ESR 4:147-155 (2008)  -  DOI: https://doi.org/10.3354/esr00050

Acoustic determination of activity and flipper stroke rate in foraging northern fur seal females

S. J. Insley1,3,*, B. W. Robson2,4, T. Yack3, R. R. Ream2, W.C. Burgess4

1University of California Santa Cruz, Institute of Marine Sciences, Long Marine Laboratory, 100 Shaffer Rd., Santa Cruz, California 95060, USA
2National Marine Mammal Laboratory, National Marine Fisheries Service, 7600 Sand Point Way, Seattle, Washington 98115, USA
3Hubbs-SeaWorld Research Institute, 2595 Ingraham Street, San Diego, California 92109, USA
4Greeneridge Sciences, 1411 Firestone Rd., Santa Barbara, California 93117, USA

ABSTRACT: Foraging effort for lactating female otariid pinnipeds is largely a function of the energy expended swimming to a site and diving in search of prey. This is especially true for northern fur seal Callorhinus ursinus females, which predictably punctuate their suckling with 7 to 12 d foraging trips at sea, with swimming distances often exceeding 400 km. In the present study we tested a unique approach (flow noise from onboard acoustic dataloggers) to empirically measure swim effort in free ranging female northern fur seals, the first such field measurements on an otariid pinniped. We first measured behavioural activity budgets of seals from a combination of satellite telemetry, pressure (depth), and onboard acoustic data. From these data we were able to quantify the time spent in each of 4 mutually exclusive forms of behaviour: locomoting, diving, resting, and surface activity. Second, flipper stroke rates and stroke rate patterns were measured from the acoustic data for each seal during 3 dive types (i.e. locomoting, shallow and mid/deep dives) and during 3 dive parts (descent, bottom time and ascent). Although stroke rates during each of the 3 dive types were similar (ca. 0.5 Hz), they were distinct during the different parts of a dive. In each case, variation among individuals was significant. Stroke rate patterns were distinct for the different dive types and dive parts. Overall, in addition to applying a unique technique to measure foraging effort in a declining population, the results emphasize the importance of accounting for individual variation to obtain accurate estimates of foraging cost.


KEY WORDS: Flipper stroke rate · Effort · Activity budget · Diving behaviour · Foraging effort · Marine mammal · Pinniped · Otariid · Fur seal


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Cite this article as: Insley SJ, Robson BW, Yack T, Ream RR, Burgess W (2008) Acoustic determination of activity and flipper stroke rate in foraging northern fur seal females. Endang Species Res 4:147-155. https://doi.org/10.3354/esr00050

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