Science Advisory Report  2014/047

Recovery Potential Assessment of Offshore Killer Whales off the Pacific Coast of Canada

Summary

• Offshore Killer Whales (OKWs) in the eastern North Pacific comprise a single population with a known range that includes continental shelf waters from southern California to the eastern Aleutian Islands, Alaska.
• Relative to other Killer Whale populations in Canadian Pacific waters, OKWs are rarely encountered. They were first identified off the British Columbia (BC) coast in 1988, and have only been encountered in the region a total of 103 times up to 2012.
• OKWs exhibit a diffuse latitudinal shift in their distribution seasonally, with encounters being most frequent off California during the winter months and off Alaska during summer. In BC waters, OKWs have been encountered or detected acoustically in all months of the year, with some evidence of peaks in March, August and December.
• Although the preferred habitat of OKWs in Canadian Pacific waters appears to be outer continental shelf waters, they also make occasional forays into protected inside passage waters.
• OKWs appear to feed primarily on sharks, including Pacific Sleeper Shark, Blue Shark, and Spiny Dogfish, although some teleost fishes such as Chinook Salmon and Pacific Halibut are also consumed.
• Population modeling using photo-identification data indicates that the OKW population is small, with an average annual abundance estimate of 300 (95% Highest Posterior Density Interval (HPDI) = 257–373).
• The population trend appears stable, with average annual survival rates of 0.98 (95% HPDI = 0.92–0.99) balanced by annual recruitment rates of 0.02 (95% HPDI = 0–0.07).
• Potential threats to OKW habitat include prey limitation, acute and chronic underwater noise, chemical and biological contamination, oil spills, and disturbance. Potential sources of human-caused mortality include entanglement in fishing gear and vessel strikes.
• A Potential Biological Removal (PBR) of 0.55 animals/year suggests that the population could sustain very little anthropogenic mortality without declining.
• There is no evidence that the small OKW population is habitat- or prey-limited, either over its total range or within Canadian waters. Although the total available biomass of their elasmobranch prey is not known, the three species known to be consumed by OKWs – Pacific Sleeper Shark, Blue Shark and Spiny Dogfish – are widespread and abundant, and there is no indication of any decline in the abundance of these species.
• Additional field studies to better document patterns of habitat use and foraging ecology of OKWs are needed in order to identify potential critical habitat and describe its function, features and attributes.
• Continued photo-identification efforts will be necessary to improve estimates of population abundance and life history parameters and to monitor future trends.

This Science Advisory Report is from the May 27th to May 28th, 2013 Recovery Potential Assessment Offshore Killer Whale. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Complete document (PDF, 413 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.