Research Document - 2007/088

Recovery Potential Assessment for West Coast Transient Killer Whales Using Coastal Waters of British Columbia

By J.K.B. Ford, G.M. Ellis, and J.W. Durban

Abstract

Mammal-eating ‘transient’ killer whales off Canada’s Pacific coast are listed as Threatened under the Species-at-Risk Act. A draft Recovery Strategy for transient killer whales was prepared by DFO in 2007, but insufficient information was available to set quantitative recovery goals in that document. Here, we present a Recovery Potential Assessment for West Coast Transient (WCT) killer whales to provide a basis for on-going recovery planning for this population. For this assessment, we used an archive of photo-identifications of individual WCT whales collected during 1479 sightings between 1974 and 2006. We applied a ‘capture-recapture’ approach to the analysis of this dataset and used Bayesian statistical techniques to estimate population abundance and dynamics. These analyses indicate that the WCT population grew rapidly from the mid-1970s to mid-1990s as a result of high survival and recruitment, the latter including immigration of animals into the nearshore study area. Population growth began slowing in the mid-1990s and has continued to slow in recent years as the population approaches an equilibrium point of around 262 whales. The rapid growth of the WCT population in the mid-1970s to mid-1990s coincided with a dramatic increase in the abundance of the whales’ primary prey, harbour seals, in nearshore waters. The recent slowing of WCT population growth suggests a carrying capacity in the mid to high 200s, given the current abundance of marine mammal prey in coastal waters. A Potential Biological Removal (PBR) of 1.60 animals/year suggests that the population could sustain very little human-induced mortality without declining.

 Complete PDF document
(38 pages; 289K)

Accessibility Notice:

This document is available in PDF format. If the following 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.

Offer to produce in both official languages:

This report uses scientific and technical terms and is published in the official language of the working group or scientific expert that produced the document. If this document is not accessible to you in the official language of your choice, please contact the Secretariat.

Date modified: