Shortfin mako (Isurus oxyrinchus) COSEWIC assessment and status report

Official title: COSEWIC Assessment and Update Status Report on the Shortfin Mako (Isurus oxyrinchus) in Canada COSEWIC Assessment and Update Status Report on the Shortfin Mako Isurus oxyrinchus Atlantic population in Canada

COSEWIC assessment and status report on the shortfin mako Isurus oxyrinchus (Atlantic population) in Canada

Shortfin Mako

Special concern 2017

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. 2017. COSEWIC assessment and status report on the Shortfin Mako Isurus oxyrinchus, Atlantic population, in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xii + 34 pp. (Species at Risk Public Registry website).

Previous report(s):

COSEWIC 2006. COSEWIC assessment and status report on the shortfin mako Isurus oxyrinchus (Atlantic population) in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 24 pp.  

Production note:

COSEWIC would like to acknowledge Scott Wallace for writing the status report on the Shortfin Mako. This report was prepared under contract with Environment and Climate Change Canada and was overseen by John Neilson, Co-chair of the COSEWIC Marine Fishes Specialist Subcommittee.

For additional copies contact:

COSEWIC Secretariat

c/o Canadian Wildlife Service

Environment and Climate Change Canada

Ottawa, ON

K1A 0H3

Tel.: 819-938-4125

Fax: 819-938-3984

COSEWIC E-mail

COSEWIC Web site

Également disponible en français sous le titre Ếvaluation et Rapport de situation du COSEPAC sur le Requin-taupe bleu (Isurus oxyrinchus), population de l'Atlantique, au Canada.

Cover illustration/photo:

Shortfin Mako - Cover image courtesy of the International Commission for the Conservation of Atlantic Tunas (A. López (‘Tokio’)).

COSEWIC  Assessment summary

Assessment Summary – April 2017

Common name

Shortfin Mako - Atlantic population

Scientific name

Isurus oxyrinchus

Status

Special Concern

Reason for designation

This species is more vulnerable than many other Atlantic shark species because of its long life span and low productivity. The species has a single highly migratory population in the North Atlantic, of which a portion is present in Canadian waters seasonally. The total North Atlantic catch and abundance are stable. Most analyses in a recent stock assessment showed a stable or increasing trend since 1971, resulting in improved status compared with the previous COSEWIC status report. However, the status is not secure, given the uncertainties in the stock assessment, the short period of improving catch rates relative to the 25-year generation time, and the low productivity of the species.

Occurrence

Quebec, New Brunswick, Prince Edward Island. Nova Scotia, Newfoundland and Labrador, Atlantic Ocean

Status history

Designated Threatened in April 2006. Status re-examined and designated Special Concern in April 2017.

COSEWIC Executive summary

Shortfin Mako (Isurus oxyrinchus)

Atlantic population

Wildlife species description and significance

Shortfin Mako (Isurus oxyrinchus) is one of two species in the genus Isurus (the other being the Longfin Mako, I. paucus) and one of five species in the family Lamnidae or mackerel sharks. Other lamnid sharks found in Canada include the White Shark (Carcharodon carcharias), Salmon Shark (Lamna ditropis), and the Porbeagle shark (L. nasus).

Based on biogeographical separation, genetic differences with other global populations, and no evidence of structuring within the North Atlantic, Shortfin Mako in the North Atlantic are considered to be a population and the single Designatable Unit (DU) in Canada is part of the wider North Atlantic population

Although this species is not directly targeted in Canada, it is caught and landed as bycatch in a limited number of Canadian fisheries. Due to its energetic displays and edibility, it is sought by sport anglers as a game fish in the United States and occasionally in Canada.

Distribution

Shortfin Mako is widespread in temperate and tropical waters of all oceans from about 50°N (up to 60°N in the northeast Atlantic) to 50°S. Shortfin Mako are distributed throughout the North Atlantic in waters south of 60˚N to the equator. In Canadian waters, Shortfin Mako is a highly migratory summer and fall visitor typically associated with warm Gulf Stream waters and represents the northern extension of the North Atlantic-wide population. It has been recorded from Georges and Browns Bank, along the continental shelf of Nova Scotia, the Grand Banks and even into the Gulf of St. Lawrence.

Habitat

Temperature appears to be the dominant factor defining Shortfin Mako distribution. Preferred water temperature is between 17-22°C and consequently it is unlikely that Shortfin Mako have extended residency in Canadian waters. A lack of data has prevented any identification of habitats necessary for critical life functions (e.g., mating, pupping) of this species in Canadian waters, while impeding investigation of whether Shortfin Mako habitat has changed over time,

Biology

Shortfin Mako are aplacental viviparous with developing embryos known to feed on unfertilized eggs during the 15-18 month gestation period. Females have 11 pups on average every three years. The estimated age at which half the individuals are mature is 8 years for males and 18 years for females. They are a low-productivity species compared with other shark species, and have a generation time of about 25 years. It appears as if females migrate to latitudes of 20°-30°N to give birth based on evidence that no pregnant females have been caught outside of this range.

This species is likely adapted to withstand natural changes in its environment as adults can readily move long distances and prey upon a wide variety of species. Based on diet studies of adults, Shortfin Makos prey upon a wide variety of species, primarily fish including Bluefish, Butterfish, tunas, mackerels, bonitos, and Swordfish.

Population sizes and trends

For Canadian waters, a catch rate series from the Canadian pelagic longline fishery from 1996 to 2014 is the only available index of abundance. The most recent data show a non-significant decline in catch rates compared to earlier in the time series. Canadian waters represent the northern fringe of the Shortfin Mako range, and therefore changes in the Canadian index may reflect distributional shifts.

Internationally there are six catch rate indices that are considered by the International Commission for the Conservation of Atlantic Tunas (ICCAT) to be the most representative of abundance. The combined interpretation is that these indices were fairly consistent in showing a decline during the 1990s followed by an increase after 2000.

A stock assessment conducted by ICCAT in 2012 concluded that updated abundance indices showed increasing or flat trends. Despite large uncertainties, the Commission concluded that the probability of overfishing was low and that the status of the population is above the maximum sustainable yield.

Threats and limiting factors

Bycatch in commercial longline fisheries targeting pelagic tunas and Swordfish is the main cause of mortality within Canadian waters and throughout the range of the Shortfin Mako. Post-release survival of Shortfin Mako shark caught by longline gear in Canada was recently estimated at 49% resulting in an historical average annual estimate of total Canadian mortality at about 69 t/year. In 2015 voluntary release of live Shortfin Mako in the Maritimes Region was supported by the longline fishing industry and is anticipated to reduce mortality in Canadian waters. Mature females comprise less than 1% of the observed Shortfin Mako caught in the Canadian Maritimes Region pelagic longline fishery with at-sea observer coverage averaging about 5% of the annual fishing effort.

Total fishing mortality for the entire North Atlantic is uncertain due to poor catch reporting, particularly in years prior to 1996. From 1996-2010, average reported landings were around 2400 t but this number was considered to be an underestimate by a recent ICCAT study that estimated the average catch (landings and discards) during this time period at 3500 t.

Due to their life-history characteristics such as relatively slow growth, late age of maturity and low reproductive rates, Shortfin Mako populations have relatively low productivity, thus the capacity to recover is limited once the population is depleted.

Protection, status and ranks

There is no targeted fishery for Shortfin Mako sharks in Atlantic Canada and there is a Canadian ban on shark finning (i.e., removing and retaining fins while discarding the shark’s body at sea). Incidentally captured individuals are permitted to be retained in some fisheries. Fishing regulations and protective measures for the Maritimes Region include a non-restrictive annual landings limit for Shortfin Mako of 100 t, corrodible circle hooks to reduce bycatch and post-release mortality in the pelagic longline fishery and a voluntary release of live Shortfin Mako. Present regulations do not limit total fishing mortality or discarding at sea.

Shortfin Mako (North Atlantic subpopulation) was last assessed in 2004 by the International Union for Conservation of Nature (IUCN) as “vulnerable”. The US National Oceanographic and Atmospheric Administration (NOAA) describes the population status as “stock is healthy, because it is not overfished and the probability that overfishing is occurring is low”. COSEWIC previously assessed the Atlantic population of Shortfin Mako as “Threatened” in 2006 but a Species at Risk Act Schedule 1 listing decision has yet to be made.

Technical summary

Scientific name: Isurus oxyrinchus

English name: Shortfin Mako (Atlantic Population)

French name: Requin-taupe bleu (population de l’Atlantique)

Range of occurrence in Canada: Quebec, New Brunswick, Newfoundland and Labrador, Nova Scotia, Prince Edward Island, Atlantic Ocean (Georges and Browns Bank, along the continental shelf of Nova Scotia, the Grand Banks and occasionally into the Gulf of St. Lawrence)

Preface

There are several new pieces of information since the writing of the 2006 Shortfin Mako COSEWIC status report including:

  • studies confirming genetic structure of the population;
  • all available tagging information from North Atlantic collated;
  • PSAT tags deployed on Canadian captured Shortfin Mako;
  • post-release survivorship information from Canadian pelagic longline fishery;
  • ICCAT assessment in 2012 which included an analysis of best available trend indices, estimates of unaccounted for catch, productivity estimates, and a stock assessment;
  • Based on new age validation studies, female age at maturity has been substantially revised from 7-8 yr to 18 yr (based on new information), implying lower population resilience than previously believed
  • Better estimates of Canadian fishing mortality

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 (2016)

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)
(Note: Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.)
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)
(Note: Formerly described as “Not in any category”, or “No designation required.”)
A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.
Data deficient (DD)
(Note: 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.)
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.

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


COSEWIC Status report on the Shortfin Mako (Isurus oxyrinchus)

Atlantic population in Canada

2017

Wildlife species description and significance

Name and classification

Shortfin Mako (Isurus oxyrinchus) is one of two species in the genus Isurus (the other being the Longfin Mako, I. paucus) and one of five species in the family Lamnidae or mackerel sharks. Other lamnid sharks found in Canada include the White Shark (Carcharodon carcharias), Salmon Shark (Lamna ditropis), and Porbeagle (Lamna nasus). There are no recognized subpopulations of Shortfin Mako.

Morphological description

Shortfin Mako are identified by a pointed snout, relatively small eyes, long smooth-edged dagger-like teeth without side cusps (on both jaws), and a U-shaped mouth (Figure 1). The lower anterior teeth protrude horizontally on jaws even when the mouth is closed. Pectoral fins are slightly curved with tips relatively narrow, anterior margins about 16 to 22% of total length and shorter than head length. Origin of first dorsal fin over or just behind the pectoral free rear tip; first dorsal-fin apex broadly rounded in young but more angular and narrowly rounded in large juveniles and adults; first dorsal-fin height greater than base length in large individuals but equal or smaller in young below 185 cm. The crescent-shaped caudal fin has a horizontal primary keel but no secondary keel. The dorsolateral colouration is brilliant blue or purplish, with white below the underside of snout in young and adults. The head is dark in colour and partially covers the gill septa. The dark colour of the flanks does not extend ventrally onto the abdomen; the pelvic fins are dark on anterior halves, white on posterior halves, with the undersides white.

 

Figure 1.	Shortfin Mako (Isurus oxyrinchus). Figure from the International Commission for the Conservation of Atlantic Tunas (attributed to A. López, (‘Tokio’)).
Figure 1. Shortfin Mako (Isurus oxyrinchus). Figure from the International Commission for the Conservation of Atlantic Tunas (attributed to A. López, (‘Tokio’)).
Figure 1. Text description

Illustration of the Shortfin Mako. The Shortfin Mako has a pointed snout and relatively small eyes. The pectoral fins are slightly curved with relatively narrow tips and anterior margins about 16 to 22 percent of total length. The first dorsal fin originates over or just behind the pectoral free rear tip. The crescent-shaped caudal fin has a horizontal primary keel but no secondary keel. The back and sides of the Shortfin Mako are brilliant blue or purplish, with white below the underside of snout. The head is dark and partially covers the gill septa.

Misidentifications have occurred in warmer waters where the two mako species ranges commonly overlap. In Canada where Longfin Mako are extremely rare, misidentification between the two species is not believed to be a problem. In Atlantic Canada, Shortfin Mako has been misidentified as Porbeagle shark and may have contributed to underestimation of Shortfin Mako landing data prior to 1996 (Campana et al. 2004a).

Population spatial structure and variability

Current understanding of the population spatial structure of Shortfin Mako globally and in the North Atlantic specifically has been achieved through over 50 years of conventional tagging, recent satellite tagging, and genetic studies over the last two decades (ICCAT 2012; Campana et al. 2015).

In 2012, the International Commission for the Conservation of Atlantic Tunas (ICCAT) collated all available conventional tagging information (i.e., wire tags) in the North Atlantic. Since 1962, a total of 9218 tags have been released and 1203 recaptured (Figure 2). Most of these tags have been deployed off the northeast coast of the United States. While Shortfin Mako were found to travel large distances of up to 3400 km across the Atlantic most movement was between south and east within the northwest Atlantic with very few captures below 20˚N and none south of 5˚N (Figure 2).

Shortfin Mako (Isurus oxyrinchus).
Figure 2. Tag and release distributions for Shortfin Mako in the Atlantic Ocean displayed as straight lines between release and recovery locations (ICCAT 2012).
Figure 2. Text description

Map illustrating tag and release distributions for Shortfin Mako in the Atlantic Ocean. Distributions are displayed as straight lines between release and recovery locations.

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