Variation in saddle patch pigmentation in populations of killer whales (Orcinus orca) from British Columbia, Alaska, and Washington State

Abstract

Patterns of pigmentation of the post dorsal fin patch, or saddle patch, were analyzed from photographs of 372 resident and 99 transient killer whales (Orcinus orca) from British Columbia, Alaska, and Washington State. Of the five types of saddle patch analyzed, all were observed on residents, but only two occurred on transients. Differences in saddle patch shapes were independent of age and sex. Saddle patch pigmentation patterns were similar among clans within a community. Pigmentation patterns differed significantly between the resident and transient forms, between northern and southern residents, between northern and Alaskan residents, and between southern and Alaskan residents. As the saddle patch shape may be heritable to a large degree, these differences suggest genetic isolation of the populations. If so, this technique may be used to delineate stocks of killer whales from other areas.

Genetic differentiation between sympatric Killer whale populations

“…The apparent partitioning of this species into reproductively isolated populations is consistent with earlier speculation on the isolation of orca populations based on colour morphology (Evans et a!., 1982;Baird & Stacey, 1988) and acoustical behaviour (Ford & Fisher, 1982;Hoelzel & Osborne, 1986). Strong behavioural differences between 'transient' (population I) and 'resident' (populations N & S) Killer whales off Vancouver Island, especially related to foraging strategy, have indicated some level of isolation between these sympatric populations (Bigg et al, 1990).…”

Estimating abundance of killer whales in the nearshore waters of the Gulf of Alaska and Aleutian Islands using line-transect sampling

“…and M.D.) and ecotype assignment was based on the examination of morphological diVerences of the dorsal Wn shape and saddle patch pigmentation, previously identiWed from long-term studies as diagnostic features to identify killer whale ecotypes (Baird and Stacey 1988;Ford et al 2000). All photographs of whales collected during an encounter were examined.…”

“…In the northeastern PaciWc Ocean, killer whale abundance and population biology has been well documented at longterm study sites in Prince William Sound, southeastern Alaska, British Columbia, and Puget Sound Olesiuk et al 1990;Dahlheim et al 1997;Ford et al 2000). These studies have documented three sympatric forms (or ecotypes) of killer whales, named 'residents', 'transients', and 'oVshores', which diVer in morphology, ecology, behavior, and genetics ; Baird and Stacey 1988;Hoelzel and Dover 1991;Matkin and Saulitis 1994;BarrettLennard et al 1996;Ford et al 1998Ford et al , 2000Hoelzel et al 1998;Baird 2000). Notably, these ecotypes diVer markedly in their feeding specializations, with residents being primarily Wsh-eaters in contrast to transients that feed mainly on marine mammals (Ford et al 1998;Saulitis et al 2000;Herman et al 2005).…”

Killer whale (Orcinus orca) photo-identification in the eastern Canadian Arctic

“…Physical characteristics such as dorsal fin shape and saddle patch pigmentation are known to vary considerably between some populations (Baird & Stacey 1988;Ford et al 2000). These populations may also vary in one or more of natural history patterns, social structure, vocal behaviour and diet (Baird & Stacey 1988;BarrettLennard et al 1996;Ford et al 1998;Ford et al 2000;Baird 2001;Foote & Nystuen 2008).…”

“…Physical characteristics such as dorsal fin shape and saddle patch pigmentation are known to vary considerably between some populations (Baird & Stacey 1988;Ford et al 2000). These populations may also vary in one or more of natural history patterns, social structure, vocal behaviour and diet (Baird & Stacey 1988;BarrettLennard et al 1996;Ford et al 1998;Ford et al 2000;Baird 2001;Foote & Nystuen 2008). One of the best examples of this occurs off the Pacific coast of North America, where two well-studied sympatric populations, termed ''residents'' and ''transients'', differ in a number of characteristics including saddle patch pigmentation patterns, dorsal fin shape and diet (Ford et al 2000;Baird 2001).…”