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

2. Blue Whale (cont'd)

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in the Gulf of Alaska matched to the California catalogue, though in a different year (J. Calambokidis and J. Barlow, unpublished data).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.