Status and trends for West Coast transient (Bigg’s) killer whales in the Salish Sea
Officially known as West Coast transients but increasingly referred to as Bigg’s killer whales, these marine mammal-eating orcas (Orcinus orca) are spending increasing time in the Salish Sea to consume their marine mammal prey including harbor seals, Steller sea lions, and harbor and Dall’s porpoise. They range from Southeast Alaska to California, but over the last 15 years more members of the population are spending increasing time in the inland waters of Washington State and British Columbia (Houghton et al. 2015, Shields et al. 2018). They have no predators (except perhaps occasionally other Bigg’s killer whales - see Towers et al. 2018), but are at risk from anthropogenic effects, including toxics and noise pollution (Ford et al. 2007).
Trends & events
Historic population trends and habitat usage of Bigg’s killer whales in the Salish Sea are not well known, as differentiation of killer whales into ecotypes did not happen until the 1980s. The population has grown steadily over the last 40 years, doubling since 1990 to a 2018 total of over 500 individuals (Towers et al. 2018). A subset of this population (approximately 350 individuals) has been identified as more likely to occur within coastal waters. Within this subset, there were 112 births and 27 deaths from 2012 to the end of 2018, resulting in a greater than 4% growth rate (Towers et al. 2019). While not all these whales use the Salish Sea on an annual basis, well over 200 individual whales in at least 50 different matrilines currently use the region on a regular basis (Shields et al. 2018), as compared to 12 matrilines 25 years ago (Baird and Dill 1995).
Usage of the Salish Sea by particular social groupings of Bigg’s killer whales are tracked via “occurrences,” defined by Houghton et al. (2015) as an encounter with a specific social group of killer whales when no encounters of that group occurred within the six days prior to or after that sighting. The intention of measuring occurrences is to account for multiple detections of the same group over consecutive days and for days a group may have been present but undetected to result in a metric of habitat usage. The number of occurrences has been tracked within the Salish Sea across three 7-year time periods: 1987-1993 (Baird and Dill 1995), 2004-2010 (Houghton et al. 2015), and 2011-2017 (Shields et al. 2018).
Natural history
Distribution and occurrence
The West Coast Transient population ranges from southeast Alaska to California. They are not migratory, so individual whales may be found anywhere within that range at any time of year, which is why they received their original common name of “transients.” There is, however, evidence that some whales show strong seasonal site fidelity to certain parts of this range, and also may time their movements through the range relative to their prey, such as harbor seals during pupping seasons (Ford et al. 2013).
Within the Salish Sea, Bigg’s killer whales use virtually the entire ecosystem, ranging from the larger Straits of Georgia and Juan de Fuca to the narrowest channels such as Saanich Inlet, Hood Canal, Sansum Narrows, and Hammersley Inlet. Visits to the region by particular matrilines typically last for several days or weeks, but occasionally extend for months, such as the occupancy of Hood Canal for 59 days in 2003 and 172 days in 2005 (London 2006). Overall, the increasing usage of the Salish Sea by Bigg’s killer whales has led to the name “transients” being less descriptive and thus being used less often.
Within the Salish Sea, Bigg’s killer whale occurrence peaks first in April-May and again in August-September, a trend that has persisted over the last 30 years of observation even while overall occurrence has steadily increased year-round. 2017 saw a marked increase relative to previous years in 10 out of the 12 months of the year (Shields et al. 2018).
What do they eat?
While killer whales around the world eat a wide variety of species, regional populations can be genetically distinct and have specialized diets, foraging selectively on specific prey (Ford and Ellis, 2014). In the case of Bigg’s killer whales, they are marine mammal specialists and have a distinct diet and also differ from resident or salmon-eating killer whales in their social organization, genetics, behavior, and acoustics (Ford et al., 1998). A summary of predation events by Bigg’s killer whales between the 1970s and the 1990s, primarily within the Salish Sea, documented kills or harassments of nine marine mammal species and seven marine bird species (Ford et al. 1998). Of documented kills, 94% were on marine mammals, with harbor seals making up more than 50% of these. Other common prey species are Steller sea lions, Dall’s porpoise, harbor porpoise, California sea lions, and Pacific white-sided dolphins. Larger baleen whales (humpback, gray, and minke) are occasionally harassed and are more rarely killed and consumed. While there was some early evidence that certain Bigg’s killer whale family groups may specialize in nearshore (pinniped) or non-nearshore (cetacean) species (Baird and Dill 1995), continued observations have shown that all regularly encountered groups predate upon both pinnipeds and cetaceans (Ford et al. 1998).
What threatens them?
Bigg’s killer whales have no predators, although one instance of intra-specific infanticide has been documented (Towers et al. 2018). Resident killer whales have been observed chasing Bigg’s killer whales, and in at least one instance the two ecotypes possibly engaged in a physical confrontation (Ellis and Ford 1999). The two ecotypes routinely avoid each other and no conflict-related deaths have ever been documented.
Despite the population’s growth over the last three decades, Bigg’s killer whales are at risk from numerous anthropogenic threats. They carry extremely high levels of persistent organic pollutants (e.g. PCBs and DDTs) due to their high trophic level (Ross et al. 2000). Concentrations of PCBs differ between males (251.2 +/- 54.7 mg kg-1) and females (58.8 +/- 20.6 mg kg-1), as females transfer some of their toxin load to their offspring through lactation, but were found to be substantially higher than in resident killer whales or St. Lawrence beluga whales who are known to be highly contaminated (Ross et al., 2000).
Bigg’s killer whales are susceptible to noise disturbance from sources such as vessels, oil and gas exploration, and military activities, particularly as it may impact their ability to hunt (Ford et al., 2007). Catastrophic oil spills could result in significant mortality of Bigg’s killer whales. After being seen swimming through oil-contaminated water after the 1989 Exxon Valdez oil spill in Prince William Sound, Alaska, 41% of the AT1 pod of transient killer whales died in the year following the spill (Matkin et al. 2008). Although Bigg’s killer whales have been documented engaging with crab and shrimp pot lines in apparent play behavior, they have also become entangled in these lines.
Finally, as with all specialized predators, Bigg’s killer whales are susceptible to declines in their primary prey sources and there has been concern about how proposed pinniped culling in both the US and Canada to help recover salmon stocks could have negative consequences on the health of the West Coast Transient population (Shields et al., 2018). As many regional salmon stocks continue to decline, one of many recovery measures being considered is predator control. While Bigg’s killer whales are not direct salmonid predators, they do predate harbor seals and Steller sea lions that consume salmon at various stages of their life cycle. Bigg’s orcas are thus at risk from future prey declines that may result from substantial pinniped removals.
Bigg’s killer whales themselves provide significant “predator control.” In 2017, conservative estimates suggest they consumed ~1,100 harbor seals within the Salish Sea, equivalent to more than 2% of the 2014 regional harbor seal population and on par with the annual rate at which humans culled harbor seals in the mid-20th century (Shields et al. 2018). Updated data on harbor seal population trends and actual predation rates (rather than modeled minimal metabolic needs) are needed to further inform this topic before policy actions are taken.
Lifespan and Reproduction
Like orcas from other populations, Bigg’s killer whales are long-lived, having an expected lifespan of 30-50 years, with some individuals living much longer. Survival among all age and sex classes is high, with an average annual survival probability across all individuals of 98% as of 2006 (Ford et al. 2007). Survival rates were reported to be slightly lower (~92%) among calves and juveniles.
Females typically have their first calf in their teenage years, and may continue to give birth every 3-5 years. It is unclear but reasonable to assume that Bigg’s killer whales undergo reproductive senescence like resident killer whales. At least one individual with an estimated birth year of ≤1969 (T034) gave birth to a calf in 2017, at a minimum age of 48, six years older than the oldest documented resident killer whale mother.
Data sources & gaps
Monitoring efforts of Bigg’s killer whales in the Salish Sea is mostly done opportunistically through reports from the public through either Orca Network or the Pacific Whale Watch Association. The US and Canadian Federal Agencies responsible for marine mammal management (NOAA Fisheries, USA and Fisheries and Oceans Canada) also monitor these populations. The Orca Network Sightings Archives are the primary publicly-available source of sightings information and were used to document increased Bigg’s killer whale presence over the last 14 years (Houghton et al. 2015, Shields et al. 2018).
Other organizations within the Salish Sea that collect data on these whales include the Center for Whale Research, Conservation Canines, Orca Behavior Institute, SR3, and the Vancouver Aquarium. The collected data includes population census information, prey and fecal samples, behavioral information, and acoustic recordings. Increasingly, the Orcasound hydrophone network has observed Bigg’s killer whales vocalizing, and potentially creating cavitation sounds during predation events.
References
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Houghton J, Baird RW, Emmons CK, Hanson MB. 2015. “Changes in the occurrence and behavior of Mammal-eating Killer Whales in Southern British Columbia and Washington State, 1987-2010”. Northwest Science 89(2):154169.
Ford JKL, Ellis GM. 2014. “You are what you eat.” In J. Yamagiwa and L. Karczmarski (eds.), Primates and Cetaceans: Field Research 75 and Conservation of Complex Mammalian Societies, Primatology Monographs, DOI 10.1007/978-4-431-54523-1_4, © Springer Japan 2014.
Ford JKB, Stedulinsky E, Towers JR, Ellis GM. 2013. “Information in support of the identification of critical habitat for Transient Killer Whales (Orcinus orca) off the West Coast of Canada”. Canadian Science Advisory Secretariat Research Document 2012/155. Available at http:// waves-vagues.dfo-mpo.gc.ca/ Library/ 349619.pdf
Ford JKB, Ellis GM, and Durban JW. 2007. “An assessment of the potential for recovery of West Coast Transient killer whales using coastal waters of British Columbia.” CSAS Research Document 2007–088.
Ford JK, Ellis GM, Barrett-Lennard LG, Morton AB, Palm RS, Balcomb KCB. 1998. “Dietary specialization in two sympatric populations of killer whales (Orcinus orca) in coastal British Columbia and adjacent waters”. Canadian Journal of Zoology 76:14561471 DOI 10.1139/z98-089.
Ford JKB, Ellis GM. 1999. “Transients: mammal-hunting Killer Whales of BC, Washington State, and Alaska”. Vancouver: UBC Press.
London JM. 2006. “Harbor seals in Hood Canal: predators and prey”. Doctoral thesis, University of Washington.
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Ross PS, Ellis GM, Ikonomou MG, Barrett-Lennard LG, Addison RF. 2000. “High PCB Concentrations in Free-Ranging Pacific Killer Whales, Orcinus orca: Effects of Age, Sex and Dietary Preference”. Marine Pollution Bulletin 40(6): 504-515.
Shields MW, Hysong-Shimazu S, Shields JC, Woodruff J. 2018. “Increased presence of mammal-eating killer whales in the Salish Sea with implications for predator-prey dynamics”. PeerJ 6: e6062. DOI 10.7717/peerj.6062
Towers JR, Muriel JH, Symonds HK, Sutton GJ, Morton AB, Spong P, Borrowman JP, Ford JKB. 2018. “Infanticide in a mammal-eating killer whale population”. Scientific Reports 8:4366 DOI 10.1038/s41598-018-22714-x.
Towers JR, Sutton GJ, Shaw TJH, Malleson M, Matkin D, Gisborne B, Forde J, Ellifrit D, Ellis GM, Ford JKB, Doniol-Valcroze T. 2019. “Photo-identification catalogue, population status, and distribution of Bigg’s killer whales known from coastal waters of British Columbia, Canada”. Canadian Technical Report of Fisheries and Aquatic Sciences 3311: vi + 299 p.
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Related Resources
- Photo-identification Catalogue of Bigg’s (Transient) Killer Whales
- Vancouver Aquarium: Bigg’s Killer Whale Adoption Program Fact Sheet
- Fisheries and Oceans Canada: Northeast Pacific Transient Killer Whale population (or Bigg’s Killer Whale)
- NOAA: 2000 Transient Killer Whale Marine Mammal Stock Assessment Report
- Ocean EcoVentures: Biggs Killer Whales Vancouver Island B.C. (video)
- Western Prince Whale Watching: The T123's hunt, eat, and socialize (video)
- Orca Behavior Institute: T2Cs on April 1, 2018 (audio)
- Beam Reach: Navy recording of transient orcas