Publication Abstract

Is one man’s trash another seal’s treasure? Investigating the role of fisheries discards in the diet of grey seals (Halichoerus grypus)

 

 

 

 

Discards form an important part of the diet of a number of generalist predators in the North Sea. The European Union is in the midst of implementing a ban on discarding at sea, which will eliminate this once abundant resource. Grey seals (Halichoerus grypus) are known to be generalist and opportunistic foragers, and have a long history, in the UK and abroad, of interacting ecologically and operationally with fisheries. It is therefore necessary to understand whether pinnipeds are benefitting from discards before this resource is removed, to avoid potentially negative consequences of such a change to the North Sea ecosystem. In this study, data on the diet and movement of grey seals in the central North Sea are used in conjunction with data on fisheries catch, fisheries discards, and fish populations to determine whether it is likely that seals are utilising discards as a food source. It was found that both the species composition and length distributions of common species in the seal diet were more similar to the wild population than to either fisheries discards or catch. However, fishing effort and catch of gadoids and flatfish were useful in modelling seal habitat usage. It was found that seal movements were strongly related to season and distance from haul out site, but also to spatial distributions of the wild populations of elasmobranchs, cottids, and clupeids. It is concluded that although seal diet cannot be directly associated with fisheries discards, fisheries effort and movement does adequately describe seal habitat usage, indicating that fisheries do affect the distribution of seals at sea to some extent. Future work should focus on utilising experiment-based methods and refinement of spatial resolution of fisheries datasets to investigate this question further.

 

L. Burke (supervisors: S.C. Smout, A. Ribeiros-Santos*, G.H. Engelhard*)

MSc Thesis, University of St Andrews, UK