Fourth International Orca Symposium and Workshop - CEBC - CNRS

Oral And Poster Presentations
SOCIAL DETERMINANTS OF POPULATION STRUCTURE IN KILLER WHALES:
INSIGHTS FROM ASSOCIATION PATTERNS, GENETICS AND ACOUSTICS.
Barrett-Lennard L.G
Vancouver Aquarium Marine Science Centre and University of British Columbia. P.O. Box 3232,
Vancouver, B.C. V6B 3X8, Canada, Canada & University of British Columbia, Department of
Zoology, 6270 University Blvd, Vancouver, B.C. V6T 1Z4, Canada, barrett@zoology.ubc.ca
Seven distinct populations of killer whales have been identified off the coasts of British
Columbia and southern Alaska. Three are fish-eating residents, three are mammal-eating
transients, and one, offshores, have an unknown diet. Each population has from 75 to several
hundred members, with the exception of one that is on the brink of extinction. Each of the
resident populations shares its usual home range with one or more transient population and
vice versa, but populations with the same feeding specializations overlap very little. The
offshores partially overlap the range of both other types. This situation is illustrated
schematically in Figure 1.
Figure 1: Approximate range of resident, transient and offshore killer whales in the northeastern Pacific ocean.
Despite their adjacent or overlapping distributions, members of different populations
avoid close contact. No emigration between populations has been documented, and genetic
analysis indicates that it is rare. This segregation into extremely small sympatric and
parapatric populations has not been described in other highly motile animals and begs
explanation. I hypothesize that it results from the concordance of four behavioural and
ecological attributes, outlined below.
1. Killer whales in the northeast Pacific have highly effective inbreeding avoidance
systems. In residents, most matings occur between individuals that belong to the same
FOURTH INTERNATIONAL ORCA SYMPOSIUM AND WORKSHOPS
SEPTEMBER 23-28 2002, CEBC-CNRS, France
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