Declining spring usage of core habitat by endangered fish-eating killer whales reflects decreased availability of their primary prey

Shields, Monika W.; Lindell, Jimmie; Woodruff, Julie

doi:10.1071/pc17041

Cited by 14 publications

(21 citation statements)

References 16 publications

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“…Moreover, we found a significant relationship between salmon abundance and the number of annual SRKW encounters over time in our study area on the west side of San Juan Island. Our results are in accordance with previous findings that suggest SRKWs are foraging less often in this once critically important region (Shields et al., 2018). Resident killer whale movement patterns are partially driven by density and distribution of their preferred prey species (Ford & Ellis, 2006; Heimlich‐Boran, 1986, 1988; Nichol & Shackleton, 1996).…”

Section: Discussionsupporting

confidence: 94%

“…Not only has a limited prey source affected SRKW individual health condition, but nutritional stress due to Chinook population declines has also been suggested as a primary driver of reduced fecundity and increased mortality rates (Ford et al, 2005; Ford, Ellis, et al, 2010; Ward et al., 2009), including late‐stage fetal loss and early infant mortality (Wasser et al., 2017), further placing the future of this population in peril. From a behavioral perspective, it is understood that prey availability likely influences distribution patterns of SRKWs (Hauser et al., 2007), the locations where the whales engage in specific activities (e.g., traveling, foraging, and resting; Noren & Hauser, 2016), visitation rates to core habitat areas (Shields et al., 2018), and social network structure (Foster et al., 2012). Yet, it is unclear to what extent prey availability has on the frequency of SABs, behaviors with potentially profound ecological and evolutionary implications.…”

Section: Introductionmentioning

confidence: 99%

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Surface behaviors correlate with prey abundance and vessels in an endangered killer whale (Orcinus orca) population

2020

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Southern Resident killer whales (SRKWs) (Orcinus orca) are an endangered population in the United States and Canada, partly due to declines of their primary prey species, Chinook salmon. Prey availability influences various aspects of SRKW behavior, including distribution patterns and social structure. Yet, it is unclear to what extent a limited prey source influences the frequency of surface‐active behaviors (SABs), behaviors with important ecological implications. Here, we used long‐term datasets (1996–2019) to examine the relationships between the abundance of Chinook salmon, vessel presence, and the frequency with which SRKWs perform SABs. Salmon abundance was a significant predictor of SAB frequency, with fewer SABs performed in times of lower salmon abundance. SRKWs displayed more SABs when more whale watching vessels were present, and the whales spent a greater amount of time in the study area, performing more milling as opposed to traveling behavior, when vessel numbers were higher. Lastly, we found pod‐specific differences, such that K pod displayed significantly fewer SABs than either J or L pods. The observed relationships between SRKW behavior and both salmon abundance and vessel presence have implications for social network cohesion and foraging success. Our study adds to a growing body of literature highlighting factors affecting SRKW behavior as they experience increased threats from decreased prey availability, habitat loss, and anthropogenic disturbance, with implications for trans‐boundary management and conservation efforts.

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Section: Discussionsupporting

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Surface behaviors correlate with prey abundance and vessels in an endangered killer whale (Orcinus orca) population

2020

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“…This finding supports previous research showing that SRKW body condition is usually at his lowest level before summer, and confirms that SRKW could undergo a more acute nutritional stress during the spring. Moreover, our results support the hypothesis that SRKW might not have enough resources in the spring months in the Salish Sea, therefore spending less time in this critical habitat during this season [ 74 ]. Interestingly, our model predicted that SRKW would consume more Chum salmon than any age classes of Chinook salmon during years where their usual Chinook salmon preys were at low levels.…”

Section: Discussionsupporting

confidence: 84%

“…Finally, our model predicted that the overall relative contribution of stocks originating from the Columbia River in the modeled SRKW diet has increased over the last 40 years, while the contribution of stocks originating from Puget Sound has decreased. When presenting those results, we assume to reflect abundance variations of different Chinook salmon stocks available to SRKW, which might partially explain why SRKW have been seen less frequently in the Salish Sea in recent years [ 74 ]. Chinook stocks of the Salish Sea have been reduced by about 60% since 1984, and SRKW could logically be feeding upon other more abundant Chinook salmon stocks passing through different areas [ 77 ].…”

Section: Discussionmentioning

confidence: 99%

Requirements and availability of prey for northeastern pacific southern resident killer whales

et al. 2022

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The salmon-eating Southern Resident killer whale (SRKW) (Orcinus orca) population currently comprises only 73 individuals, and is listed as ‘endangered’ under the Species at Risk Act in Canada. Recent evidence suggests that the growth of this population may be limited by food resources, especially Chinook salmon (Oncorhynchus tshawytscha). We present spatio-temporal bioenergetics model for SRKW in the Salish Sea and the West Coast of Vancouver Island from 1979–2020 with the objective of evaluating how changes in the abundance, age-structure, and length-at-age of Chinook salmon populations has influenced the daily food consumption of the SRKW population. Our model showed that the SRKW population has been in energetic deficit for six of the last 40 years. Our results also suggested that the abundance of age-4 and age-5 Chinook salmon are significant predictors of energy intake for SRKW. We estimated that the annual consumption (April-October) of Chinook salmon by the whales between 1979 and 2020 ranged from 166,000 216,300. Over the past 40 years, the model estimated that the contribution in the predicted SRKW diet of Chinook salmon originating from the Columbia River has increased by about 34%, and decreased by about 15% for Chinook salmon stocks originating from Puget Sound. Overall, our study provides an overview of the requirements and availability of prey for SRKW over the last 40 years, while supporting the hypothesis that SRKW were limited by prey abundance in the study period.

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“…In recent years, however, both of these patterns have been changing. 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%

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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Declining spring usage of core habitat by endangered fish-eating killer whales reflects decreased availability of their primary prey

Cited by 14 publications

References 16 publications

Surface behaviors correlate with prey abundance and vessels in an endangered killer whale (Orcinus orca) population

Surface behaviors correlate with prey abundance and vessels in an endangered killer whale (Orcinus orca) population

Requirements and availability of prey for northeastern pacific southern resident killer whales

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

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