Steller Sea Lions (Eumetopias jubatus) in the Pacific Rim Biological Uncertainty and Extinction Risk

Abstract

Abstract In this chapter I develop a simple model for Steller sea lions (Eumetopias jubatus) and use this model to examine the sensitivity of population status to uncertainty in population parameters and potential response to management actions. I describe key biological attributes of this marine mammal that may be considered in using RAMAS for modeling extinction risk for marine mammals. Steller sea lions (SSLs) offer an interesting example of using population viability analysis (PVA) as a tool for making conservation decisions. Among marine mammals for which reasonable population estimates are available, Steller sea lions are the most abundant species to be listed as “endangered” pursuant to both the Endangered Species Act (ESA) and the World Conservation Union (IUCN) (Gerber and VanBlaricom 2001). Hypotheses for the decline of Steller sea lions include predation, disease, and variability in abundance and distribution of prey; environmental change; nutritional stress; direct kills; intentional and incidental kills by fisheries; entanglement in marine debris; pollution; and other disturbances at a variety of spatial scales. However, the relative importance of these various processes is far from certain. I use RAMAS to examine the degree to which hypothesized causes might affect different life history stages and compare trajectories for alternate scenarios. I then examine the effect of uncertainty in environmental stochasticity, density dependence, and catastrophes on estimates of extinction risk.