ESR 10:135-143 (2009)  -  doi:10.3354/esr00220

Spatially explicit detection of predation on individual pinnipeds from implanted post-mortem satellite data transmitters

Markus Horning1,*, Jo-Ann E. Mellish2,3

1Department of Fisheries and Wildlife, Marine Mammal Institute, Oregon State University, 2030 SE Marine Science Drive, Newport, Oregon 97365, USA
2Alaska Sea Life Center, 301 Railway Ave., Seward, Alaska 99664, USA
3School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Alaska 99775, USA

ABSTRACT: To directly determine mortality and predation in the endangered western Steller sea lion Eumetopias jubatus, we deployed implanted, satellite-linked post-mortem data transmitters in 21 juveniles. Data recovered from 4 of 5 detected mortalities exhibited precipitous drops in ambient temperatures followed by immediate onset of transmissions (N = 3), or gradual cooling and delayed transmissions (N = 1). Precipitous drop data sets were classified as acute death at sea by trauma. A model to estimate algor mortis (body cooling) as a function of mass and ambient conditions was validated through simulations on 4 carcasses. Model outputs suggest that cooling rate masses can be qualitatively distinguished if well outside the prediction uncertainties. The observed gradual cooling rate was best described by a modeled mass one-sixth the animal’s mass at release, supporting the classification of the fourth event as acute death at sea by trauma. This suggests that at least 4 in 5 detected mortalities likely represent acute deaths at sea, probably due to predation. We conclude that precipitous drop events with immediate transmissions can be classified as acute death likely by predation, but gradual cooling events with delayed transmission should be reviewed on a case-by-case basis. In 3 cases that provided both ante-mortem and post-mortem locations from external and implanted transmitters, respectively, these differed by less than 17 km, illustrating that this technique provides spatially explicit data of predation on individual sea lions.

KEY WORDS: Predation . Mortality . Algor mortis . Telemetry . Eumetopias jubatus . Steller sea lion

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Cite this article as: Horning M, Mellish JAE (2009) Spatially explicit detection of predation on individual pinnipeds from implanted post-mortem satellite data transmitters. Endang Species Res 10:135-143

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