Changes in the Occurrence and Behavior of Mammal-Eating Killer Whales in Southern British Columbia and Washington State, 1987–2010

Houghton, Juliana; Baird, Robin W.; Emmons, Candice K.; Hanson, M. Bradley

doi:10.3955/046.089.0207

Cited by 13 publications

(21 citation statements)

References 39 publications

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“…Clearly, MEKW predation, even if rarely observed and targeting mainly calves and subadults, represents a threat to humpbacks that is persistent, widespread, and perhaps increasing (Houghton et al 2015, Pitman et al 2015; see also Discussion). As such, humpbacks could be expected to show some specific antipredator behaviors, and indeed some have been suggested.…”

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confidence: 85%

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Humpback whales interfering when mammal‐eating killer whales attack other species: Mobbing behavior and interspecific altruism?

Pitman

Deecke

Gabriele³

et al. 2016

Marine Mammal Science

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Humpback whales (Megaptera novaeangliae) are known to interfere with attacking killer whales (Orcinus orca). To investigate why, we reviewed accounts of 115 interactions between them. Humpbacks initiated the majority of interactions (57% vs. 43%; n = 72), although the killer whales were almost exclusively mammal-eating forms (MEKWs, 95%) vs. fish-eaters (5%; n = 108). When MEKWs approached humpbacks (n = 27), they attacked 85% of the time and targeted only calves. When humpbacks approached killer whales (n = 41), 93% were MEKWs, and ≥87% of them were attacking or feeding on prey at the time. When humpbacks interacted with attacking MEKWs, 11% of the prey were humpbacks and 89% comprised 10

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confidence: 85%

mentioning

confidence: 99%

Humpback whales interfering when mammal‐eating killer whales attack other species: Mobbing behavior and interspecific altruism?

Pitman

Deecke

Gabriele³

et al. 2016

Marine Mammal Science

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“…Additionally, most prey species that WCT killer whales target have been steadily increasing in coastal waters over the last few decades 63 – 69 . These increases in prey availability have been commensurate with increasing social activity 70 and higher recruitment within the WCT population 39 suggesting that it is not nutritionally stressed. Thus, this incident is not easily explained by the predation hypothesis.…”

Section: Discussionmentioning

confidence: 94%

Infanticide in a mammal-eating killer whale population

Towers

Hallé²,

Symonds³

et al. 2018

Sci Rep

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Infanticide can be an extreme result of sexual conflict that drives selection in species in which it occurs. It is a rarely observed behaviour but some evidence for its occurrence in cetaceans exists in three species of dolphin. Here we describe observations of an adult male killer whale (Orcinus orca) and his post-reproductive mother killing a neonate belonging to an unrelated female from the same population in the North Pacific. This is the first account of infanticide reported in killer whales and the only case committed jointly by an adult male and his mother outside of humans. Consistent with findings in other social mammals, we suggest that infanticide is a sexually selected behaviour in killer whales that could provide subsequent mating opportunities for the infanticidal male and thereby provide inclusive fitness benefits for his mother.

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“…The Southern Residents have been utilizing the Salish Sea less, particularly in the spring months (Shields, Lindell & Woodruff, 2018). Meanwhile, transient killer whales have expanded their usage of the Salish Sea from a small number of whales visiting primarily in August and September in the late 1980s and early 1990s (Baird & Dill, 1995) to visiting in increasing numbers with a second peak in visitation in April and May as of the mid-2000s (Houghton et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

“…Meanwhile, while the West Coast Transient population is listed as threatened in Canada, their population has doubled between 1990 and 2012 (Towers, Ellis & Ford, 2012). Usage of the Salish Sea by mammal-eating killer whales has been documented during two previous seven-year time periods from 1987 to 1993 (Baird & Dill, 1995) and 2004–2010 (Houghton et al, 2015), with the increased occurrence in the Salish Sea between these two time periods credited to both an increase in prey and an overall increase in population size.…”

Section: Introductionmentioning

confidence: 99%

Increased presence of mammal-eating killer whales in the Salish Sea with implications for predator-prey dynamics

Shields¹,

Hysong-Shimazu²,

Shields³

et al. 2018

PeerJ

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The inland waters of Washington State and southern British Columbia, collectively known as the Salish Sea, comprise key habitat for two regional populations of killer whales (Orcinus orca): the mammal-eating West Coast Transients and the endangered fish-eating Southern Residents. These two populations are genetically distinct and may avoid each other. Transient killer whale usage of the Salish Sea has been previously assessed over two seven-year time periods, showing an increase from 1987 to 2010. We documented a continued significant increase in mammal-eating killer whale presence in the Salish Sea from 2011 to 2017, with intra- and inter-annual variability and with record sightings in 2017. This continued increase, likely in response to abundant marine mammal prey, is related to both a growing population and an increase in the number of West Coast Transients visiting the area. Additionally, a negative binomial regression shows that absence of Southern Residents is correlated to transient presence. Finally, both populations of killer whales have been linked to regional harbor seal populations; harbor seals are salmonid-eating competitors of the Southern Residents and are prey for the mammal-eating transients. With Southern Residents listed as endangered, culling harbor seals has been proposed as a measure to help in their recovery. With this in mind, we developed an energetic model to assess the minimum number of harbor seals consumed by transient killer whales. Using the actual number of whales present in each age-sex class for each day of the year, we estimate that, at a minimum, transients in the Salish Sea consumed 1090 seals in 2017. This is more than 2% of the 2014 estimated harbor seal population the Salish Sea. The population controlling effects of transient killer whale predation on harbor seals should be considered when evaluating any pinniped management actions in the Salish Sea.

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Changes in the Occurrence and Behavior of Mammal-Eating Killer Whales in Southern British Columbia and Washington State, 1987–2010

Cited by 13 publications

References 39 publications

Humpback whales interfering when mammal‐eating killer whales attack other species: Mobbing behavior and interspecific altruism?

Humpback whales interfering when mammal‐eating killer whales attack other species: Mobbing behavior and interspecific altruism?

Infanticide in a mammal-eating killer whale population

Increased presence of mammal-eating killer whales in the Salish Sea with implications for predator-prey dynamics

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