Tennessen,
J.B., Holt, M.M., Hanson, M.B., Emmons, C.K., Giles, D.A., Hogan, J.T.
2019. Kinematic signatures of prey capture from archival tags reveal sex
differences in killer whale foraging activity. Journal of Experimental Biology 222, jeb191874. doi:10.1242/jeb.191874
Studies of odontocete foraging ecology have been limited by the
challenges of observing prey capture events and outcomes
underwater. We sought to determine whether subsurface
movement behavior recorded from archival tags could accurately
identify foraging events by fish-eating killer whales. We used
multisensor bio-logging tags attached by suction cups to Southern
Resident killer whales (Orcinus orca) to: (1) identify a stereotyped
movement signature that co-occurred with visually confirmed prey
capture dives; (2) construct a prey capture dive detector and validate it
against acoustically confirmed prey capture dives; and (3)
demonstrate the utility of the detector by testing hypotheses about
foraging ecology. Predation events were significantly predicted by
peaks in the rate of change of acceleration (‘jerk peak’), roll angle and
heading variance. Detection of prey capture dives by movement
signatures enabled substantially more dives to be included in
subsequent analyses compared with previous surface or acoustic
detection methods. Males made significantly more prey capture dives
than females and more dives to the depth of their preferred prey,
Chinook salmon. Additionally, only half of the tag deployments on
females (5 out of 10) included a prey capture dive, whereas all tag
deployments on males exhibited at least one prey capture dive (12 out
of 12). This dual approach of kinematic detection of prey capture
coupled with hypothesis testing can be applied across odontocetes
and other marine predators to investigate the impacts of social,
environmental and anthropogenic factors on foraging ecology.
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Kind regards,
Jennifer, Marla, Brad, Candice, Giles and Jeff