Dulisse and Hausleitner 2010; Voordouw et al. 2010). As of September 2011, there were 86 known tiger salamander breeding sites in British Columbia (BC CDC 2012). The number of occupied sites fluctuates annually but is likely unchanged from the last surveys in 2006 (Noble and Spendlow 2006). Given the restricted distribution of the species and persistent survey efforts, there are unlikely to be many undiscovered populations within the Southern Mountain population. There may still exist some unknown populations in oxbows on private land, but the presence of fish (native and introduced) and possibly Bullfrog (Lithobates catesbeianus) restricts this possibility (Ashpole pers. comm. 2011).

In the Prairie provinces, there have been no systematic surveys for Western Tiger Salamanders. In Alberta, the Fish and Wildlife Management Information System database provides records of the presence of tiger salamanders. The database consists of information by individuals that require a permit to conduct research on wildlife, but also receives reports from volunteer groups such as the Alberta Volunteer Amphibian Monitoring Program (AVAMP) and Researching Amphibian Numbers in Alberta (RANA). In addition to these volunteer networks, the national monitoring program Frogwatch, which focuses on calling anurans, provides occasional reports of salamander occurrence. An ongoing program to sample biodiversity throughout Alberta in 20 km² grid cells (Alberta Biodiversity Monitoring Institute 2008) will help fill knowledge gaps within the eastern prairie and parkland regions. Graduate student and academic research has included regional surveys for amphibians, some of which have focused on tiger salamanders in Manitoba (Alperyn 2005; Benoy et al. 2005, 2008). Other studies in Alberta and Saskatchewan have involved opportunistic observations of tiger salamanders (Puchniak 2002; Eaves 2004; Browne 2010; Pagnucco 2010; Scheffers 2010; Anderson pers. comm. 2011; Taylor pers. comm. 2011). Older records from museum collections dominate the occurrences for tiger salamanders in Saskatchewan and Manitoba, but there are anecdotal reports that salamanders still persist within the expected range (Didiuk pers. comm. 2011; Vanderschuit pers. comm. 2011).

Habitat

Habitat Requirements

Western Tiger Salamanders are widely distributed in a variety of habitats including grasslands, parklands, subalpine meadows, and semi-deserts in arid regions. Key habitat features include sandy or friable soils surrounding semi-permanent to permanent fishless water bodies (Petranka 1998). The salamanders also appear to require burrows of small mammals for daily refuge use and overwintering sites (Whiteman et al. 1994; Koch and Peterson 1995; Richardson et al. 2000).

Aquatic breeding habitats must hold water for the 3 to 7 months required to complete development up to metamorphosis (McMenamin and Hadly 2010). Differences in hydroperiods can affect the number of metamorphs emerging from breeding sites, with more emerging from water bodies with a longer hydroperiod (Richardson et al. 2000; Wissinger et al. 2010). Longer hydroperiods may be required in cooler environs due to slower growth and prolonged time required to metamorphosis. Neotenic, aquatic populations require permanent water bodies lacking predatory fish and appear to be associated with cooler water bodies in mainly subalpine habitats. Western Tiger Salamanders are tolerant of alkaline or slightly saline environments, such as Tyrell Lake in Alberta, and of nutrient rich water bodies (Miller and Larsen 1986; Matsuda et al. 2006). 

Terrestrial habitats of adults and metamorphosed juveniles include grassland, open woodlands such as found in the parkland of the Prairie provinces, and shrub-steppe in British Columbia. Western Tiger Salamanders occur in cultivated regions of the Prairie provinces. Individuals are often found inhabiting small mammal burrows or underneath debris or rocks. The extent of terrestrial habitat required is likely to vary depending on its configuration and quality. Movements are usually within 250 m from aquatic breeding habitats based on radio-telemetry studies (Richardson et al. 2000; Steen et al. 2006), but individuals are occasionally found over 1000 m from the nearest suitable water body (Sarell and Robertson 1994). During the fall migration, biologists are commonly inundated with calls that salamanders have fallen in window wells, sump pumps, or in-ground pools, or are found in basements (Ashpole pers. comm. 2011; Kendall pers. comm. 2011). These large urban pitfall traps highlight the degree to which salamander habitat has been modified and fragmented. The role of habitat fragmentation and use of corridor habitats for movements and dispersal by Western Tiger Salamanders have not received sufficient attention.

Habitat Trends

Habitat loss continues throughout the range of the Western Tiger Salamander. In British Columbia, much of the species’ habitat occurs on private lands, which continue to be converted to agriculture (formerly orchards and now vineyards), leading to the additional threats of contamination of breeding sites from run-off. It was estimated that by the late 1980s, only 10% of natural ecosystems within the southern Okanagan remained relatively undisturbed (Redpath 1990). Of the riparian and upland habitat, about half has been lost to urban or agricultural development (Cannings et al. 1999), and only 15% of the original valley bottom riparian habitat remains (B.C. Ministry of Environment, Lands and Parks 1998). Habitat loss to urban and agricultural developments continues to threaten aquatic and terrestrial habitats of tiger salamanders and disrupt habitat connectivity (Southern Interior Reptile and Amphibian Recovery Team 2008). A number of small wetlands have been constructed for amphibians over the past 5 years (21 ponds, of which 4 are suitable for tiger salamanders; Ashpole pers. comm. 2011), but these do not nearly compensate for the loss of natural wetlands and habitat fragmentation occurring in the region. Habitat fragmentation is of growing concern due to increased traffic volumes, especially in South Okanagan, and high road mortality rate of tiger salamanders when migrating to and from breeding sites (see Threats and Limiting Factors). Large-scale loss of wetlands has also occurred throughout the salamander’s range in the Prairie provinces (Millar 1989; Watmough and Schmoll 2007). Drainage and infilling still occur, especially in association with urban developments and agriculture (Dahl and Watmough 2007; Bartzen et al. 2010).

Further reducing habitat quality and availability throughout the species’ Canadian range is the purposeful (legal and illegal) introduction of trout (mainly Rainbow Trout, Oncorhynchus mykiss) and more recently in British Columbia Largemouth Bass (Micropterus salmoides) and Smallmouth Bass (M. dolomieu), into water bodies that formerly lacked large predatory fish (Carl and Guiguet 1958; Alberta FWMIS 2011; Sarell pers. comm. 2011; Saskatchewan Fish and Wildlife 2012). Figure 6 shows the prevalence of sport fish stocking in Alberta; a similar pattern is evident in the other provinces where the salamanders occur. Western Tiger Salamanders have reduced growth and survival in the presence of predatory fish (reviewed in Wind 2005). Neotenic salamander populations are at greatest risk after the introduction of predaceous fish, which consume both larvae and adult salamanders (Mitchell and Prepas 1990; Goater pers. comm. 2011; Haag pers. comm. 2011).

Figure 6. Distribution of water bodies that have been stocked with game fish in Alberta since 1920 (blue) and known Western Tiger Salamander records from central and southern Alberta (red)

Fish stocking is similarly prevalent in British Columbia, Saskatchewan, and Manitoba, but data were not available for detailed mapping. Map prepared by A. Whiting.

Although adapted to arid and semi-arid regions, Western Tiger Salamander populations are vulnerable to prolonged and frequent droughts (Richardson et al.2000), such as predicted under climate change, which can exacerbate effects of habitat loss and fragmentation. Since 2001, there have been two major droughts (in 2003 and 2009) (BC MOE 2010), the effects of which had subsided somewhat in 2010 and 2011 (Agriculture and Agri-Food Canada 2012). Hydroperiods and water levels were so low during the last decade that wetlands formerly known to be inhabited by salamanders were dry during the 2005 and 2006 breeding seasons (Tarangle and Yelland 2005; Noble and Spendlow 2006). The prairies have experienced a number of multi-year droughts, the most recent during 1999-2005 (Khandekar 2004; Bonsal et al. 2011; Hanesiak et al.2011). Water deficits and short hydroperiods remain of concern.

Biology

Life Cycle and Reproduction

In British Columbia, breeding occurs in permanent or semi-permanent lakes and ponds from March to May, soon after spring rains and when overnight temperatures reach 12°C (Richardson et al. 2000; Sarell pers. comm. 2011). Throughout the rest of the species’ Canadian range, breeding occurs soon after water is free of ice, in April to May after spring rains, in permanent or semi-permanent standing water, which may be less than 10°C (Russell and Bauer 2000).

Males may outnumber females at breeding sites, with sex ratios of 1.7:1 reported in Saskatchewan and Manitoba (Schock pers. comm. 2011). After courtship, the male deposits a spermatophore (sperm packet) on the bottom of the pond, which the female picks up with her cloaca. Shortly after mating, the female lays small eggs (< 10 mm in diameter) and attaches them either singly or in small clusters to twigs or stems of emergent plants or to stones or debris about 30 cm or more below the surface of the water (Russell and Bauer 2000; Sarell 2004; Matsudaet al. 2006). Clutch sizes have not been recorded for Canadian populations, but in the U.S. they range from a high of 5000 eggs (Bishop 1943; Rose and Armentout 1976) to a low of 100 eggs (Gopurenko et al. 2006), depending on geographic location and the female’s body size. Hatching times vary based upon water temperature (Tanner et al. 1971; Sever and Dineen 1978), but eggs typically hatch in 2 – 3 weeks (Schock 2001; Sarell pers. comm. 2011).

Development of larvae to metamorphosis usually takes approximately 3-4 months and is dependent on water temperature, food availability, density of larvae, and pond hydroperiod (Wilbur and Collins 1973; Sexton and Bizer 1978; Collins and Cheek 1983). Metamorphosis has been observed as early as July 22 in the Okanagan (Sarell pers. comm. 2011), but generally metamorphs emerge in August throughout most of the Canadian distribution (Anderson pers. comm. 2011; Collicutt pers. comm. 2011; Didiuk pers. comm. 2011; Sarell pers. comm. 2011; Vanderschuit pers. comm. 2011). Metamorphosis occurs at larval total lengths of 80-150 mm, but varies depending on growing conditions, such as prey availability and larval density. In permanent water bodies without predatory fish in British Columbia and Alberta, larvae have been reported to overwinter occasionally and emerge the following summer at a much larger body size or remain as aquatic neotenic adults (B.C.: Ashpole pers. comm. 2011; Alberta: Anderson pers. comm. 2011; Goater pers. comm. 2011). In some montane populations of A. m. nebulosum in Colorado, metamorphosis may occur in the 2^nd or 3^rd summer, or individuals may simply remain as neotenic aquatic adults (Wissinger et al. 1999, 2010). 

After metamorphosis, individuals migrate to the upland taking up residence in underground refuges and rarely emerge during the day. Migration from the water bodies seems to be triggered by rain in late summer, when the salamanders emerge by hundreds from breeding ponds (Patch and Stewart 1934). Overwintering likely occurs in small mammal burrows and forested areas near aquatic habitats (Whiteman et al. 1994; Koch and Peterson 1995; Richardson et al. 2000).

The prevalence of neoteny is not well studied in Canadian populations but has been reported from approximately 5 sites in British Columbia (Southern Interior Reptile and Amphibian Recovery Team 2008), at Tyrell Lake  and several other sites in Alberta (Cormie 1975; Goater pers. comm. 2011; Paszkowski pers. comm. 2011), and in Saskatchewan (Didiuk pers. comm. 2011). There are no confirmed reports of neoteny from Manitoba, although it is suspected to occur in Ninette Lake (Preston 1982). Facultative pedomorphosis, the ability to metamorphose after sexual maturity, may occur during drought periods, but neotenic populations may be lost due to drying of the aquatic habitat.

Survivorship and Generation Time

Western Tiger Salamanders demonstrate an “r-selected” survival strategy: many eggs are produced, but larval mortality is high (Pfennig et al. 1991). High reproductive potential allows tiger salamanders to rapidly exploit recently filled water bodies (Sarell 1996). Survival to metamorphosis can be highly variable depending upon larval density, presence of cannibal morphs, food availability, and hydroperiod (Wissinger et al. 2010). The highly variable larval survival results in pulses of recruits that can vary enormously from year to year, resulting in high fluctuations in adult population size on a multi-year basis.

Inferred overwinter survival is low for young-of-the-year based on large numbers of metamorphs in fall and low numbers that return to the wetland the following spring in any given year (Richardson et al. 2000; Wissinger et al. 2010; Schock pers. comm. 2011). Time to sexual maturity is variable throughout the range, especially within montane regions, and may range from 1 to 4 years (Webb and Roueche 1971; Wissinger et al. 1999, 2010). Farther south in the US, individuals of A. tigrinum may return to breed the year after hatching, but are more likely to return in their second year of life (Semlitsch 1983). Females may take longer to mature than males (Schock, unpubl. data) and either breed every year or every second year, depending on climate and energy stores (Bailey et al. 2004; Church et al. 2007).

Adult survival estimated for three populations of A. tigrinum in the US over 4 years was 0.85, but varied with year and site (female annual survival range ~0.51 to 1.00; Church et al. 2007). Tiger salamanders are long-lived, with maximum life spans recorded at 16 (Russell and Bauer 2000) to 25 years (Tyning 1990). However, assuming constant survival each year, the probability of individuals reaching 16 years of age is 7% and may therefore occur only rarely. Schock (2001) reported individuals that were at least 5 years of age from a population from Saskatchewan, but a skeletal chronology study from neotenic and terrestrial populations found no individuals greater than 6 years of age (Allison, unpubl. data cited in Schock 2001).

The generation time using the harmonic average survival is 6.3 – 8.3 years, calculated as follows: age of maturity + (1/annual mortality rate), where age at maturity is 1 – 3 years, and annual mortality rate is 0.19, as per Church et al. 2007 for A. tigrinum). However, in exceptionally dry years mortality rate was 0.45 and would result in generation times of 3.2 to 5.2 years using the same equation. A generation time of 5 – 6 years is used in this report.

Physiology and Adaptability

Facilitated by their fossorial nature and use of underground refuges, Western Tiger Salamanders are capable of inhabiting dry upland habitats. The salamanders are active in burrows, where they feed and may be thermoregulating underneath the ground (Sarell pers. comm. 2011). However, in the absence of burrows or friable soils into which they can dig, the salamanders avoid habitats that increase desiccation rates (Cosentino et al. 2011). Tiger salamanders can occur in urban areas, where they have been found in gardens, earthen basements, and septic systems (Ashpole pers. comm. 2011; Kendall pers. comm. 2011); these novel habitats may either represent refuges or accidental entrapment while migrating across the landscape.

Larvae and adults are known to inhabit brackish and alkaline waters, and have been reported from waters with conductivity > 12000 µS cm-1 (Deutschmann and Peterka 1988) and total dissolved solids > 7000 mg/L (Mitchell and Prepas 1990). Tiger salamanders are also tolerant of acidic conditions, with egg mortality of 50% at pH of 4.2 (Whiteman et al. 1995). Western Tiger Salamanders can breed from cool subalpine waters to warmer prairie pothole wetlands. Although they are tolerant of a wide variety of aquatic conditions, large reductions in the length of hydroperiods due to droughts is detrimental and can limit recruitment of young or result in complete reproductive failure (Richardson et al. 2000; Wissinger et al. 2010).

Dispersal and Migration

Breeding migration occurs in spring and appears synchronized with adults of both sexes arriving within a few days of each other, and coincides with rain and relatively warm weather (Richardson et al. 2000; Wissinger et al. 2010; Sarell pers. comm. 2011). Fall migrations, similar to spring migrations, are associated with rain; however, temperature has less of an impact on the timing in fall than in spring (Patch and Stewart 1934; Richardson et al. 2000). Migrations of recently metamorphosed individuals are commonly reported in the Prairies during mid-late August (Didiuk pers. comm. 2011; Kendall pers. comm. 2011; Vanderschuit pers. comm. 2011).

In British Columbia, radio-tagged adults rarely moved more than 250 m from the wetland of capture, and their movements appeared unaffected by agricultural land use in the surrounding landscape (Richardson et al. 2000; Steen et al. 2006). Daily movements were generally constrained within a 5 m-radius and were often centred on abandoned animal burrows (Richardson et al. 2000). Anecdotal reports exist of salamanders found up to 3 km from the nearest wetland (Sarell and Robertson 1994). Mark-recapture studies in the US indicate that juveniles are more likely to disperse than are adults (up to 20% of juveniles versus 3-6% of adults moving between wetlands in any given year; Church and Wilbur, unpubl. data cited in Church et al. 2007). Denoel et al. (2007) reported inter-pond dispersal rates of 40% for adult A. m. nebulosum between years for a series of 8 ponds where the maximum distance between ponds was 100 m. In Yellowstone National Park, rivers and open habitats facilitated gene flow, whereas elevation and distance to nearest wetland (mean 21.8 km, range 0.5 to 53 km from n = 10 ponds) reduced gene exchange based on microsatellite analysis (Spear et al.2005; McMenamin and Hadly 2010).

Interspecific Interactions

Tiger salamanders are opportunistic predators, and in some studies their stomach contents matched the diversity of pond invertebrates sampled with aquatic nets (Wissinger et al. 1999). However, in other studies larvae showed preferences for certain taxa (Leff and Bachman 1986; Zerba and Collins 1992). Diets of larval tiger salamanders vary by site but consist mainly of aquatic invertebrates such as dipterans, ostracods, gastropods, odonates and other zoobenthos like mayfly larvae (Holomuzki et al. 1994; Johnson et al. 2003; Benoy 2008). Diets may include larger prey, such as larval anurans (Loeb et al. 1994), larger macroinvertebrates (Alperyn 2005; Benoy 2005, 2008), and other salamander larvae including other tiger salamanders.

Tiger salamander larvae and adults are described as voracious predators of amphibians (Ferrari and Chivers 2008, 2009) and other prey in aquatic habitats (Benoy2005, 2008). Neotenic individuals show divergence in diet from metamorphic adults during the breeding season (Denoel et al. 2007). In fishless ponds, larvae may function as top predators, assuming the role usually taken by large predatory fish (Zaret 1980): they reduce the invertebrate abundance, thereby increasing phytoplankton (Holomuzki et al. 1994). Larvae have been shown to decrease the density of several invertebrate taxa and may compete with dabbling ducks in fishless prairie pothole wetlands (Benoy et al. 2002; Benoy 2005). Whereas larval salamander density was positively correlated with diving duck occurrence, it was negatively correlated with dabbling duck distribution within and among wetlands (Benoy et al. 2002). In addition, there is a high degree of overlap among diets of the Western Tiger Salamander and introduced fish species such as Rainbow Trout (Olenick and Gee 1981). Tiger salamanders have been known to interfere with fish rearing operations in dugouts through competition for food, reducing fish growth (Schock 2001).

Larval tiger salamanders respond to predatory invertebrates with reduced activity and show reduced weight and increased tail fin depth (Storfer and White 2004). Increased tail fin depth provides for a rapid escape response to natural predators over short distances (Fitzpatrick et al. 2003). Natural predators include sit-and-wait invertebrate predators such as dragonfly larvae, dytiscid diving beetles, and giant water bugs (Belostomatidae) (Fitzpatrick et al. 2003). Transient predators that may have large impacts on larval populations include pelicans, herons, and cranes. The introduction of predatory fish represents a largely novel predator to the naturally fishless systems that Western Tiger Salamanders inhabit. Rapid escape responses by salamander larvae are not effective for avoiding active predators such as fish (i.e., trout and bass), which may make salamanders extremely vulnerable to fish introductions (Semlitsch 1987; Sepulveda and Lowe 2011).

Western Tiger Salamanders appear to be associated with the presence of burrowing small mammals. In British Columbia the distribution of salamanders has been suggested to reflect the presence of Northern Pocket Gophers (Thomomys talpoides) (Sarell pers. comm. 2011). Eradication of ground squirrels and pocket gophers on agricultural lands may ultimately limit the dispersal and overwintering sites available to salamanders in local areas (Kendall pers. comm. 2011; Sarell pers. comm. 2011).

Population Sizes and Trends

Sampling Effort and Methods

Few studies have attempted to assess abundance of Western Tiger Salamanders in Canada. Two studies were conducted near Crow’s Nest Pass, Alberta by Cam Goater and in the vicinity of White Lake, British Columbia by John Richardson and colleagues. Most studies have noted only the presence of the species or have sampled tiger salamanders for disease agents without assessment of population density (Schock et al. 2009).

The most common methods of detecting the presence of Western Tiger Salamanders are the use of beach seining or terrestrial drift-fence arrays with pitfall traps. Other methods include minnow traps and other aquatic funnel traps, which commonly capture larvae and occasionally adult salamanders. Dip netting has proven to be inefficient at capturing or assessing the density of tiger salamanders (Donald pers. comm. 2011). Nightly road surveys are commonly employed in B.C. (Sarell pers. comm. 2011).

The only information on recent trends of the relative number of individuals comes from road mortality surveys in British Columbia (Crosby, unpubl. data; Sarell pers. comm. 2011). Few studies involving Western Tiger Salamanders in Canada have been long enough to identify trends in population size as most are rarely longer than 2 years (Richardson et al. 2000 and unpubl. data). Occasional short-term studies for other amphibians have recorded the relative abundance or occurrence of tiger salamanders (Puchniak 2002; Eaves 2004; Pagnucco 2010).

Abundance

The abundance of Western Tiger Salamanders in Alberta, Saskatchewan, and Manitoba is unknown. There is no formal database in either Saskatchewan or Manitoba that tracks occurrence records for the species, but changes to reporting and tracking are underway in both provinces (Keith pers. comm. 2011).

In British Columbia, adults at breeding ponds may number in the hundreds in good years, but the numbers can drop to well below 100 adults inter-annually, as estimated from pitfall trapping and partial drift fence arrays around ponds (Richardson et al. 2000 and unpublished data for 5 breeding sites in the White Lake area, trapped for 2 years in spring and 3 years in fall). The number of juveniles emerging from the ponds varied widely among sites and years, ranging from 7200 to 200 animals.

The BC CDC (2012) postulates that there are from 2,500 to 10,000 adults within the Southern Mountain population of British Columbia, but no accurate estimates are available. Assuming that there are 86 breeding sites and if each site supports 100 adults, the total population size could be roughly 8,600 adults. However, the numbers may be greater following wet years conducive to breeding; they could drop well below this value in years following prolonged multi-year droughts that can greatly reduce the breeding population size due to lack of recruits from sites that dry up before development is complete and produce no young.

Population Trends

In Saskatchewan and Manitoba, there are no studies or processes to document changes in abundance or trends in tiger salamander populations. In southern Alberta, unsuccessful searches for larvae in water bodies near Lethbridge suggest that formerly occupied sites no longer contain salamanders (Goater pers. comm. 2011). The species occurs at only one of 7 RANA monitoring sites in Alberta, at Cypress Hills, where amphibians have been monitored from 1998 – 2006. The population may be declining, but small and fluctuating numbers of adults complicate discerning trends. The long history (since early 1900s) and widespread practice of fish stocking throughout the prairies suggest that salamander populations may have similarly declined in Manitoba. Other factors contributing to possible declines may be the emergence of Ambystoma tigrinum virus, which can cause localized mass mortalities.

In British Columbia, populations are becoming increasingly limited to temporary wetlands as water bodies that retain water year-round are now inhabited by introduced fish (stocked trout and Large and Smallmouth Bass; BC CDC 2012). Sites where salamanders may have persisted after trout introduction are likely to be lost after the introduction of bass (Sarell pers. comm. 2011). Goldfish (Crassius crassius) have been introduced into some water bodies not suited to fish stocking, and anecdotal evidence suggest they have limited or eliminated salamander recruitment within those water bodies (Ashpole pers. comm. 2011). Ashpole et al. (2011) reported the disappearance of tiger salamanders from a breeding pond monitored from 2003 – 2005, after 2003 for unknown reasons, which may include pollutant run-off from surrounding agricultural area, introduction of Goldfish, or disease.

Occasional mass die-offs of larval Western Tiger Salamanders occur due to pond drying. The recent droughts in British Columbia and Washington have resulted in lack of normal seasonal filling of wetlands where salamanders were previously found (Dyer pers. comm. 2011; Hallock pers. comm. 2011; Sarell pers. comm. 2011). In some cases, there are more permanent water bodies nearby, but they either contain native or introduced predaceous fish (trout, bass), which limit populations and may prevent recovery. Current predictions of climate change indicate reduced precipitation in the prairie and parkland regions of Alberta and Saskatchewan (Hogg and Hurdle 1995; Frelich and Reich 2010), which could result in further breeding habitat loss for Western Tiger Salamanders and consequent population declines.

In British Columbia, only a few (1-3) occurrences are ranked as having good viability (BC CDC 2006). Although formal population viability analysis has not been conducted, there are virtually no populations that are not impacted by predatory fish, traffic mortality, or water levels that are so low that extended periods of drought prevent reproduction (BC CDC 2012). White Lake where tiger salamanders were studied in the late 1990s has been consistently dry since 2000 (Dyer per. comm. 2012).

Population Fluctuations

Pond-breeding amphibians often fluctuate greatly in abundance from year to year or on multi-year basis (Green 2003). Western Tiger Salamander populations are expected to fluctuate in size similar to tiger salamander populations in other areas (Pechmann et al. 1991; Semlitsch et al. 1996; Trenham et al. 2000), but there are no long-term studies of this species from Canada. Fluctuations in the number of larvae emerging from wetlands are notable but may be a poor indicator of adult population size (Semlitsch 1983). Richardson et al. (unpubl. data) found that the tiger salamander population from White Lake, British Columbia, decreased from 259 adult salamanders in one year to 98 the following year; there was a complete reproductive failure in the 3 subsequent years due to dry conditions. Such fluctuations in breeding population size may at least partially reflect reduced breeding activity in some years in response to unsuitable conditions, rather than true fluctuations in adult numbers. However, the resulting pulsed breeding pattern is expected to contribute to fluctuations in adult numbers, as the number of recruits to the adult population will vary on a multi-annual basis. Observed patterns of periodic low water tables may be the result of oscillating cycles in weather patterns such as the Pacific Decadal Oscillations or El Niño – Southern Oscillation, in which case tiger salamander populations that depend on wetlands may show corresponding long-term patterns in population size (Richardson 2002). Given that there can be a complete failure of reproduction in drought years and that multi-year droughts associated with pond-drying appear to be and are predicted to become more frequent in the arid environments inhabited by the salamanders, fluctuations in salamander population size are expected occur simultaneously over relatively large areas. The synchronicity of fluctuations may be particularly applicable for the Southern Mountain population, which occupies a relatively small geographic area that is subject to similar weather patterns.

Fluctuations from a low of 200 to 3,000 individuals (all life stages combined) over a 20-year period were observed for A. m. nebulosum at a site in Colorado (Wissinger et al. 2010). Adult neotenic individuals increased from 200 to nearly 1400 individuals in one year, but declines in the same population were rarely above 50%. A population of A. tigrinum in South Carolina has been observed to vary by as much as an order of magnitude over a 12-year period (Pechmann et al. 1991; Semlitsch et al. 1996). At one California Tiger Salamander (A. californiense) breeding site, adult female numbers varied by an order of magnitude (16-140; Trenham et al. 2000) and a similar pattern was observed at another site 200 km to the north (Loredo and Van Vuren 1996). Whether these results apply to Western Tiger Salamanders and Canadian populations is unknown. 

Fragmentation of Populations

Severe fragmentation for the Southern Mountain population can be inferred from a) natural fragmentation of habitats and availability of suitable breeding sites; b) exacerbation of this fragmentation by human developments and activities, including roads, throughout the species' distribution in British Columbia, and particularly within the core area in South Okanagan; c) questionable viability of populations at most breeding sites due to threats from introduced fish, roads, and/or low water levels. In British Columbia, most of the known 86 breeding sites are within fragmented habitats, and most breeding sites are within the South Okanagan, where habitats continue to be lost and fragmented at a rapid pace. All breeding sites are within 700 m of a primary or secondary roadway, and successful migration between aquatic and terrestrial habitats may be hindered by the number of roads and developments in the upland habitat. Comparing the average nearest distance between any two breeding sites, there is 5.2 km between wetlands (range 131 m to 10.2 km). These distances exceed the typical between-site movements by Western Tiger Salamanders (see Dispersal and Migration). Not only are breeding sites far apart from each other, but they are also interspersed by water bodies that contain predacious fish and increasingly urbanized or agricultural areas. The viability of individual populations is unknown, but many populations are suspected to be small and declining. BC CDC assessed that only 1-3 of 48 breeding sites that had been mapped contained populations with good viability; this assessment was based on habitat condition following NatureServe Element of Occurrence Rank Assessment methodology (Gelling pers. comm. 2012). Although the assessment included only approximately one half of the known 86 sites, it is unlikely that there would now be more than 40 breeding sites (50%) with good viability considering continuing threats from roads, reduced water levels, fish and other sources. With predicted increase in droughts and drying up of breeding sites over periods of multiple years, a phenomenon that is already occurring, the persistence of local populations is expected to be perilous. For example, White Lake, a partially protected area where a population of tiger salamanders was studied in the late 1990s (Richardson et al. 2000), has been consistently dry for the past 10 years (Dyer pers. comm. 2012).

Populations within the Prairie / Boreal Tiger Salamander population may also be fragmented, but there is much uncertainty due to information gaps on the distribution and abundance of the species there. Because of the large area where the salamanders occur, multi-year fluctuations are unlikely to be synchronous across the entire distribution.

Rescue Effect

Dispersal of tiger salamanders from U.S. populations into southern British Columbia is possible, but the likelihood is low. The possibility of rescue from the US depends on salamanders dispersing longer than normal distances across dry mountainous terrain. The nearest known US population is 17 km SW of Oroville in Washington State, a distance greater than 20 km from the nearest Canadian population. The presence of the Oroville population was last confirmed in 1999 (Hallock pers. comm. 2011). There is no possibility of rescue of the Southern Mountain population from the Prairie / Boreal population. The two populations are separated by the Rocky Mountains and several hundred kilometres of inhospitable rocky terrain. 

Connectivity is likely among populations in the Prairie provinces and those in adjacent areas in the U.S. However, poor knowledge of the status of tiger salamander populations on both sides of the border precludes an accurate evaluation of the potential for rescue.

Threats and Limiting Factors

Western Tiger Salamanders face the same pressures and threats as other amphibians with biphasic life-histories and separate requirements for terrestrial adults and for aquatic developmental phases and include habitat loss and fragmentation. The IUCN Threats Calculator was applied to the Southern Mountain population and Prairie / Boreal population of the Western Tiger Salamander during separate conference calls that included species experts and the report writer, as well representatives from the B.C. government familiar with the species and with habitat trends within the range of the Southern Mountain population. The calculated overall threat impact was “very high – high” for both populations (Appendix 1 and 2). For the Southern Mountain population, “Transportation and Service Corridors”, mainly “Roads and Railroads”, were identified as the highest threat, whereas for the Prairie / Boreal population, “Natural System Modification”, mainly “Dams and Water Management”, was identified as the greatest threat. The main threats are discussed below.

Habitat Loss, Conversion and Fragmentation

Habitat change and wetland infilling continue to affect local populations throughout the Western Tiger Salamander’s range. Infilling of breeding ponds is particularly detrimental and can result in rapid loss of local populations. In developed landscapes, upland migration routes of salamanders can be disrupted and terrestrial refuge sites eliminated or degraded. In agricultural and range lands, soil compaction and the eradication of small burrowing mammals (Thomomys and Spermophilus species) can reduce terrestrial refuge and overwintering sites for salamanders (Ashpole pers. comm. 2011).

For the Southern Mountain population, conversion of land to housing, orchards, and vineyards is widespread and continues to degrade salamander habitats (Southern Interior Reptile and Amphibian Recovery Team 2008). Increase in urbanization is most notable in the Okanagan Valley, where populations occur in close proximity to human habitation and roadways. Salamanders may persist or continue to migrate through urban environments, but can become trapped within urban dwellings (sump pumps and basement) or fall into pools and hence be lost from the breeding pool (Ashpole pers. comm. 2011).

Within the range of the Prairie / Boreal population, mainly in Alberta and to a lesser extent in Saskatchewan and Manitoba, there has been a change from grazing and small farms to increased large-scale farming and conversion of habitat to accommodate growing urban populations and expansion of oil and gas developments (Rashford et al. 2011; Statistics Canada 2012). Continued infilling of wetlands throughout the species’ range (Dahl and Watmough 2007; Bartzen et al. 2010) is expected to increase fragmentation of regional populations and increase isolation of small populations, thereby limiting their long-term persistence (Trenham and Shaffer 2005). Water management and use occurs throughout the species' range in the prairies, as every type of agriculture requires water management. Some impacts may be positive (digging of ponds) but most are probably negative, resulting from changes to hydro-periods at breeding sites and disturbance to the shoreline habitat.  Tiger salamanders continue to persist in some urban environments (e.g., near Edmonton: Paszkowski pers. comm. 2011), but long-term viability of these populations is unknown.

Road Mortality

Western Tiger Salamanders are susceptible to road kill where roads intersect migration routes to and from breeding sites. Reductions in amphibian populations are correlated with increasing traffic volume (Fahrig et al. 1995; Clevenger et al. 2003 specifically forA. m. melanostictum). Installation of culverts or other underpasses can be effective in alleviating road mortality (Pagnucco et al. 2011), but salamander mortality on the vast majority of roads is unmitigated.

Within the Southern Mountain population, all known Western Tiger Salamander breeding sites are within 750 m of roads (based calculations from TRIM maps by Orville Dyer, B.C. Ministry of Natural Resource Operations). Recent expansion of Highway 97 to 4 lanes (Transport Canada 2012) to accommodate growing human populations and vineyard visitors has increased traffic volumes and roadkill threat to migrating salamanders. Traffic volumes in the South Okanagan along Highway 97 record a range of 6000-24,000 vehicles per day between April and September when tiger salamanders are active (4-16 vehicles per minute; B.C. Ministry of Transportation and Highways 2012). Mortality on B.C. roads has been documented by biologists (Richardson et al. 1998; Ashpole pers. comm. 2012; Sarell, unpubl. data). Richardson et al. (1998) reported 50 road mortalities in one day near a breeding site. Recent (2010-2011) surveys along a stretch of road near Oliver, B.C. also found high mortality rates (Crosby, unpubl. data). It is unclear how many salamanders attempted to cross the road.

Within the Prairie / Boreal population, road mortality may not be as great a threat as in British Columbia due to the widespread distribution of salamanders, combined with reduced traffic densities away from urban centres. However, there has been an increase in rural traffic in Saskatchewan, combined with an increase in industrial and rural development, as larger populations are now residing outside of urban areas. Road traffic in Saskatchewan has increased on average 16%, from 2006 to 2011 across the range of the salamanders (Saskatchewan Ministry of Highways and Infrastructure 2013a,b). A large number of citizens have reported mass migrations of tiger salamanders across roads and highways in fall in the Prairies (Didiuk pers. comm. 2011; Kendall pers. comm. 2011; Vanderschuit pers. comm. 2011), but no efforts have been made to quantify the losses and their significance to populations. The only well documented record of road mortalities is adjacent to Banff National Park, near Seebe on the TransCanada Hwy, where 183 Western Tiger Salamander were found dead within a 300 m section of the road, 163 of which occurred over a 4-day period in August (Clevenger et al. 2001).

Introduced Species: Fish

Ambystomatid salamanders do not coexist well with predatory fish such as trout and have poor anti-predator abilities towards fish predators (Kats et al. 1988; Tyler et al. 1998; Sih et al. 2003; Dunham et al. 2004). Introduced sport fish prey on both adult and larval tiger salamanders. Tiger salamander larvae are adapted for rapid acceleration rather than sustained swimming (Hoff et al. 1989), a behaviour effective against  common sit-and-wait predators such as giant water bugs (Hemiptera: Belostomatidae), dragonfly nymphs (Odonata: Anisoptera), and predaceous diving beetle larvae (Choleoptera: Dytiscidae) (Fitzpatrick et al. 2003).

Many formerly fishless water bodies, including reservoirs, have been stocked with fish throughout the Western Tiger Salamander’s range. Introductions of sport fish, mosquito fish (Gambusia sp.), and other small bodied, non-native fish into tiger salamanders habitats or nearby larger water bodies, from where they can spread, all pose risks. Introductions of Green Sunfish (Lepomis cyanellus) have directly caused local extinction of A. m. stebbinsi in the U.S. (Storfer et al. 2004). Mosquitofish consumed more A. tigrinum larvae compared to the consumption of anuran larvae present (except Pseudacris triseriata) in laboratory experiments (Zeiber et al. 2008). Genetic evidence of recent and historical declines of tiger salamanders due to fish stocking (mainly trout), combined with drought and potentially disease, was reported in Yellowstone National Park in Montana and Wyoming (Spear et al. 2006).

Within the range of the Southern Mountain population, sport fish stocking is widespread, and all water bodies that can support fish do or will eventually have fish (Southern Interior Reptile and Amphibian Recovery Team 2008; Herborg pers. comm. 2012). Introduction of trout and bass (Micropterus dolomieu and M. salmoides) are inferred to have reduced or extirpated several salamander populations in the Okanagan Valley (Sarell 1996 and pers. comm. 2011).

Introduction of Goldfish (Crassius crassius) in small water bodies has been practised in southern British Columbia to control mosquito populations as part of pro-active West Nile Virus mitigation. Other species of fish, including non-native Pumpkinseed (Lepomis gibbosus), Yellow Perch (Perca flavescens), and native shiners (Richardsonius spp.) and sculpins (Cottus spp.) have been introduced to formerly fishless small lakes and ponds in this province. Introductions into formerly fishless waters are likely to reduce the persistence of salamander populations (Sarell 1996; Monello and Wright 2001; Ashpole et al. 2011).

In the Prairies, there has also been widespread introduction of sport fish throughout the range of the Western Tiger Salamander (Figure 6). In Alberta, fish stocking is ongoing and continues to expand within the foothills region. Tyrell Lake in Alberta used to be known for its large population of tiger salamanders, including neotenic forms. After the introduction of Rainbow Trout in 1962, this population declined. In October 1962, 250 kg of salamanders were caught in one day, but only one salamander was caught in 1973 and a few in 1988 (Mitchell and Prepas 1990). Rainbow Trout continue to be stocked (last stocked with 450,000 fingerlings in April 2009; Alberta Fisheries Management Information System 2009). Salamanders remain at low densities in Tyrell Lake (Goater pers. comm. 2011).

Introduced Species: Bullfrogs

American Bullfrogs (Lithobates catesbeianus) have been introduced to the Southern Okanagan. Although tiger salamandersmay consume Bullfrog tadpoles in laboratory experiments (McIntyre and McCollum 2000), adult Bullfrogs are a threat to Western Tiger Salamanders and other amphibians throughout their introduced range (Dumas 1966; Kiesecker and Blaustein 1997; Boone et al. 2004). Bullfrogs have a voracious appetite, are capable of laying up to 20,000 eggs in a clutch (Schwalbe and Rosen 1999), and unlike tiger salamanders are capable of coexisting with predatory fish (Hecnar 1997; Adams et al. 2003). Individual Bullfrogs are capable of dispersal distances up to 7-8 km (Schwalbe and Rosen 1999), and their breeding pond habitat preferences are similar to those of tiger salamanders in that both species require water bodies with relatively long hydro-periods required for larval development.

Bullfrog control is ongoing in the Okanagan, but eradication is extremely difficult, and Bullfrogs remain at low densities at some sites (Ashpole pers. comm. 2011). There is little direct evidence that Bullfrogs have contributed to the decline of tiger salamander populations in British Columbia (Southern Interior Reptile and Amphibian Recovery Team 2008). However, it is possible that Bullfrogs will become more widespread, adding to threats from introduced fish, road mortality, and habitat loss. Bullfrogs may also act as a reservoir host of amphibian chytrid fungus, which can cause disease and result in catastrophic declines (Daszak et al.2004; Pearl et al. 2007).

Bullfrogs are not currently a threat for the Prairie / Boreal population.

Agriculture and Chemical Contaminants

Chemical contaminants (herbicides, pesticides and fertilizers) directly or indirectly affect all life stages of Western Tiger Salamanders (Bishop 1992; Larson et al. 1998; Bishop et al. 1999; Pauli et al. 2000; Griffis-Kyle and Ritchie 2007). The use of glyphosate-based herbicides in conjunction with different surfactants reduces the growth and survival of larval A. tigrinum (Brodman et al. 2010). Organophosphate insecticides (Malathion®) can reduce larval growth, although they may not result in direct mortality (Ramsey et al. 2008). Fertilizers do not directly reduce survival of salamander larvae (Griffis-Kyle 2005, 2007; Griffis-Kyle and Ritchie 2007), but indirect effects are of concern.

Mixtures of chemicals may combine synergistically and alter immune function. A study comparing the susceptibility of A. tigrinum to the Ambystoma tigrinum virus found that larvae exposed to a herbicide (Atrazine®) were more likely to contract and die of infections (Forson and Storfer 2006a,b) than were unexposed larvae. In contrast, an insecticide (Deltamethrin®), which on its own can cause acute toxicity in A. tigrinum, triggered no immunosuppression based on assays (Froese et al. 2009), but the study did not expose animals to live viral cultures.

Within the range of the Southern Mountain population, the use of chemicals in fruit farming continues to be of concern to salamander and other amphibian populations (Bishop 1992). Malathion® is the recommended pesticide for the control of mosquito populations to reduce the threat of West Nile Virus to humans. Malathion® has also been cleared for use to control the Spotted Wing Drosophila (Drosophila suzukii), an introduced pest that lays eggs in ripening fruit (United Agri Products 2010; B.C. Ministry of Agriculture 2011). Private landowners may apply Malathion® without a licence (Mullan pers. comm. 2012). Given the importance of agriculture within the species’ range, the risk of chemical contaminants in salamander breeding sites is high.

The range of the Prairie / Boreal population overlaps with the main grain growing area of western Canada. The use of chemicals to augment crop production is of concern to salamander populations nearby crops. In urban wetlands, the use of pesticides, such as Malathion®, to control mosquitoes poses a risk to salamander populations.

Disease

Emerging infectious diseases have been implicated in the decline of amphibian populations worldwide (Daszak et al. 1999). Two diseases in particular pose threats to Western Tiger Salamanders: Ambystoma tigrinum virus (ATV) and amphibian chytrid fungus (Batracochytridium dendrobatidis or Bd). ATV, a ranavirus, is part of a group of closely related viruses belonging to the group Iridoviridae that infect many fishes and amphibians (Jancovitch et al. 2001). ATV has been identified as the causative agent in localized mass mortality events of Western Tiger Salamanders in Saskatchewan, Manitoba, and Alberta (Bollinger et al. 1999; Schock et al. 2009; Goater pers. comm. 2011) and in neighbouring U.S. states (Docherty et al. 2003). It was responsible for a mass die-off during the summer of 2011 in Waterton Lake National Park (Johnston pers. comm. 2011). The prevalence of ATV at any site in Alberta, Manitoba and Saskatchewan is high (up to 50%) in most populations examined in any given year (Goater pers. comm. 2011; Schock pers. comm. 2011).

Observations of mortality due to ATV are sporadic. Models of infection suggest that ATV spread increases with salamander density, but frequency-dependent mechanisms (including repeated exposure from surviving metamorphs) can maintain the virus within the environment even at low salamander densities (Brunner et al. 2004). Transmission of ATV in the water appears to involve close proximity of salamanders (Jancovitch et al. 2001; Brunner et al. 2007). Transmission may occur through consumption of dead infected salamanders, scavenging, or aggressive behaviours (cannibalism, nipping and biting) (Pearman et al. 2004; Brunner et al. 2005; Harp and Petranka 2006). The virus can be stored in substrates and may remain infectious in water for > 97 days (reviewed by Whittington et al. 2010). Host switching may be important for maintaining the virus in the system (in frogs: Schock et al. 2008; in fish: Jancovitch et al. 2005; Picco and Collins2008; Picco et al. 2010). ATV may reside in persistent carriers such as metamorphosed amphibians that overwinter with the infection and then re-infect the population the following spring (Brunner et al. 2004). Individuals that do not die from infections within the first 2-3 weeks of exposure show reduced growth, which may prolong development and decrease the chance of surviving to metamorphosis as the pond dries (Parris et al. 2005). Western Tiger Salamanders may be particularly susceptible to the spread of ATV given low genetic diversity present at some sites (Spear et al. 2006; McMenamin and Hadly2010) and the positive correlation between lack of genetic variability and increased susceptibility to disease (Pearman and Garner 2005).

The prevalence of ATV within the Western Tiger Salamander’s range in British Columbia has not been assessed (Ashpole pers. comm. 2011), but its presence is probable given its widespread distribution in the prairies and in montane regions of the U.S. (Spear et al. 2006). Reports of mass mortalities due to ATV are numerous in Alberta and in parts of Saskatchewan and Manitoba where it has been investigated. Populations generally contain ~50% of individuals that test positive for the virus but show no mortality or morbidity except in apparently random years (Schock et al. 2010; Goater pers. comm. 2011). Other stress factors may be involved in disease outbreaks.

A second disease agent which may cause population declines is the amphibian chytrid fungus, Bd, which is linked to amphibian declines worldwide (Daszak et al. 1999; Schloegel et al. 2006). Bd is capable of infecting tiger salamanders (Davidson et al. 2003) and has been implicated in mortality events in Saskatchewan and Manitoba (Bollinger et al. 1999). However, the putative role of Bd in these declines is unclear in light of the prevalence of ATV in the region (Schock et al. 2010).

Bd is widespread in various species of amphibians in British Columbia (Deguise and Richardson 2009; Voordouw et al. 2010), but data for tiger salamanders are lacking. A recent survey of the occurrence and prevalence of Bd in Alberta found that it occurred at 44% of sites (n = 92 sites) across the province with a prevalence of 22% of individual amphibians at each site; however, no tiger salamanders (n = 3) were positive for Bd (Stevens et al. 2012). There is currently no evidence of chytrid-associated population declines in Alberta. Bd has also been reported from Saskatchewan, but no province-wide study has been completed (Canadian Cooperative Wildlife Health Centre 2011). The main disease threat is more likely to be ATV as there are few reports of Bd in Western Tiger Salamanders (Bollinger pers. comm. 2011).

The practice of using tiger salamander larvae as bait for fishing in some areas may facilitate the spread of ATV (Jancovitch et al. 2010) and Bd among watersheds. In B.C., live bait is not allowed. In some areas, including Manitoba and Alberta, collection of salamanders for personal use is legal. In Alberta live bait can be collected for personal use in fishing but has to be used within that site and not moved to another lake.

Number of Locations

Southern Mountain population:

The greatest new threat to the salamanders in the Okanagan is introduced Bullfrogs, which could invade lakes and wetlands where salamanders occur. Based on the potential rate of spread of Bullfrogs and considering the likelihood of their establishment with respect to the topography of the area, it is estimated that Bullfrogs account for 1 location in the Okanagan and other threats account for 13 locations within the remaining part of the range of the Southern Mountain population; therefore there are 14 threat-based locations for this population.

Bullfrogs are already established in the South Okanagan and could spread into the Osoyoos area, even if unassisted by humans. This area is counted as 1 location, based on Bullfrog threat. Given the topography and a greater distance requiring dispersal, Bullfrogs are unlikely to reach the lower Similkameen or Kettle rivers within the next 15 - 20 years without human aid. Disease or habitat destruction/alteration are considered most important threats at 4 locations near Grand Forks and at 9 locations along the Kettle River west of Midway. Introduced predatory fish will impact individual subpopulations where fish have been or will be introduced, but introductions may also spread into entire watersheds and into separated but adjacent ponds during flooding events.

Prairie / Boreal population:

There are 597 known sites. This is a conservative estimate due to limited surveys and occurrence information. The greatest threats are disease, fish stocking, and habitat loss due to urban, agricultural and industrial development. These threats are likely to have their greatest impact at the local population or site level, and therefore the estimated number of IUCN threat-based locations is large, probably over 500.

Protection, Status, and Ranks

Legal Protection and Status

The Southern Mountain population of the Western Tiger Salamander is listed federally as Endangered in Canada and is in Schedule 1 of the Species at Risk Act. The British Columbia Wildlife Act affords protection such that the tiger salamander cannot be killed, collected, or held in captivity without special permits.

The Prairie / Boreal population has no legal federal status, based on the previous assessment of tiger salamanders and their designation as Not at Risk by COSEWIC in 2004. This assessment included the taxon now known as Eastern Tiger Salamander, A. tigrinum, from Manitoba. The Prairie / Boreal population as defined in this report has not been previously assessed by COSEWIC as a separate entity.

Non-Legal Status and Ranks

The Canadian Endangered Species Conservation Council lists the Western Tiger Salamander as Secure in Alberta, Saskatchewan, and Manitoba and At Risk in British Columbia (CESCC 2011). NatureServe (2011) lists A. mavortium (Barred Tiger Salamander) as G5 (secure) globally, N5 (secure) nationally in Canada and in the U.S., S4S5 (apparently secure to secure) in Manitoba, and S2 (imperiled) in British Columbia, where the species is also on the provincial Red List of species at risk. NatureServe (2011) lists the species as A. tigrinum (Tiger Salamander) with a rank of S4 (apparently secure) in Alberta and with a rank of S5 (secure) in Saskatchewan.

In the U.S. adjacent to Canada, NatureServe (2011) lists this species as A. tigrinum (Tiger Salamander) with a rank of S5 in Idaho, S4 in Montana, and S3 in Washington State, where the species is also a “State Monitor” species (Washington Herp Atlas 2011).

Habitat Protection and Ownership

In British Columbia, 14 breeding sites (16.2% of 86 known sites) are within protected areas in parks (9 sites) or in Wildlife Habitat Areas on Crown land (5 sites). An additional 23 sites (26.7%) receive or are expected to receive some form of protection through voluntary stewardship agreements. There are no known breeding sites in the large South Okanagan Wildlife Management Area, probably due primarily to the invasion/introduction of predatory fish. Important protected sites include South Okanagan Grasslands Provincial Park, White Lake Grasslands Provincial Park, and the Kilpoola property acquired by The Nature Trust of B.C. A few wetlands occupied by Western Tiger Salamanders occur on Ducks Unlimited property, with additional small wetlands being constructed (Ashpole pers. comm. 2011). There are only two protected sites in the Kettle Watershed and none in the Similkameen or at the northern edge of the species’ range around Summerland (BC CDC 2012). The remaining 57% of known breeding sites occur on unprotected private lands (BC CDC 2012). The Southern Interior Amphibian and Reptiles Recovery Team is attempting to build support for habitat protection by stakeholders and the public to secure both aquatic and terrestrial habitat within the core of the species’ distribution.

In Alberta, Saskatchewan and Manitoba, there are no areas set aside for Western Tiger Salamanders, but they are found within nature preserves, natural areas including Nature Conservancy of Canada properties, provincial and national parks, and other types of Crown land in all three provinces. There are 188 sites (22%) within protected lands in Alberta, 21 sites (6.4%) in Saskatchewan, and 13 sites (8%) in Manitoba. Within those areas, the salamanders are afforded some form of protection through relevant provincial or federal wildlife or protected areas legislation (e.g. Alberta Parks Act 45.1 and the Canada National Parks Act). Outside these areas, they are not afforded any special protection.

Acknowledgements and Authorities Contacted

The following people and organizations provided distribution data: D. Schock, J. Crosby, B. Scheffers, M. Taylor, N. Anderson, B. Johnson, L. Wilkinson, L. Bilyk, D. Collicutt, D. Forsyth, G. Benoy, D. Nemberg, W. Vanderschuit, G. Scrimgeour, S. Humphries, C. Pacas, K. Khidas, M. Steigerwald, Katrina Stipec (BC CDC), G. Berg, J. Wagner, D. Demarchi (BC-SPI), and O. Dyer. Thank you to N. Anderson, A. Didiuk and R. Mooi for providing photos, and C. Neilson for GIS assistance.

Authorities contacted

Robert Anderson, Federal Biodiversity Information, Ottawa, Ontario

Sara Ashpole, University of Waterloo, Waterloo, Ontario

Lonnie Bilyk, Alberta Sustainable Resource Development, Edmonton, Alberta

Christine Bishop, Environment Canada – Recovery Team, British Columbia

Trent Bollinger, Canadian Cooperative Wildlife Health Centre, Saskatoon, Saskatchewan

Doug Collicutt, Nature North – Manitoba Herp Atlas, Winnipeg, Manitoba

Andrew Didiuk, CWS, Saskatoon, Saskatchewan

Orville Dyer, Ministry of Natural Resource Operations – Recovery Team, Penticton, British Columbia

Nicole Firlotte, Manitoba Consevation Data Centre, Winnipeg, Manitoba

Dave Fraser, BC Ministry of Environment, Victoria, British Columbia

Lisa Hallock, Washington Department of Fish and Wildlife, Olympia, Washington, USA

Briar Howes, Parks Canada, Gatineau, Quebec

Jeff Keith, Saskatchewan Conservation Data Centre, Regina, Saskatchewan

Randy Mooi, Manitoba Museum, Winnipeg, Manitoba

Dean Nernberg, National Defence, Ottawa, Ontario

Jeanette Pepper, Saskatchewan Ministry of Environment, Regina, Saskatchewan

Mike Sarell, Ophiuchus Consulting, Oliver, BC

Danna Schock, Keyano College, Fort McMurray, Alberta

Katrina Stipec, British Columbia Conservation Data Centre

Bill Watkins, Manitoba Department of Conservation, Winnipeg, Manitoba

Lisa Wilkinson, Alberta Fish and Wildlife, Edson, Alberta

Information Sources

Adams, M.J., C.A. Pearl, and R.B. Bury. 2003. Indirect facilitation of an anuran invasion by non-native fishes. Ecology Letters 6:343-351.

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Biographical Summary of Report Writer

Arthur Whiting received his B.Sc. in Zoology at the University of Guelph in 1999, where he completed a project on isozyme inheritance in Ambystoma maculatum with Jim Bogart. He completed his M.Sc. (“Population ecology of the western chorus frog Pseudacris triseriata”) at McGill University in 2004. Arthur completed his Ph.D. on the “Factors affecting larval growth and development of the boreal chorus frog Pseudacris maculata”in 2010.Arthur is currently engaged in postdoctoral research on the phenology of amphibians and birds in response to climactic conditions and global change as part of a continental network of researchers TWGCRN.

Arthur’s research has focused on the determining factors that affect the recruitment, growth and diet of larval anurans, and determining habitat use of terrestrial anurans; much of his effort centres on chorus frogs (Pseudacris), but he maintains a healthy interest in all amphibians. He has recently instructed courses on Population Ecology at the University of Alberta and is currently a sessional instructor at NAIT for Limnology.

Collections Examined

University of Alberta Zoological Museum, specimen 2999, to verify locality (tag locality differed from Museum database – tag locality was chosen based on distribution map).

Photos of Manitoba Museum specimens MM365, MM367, MM368, MM373, MM375, MM377, MM379, MM380, MM384 to confirm identity of Barred Tiger Salamanders versus Eastern Tiger Salamanders (MM375).

Appendix 1: Threats Calculator results for the Southern Mountain population of the Western Tiger Salamander in British Columbia (February 2012).

Species or Ecosystem Scientific Name:
Ambystoma mavortium - Southern Mountain population

Date:
23/02/2012

Assessor(s):
Original assessment by P Chytyk 2008; L Gelling transferred reviewed scores in 2008. Reviewed and updated in Feb 2012 by K. Ovaska, P. Govindarajulu, D. Fraser, L. Gelling, M. Herborg , S. Ashpole, A. Whiting, J. Hobbs, L. Ramsay

References:
2012 draft COSEWIC status report; 2008 Recovery Strategy

Overall Threat Impact Calculation Help:

 

Appendix 2: Threats Calculator results for the Prairie / Boreal population of the Western Tiger Salamander (September 2012).

Species or Ecosystem Scientific Name
Ambystoma mavortium – Prairie / Boreal population

Date:
11/09/2012

Assessor(s):
C. Paszkowski, K. Ovaska, D. Schock, A. Whiting

References:
2012 COSEWIC status report (draft)

Overall Threat Impact Calculation Help: