Evidence of low spatial overlap between grey seals and a specific whitefish fishery off the west coast of Ireland

Abstract

Competition between seals and man for valuable fish resources is a long-standing contentious issue and of concern with fish stocks in global decline. Estimating resource overlap between seals and fisheries is difficult and generally achieved by comparing seal consumption with fisheries catches and stock size; however spatial partitioning may mean that marine mammals and fisheries are not actually depleting the same local stocks. With the relatively recent availability of fine scale fishing effort data from Vessel Monitoring System (VMS) it is now possible to study the spatial overlap between fisheries and predators in more detail. We used VMS and fast acquisition GPS to compare the distribution of fisheries and seals in Irish waters on the same spatial and temporal scales to quantify overlap. Our findings suggest a significantly low rate of spatial overlap between a sample of female grey seals (Halichoerus grypus) and the offshore whitefish fishery on the Irish continental shelf, suggesting direct competition for the resource may be far less than expected, if the sample is representative. Seal/fisheries interactions in Irish waters could therefore be more of an issue at the operational and individual level suggesting population control measures such as culling will be ineffective and therefore unjustifiable. The approach could be applied elsewhere to examine spatial overlap of humans and key marine species such as turtles, seals and seabirds, providing critical data for the development of mitigation measures which will ultimately contribute to the conservation of these species, many of which are fundamental for healthy ecosystem functioning.