KILLER WHALE (Orcinus orca): West Coast Transient Stock

s . , r a h s f t l. e d 90, on and cey 02; 8). of Figure 1. Approximate distribution of transient killer whales in the eastern North Pacific (shaded areas). The distribution of resident and transient killer whale stocks in the eastern North Pacific largely overlap (see text). The U.S. Exclusive Economic Zone is delineated by a black line. and Dahlheim 1978). Although reported from tropical and offshore waters, killer whale occur at higher densities in colder and mor productive waters of both hemispheres, wit the greatest densities found at high latitude (Mitchell 1975, Leatherwood and Dahlheim 1978, Forney and Wade 2006). Killer whale are found throughout the North Pacific Ocean Along the west coast of North America seasonal and year-round occurrence of kille whales has been noted along the entire Alask coast (Braham and Dahlheim 1982), in Britis Columbia and Washington inland waterway (Bigg et al. 1990), and along the outer coasts o Washington, Oregon, and California (Green e al. 1992; Barlow 1995, 1997; Forney et a 1995). Killer whales from these areas hav been labeled as “resident,” “transient,” an “offshore” type killer whales (Bigg et al. 19 Ford et al. 2000, Dahlheim et al. 2008) based aspects of morphology, ecology, genetics, behavior (Ford and Fisher 1982; Baird and Sta 1988; Baird et al. 1992; Hoelzel et al. 1998, 20 Barrett-Lennard 2000; Dahlheim et al. 200 Through examination of photographs recognizable individuals and pods, movements of whales between geographical areas have been documented. For example, whales identified in Prince William Sound have been observed near Kodiak Island (Matkin et al. 1999) and whales identified in Southeast Alaska have been observed in Prince William Sound, British Columbia, and Puget Sound (Leatherwood et al. 1990, Dahlheim et al. 1997). Movements of killer whales between the waters of Southeast Alaska and central California have also been documented (Goley and Straley 1994, Black et al. 1997, Dahlheim and White 2010). Several studies provide evidence that the resident, offshore, and transient ecotypes are genetically distinct in both mtDNA and nuclear DNA (Hoelzel and Dover 1991; Hoelzel et al. 1998, 2002; Barrett-Lennard 2000). Genetic differences have also been found between populations within the transient and resident ecotypes (Hoelzel et al. 1998, 2002; Barrett-Lennard 2000). A global genetic study of killer whales using the entire mitochondrial genome found that some killer whale ecotypes represent deeply divergent evolutionary lineages and warrant elevation to species or subspecies status (Morin et al. 2010). In particular, estimates from mitogenome sequence data indicate that transient killer whales diverged from all other killer whale lineages approximately 700,000 years ago. In light of these differences, the Society for Marine Mammalogy’s Committee on Taxonomy currently recognizes the resident and transient North Pacific ecotypes as un-named Orcinus orca subspecies (Committee on Taxonomy 2019). In recognition of its status as an un-named subspecies or species, some researchers now refer to transient-type killer whales as Bigg’s killer whales (e.g., Ford 2011, Riesch et al. 2012), in tribute to the late Dr. Michael Bigg. The first studies of transient killer whales in Alaska were conducted in Southeast Alaska and in the Gulf of Alaska (from Prince William Sound, through the Kenai Fjords, and around Kodiak Island). In the Gulf of Alaska, Matkin et al. (1999) described two genetically distinct populations of transients which were never found in association with one another, the so-called “Gulf of Alaska” transients and “AT1” transients. In the past, neither of these populations were known to associate with the population of transient killer whales that ranged from California