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Recovery Strategy for Blue, Fin, and Sei Whales in Pacific Canadian Waters [Proposed]

3. The Fin Whale(cont'd)

3.3.  Population size, trends, and distribution

Fin whales have a cosmopolitan distribution, though they are more abundant in temperate and polar latitudes. In the North Pacific, the known summer range extends northward to 50°N in the Sea of Okhotsk, 60°N in the Bering Sea and 58°N in the Gulf of Alaska, and southward to 40°N in the Sea of Japan and 32°N off the coast of California. The known winter range extends from Korea to Taiwan, the Hawaiian Islands and to the Baja California peninsula, although this distribution is believed to be primarily offshore (Leatherwood et al. 1988).

Fin whales summer at various locations along the eastern North Pacific coast, and are known to occupy some regions (at least the Gulf of California and south/central California) on a year-round basis. Summer aggregations have been documented off Oregon, and summer-fall groups have been observed in the Shelikof Strait/Gulf of Alaska region (Carretta et al. 2003). Acoustic detection occurs year-round off northern California, Oregon and Washington, with a concentration of activity between September and February (Moore et al. 1998).

NMFS recognizes three stocks in U.S. waters of the North Pacific: the Northeast Pacific stock, the Hawaiian stock, and the California/Oregon/Washington stock (Carretta et al. 2003). Fujino (1960) concluded that the North Pacific contains an eastern and a western population based on histological and marking data. The marking data further suggest that the fin whales off British Columbia may have been isolated to some degree.

Oshumi and Wada (1974) estimated pre-exploitation abundance in the North Pacific at 40,000 – 45,000. Whaling reduced the numbers to an estimated 13,000 – 19,000 by 1973, of which 8500 – 11,000 were assumed to be from the eastern North Pacific (Oshumi and Wada 1974). The most recent estimate of the size of the California/Oregon/Washington stock based on ship surveys is 3279 (Coefficient of Variation (CV) = 0.31) (Barlow and Taylor 2001 cited in Carretta et al. 2003). Vessel surveys in July-August 1999 produced an estimate of 4951 (CV=0.29) fin whales in the Bering Sea, though these numbers did not provide an indication of the size of any of the putative stocks (Angliss and Lodge 2003). To date, the available data are not sufficient for estimating population trends.

The population structure in Pacific Canadian waters is equivocal. There is no way to presently determine whether animals sighted in Pacific Canadian waters are from either of the two stocks defined by NMFS. Indeed, there is currently no evidence to determine whether these two putative stocks are truly distinct populations or whether they represent a single, eastern North Pacific population.

3.3.1.  Canadian Pacific

Pike and MacAskie (1969) regarded the fin whale as the most abundant baleen whale in Pacific Canadian waters, and suggested that the waters off Vancouver Island contained a summer feeding aggregation. Historically, fin whales were frequently observed in exposed coastal seas (Hecate Strait and Queen Charlotte Sound) and occasionally in the more protected waters of Queen Charlotte Strait and the Strait of Georgia (Pike and MacAskie 1969). Only 17% of the catch for which positions were recorded by British Columbia coastal whalers was on the continental shelf (Figure 1 and Gregr 2004).

Based on a comparison of whaling records from coastal stations around the Gulf of Alaska, Gregret al. (2000) concluded that the species did not appear restricted latitudinally. An analysis of whaling records from British Columbia whaling stations identified fin whale habitat along the continental shelf, in the exposed inland waters of Dixon Entrance and Hecate Strait, and in a region offshore of northern Vancouver Island (Figure 1, from Gregr and Trites 2001).

Contemporary sightings of fin whales in Pacific Canadian waters are predominantly from the west coast of Vancouver Island, Hecate Strait and Queen Charlotte Sound, and occur in summer and winter. Recent annual spring research cruises (CRP-DFO) have recorded 75 fin whale sightings between 2002 and 2004 in off-shelf waters, near the shelf break boundary of Queen Charlotte Sound, in Hecate Strait, and in Dixon Entrance (Figure 3a). Summer cruises in 2002 and 2003 sighted 12 fin whales in Queen Charlotte Sound (Figure 3b). Recent summer sightings have also been made off southern Vancouver Island (COSEWIC 2004). An opportunistic winter cruise in February 2004 resulted in sightings off the north end of Vancouver Island and in Hecate Strait (CRP-DFO, unpublished data). The BCCSN database contains 48 high confidence fin whale sightings.

In contrast to the relatively frequent sightings off British Columbia, NMFS conducted 2-week summer surveys in the northern offshore waters of Washington State each year from 1995 to 2002 and did not sight a single fin whale (Calambokidis et al. 2004b). Similarly, aerial surveys off the west coast of Washington in the early 1990s also did not spot any fin whales (Green et al. 1992 cited in Calambokidis et al. 2004b).

It may be that this pattern of sightings represents the re-occupation of the historic fin whale feeding grounds in Pacific Canadian waters. Alternatively, it may also be a reflection of increased observational effort, or some other demographic shift in the local population(s).

3.4. Biological needs, ecological role and limiting factors

Fin whales forage on a variety of species. Generally in the northern hemisphere they eat small invertebrates, schooling fishes and squids. Consequently, it has been suggested that fin whale diet is as much a function of availability as preference (Gambell 1985b).

In the North Pacific, the diet is dominated by euphausiids (70%) followed by copepods (25%) with some fish and squid (Kawamura 1980). Flinn et al. (2002) examined records of stomach contents for fin whales taken in British Columbia and found similar results.

Due to the global overlap in range and diet with other baleen whales, inter-specific competition is likely (Aguilar and Lockyer 1987). Mixed groups of fin and blue whales are common and hybrids occur with surprising frequency in the North Atlantic (Bérubé and Aguilar 1998), although hybrids have not been identified in the St. Lawrence with 40% of fin and blue whales analysed (R. Sears pers. comm.). The degree to which hybridization may occur in the North Pacific is unknown.

Consequent to their depletion by whaling, large baleen whales may have been ‘replaced’ in the ecosystem to some extent by ecologically-equivalent finfish stocks (Payne et al. 1990). Trites et al. (1999) suggested that some species of fish are significant competitors of whales in the Bering Sea. Another possible consequence of whaling is that the remaining populations may be too small to recover. However, while there is insufficient population data for an unequivocal assessment, this is not believed to be a limiting factor for fin whales.

Some predation of fin whales is possible by killer whales and sharks, though the degree of predation is unknown (Reeves et al. in press). Increased abundance could lead to increased predation.

3.5. Habitat needs

The summer habitat of fin whales tends to consist of areas with dense prey concentrations (Kawamura 1980, Gaskin 1982). Woodley and Gaskin (1996) found that in the Bay of Fundy, fin whales occurred primarily in shallow areas with high topographic relief, and their occurrence was correlated with herring and euphausiid concentrations.

Fin whale distribution is associated with low surface temperatures off the northeastern U.S. and in the Bay of Fundy during summer months (Woodley and Gaskin 1996). Hain et al. (1992) documented an association with oceanic fronts, areas known for high biological productivity (Herman et al. 1981).

Conception and calving are believed to occur in low latitudes during winter, but no specific breeding grounds have yet been identified (e.g., Mizroch et al. 1984) . Payne (2004) suggested that the long-distance communication abilities of the species may allow mating to occur without the need for aggregating on breeding grounds.