Recovery Strategy for the North Pacific Right Whale (Eubalaena japonica) in Pacific Canadian Waters

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1.  Background1

1.1  Species Assessment Information from COSEWIC

Date of Assessment: November 2004

Common Name (population): North Pacific Right Whale
 
Scientific Name: Eubalaena japonica

COSEWIC Status: Endangered

Reason for Designation: Although there have not been sightings of this species in the last 50 years in Canadian waters, there have been sightings both south and north of British Columbia waters.  Therefore, it is not appropriate to classify the species as extirpated.  The total population in the eastern North Pacific likely numbers a few tens of animals.
 
Canadian Occurrence: Pacific Ocean

COSEWIC Status History: The Right Whale was considered a single species and designated Endangered in 1980.  Status re-examined and confirmed in April 1985 and April 1990.  Split into two species in May 2003.  North Pacific Right Whale was not re-evaluated in May 2003; it retained the Endangered status of the original Right Whale.  Status re-examined and confirmed Endangered in November 2004.  Last assessment based on an update status report.

1.2  Description of the Species

The North Pacific Right Whale, Eubalaena japonica (Lacépède 1818, Rosenbaum et al. 2000b), is a large, robust, baleen whale.  All of the right whale species have similar physical descriptions.  Adults can reach up to 18 meters in length, and may weigh over 100 tonnes (Kenney 2002).  Females are larger than males, and newborns are 4.5 to 6 meters long at birth.  Right whales are distinguished by a stocky body, black colouration (sometimes with white patches on the ventral surface), lack of a dorsal fin, a large rostrum (about ¼ of the body length), strongly bowed lower lip, and callosities on the head region.  Callosities are irregular patches of thickened, keratinized tissue, which can be inhabited by dense populations of specialized amphipod crustaceans, known as cyamids (Kenney 2002).  Two rows of long (up to 2.5 m in length), dark baleen plates hang from the upper jaw, with about 225 plates on each side.  The tail is very broad, deeply notched, and all black with a smooth trailing edge.  They have a distinct V shaped blow, upwards of 5 meters in height.  Right whales lack elastic throats, unlike other baleen whales that have pleated, expandable throats used to gulp food consisting of large krill or fish.  The right whale feeds almost exclusively on copepods (Calanus spp.), which are gathered by moving through dense patches of these organisms with their huge mouths open at the surface.  Filter feeding can also take place at depth.  Feeding dives in the bottom boundary layers have been observed in North Atlantic Right Whales (Baumgartner and Mate 2003, Gregr and Coyle 2009). 

1.3  Populations and Distribution

1.3.1  Nationally Significant Populations

Recent studies indicate that North Pacific, North Atlantic and Southern Right Whales are three distinct species with complete and long-established isolation (Rosenbaum et al. 2000a, Brownell et al. 2001).  The Southern Right Whale has long been recognized as a separate species, E. australis.  Although the North Pacific Right Whale was formerly considered to be the same species as the North Atlantic Right Whale (E. glacialis), genetic data show that the North Pacific Right Whale is more closely related to the Southern Right Whale (Rosenbaum et al. 2000a).  Rosenbaum et al. (2000a) reviewed genetic data on right whales worldwide and concluded that three species should be recognized. The International Whaling Commission Scientific Committee accepted Rosenbaum et al.’s analysis and proposed nomenclature, and three species – E. japonica in the North Pacific, E. glacialis in the North Atlantic, and E. australis in the southern hemisphere – were formally recognized (IWC 2001b). More recently, Gaines et al. (2005) confirmed this species delineation by examining both mitochondrial and nuclear DNA.

The historical population structure for right whales in the North Pacific is not clear.  What is known about historical distribution is inferred from charts prepared by Matthew Fontaine Maury in the early 1850’s and Charles Haskins Townsend in the 1930s based on data from American whalers’ logbooks (Josephson et al. 2008).  Townsend’s charts (1935; see Figure 1 for eastern North Pacific chart) show a discontinuous distribution across high latitudes, with few catches in the mid-Pacific region.  These data have been used by numerous authors as evidence to support the hypothesis of discrete eastern and western populations in the North Pacific (Brownell et al. 2001).  However, Scarff (1991) noted that Maury’s charts (Maury 1852, Maury 1853) suggest a more continuous distribution of right whales (relative to effort), across the North Pacific (Figure 2; Scarff 1991), and that the apparent discrete populations of right whales in the eastern and western North Pacific reflected in the Townsend charts is largely an artifact of the non-random distribution of whalers in the North Pacific and their concentration on the eastern (Gulf of Alaska “Northwest Ground’) and western (Kamchatka/Sea of Okhostk) areas.  However, the depiction of data in the Maury charts has recently been proven to be erroneous. Reeves et al. (2004) provide direct evidence that the distribution of North Atlantic Right Whales in an offshore area called ‘Maury’s Smear’ shown in the 1852-53 charts is at least partially and possibly entirely erroneous, due to errors in extraction and transcription of data in the making of the charts.  This finding casts doubt on the reliability of inferences about the historical distribution of right whales from the Maury charts in other areas.  Josephson et al. (2008) subsequently analyzed the Maury data for the North Pacific Right Whale, and determined that plotting errors were also made in this region.  This analysis showed that right whales were likely not distributed continuously across the North Pacific as the Maury charts depict, but instead had a pronounced longitudinally bimodal distribution, and were not frequently encountered in the central-northern North Pacific (Figure 3).  This bimodal distribution is similar to the distribution shown in the Townsend (1935) charts (Josephson et al. 2008), and supports the two stock (eastern and western populations) hypothesis.

Figure 1. Map of historical right whale catches from 1785 – 1913 in the eastern North Pacific from logbook records of American whaleships (replicated from Townsend 1935). The dot colour represents month of catch.  The discontinuous distribution across high latitudes has been used to support the hypothesis of discrete eastern and western populations in the North Pacific (Brownell et al. 2001).

Figure 2. Encounter rates (number of right whale days divided by the number of whaling days) by 5° square and month as portrayed on Maury’s charts (as tabulated by Scarff 1991) (Adapted from Josephson et al. 2008).  This depiction of the data showing continuous distribution across the Pacific has recently been proven to be erroneous (Reeves et al. 2004, Josephson et al. 2008).

Figure 2 . Encounter rates (number of right whale days divided by the number of whaling days) by 5° square and month as portrayed on Maury’s charts (as tabulated by Scarff 1991) (Adapted from Josephson et al. 2008).  This depiction of the data showing continuous distribution across the Pacific has recently been proven to be erroneous (Reeves et al. 2004, Josephson et al. 2008).

Figure 3. Encounter rates (number of right whale days divided by number of whaling days) by 5° square and month from selected Maury Abstracts. The encounter rates in five 5° squares are listed by month to illustrate the vertical scale, followed by the numbers of right whale days and whaling days in parentheses (Adapted from Josephson et al. 2008).  Re-analysis of the Maury data by Josephson et al. (2008) show that right whales were not distributed continuously across the North Pacific (as the Maury charts depict) but instead exhibit pronounced longitudinally bimodal distribution.

Figure 3 . Encounter rates (number of right whale days divided by number of whaling days) by 5° square and month from selected Maury Abstracts. The encounter rates in five 5° squares are listed by month to illustrate the vertical scale, followed by the numbers of right whale days and whaling days in parentheses (Adapted from Josephson et al. 2008).  Re-analysis of the Maury data by Josephson et al. (2008) show that right whales were not distributed continuously across the North Pacific (as the Maury charts depict) but instead exhibit pronounced longitudinally bimodal distribution.

Patterns of sightings in the 20th century, and apparently distinct catch and recovery histories of right whales in the eastern and western North Pacific, provide further support for the two stock hypothesis, at least with regard to concentrations on feeding grounds (Brownell et al. 2001).  Although some authors (e.g., Kenney 2002) have argued that there are insufficient genetic or re-sighting data to support this separation, most support the distinction between western and eastern North Pacific Right Whale populations, and a review by the IWC (2001b) concluded that the east-west population distinction should remain in place until new data are available.  As a result, this report will also recognize the east-west population distinction.  The degree of genetic exchange between the eastern and western populations in high latitudes or on a possible offshore breeding ground is unknown (Brownell et al. 2001).

1.3.2  Global Range

The recent re-analysis of the Maury whaling data (see Section 1.3.1 Nationally Significant Populations) by Josephson et al. (2008) represents the best available information on the distribution of North Pacific Right Whales in the 1840s.  In summer, the density was high in the Gulf of Alaska and along the eastern coast of Kamchatka, around the Kuril Islands and northward into the Sea of Okhotsk, and in the Sea of Japan (Figure 3; Josephson et al. 2008).  At all latitudes between longitudes 170° E and 160° W, the density of right whales was much lower than suggested in the Maury charts (Josephson et al. 2008).  Right whales were encountered by American whalers farther south in the spring than in other seasons.  This is consistent with the hypothesis that right whales moved seasonally northward from regions south of where American whalers usually searched, but does not necessarily suggest the locations of wintering or calving grounds (Josephson et al. 2008).  The historical distribution shown in Figure 3 is similar to the right whale catch distribution shown in charts by Townsend (1935), which do not account for search effort. 

Post-exploitation distribution of the North Pacific Right Whale is poorly known, but it is clearly much more restricted than the historical distribution (Brownell et al. 2001).  There are very few data on current summering and wintering grounds.  Gaskin (1987) indicated that whaling data assembled by Nemoto (1957, 1959, and 1962) and Gaskin (1976) suggest that most remaining eastern North Pacific Right Whales gather together in summer on the southeastern shelf of the Bering Sea, around the eastern Aleutian Islands, and Kodiak Island.  Further studies of historical concentrations and some recent summer sightings indicate that the Bering Sea and Gulf of Alaska may contain important feeding grounds (Scarff 1986, Scarff 1991, Moore et al. 2000, Brownell et al. 2001, Clapham et al. 2004, Josephson et al. 2008, Munger et al. 2008).  Post-whaling sightings have been reported as far south as central Baja California in the eastern North Pacific, and Hawaii in the central North Pacific and as far north as the sub-Arctic waters of the Bering Sea and Sea of Okhotsk in the summer (Herman et al. 1980, Berzin and Doroshenko 1982, NMFS 1991, LeDuc 2004, Wade et al. 2006).

The calving or wintering grounds of the eastern North Pacific Right Whale are unknown.  Scattered reports exist of right whales seen off Washington, northern Oregon, California and Hawaii during winter months (Scarff 1986, Gaskin 1987, Scarff 1991), but other than these sightings Brownell et al. (2001) found little evidence that these areas were ever important habitats for North Pacific Right Whales.

Migratory patterns of the North Pacific Right Whale are unknown, although other right whale species generally spend the summer on high-latitude feeding grounds (Braham and Rice 1984). Among North Atlantic Right Whales, part of the population moves south in the winter (pregnant females, some juveniles and few adult males) while the rest is thought to remain at higher latitudes (Brown et al. 2009; L. Murison, Grand Manan Whale and Seabird Research Station, personal communication, 2010). Historically, North Pacific Right Whales were found across a wide range of latitudes during both summer and winter, which is evidence of a staggered or diffuse migration (Scarff 1991).  Seasonal movement is also evident in monthly plots of twentieth century and historical records (Clapham et al. 2004, Josephson et al. 2008). 

1.3.3  Canadian Range

Historical whaling data (Figures 1 and 3) indicate that right whales were present in Pacific Canadian waters from April to October (Townsend 1935, Clapham et al. 2004, Josephson et al. 2008), possibly feeding or migrating to or from calving grounds. 

Due to insufficient data, it is not possible to confirm the presence or describe the distribution of this species in Canada.  Only seven right whales were taken by B.C. whalers, who worked mainly in coastal waters (Table 1, Figure 4).  The last confirmed right whale sighting that may have been in Pacific Canadian waters was in 1970 from a Japanese scoutboat west of the Haida Gwaii (Queen Charlotte Islands) (Table 1; Wada 1975).  However, due to the range of coordinates given for this sighting, there is a possibility that it did not occur in Pacific Canadian waters.  An unconfirmed right whale sighting in Pacific Canadian waters was made in 1983 at the mouth of Juan de Fuca Strait (Table 1; Reeves and Leatherwood 1985).  No sightings of right whales have been made during 28,725.33 km of shipboard cetacean surveys undertaken during 2002-2008 in coastal Pacific Canadian waters by the Cetacean Research Program, Pacific Biological Station, Fisheries and Oceans Canada (Ford et al. 2010a).  Although survey effort over this time period was extensive (see App. A), it was focused primarily on nearshore species and was minimal in offshore areas (> 10 nautical miles from shore) that were historically occupied by right whales as indicated by whaling catches (Figure 1).  No right whale vocalizations have been detected during the initial phase (2006 and 2007)2 of passive acoustic monitoring conducted by Fisheries and Oceans Canada in coastal Pacific Canadian waters (Ford et al. 2010b).

Table 1.  Right whale catches and sightings in British Columbian waters, 1900-2008.

DATE

LOCATION

TYPE

NUMBER
OF
WHALES

WHALING
STATION

REFERENCE

June, 1914

Haida Gwaii
 (no coordinates)

Catch

1

Naden Harbour

Nichol et al. 2002

June, 1918

Haida Gwaii
(no coordinates)

Catch

1

Rose Harbour

Nichol et al. 2002

June 15, 1924

W of Dixon Entrance
(54°35 N, 133°55 W)

Catch

1

Naden Harbour

Nichol et al. 2002

June 24, 1924

W of Graham Island
 (54°05 N, 133°40 W)

Catch

1

Naden Harbour

Nichol et al. 2002

June 10, 1926

W of Graham Island
(53°40 N, 133°45 W)

Catch

1

Naden Harbour

Pike and MacAskie 1969

June 10, 1929

Haida Gwaii
(no coordinates)

Catch

1

Rose Harbour

Nichol et al. 2002

July 18, 1951

Off NW Vancouver Island
(50° N, 128° W)

Catch

1

Coal Habour

Pike and MacAskie 1969

1970

W of Haida Gwaii
(50-55° N, 130-140° W)

Sighting

2

-

Wada 1975 †

1983

Juan de Fuca Strait
(48° 33 N, 124° 39 W)

Sighting

2

-

Reeves and Leatherwood
1985 in Braham 1986††

† Due to the range of coordinates given for this sighting, there is a possibility that this sighting occurred just outside of Canadian waters.
†† This is an unconfirmed sighting.

Figure 4. Right whale sightings and catches in British Columbia waters and in U.S. waters adjacent to the Canadian border, 1900-2008.  Note that coordinates were not found for several catches positioned at whaling stations (see Table 1), and that the range of coordinates for the 1970 sighting (Wada 1975) is too broad to plot on this map.

Figure 4 . Right whale sightings and catches in British Columbia waters and in U.S. waters adjacent to the Canadian border, 1900-2008.  Note that coordinates were not found for several catches positioned at whaling stations (see Table 1), and that the range of coordinates for the 1970 sighting (Wada 1975) is too broad to plot on this map.

Sightings Adjacent to Canadian Waters

Three nearshore sightings of seven animals have been documented in U.S. waters near the B.C./Washington border (Table 2, Figure 4). The proximity of these sightings to Canadian waters suggests that these animals could potentially be using similar habitats in Canadian waters, or be passing through Canadian waters on their way to the Bering Sea and Gulf of Alaska where right whales have been observed in the summer.  Between 1958 and 1977, eight sightings in offshore (i.e., outside the 200 mile limit to 145° W) waters are recorded (Table 2).

Table 2 . North Pacific Right Whale sightings in nearshore and offshore areas adjacent to Pacific Canadian waters, 1900-2008.

DATE

LOCATION

NUMBER
OF
WHALES

REFERENCE

Nearshore

April 8, 1959

SW of Grays Harbour, Washington
(45°55 N, 125°25 W)

3

Fiscus and Niggol 1965

January 17, 1967

W of Cape Flaherty, Washington
(48°20 N, 125°06 W)

3

Rice and Fiscus 1968

May 24, 1992

NW of Grays Harbour, Washington
(47°17 N, 125°11 W)

1

Rowlett et al. 1994

Offshore

1958-1967

50° N, 145° W

2

Pike and MacAskie 1969

1958-1967

54° N, 155° W

1

Pike and MacAskie 1969

1973

45-50° N, 140-150° W

1

Wada 1975

1974

40-50° N, 140-160° W

1

Anonymous 1976

1975

40-45° N, 140-150° W

2

Wada 1977

1977

40-50° N, 140-145° W

1

Wada 1979

1977

45-50° N, 135-140° W

2

Wada 1979

1.3.4  Population Sizes and Trends

North Pacific Right Whales were hunted intensively from 1835 to 1900 until the species was too severely depleted to support commercial whaling (Scarff 1986, Scarff 2001).  Pre-exploitation abundance has been estimated to be at least 11,000 animals (NMFS 1991).  However, Scarff (2001) analyzed total whaling-related mortality from 1839 to 1909, including mortality of struck-but-lost whales and mortality by non-American whalers, and estimated pre-exploitation abundance to be in the range of 26,500-37,000 animals.  Among the large whales, North Pacific and North Atlantic Right Whales have shown the fewest signs of recovery following depletion due to whaling.  Because so little is currently known about the North Pacific population, it is impossible to determine population trends at this time and only recently have the first population abundance estimates been presented (Wade et al. 2010).

Most estimates of recent population abundance and trends are speculative, being based upon general patterns of sightings (e.g. Berzin and Yabokov 1978, Braham and Rice 1984, Berzin and Vladimirov 1989, Vladimirov 1994, Vladimirov 2000 cited in Brownell et al. 2001).  Even the most quantitative studies (e.g., Ohsumi and Wada 1974, Miyashita and Kato 1998) have high variance in abundance estimates due to extrapolations from small sample sizes over large geographic areas (Brownell et al. 2001).  North Pacific Right Whales almost certainly do not number more than those found in the western North Atlantic (~300; IWC 1999, Brown et al. 2009), and most occur in the western North Pacific.  The western North Pacific population is little studied but may be growing (Miyashita and Kato 1998).  A population estimate of 922 (CV=0.433; 95% CI 404-2108) was calculated for the Okhotsk Sea for 1989-1992 (Miyashita and Kato 1998).  However, the reliability of this estimate is low (95% CI 404-2108).  Many still believe it is unlikely that there are more than a few hundred animals in the western population (Knowlton et al. 1994, IWC 1999, IWC 2001a, Kraus et al. 2001). 

Ohsumi and Wada (1974) and Wada (1976) estimated a population size of 120 for the eastern North Pacific.  More recently, a lack of sightings despite considerable survey effort by Japan and the U.S. suggest that the population may number in the tens (Miyashita and Kato 1998, Scarff 1986, LeDuc et al. 2001, NMFS 2006).  Clapham et al. (2005) believe that the total eastern North Pacific population is considerably less than 100 individuals.  First abundance estimates of 31 individuals (95% CL 23-54) based on photo-identification data and 28 individuals (95% CL 24-42) based on genetic data for the Bering Sea and Aleutian Islands have been developed by Wade et al. (2010) using mark-recapture methods.  While these estimates may represent a sub-population with a strong site fidelity to the southeastern Bering Sea, the total eastern North Pacific population is not thought to be much larger (Wade et al. 2010).

Recent sightings of right whales in the eastern North Pacific have been rare. Following a 1996 sighting of a group of right whales in the southeastern Bering Sea (Goddard and Rugh 1998), dedicated photo-identification studies, acoustically-aided ship based studies, and long-term passive acoustic monitoring studies have been conducted in this area, with most effort focused on shelf and slope waters of the southeastern Bering Sea and Gulf of Alaska (Shelden et al. 2005). Since the beginning of these studies, a few animals- from 4 to 23 individuals– have consistently been sighted and acoustically detected in the southeastern Bering Sea and the Gulf of Alaska in the summer (Tynan 1999, Brownell et al. 2001, LeDuc et al. 2001, McDonald and Moore 2002, LeDuc 2004, Mellinger et al. 2004, Wade et al. 2006, Munger et al. 2008). Acoustic detection suggests that right whales occur in the southeastern Bering Sea from May until December, and based on higher calling rates, that right whale habitat use in the southeastern Bering Sea may increase in mid-summer through early fall (Munger et al. 2008). In the summer of 2004 one satellite-tagged right whale3 moved throughout the southeast Bering Sea shelf over 40 days, including outer shelf areas where right whales have not been seen for decades. Photo-identification and genetic analyses of 23 right whales in 2004, confirmed 16 individuals– six females and ten males, of which two were calves (Wade et al. 2006, Wade et al. 2010). Of these 16 whales, at least one male had been previously photographed, and four animals previously biopsied (Wade et al. 2006, Wade et al. 2010). This was a significant sighting, as the only other female and calf identified during recent studies in the eastern North Pacific were sighted in the Bering Sea in 2002 (Ferrero et al. 2000, Wade et al. 2006).

1.4  Needs of the North Pacific Right Whale

1.4.1  Habitat and Biological Needs

The current abundance, reproductive rates, distribution patterns, migration routes, feeding and calving grounds of North Pacific Right Whales are not known. Based on information from other right whale populations around the world, the International Whaling Commission (IWC) has identified four categories of right whale habitats (NMFS 2009):

  1. Feeding areas having high copepod and krill densities, where right whales routinely feed and visit seasonally.  Feeding takes place in spring, summer and fall at higher latitudes, where ocean temperatures are cool, and biological production is high (Kenney 2002).
  2. Calving areas that are routinely used for calving and neonatal nursing.  Calving occurs at low latitudes in the winter, and where calving grounds are known, they are in shallow coastal regions or bays (Kenney 2002; NMFS 2006).
  3. Nursery aggregation area(s) where nursing females feed and suckle.
  4. Breeding locations where mating behaviour occurs.  Breeding occurs in the winter and can take place away from calving grounds3 (Kenney 2002). 

It is the right whale’s dependence on large, dense, aggregations of prey that determines much of its distribution (NMFS 2006).  Right whales are low trophic-level filter feeders.  They feed entirely on zooplankton, primarily copepods. Limited stomach contents and field observations suggest that North Pacific Right Whales are less monophagous than North Atlantic Right Whales (Gregr and Coyle 2009) which depend heavily on the copepod Calanus finmarchius (now recognized as C. marshallae) (Brown et al. 2009). Western North Pacific Right Whale stomach contents included Neocalanus plumchrus, C. finmarchicus, N. cristatus, Metridia spp., and a small amount of euphausiids (Omura 1958 cited in NMFS 2006).  Eastern North Pacific Right Whale stomach contents included N. plumchrus, N. cristatus, and E. pacifica (krill) (Omura et al. 1969, Omura 1986), and zooplankton sampling near feeding whales has suggested feeding on C. marshallae (Tynan 1999, Tynan et al. 2001, Coyle 2000 cited in NMFS 2006).  A single whale can eat several tonnes of copepods a day. Bio-energetic modeling suggests that right whales require between 407,000 and 1,140,000 calories per day– the equivalent of 0.25-2.6 billion late-stage C. finmarchicus copepods (Kenney et al. 1986). 
Important North Pacific Right Whale habitat has not been identified in Pacific Canadian waters due to the lack of long-term survey effort and right whale sightings.  Oceanographic modeling may allow the prediction of potentially important habitat, and help to focus future survey efforts.presented hypotheses about how patches of prey suitable for North Pacific Right Whale foraging might be formed in the eastern North Pacific. These hypotheses, combined with distribution data and descriptions of the ocean environment, may allow for prediction of potential right whale foraging habitat in the future (Gregr and Coyle 2009).  However, moving from predictions of potential foraging habitat to predictions of how right whales use the habitat is another step, and it is not yet known how North Pacific Right Whales use their environment and locate prey patches.  It is suggested that if experience is accumulated over generations of right whales, long-term suitability of foraging habitat could be determined by long-term oceanographic conditions (Gregr and Coyle 2009).

1.4.2  Ecological Role

It is thought that patterns of food consumption by large cetaceans (such as the right whale) have had strong effects on community structure in the Bering Sea (NRC 1996).  Laws (1985) estimated that the enormous reduction in the biomass of large whales in the Antarctic (caused by commercial whaling) may have released 150 million tonnes of krill annually to remaining predators, resulting in an increase in smaller whales, seals, seabirds, and fish.  Similarly, a reduction in major consumers of plankton, such as the right whale, and the resulting increase in plankton, may have greatly contributed to the shift in dominant fisheries seen in the Bering Sea during the 1970s and 1980s (Bowen 1997). 

The reduction of baleen whales and this shift in dominant fisheries took place concurrently with physical changes throughout the Pacific.  Primary and secondary production increased in the North Pacific, due to changes in the depth of mixed layers of different regions (Venrick et al. 1987, Venrick 1994, Polovina et al. 1995).  The combined changes in species abundance, community composition, trophic organization and physical factors indicate that a regime shift occurred (Benson and Trites 2002).  Such a regime shift could likely be accelerated by an abrupt change in biomass of large whales, thus increasing the amount of plankton available to remaining predators.  It has been recently postulated however, that marine mammals may exhibit a top-down effect on plankton production and that the impacts of whaling may have directly altered marine pelagic ecosystem structures (Smetacek 2009).

1.4.3  Limiting Factors

The following biological limiting factors could prevent or slow the recovery of the North Pacific Right Whale, regardless of the impacts of potential threats to the species’ population viability and habitat discussed below (see Section 1.5 ‘Threats’).

Population Numbers and Genetic Diversity (Inbreeding Depression)

North Pacific Right Whales have a critically small population, which could result in low genetic diversity leading to inbreeding depression, thus restricting their recovery.  Inbreeding depression is of major concern in the management and conservation of endangered species (Hedrick and Kalinowski 2000).  Rosenbaum et al. (2000a) determined that mtDNA haplotype diversity (in extant individuals) is low in the North Atlantic Right Whale, and is even lower in the North Pacific species (5 and 2 haplotypes, respectively).  This low genetic variation is a potential limiting factor for population health because of the possibility of inbreeding depression (Schaeff et al. 1997).  A population exhibiting inbreeding depression could have reduced reproduction and recruitment resulting from reduced fecundity, decreased neonate and juvenile survival, or lowered resistance to disease (Charlesworth and Charlesworth 1987, Haebler and Moeller 1993, Frankham 1995a, Frankham 1995b, Hedrick and Kalinowski 2000).  Evidence from mtDNA suggests that the North Atlantic Right Whale went through a very small genetic “bottleneck” (Schaeff et al. 1993), which may have resulted in a reduced reproductive rate and increased calving interval (Knowlton et al. 1994).  Because of the rarity of this species, inbreeding depression should be considered a major factor limiting the recovery of the North Pacific Right Whale.

Depensation (Allee effect)

The Allee effect, or depensation, is defined as the negative impact on reproductive rates due to reduced social interactions necessary for breeding (i.e., as seen in North Atlantic Right Whale “surface-active groups” which require severalmales; Kraus and Hatch 2001) and loss of mating opportunities (probability of finding a viable mate is low) in a small population (Anonymous 2000, NMFS 2006).  However, it will always be difficult to verify that depensation is the cause of reduced reproductive success when alternative explanations exist. 

Life History Characteristics

Although there are no data for right whales in the North Pacific, studies on other right whale populations suggest that they are long-lived, with a lifespan of at least 30 years (Brown et al. 2009) and as long as 70 years (Hamilton et al. 1988; Kenney 2002).  Females have a late age of sexual maturity, estimated at nine or ten years (Hamilton et al. 1988); and have a long calving interval of approximately three to four years (Knowlton et al. 1994).  These biological characteristics make right whales particularly susceptible to exploitation, environmental variation, and demographic stochasticity, which may impact recovery (Clapham et al. 1999).  Until sightings of a female and calf in the Bering Sea on August 24, 2002 and of two calves in September 2004 (Wade et al. 2006), there had been no sightings of calves in the eastern North Pacific since 1900 (Ferrero et al. 2000). 

Climate Change and Food Supply

Climate-driven regime shifts cause major changes in ecological relationships over large-scale oceanographic areas (Francis and Hare 1994), and are manifested faster at lower trophic levels in marine ecosystems (Benson and Trites 2002).  An increase in surface water temperature could result in a declining zooplankton population (Roemmich and McGowan 1995), thus changing the carrying capacity of the Pacific (Venrick et al. 1987).  Because right whales require high densities of copepod prey (Omura et al. 1969), which are dependent upon physical factors, the species may be more sensitive than other cetaceans to impacts from global climate change (Kenney 2002). 

The potential effects of inadequate food supply on right whales could be either a reduction in individual growth rates, thus delaying sexual maturity, or insufficient blubber reserves needed for females to sustain pregnancy or lactation (Kenney et al. 1986).  Reduction in the abundance of copepods, caused by either climate change or competition, is a possible explanation for the low population growth rate observed in North Atlantic Right Whales (Kenney 2002).  However, it is important to note that although food supply may be a contributing factor, demographic constraints are much more likely to be the main cause of low population growth rates for the North Pacific Right Whale.  Furthermore, any impacts may be amplified by matrilineal fidelity to feeding grounds (Kenney 2002, Schaeff et al. 1993), and possibly a reduced ability to locate new feeding grounds when changing conditions lead to a shift in prey distribution.


1SARA requires that the recovery strategy identify “a description of the species and its needs that is consistent with the information provided by COSEWIC [SARAs.41(1)(a)].

2 Passive acoustic monitoring was conducted at Union Seamount and La Perouse Bank (see App. A).  1915 hours over 160 days were recorded in 2006 at Union Seamount and 1437 hours over 120 days were recorded in 2007 at La Perouse Bank (Ford et al. 2010b).

3 One of two animals fitted with satellite-tags in summer 2004 (Wade et al. 2006)

4 This is the case for the North Atlantic Right Whale where most of the population is thought to remain at higher latitudes in the winter, while the pregnant females along with some juveniles and few adult males move south to the calving grounds (Brown et al. 2009; L. Murison, Grand Manan Whale and Seabird Research Station, personal communication, 2010).

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