Elvira S. Poloczanska’s research while affiliated with University of Glasgow and other places

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.

Sandeels (sand lance) are important prey for fish, bird and mammal predators. In the North Sea, they are also the target of the region's largest 'single-species' fishery, with annual yields of ca. 0,8 million tonnes, mostly (> 90%) comprising the species Ammodytes marinus. This species is relatively short-lived, and has large, naturally occurring, population fluctuations that confound the use of traditional methods of fishery forecasting for their management. Here we present a stochastic age-structured model that describes the population dynamics of North Sea sandeels. Recruitment to the population occurs according to a stochastic, autocorrelated Ricker function. Uncertainty in the recruitment parameters was quantified by bootstrap analysis, leading to 3 different versions of the model that allowed a range of potentially viable recruitment scenarios to be explored. Monte Carlo simulations were performed under different fishing mortality levels, and the responses of the population assessed. The model is used to quantify recruitment and the likelihood of the sandeel spawning stock biomass falling below 600000 and 430000 t, which represent the precautionary and biomass limit levels, respectively, imposed by managers upon the stock.