Suspected surplus killing of harbor seal pups (Phoca vitulina) by killer whales (Orcinus orca)
Gaydos, J.K., S. Raverty, R.W. Baird and R.W. Osborne. 2005. Suspected surplus killing of harbor seal pups (Phoca vitulina) by killer whales (Orcinus orca). Northwestern Naturalist 86:150-154
Within the inland waters of Washington State and southern British Columbia Province, 3 distinct ecotypes of killer whales (Orcinus orca) occur. The better known ‘‘resident’’ and ‘‘transient’’ populations each display unique genetic (Hoelzel and others 2002), dietary (Baird and Dill 1995; Ford and others 1998), behavioral (Baird 2000), vocal (Ford 1990) and morphological differences (Baird and Stacey 1988). The resident pods, also known as the ‘‘southern resident’’ population, eat primarily fish and occur in large stable groups (Bigg and others 1990). Transients feed primarily on other marine mammals and occur in smaller and less stable groups (Baird and Dill 1995, 1996; Baird and Whitehead 2000; Baird 2000). The 3rd population, which is seen occasionally in the area, is called the ‘‘offshore’’ ecotype (Wiles 2004). These killer whales are believed to be primarily fish eaters (Hoelzel and others 2002) that are smaller in size than other ecotypes and genetically distinct from both residents and transients, although more closely related to the resident killer whales. We recently identified a novel mortality pattern in harbor seals (Phoca vitulina) that strongly suggests 1 or more individuals from 1 of these ecotypes killed seal pups for reasons other than consumption.