Distribution and abundance of the fished population of Loligo forbesi in Scottish waters: analysis of research cruise data

Abstract

Length-frequency data on squid (Loligo forbesi) collected during trawling surveys in Scottish waters from 1980 to 1994 were analysed to describe temporal and spatial patterns in abundance and to examine the prospects for using survey abundance to forecast fishery abundance. Loligo was patchily distributed in space and time. Distribution patterns in the North Sea in February appeared to be strongly related to bottom temperature (squid avoided waters <7°C) and, to a lesser extent, salinity (more squid in more saline water). For other areas and times, no temperature or salinity data were available, but there were trends for squid on the west coast to be more abundant in westerly areas and higher latitudes, and for squid at Rockall to be more abundant in shallow water. Inter-annual trends in abundance differed between the North Sea, west coast and Rockall, but average survey abundances for the North Sea and west coast tended to be positively correlated. For the North Sea and west coast, survey abundance was positively correlated with fishery abundance for the same month and area, and average abundance for the February North Sea survey was a reasonable predictor of commercial CPUE in the autumn of the same year (the peak of the fishery). Some of the observed trends were consistent with the existence of a stock-recruitment relationship but may indicate that abundance in a given calendar year is linked to climatic factors.