The diet and ecological importance of Illex coindetii and Todaropsis eblanae (Cephalopoda: Ommastrephidae) in Irish waters

Abstract

Between November 1993 and May 1997, the stomach contents of trawl-caught Illex coindetii and Todaropsis eblanae from the edge of the continental shelf west and south-west of Ireland were examined. When visually assessed, 82.1% of the I. coindetii stomachs and 73.4% of the T. eblanae stomachs had no food remains present. In both I. coindetii and T. eblanae stomachs with prey, crustaceans, particularly euphausids, are relatively more important as prey in smaller squid. As the squid grow, fish and squid become increasingly important prey. The small mesopelagic fish Maurolicus muelleri is a particularly important prey item of both species, occurring in 48.3% of I. coindetii and 34.7% of T. eblanae stomachs with prey remains. M. muelleri otoliths were also often found in high numbers. In one I. coindetii stomach, 43 pairs of otoliths were found. However, this great abundance may be an over-representation of their importance in the diet as a result of the techniques used to identify prey remains in squid stomachs. Three other pelagic fish, Gadiculus argenteus, Micromesistius poutassou, Argentina sp. and the euphausid Meganyctiphanes norvegica, are also important prey of both species. Data on possible trawlnet-associated feeding are also presented, although the importance of this as a source of error in diet studies is unclear. Using data from research vessel surveys, there seems to be a peak in feeding intensity in the early morning in I. coindetti.