Publication Abstract

The distribution and abundance of cephalopod species caught during demersal trawl surveys west of Ireland and in the Celtic Sea

The distribution and abundance of cephalopod species caught during demersal trawl surveys west of Ireland and in the Celtic Sea

C. Loudon, S. Warnes, T.F. Cross and G.M. Burnell

Demersal trawl surveys are an integral part of the finfish stock assessment process. Data from these surveys provide a unique insight into species distributions and abundance, being independent of the biases and errors of commercial fisheries data, such as discarding, mis-identification and mis-reporting and changes in effort and catchability. Cod-end fine mesh liners are used in demersal surveys. As a result, small individuals and small species not normally caught in commercial gears are caught, thus providing recruitment information for the main commercial species. The surveys are also used to monitor changes in the commercially important stocks, to collect biological data on the more important species and to support the shore-based sampling programs. To date, data on cephalopod distributions have been regarded as of secondary importance to the data on commercial finfish species. Cephalopods play an extremely important role in marine ecosystem and are becoming an increasingly important fisheries resource in the waters around Ireland (Collins et al., 1994 & 1995, Lordan et al., 1995, 1998 and in press). There is little information on abundance and fine scale distributions of cephalopod species in this area in the literature. Investigations at the start of the 20th century provide the first information on the occurrence of cephalopod species in the waters around Ireland (Massy, 1909; Massy, 1928). More recently, Collins et al., (1995a) used demersal trawl survey data in the Irish Sea to investigate the distribution and demography of Loligo forbesi Steenstrup (1856) and also reported catches of other cephalopod species. Pierce et al. (1998) used Scottish demersal trawl survey data to describe the spatial distribution and density of Loligo forbesi in the North Sea, Rockall, west of Scotland, west and south west of Ireland. The distribution of deepwater benthic and bentho-pelagic cephalopods caught commercial and research trawls has also recently been described (Collins et al., 2001).

In this study data from three demersal trawl survey series in waters around Ireland are examined. The aim of this study is firstly, to establish which cephalopod species are routinely caught during these surveys. Secondly, to investigate the spatial and bathymetric distributions of the species caught. Thirdly, a time series of five years is available for one of the surveys and this is used to investigate inter-annual variations in spatial distribution and densities of the more abundant cephalopod species.

Reference:

C. Loudon, S. Warnes, T.F. Cross and G.M. Burnell (2001) The distribution and abundance of cephalopod species caught during demersal trawl surveys west of Ireland and in the Celtic Sea. Irish Fisheries Investigations, (8): 26p.

C. Loudon, S. Warnes*, T.F. Cross and G.M. Burnell

Irish Fisheries Investigations, (8): 26p.