Dear MARMAMers a new publication on the impacts of predation on juvenile western Steller sea lions is now freely available via Open Access at PLoS ONE: http://dx.plos.org/10.1371/journal.pone.0030173
Horning M, Mellish JE. 2012. Predation on an Upper Trophic Marine Predator, the Steller Sea Lion: Evaluating High Juvenile Mortality in a Density Dependent Conceptual Framework. PLoS ONE 7(1):e30173. doi:10.1371/journal.pone.0030173 Abstract: The endangered western stock of the Steller sea lion (Eumetopias jubatus) – the largest of the eared seals – has declined by 80% from population levels encountered four decades ago. Current overall trends from the Gulf of Alaska to the Aleutian Islands appear neutral with strong regional heterogeneities. A published inferential model has been used to hypothesize a continuous decline in natality and depressed juvenile survival during the height of the decline in the mid-late 1980’s, followed by the recent recovery of juvenile survival to pre-decline rates. However, these hypotheses have not been tested by direct means, and causes underlying past and present population trajectories remain unresolved and controversial. We determined post-weaning juvenile survival and causes of mortality using data received post-mortem via satellite from telemetry transmitters implanted into 36 juvenile Steller sea lions from 2005 through 2011. Data show high post-weaning mortality by predation in the eastern Gulf of Alaska region. To evaluate the impact of such high levels of predation, we developed a conceptual framework to integrate density dependent with density independent effects on vital rates and population trajectories. Our data and model do not support the hypothesized recent recovery of juvenile survival rates and reduced natality. Instead, our data demonstrate continued low juvenile survival in the Prince William Sound and Kenai Fjords region of the Gulf of Alaska. Our results on contemporary predation rates combined with the density dependent conceptual framework suggest predation on juvenile sea lions as the largest impediment to recovery of the species in the eastern Gulf of Alaska region. The framework also highlights the necessity for demographic models based on age-structured census data to incorporate the differential impact of predation on multiple vital rates. Best Regards, Markus Horning __________________________________________________ Dr. Markus Horning, Pinniped Ecology Applied Research Lab Marine Mammal Institute, Oregon State University 2030 SE Marine Science Drive, Newport, OR 97365, USA Tel. 541.867.0202 Fax 541.867.0128 [email protected]<mailto:[email protected]> http://mmi.oregonstate.edu/pearl/ www.sealtag.org<http://www.sealtag.org/>
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