Hobart

Seminar abstract

Wednesday 25 October 2006, 11.30 am (Tas time)
CSIRO Auditorium, Hobart

Marc Mangel
Ernest Frohlich Fellow
University of California, Santa Cruz

Understanding the decline of the western Alaskan Steller sea lion:
assessing the evidence concerning multiple hypothesis

Although millions of dollars have been spent exploring the cause, and a wide variety of hypotheses have been proposed, the precipitous decline of the western population of Steller sea lions (Eumatopias jubatus) since the late 1970's has proven to be very difficult to explain. This as an opportunity for ecological detection, a process in which multiple hypotheses simultaneously compete and their success is arbitrated by the relevant data. The authors of a recent comprehensive review of the problem emphasized repeatedly that the system is in dire need of a modeling approach that takes advantage of the data available at small spatial scales (at the level of the rookery).

I begin by summarizing the biology of the Steller sea lion, including life history, prey base and relevant fisheries, and other marine mammals. The various competing hypotheses can be viewed in the context of different food webs of increasing complexity. For the case of Steller Sea lions, there exist sufficient data to investigate 10 hypotheses. I will describe a series of models that allow us to link the hypotheses and the data. Unknown parameters are estimated by comparing the predictions of the stochastic population model with observed counts. For each parameter, we compute a profile likelihood interval by finding the area under the curve that contains 95% or 99% of the total area. We are thus able to determine whether there is strong, weak or no evidence for an effect, and from the model whether the effect is strong, moderate or weak/not at all. For example, the answer to the oft-asked question “Is it food” is yes and that it is both quality and quantity of food. The more recent question “Is it killer whale predation” can be answered too – sometimes, if harbor seal populations are sufficiently low, but not with a large reduction in survival. The results also suggest various kinds of adaptive management.

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Location:
CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
To schedule a seminar, contact:
Karen Wild-Allen, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5010
Piers Dunstan, (Biological seminars) CSIRO Marine and Atmospheric Research
(03) 6232 5382
Annabel Ozimec (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5462
Sandra Zicus, Antarctic Climate and Ecosystems CRC (03) 6226 7888
Margaret Hazelwood, Institute of Antarctic and Southern Ocean Studies (IASOS) University of Tasmania (03) 6226 2971

Last updated 13/10/06