Robin W. Baird
Contract report submitted to the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Reviewed and evaluated by COSEWIC in April 1999. Published in the Canadian Field-Naturalist in 2001. Download an Adobe PDF version of this report
Summary
Killer whales can be found in all three of Canada's oceans, as well as occasionally in Hudson Bay and in the Gulf of St. Lawrence. Little is known about their occurrence or biology in the Atlantic or Arctic, but killer whales appear to be uncommon in most parts of these areas. In the Canadian Arctic and western Atlantic small numbers were killed historically in commercial whaling operations (or shot incidentally to such operations), and small numbers have been documented taken by natives. Predictable concentrations of killer whales are found in British Columbia (B.C.), and populations in B.C.'s nearshore waters are among the most well-known populations of cetaceans world-wide. Killer whales off the Pacific coast can be classified into two distinct "types" or "forms" (termed residents and transients), which differ in diet (residents feed on fish, transients feed on marine mammals), morphology, genetics and behaviour. The exact taxonomic relationship between these two types is unclear, though some authors have termed them "races", others consider them separate species. Regardless, from both a scientific and management perspective these populations should be treated as distinct. Within B.C. waters residents appears to be sub-divided into three geographic communities or populations (termed the "northern" and "southern" residents, and "offshore" killer whales), based on association patterns, genetics and morphology. Relatively little is known of the "offshore" population of killer whales. All populations (including transients and the three resident populations) are small (in the low hundreds), and have low potential rates of increase. No trend information is available for "offshore" or transient killer whales. The "northern" resident population has been growing steadily in size since the 1970s (when live-capture fisheries stopped and shooting declined), while the "southern" resident population has been growing only sporadically, and is currently smaller than the pre-live-capture population estimate from the 1960s. Given the small population sizes and their low potential rates of growth, killer whales are potentially at risk from anthropogenic influences in two primary ways: due to immunotoxic affects of persistent toxic chemicals (levels in "southern" residents are three times higher than levels known to cause immunotoxicity in harbour seals), and due to a reduction in prey availability. It is also possible that the large and growing commercial and recreational whale watching industry on the west coast may be having an impact, though such impacts are as yet unclear. In terms of natural factors, periodic events such as mass strandings or entrapments in narrow inlets or ice have the potential to drastically reduce local populations. Since virtually all of these factors should impact killer whales throughout Canadian waters, all populations, at the least, should be classified by COSEWIC as Vulnerable, that is, as "species of special concern because of characteristics which make them especially sensitive to human activities or natural events". As the "southern" resident population is extremely small (89 individuals in 1998), has declined by 10% in the last three years due to an increase in mortality rates (primarily of adult females), is more subject to anthropogenic influences than other populations, and these influences are not expected to decrease in the foreseeable future, it should be listed as Threatened by COSEWIC. Further research, particularly on Arctic, Atlantic and "offshore" populations, is clearly needed.
Portions of the text of this report can be found at the following pages:
Introduction, Population Discrimination etc
Special Significance and Evaluation