The waters of the Salish Sea, on the west coast of North America, are home to several ecologically distinct populations of orcas (Orcinus orca). The area supports three major ecotypes of orcas: northern residents, southern residents, and transients. A fourth ecotype, the offshore orcas, occasionally venture into nearshore waters. Little to no interaction occurs between the different ecotypes. Resident and transient orcas have not been observed interbreeding, although occasional brief interactions occur.
Studied since the 1960s, the orcas of the Salish Sea region have become well-known in cetacean research. According to John KB Ford, Graeme B Ellis, and Kenneth C Balcomb, the resident orcas represent "the most intensively studied population of marine mammals in the world." The frequency of sightings of orcas in the Puget Sound region, combined with their prominent place in the ecosystem and their charisma, have made them icons of the region, and their likeness features prominently in Native American culture in the Northwest. Additionally, they are one of the main interests of the many whale watching industries that have sprung up in the region.
Overview Southern resident orcas
The primary range of the Southern resident orcas stretches approximately from the Strait of Juan de Fuca and the south coast of Vancouver Island to the Tacoma Narrows and occasionally Hood Canal, with seasonal ranges encompassing the Pacific coast from British Columbia to Monterey Bay. As of October 2023, the estimated population size is 75 individuals. The population is primarily separated into three pods: J, K, and L. However, all individuals in the Southern resident population are descended from a single bloodline and are considered part of a single clan. The primary distinguishing factor between the Southern and Northern resident orcas is not linked to appearance, but rather matriarchal status, with males descended from living mothers doing more hunting than males without living mothers among southern residents.
In a 1973 study of Northern resident orcas in the Georgia Strait, British-Canadian scientist Michael Bigg found that minor injuries, such as dents in the dorsal fins, did not fully heal over time and remained prominent on the individual for the rest of their lives. This led to the use of these marks as the primary method for individual identification in the wild. In addition to individual markings, distribution during the summer breeding season can be used to distinguish the northern or southern resident groups. This, along with charting the distribution of each group during summer and winter, is the most prominent way of recognizing both individual orcas and the group to which they belong. Both residents and transients are catalogued in this way, and both the Canadian Department of Fisheries and the Center for Whale Research use these methods to track all individual orcas within the Salish Sea. As of 2023, all 73 known southern residents, 310 northern residents, and 349 Bigg's orcas in British Columbia and Washington have been catalogued. In BC, cataloging orcas is primarily done by the provincial government, while in Washington, it is primarily done by the NGO nonprofit Center for Whale Research.
Both resident groups of orcas are known for having a more rounded and straight, somewhat slanted towards the back, upward-facing dorsal fin compared to transients, which have a more pointed, shark-like fin going straight up, and a more prominent, grayish "cape" on their backs. The eyespot of residents is usually smaller than transients, and is more in line with the body, having an upward slant near its rear edge. Differences in body size cannot be determined visually; however, residents overall are smaller than transients, with southern residents being the smallest of the three ecotypes.
Southern resident orcas feed exclusively on fish, with salmon being their preferred prey; it is estimated that up to 80% of the diet of southern residents consists of chinook salmon, mostly coming from the Fraser River. Other types of salmon, herring, halibut, and lingcod are also consumed. While there is no record of southern resident orcas eating harbor porpoises, at least 78 incidents have been recorded since 1962 involving orcas harassing harbor porpoises, of which 28 resulted in the porpoise's death; it has never been confirmed whether this is the result of competition for food, rough play, or true aggression.
Low reproductive rates hinder population growth among orcas. Females do not mature until they are 10 to 13 years old, and gestation is approximately 15 months. With the female maintaining care for her calf until it is two years old, orcas are only able to produce a calf once every 39 months, and thus cannot recover quickly from population decline. Inbreeding also has a negative effect on the population. The total mortality level in young of the year orcas can be as high as 43%.
Northern resident orcas
The larger population of northern residents primarily ranges from the mid-coast of Alaska south into British Columbia through the Strait of Georgia and both sides of Vancouver Island south to Gray's Harbor, with the bulk of their range encompassing the Strait of Georgia and most of Vancouver Island, and north to Haida Gwaii. The northern residents number over 300 whales. They demonstrate seasonal shifts, generally inhabiting Chatham Sound in summer, Johnstone Strait in fall, and the San Juan Islands in winter. Northern resident orcas are divided into three clans totaling 16 pods, showing higher genetic diversity compared with southern residents. As with southern residents, northern residents subsist mostly on salmon, with chinook constituting the bulk of their diet. However, the unique hunting techniques of northern residents may have assisted in their recovery compared to southern residents. In northern residents, females do most of the herding and hunting of salmon, whereas in southern residents, males do most of the hunting. It has been found that female southern residents do not actively forage when nursing calves, so males must hunt in their place; in northern residents, females continue to hunt even when nursing calves. Lack of foraging by female southern residents during calving season may reduce the ability of the group to hunt cooperatively and deprive it of valuable foraging experience.
Northern residents do not differ morphologically from southern residents aside from individual markings. Their calls closely resemble one another, as do overall body shapes, and life history is assumed to be similar for both types. Differentiation between groups focuses primarily on their distribution; only southern residents are known to enter Puget Sound and the Whidbey Island area, and are the primary species found within the San Juan Islands and the southern part of Vancouver Island; whereas northern residents do not usually leave the Strait of Georgia or Johnstone Strait. However, given that both types can inhabit the San Juan Islands and southern residents occasionally enter BC waters, individual and pod identification are the only clear means of differentiating the northern and southern residents pods. No known direct interactions between northern and southern resident pods have been documented.
Transient orcas
Little is known about the genetics and life history of transient orcas, also known as Bigg's orcas. Unlike residents, much less individual identification via photo-ID has been conducted, largely due to increased spatial movement and less knowledge of overall pod structure compared to residents. Nevertheless, transients have been identified in increasing numbers over the years, and like residents, can be identified individually by marks and scars on their bodies. Known for their more shark-like fins, large size, solid gray patches, and larger eyespots, transient orcas are found throughout the Salish Sea region, which appears to be their main area of occurrence. Their primary calls, which differ from residents, are composed of a series of click-like vocalizations and harsh, screaming sounds primarily used to frighten and trap prey when hunting. The primary diet of transient orcas includes harbor seals, Steller sea lions, harbor porpoises, Dall's porpoises, Pacific white-sided dolphins, and Minke whales. Among these, the harbor seal is the most common prey; one survey estimated that more than half of the diet of transients in the Salish Sea region consists of harbor seals. Attacks on large whales in the region are relatively rare and no incidents of successful predation have occurred, although isolated incidents of transients harassing gray whales and humpback whales, including predation, have been observed outside the Salish Sea. However, interactions do sometimes become spectacular; in October 2022, a rare battle near Vancouver was observed between a pod of transients and humpbacks that ended with the group disappearing into the fog, with the ultimate outcome unknown.
Having split from other orcas 750,000 years ago, no interbreeding occurs between transient and resident orcas. Interactions between transients and residents are very rare; they actively avoid one another and are never known to socialize. Nevertheless, when interactions do occur, it seems the residents, despite being smaller and less carnivorous, dominate the transients. In 2021, southern residents K16 and L72 surfaced in the midst of a pod of transient pod's hunt of an unknown prey species. After a short scuffle, the transients quickly departed the area, leaving the area to the residents. A similar but more brutal encounter was recorded in 1993, when transients were attacked by members of the J-pod and almost forced onto the rocks at Nanaimo. After a battle that lasted for at least several minutes, the transients fled the area with scars, leaving the victorious residents to regroup.
Offshore orcas Offshore orcas, first described in 1979, are primarily found more than 10 miles (16 km) from shore. Just over 280 offshore orcas are known from the Eastern North Pacific, primarily occurring off the coast of British Columbia. Although forays into the Salish Sea are rare, the area immediately offshore, including the Barkley submarine canyon, is home to large numbers. In contrast to transient and resident orcas, the teeth of offshore orcas are usually quite worn-down and often blunt, potentially shortening their lives; this has been confirmed to be linked to their primary diet - sharks - and the tough skin they possess. The sharks most commonly taken are mako, thresher, sevengill, and on rare occasions, great white sharks. The first recorded incidence of orca predation on great white sharks, in 1997, may have involved an offshore whale.
Human history