[MARMAM] New publication on mammal-eating killer whales in the Salish Sea

[Monika Wieland]

Dear Colleagues,

On behalf of the Orca Behavior Institute, I'm pleased to announce our 
latest publication in PeerJ:

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 
https://doi.org/10.7717/peerj.6062

Abstract: 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.

Full paper available open access here: https://peerj.com/articles/6062/

Best regards,

Monika Wieland Shields
Orca Behavior Institute
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