Status of Baltic grey seals: Population assessment and extinction risk

Abstract

The grey seal (Halichoerus grypus) population in the Baltic Sea is recovering after a century of bounty hunting and 3 decades of low fertility rates caused by environmental pollution. A con-servative estimate of the population size in 2003 was 19,400 animals, and available data suggest an annual rate of increase of 7.5 % since 1990. The growing population has led to increased in-teractions with the fishery, and demands are being raised for the re-introduction of the hunt. We provide a demographic analysis and a risk assessment of the population, and make recommen-dations on how to decrease the risk of overexploitation. Although hunting increases the risk of quasi-extinction, the risk can be significantly reduced by the choice of a cautious hunting regime. The least hazardous regimes allow no hunting below a ‘security level ’ in population size. Obvi-ously, to implement such a hunting regime detailed knowledge of the population size and growth rate is required. It is not possible to estimate “true ” risks for quasi-extinction, but we used an ap-proach where the relative difference for different scenarios can be compared. With a security level at 5,000 females, the population quasi-extinction risk increases 50 fold at an annual hunt of 500 females compared with a scenario with no hunting. The risk of quasi-extinction is very sensitiv