Fishing vs. natural recruitment variation in sandeels as a cause of seabird breeding failure at Shetland: a modelling approach

Abstract

Abstract Sandeels represent a major component in the diet of fish, bird, and mammal predators as well as supporting a large industrial fishery. The availability of young sandeels in coastal waters around Shetland is generally considered a key factor influencing the breeding success of many seabird species in the area, but the risk to the populations as a direct consequence of the fishery is unknown. Low exploitation rates coupled with high natural mortality rates make assessment of the Shetland sandeel stock problematic and safe biological limits have not yet been defined. We use stochastic models to evaluate the likely effect of varying fishing mortality on kittiwake breeding success. The models consider some main sources of uncertainty about natural processes, such as recruitment and natural mortality, which may affect the design of robust management strategies. The type of model tested had a stronger influence on sandeel recruitment than the level of fishing pressure. Even with low exploitation rates, poor years for seabird breeding were inevitable.