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


2 Blue Whale Background

2.1 Current status

Common name:  Blue whale

Scientific name: Balaenoptera musculus

Legal listing (SARA): January 2005 (Endangered)

COSEWICstatus: Endangered

Assessment summary: May 2002

Reason for designation: Blue whales off the coast of British Columbia are likely part of a population based in the northeastern Pacific. The population was reduced by whaling. The rarity of sightings (visual and acoustic) suggests their numbers are very low (significantly less than 250 mature individuals). Threats for blue whales along the coast of British Columbia are unknown but may include ship strikes, pollution, entanglement in fishing gear, and long-term changes in climate (which could affect the abundance of their zooplankton prey). (www.cosewic.gc.ca)

Occurrence in Canada: North Pacific, North Atlantic

Status history: Entire Canadian range was designated as Special Concern in April 1983. Split into two populations in May 2002. The Pacific population was up-listed to Endangered in May 2002, based on an updated status report.

2.2 Species description

Blue whales are the largest animals on the planet and are found in most oceans of the world. Blue whales range from the pack ice of both hemispheres to temperate and tropical waters, with distinct populations found in the North Atlantic, North Pacific, Southern Hemisphere, and the northern Indian Ocean (Mizroch et al.1984, Rice 1998). These populations are further separated into six “stocks” (i.e., populations) by the International Whaling Commission (IWC) despite a poorly understood stock structure (Donovan 1991).

The longest blue whale ever recorded (33.6 m; 110 ft) was caught in the Antarctic. In the North Pacific, the longest animal caught was 27.1 m (89 ft) (Sears and Calambokidis 2002). Body weights range from 80-150 tons (73,000-136,000 kg) with one report of a 190 ton (173,000 kg) female killed off South Georgia in 1947 (Tomilin 1967). Females are generally larger and longer than males and animals are larger on average in the southern hemisphere than in the northern hemisphere.

Blue whales have a light to slate-grey appearance above water with a characteristic mottled pigmentation. The pigmentation can range from a sparse mottling pattern to highly mottled individuals with splotches along the flanks, back and ventral surface. Chevrons often curve down and back on both sides of the rostrum behind the blowholes. This highly variable pigmentation and mottling patterns are distinctive and stable throughout life allowing individuals to be tracked using photo-identification (Sears and Calambokidis 2002).

The blue whale has a large, broad U-shaped head that comprises nearly 25% of its body length. The top of the head has a prominent rostral ridge that runs from the upper jaw and mandibles to the splash-guard in front of two blowholes. The dorsal fin is relatively small compared to other balaenopterids and is highly variable in shape. The flippers are approximately 4 m in length (15% of body length) with blunt tips. The flukes are broad and triangular with a straight or slightly curved trailing edge, grey in colour, possibly with variable white patches on the underside.

Females give birth every 2-3 years in winter following a 10-12 month long gestation period. The calf weighs 2-3 tonnes and measures 6-7 m at birth. Blue whales nurse until 6-7 months of age and are likely weaned during the summer when on feeding grounds. Blue whales are thought to reach sexual maturity between 5-15 years for both sexes, and live 70-80 years (Sears and Calambokidis 2002). Calving rates are not well known, however, observations of calves from the Sea of Cortez (R. Sears, personal communication. Mingan Island Cetacean Study, 285 rue Green, St. Lambert, Québec, J4P 1T3), and California (J. Calambokidis, personal communication. Cascadia Research, 218 1/2 W 4th Ave., Olympia, WA 98501) indicate that reproduction is taking place.

2.3 Population size, trends, and distribution

Blue whales undertake extensive, seasonal north-south migrations each year from wintering grounds in the low latitudes to summer feeding grounds in productive mid to high latitude waters. Their historic distribution is better described at higher latitudes due to the extensive whaling that took place on these feeding grounds.

The extensive range and dispersion of blue whales coupled with low sampling effort and depleted populations makes reliable estimates of population size difficult. Global population estimates range from 5000-12,000, though the accuracy of these estimates is questionable (Carretta et al. 2003). Historically, Southern Ocean populations were the largest with an estimated 300,000 animals pre-exploitation. Recent estimates of 710-1265 have been calculated for summer feeding grounds in Antarctic waters (IWC 1990, Butterworth et al. 1993, IWC 1996).

Historically, blue whales ranged throughout the coastal and pelagic waters of the North Pacific. Data on population structure come primarily from historic whaling records, sightings, and acoustic recordings of vocalizations. Based on whaling records, Gambell (1979) suggested that there were three blue whale populations in the North Pacific, while Reeves et al.(1998) concluded that as many as five sub-populations, including ones in the eastern Gulf of Alaska and California/Mexico, inhabited the North Pacific with an uncertain level of mixing between them. The lack of recent sighting data in much of the species’ former range suggests that some sub-populations may have been extirpated by commercial whaling.

Analysis of blue whale calls has revealed two distinct call types; one prevalent in the western and central North Pacific and the other in the eastern North Pacific (Stafford et al.2001), suggesting at least two populations of blue whales in the North Pacific.

The U.S. National Marine Fisheries Service (NMFS) manages blue whales as two populations, an eastern North Pacific stock and a Hawaiian stock. The eastern North Pacific population ranges as far south as Mexico and Central America during the winter and spring. It is regularly sighted feeding off California during the summer and fall. Migration occurs in spring north from the Gulf of California, Mexico, and the offshore waters of Central America and moves along the west coast of North America to concentrations off California, peaking in July to September.

Due to a continued rarity of sightings at higher latitudes, the northern range of this population is unclear. Blue whale calls have been detected off Vancouver Island and further north in the Gulf of Alaska. The call intensity (defined as dB above ambient) off Vancouver Island from September to February (Burtenshaw et al. 2004) suggests that the animals off California may disperse northward and possibly offshore after September, before, presumably, returning to southern latitudes for the winter. A blue whale identified in the Gulf of Alaska, south of Prince William Sound, in 2004 had been identified frequently off California in previous years (J. Calambokidis and J. Barlow, unpublished data). In light of this information, it is presumed that the animals using Pacific Canadian waters belong to the putative eastern North Pacific population as defined by NMFS.

The size of the eastern North Pacific population has been estimated using both line transect and mark-recapture (photo-identification) techniques. The population has been increasing since the moratorium on commercial whaling (Barlow 1994) and is currently reliably estimated at 2000 animals (Calambokidis and Barlow 2004). However, the rate of increase is too great to be attributed to population growth alone (Barlow 1994) and may reflect a shift in distribution. Sparse sighting data throughout the northern Gulf of Alaska from Canada to the Aleutian Islands indicates that this increase does not apply to all regions of the eastern North Pacific (Sears and Calambokidis 2002). The relative contributions of population growth, distributional shifts, and habitat contraction to the increasing trends observed off California is unclear. Nevertheless, given available population estimates, the eastern North Pacific population represents a large proportion of the known blue whales in the world.

2.3.1  Canadian Pacific

Sighting data from Japanese scouting surveys (1965 – 1978) throughout the North Pacific include blue whale sightings in Pacific Canadian waters. While these data are difficult to translate into densities or abundances, they do show a relatively higher sighting rate for waters off British Columbia compared to most other areas surveyed (Sears and Calambokidis 2002).

“Discovery” tags, used to examine the movements of commercially hunted whales, showed a blue whale tagged on 4 May 1963 off Vancouver Island later killed on 21 June 1964 south of Kodiak Island (Ivashin and Rovnin 1967). This was the longest distance recorded from this tagging program and provides evidence of exchange between Pacific Canadian and Alaskan waters. Historic records show an on-shelf to deep water distribution off British Columbia (Figure 1a), and a seasonal peak in abundance in July to September (Figure 2).

More recently, two blue whales photo-identified off the Queen Charlotte Islands in northern British Columbia both matched to animals seen off California (Calambokidis et al. 2004a). A whale identified on 12 June 1997 was re-sighted in the Santa Barbara Channel on 10 July 1997. It had therefore travelled at least 2500 km in 28 days representing a minimum swimming speed of 3.7 km/h (Sears and Calambokidis 2002). This individual represents the first confirmed movement between Californian waters and higher latitude feeding areas. Two blue whales were sighted near the shelf-break off Queen Charlotte Sound in the spring of 2002, during the first of two bi-annual cruises now conducted annually by the Cetacean Research Program - Fisheries and Oceans Canada (CRP-DFO) (Figure 3a). A blue whale photo-identified south of Cape St James on a joint DFO/Cascadia Research cruise in August 2003 (Figure 3b) also matched to the California catalogue. A blue whale seen in 2004 in the Gulf of Alaska matched to the California catalogue, though in a different year (J. Calambokidis and J. Barlow, unpublished data). In summer 2004, a blue whale tagged off California travelled as far north as Estevan Point, west coast Vancouver Island (B. Mate, personal communication. Hatfield Marine Science Center, 2030 SE Marine Science Drive, Newport, Oregon 97365).

The British Columbia Cetacean Sightings Network (BCCSN) database (courtesy of D. Sandilands, Cetacean Research Lab, Vancouver Aquarium Marine Science Centre, 845 Avison Way, Vancouver, BC, V6G 3E2) contains whale sightings from 1972 – 2004, with the majority collected since 1999 and virtually all of them provided by recreational boaters. Such opportunistically collected data provide an indication of the distribution and relative abundance between species; however they are not corrected for effort, and observers have variable species identification skills. Consequently these data cannot be used to estimate population abundance or trends. The database contains 3 high confidence sightings of blue whales.

While visual sightings have been rare in recent years off British Columbia, Washington, and southeast Alaska, calls presumed to be from the eastern North Pacific population of blue whales have been consistently detected by bottom-mounted hydrophones from California to British Columbia and Alaska (Sears and Calambokidis 2002). Burtenshaw et al. (2004) showed a significant, almost constant intensity of blue whale calls off British Columbia from October to February. Thus, Pacific Canadian waters appear to represent an important feeding ground for a large portion of the world’s blue whales.

2.4 Biological needs, ecological role and limiting factors

Blue whales are low trophic level foragers requiring several tonnes of prey per day per individual. Thus, the viability and recovery of the blue whale population could be constrained by factors that limit availability of food. Given the large quantities of zooplankton required to maintain a blue whale population, their presence in, or absence from, an ecosystem is likely significant (Sears and Calambokidis 2002).

Changes in ocean climate (See Section 5.2.4) could affect both the total available prey for, and the foraging effectiveness of, blue whales. Such lower trophic foraging specialists may be more immediately affected by large-scale oceanographic shifts than other species with more diverse diets (Benson and Trites 2002).

Killer whale predation may be a source of mortality for blue whales, however, the prevalence in Pacific Canadian waters is unclear and few data on scarring are available from this region. Scars associated with killer whale (Orcinus orca) attacks are present on 25% of the blue whales sighted in the Sea of Cortez, however these scars are rare on blue whales in the St. Lawrence (Sears and Calambokidis 2002). One report describes an attack by a group of killer whales on a blue whale off Baja California (Tarpy 1979). While the rate of predation is unknown, increasing whale populations could lead to increased predation by killer whales. Killer whale predation may be more prevalent off California and Mexico than elsewhere based on the scarring rate of humpback whales (Megaptera novaeangliae) (G. Steiger, personal communication. Cascadia Research, 218 1/2 W 4th Ave., Olympia, WA 98501). Nevertheless, mortality rates are not known (Reeves et al. in press).

2.5 Habitat needs

Higher-latitude habitat is likely best defined by its suitability as a foraging ground. Blue whales feed along productive shelf-break upwellings in temperate to polar waters from spring to early winter. They feed primarily on euphausiids (Euphausia pacifica, Thysanoessa spinifera, T. inermis, T. longpipes, T. raschii, and Nematoscelis megalops), though calanoid copepods (Calanus spp.) and pelagic red crab (Pleuroncodes planipes) also occur in the diet. They exploit dense concentrations of these prey species by engulfing prey with their large mouths and expanding throat pleats.

Reproductive activity occurs in the winter season in tropical and sub-tropical waters, but no specific breeding grounds have yet been identified for eastern North Pacific blue whales (Sears and Calambokidis 2002) or any other blue whale population.