Science Advisory Report  2013/025

Information in Support of the Identification of Critical Habitat for Transient Killer Whales (Orcinus orca) off the West Coast of Canada

Summary

• West Coast Transient (WCT) killer whales (Orcinus orca) are apex predators of marine mammals in coastal waters of British Columbia.  This population has been studied annually since the early 1970s by means of photographic identification of individual whales using natural markings.
• A population of about 500 mammal-hunting WCT killer whales is known to use coastal waters of British Columbia.  Two putative subpopulations occur in this area – “inner coast” WCT killer whales are commonly found in inshore, protected waters and in nearshore waters along the exposed west coasts of Vancouver Island and Haida Gwaii, and “outer coast” WCT killer whales are that rarely encountered, occurring mostly in deeper waters closer to the continental shelf break. 
• A total of 304 individuals have been identified and assigned to the inner coast subpopulation based on frequency of encounters.  An additional 217 rarely-seen individuals are considered to be members of the outer coast WCT subpopulation.  The inner coast subpopulation appears to be increasing.  The status of the outer coast subpopulation is unknown.
• WCT killer whales are highly mobile in Canadian nearshore waters. Most individuals have been recorded in multiple regions, from southern Vancouver Island to the Alaskan border.  Despite this mobility, there is considerable site fidelity with many individuals returning repeatedly to particular regions, likely in order to benefit through familiarity with local habitats. 
• Fine-scale movements of WCT killer whales can be characterized as constant, unpredictable and erratic.  Feeding or travelling between foraging locations are their predominant activity states.  WCT killer whales hunt most marine mammals found in nearshore waters, especially harbour seals, harbour porpoises, Steller sea lions and Dall’s porpoises.  Their hunting tactic is to use stealth to surprise and capture unsuspecting prey.  They hunt opportunistically, with no evidence of specialization on particular prey species.  
• The primary prey species of WCT killer whales are distributed widely in nearshore waters of the whales’ habitat.  WCT killer whales are likely vulnerable to local resource depression in foraging locations, whereby prey becomes alert to the whales’ presence and less vulnerable to predation.  For this reason, the whales tend to move continuously through their habitat and do not remain long in particular locations.
• Due to the high mobility of these whales and the large-scale movements of individuals throughout their coastal range, a substantial portion of their area of occupancy is essential habitat to ensure recovery.  The widespread distribution of their prey, as well as the probable need for the whales to continually move between foraging locations to avoid the effects of local resource depression, similarly indicate that extensive habitat is required.
• Site fidelity of individuals to various regions within the population’s overall range also highlights the importance of habitats distributed broadly throughout the area of occupancy.
• It is proposed that Pacific coast marine waters within 3 nautical miles (5.56 km) of the nearest shoreline be considered as the habitat necessary to meet the population and distribution recovery objectives for WCT killer whales.  This area encompasses the locations of 92% of all individual identifications of inner coast WCT killer whales and 64% of identifications of outer coast WCT killer whales made in BC waters between 1990 and 2011.  Furthermore, this area also includes the locations of 90% of all predation events observed during the same period.  This area comprises 40,358 square km, or about 8.9% of Canadian west coast waters.
• The biophysical functions, features and attributes of habitat considered necessary for recovery of WCT killer whales are described.  These whales are year-round residents off Canada’s west coast and thus this habitat must support all life processes necessary for the survival and recovery of the population.
• Feeding is a primary biophysical function, but other vital life processes include reproduction, socializing, and resting. No specific habitat area appears to serve particular functions other than feeding. The biophysical features and attributes to support the feeding function of this habitat are adequate year-round supplies of the whales’ primary prey species that are distributed over a sufficient geographical area to allow exploitation of locally abundant prey resources that may vary seasonally, and to offset the probable effects of resource depression. 
• Another important feature is the underwater acoustic environment, which must be of sufficient quality (i.e., low levels of anthropogenic ambient noise) that it enables the animals to utilize passive listening to detect prey and to communicate vocally. 
• Activities or events that could destroy WCT killer whale habitat that is essential for recovery include the following:
• any activity that would reduce prey abundance or accessibility, such as an oil spill resulting from a marine transportation accident or other incident, which has the potential to deplete prey;
• developments in confined passages, such as the installation of tidal energy devices, which could present barriers to movements through the whales’ foraging habitats or affect the distribution of their prey;
• introduction of persistent bioaccumulating toxins (PBTs) into the habitat;
• acoustic disturbance from anthropogenic noise; and,
• physical disturbance from vessels or other marine activities.
• The degree of habitat destruction from anthropogenic activities would depend on the geographic extent, duration and intensity of the activity.  In some cases, particularly those related to PBT contamination and anthropogenic noise, effects are poorly known.  Further research is needed to establish thresholds that would constitute destruction under SARA.
• Additional research is needed to improve understanding of population structure of WCT killer whales in the region and to identify habitats that are essential to the putative outer coast WCT subpopulation.

This Science Advisory Report is from the October 29 to November 2, 2012 Annual meeting of the National Marine Mammal Peer Review Committee (NMMPRC).  Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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