M. W. Clarke, L. Borges and R. A. Officer
Marine Institute, Abbotstown, Dublin 15, Ireland
Publication (Upload) date: 4 April 2005
CLARKE, M. W., L. BORGES, and R. A. OFFICER. 2005. Comparisons of Trawl and Longline Catches of Deepwater Elasmobranchs West and North of Ireland. J. Northw. Atl. Fish. Sci., 35: 429-442. doi:10.2960/J.v35.m516
A comparison was made between catches from deepwater trawl and longline surveys (1993–2000) in the Northeast Atlantic. Longline catches were dominated by elasmobranchs, particularly squalid sharks and species numbers were low. Trawl catches had higher species numbers, with more teleosts, though elasmobranchs were still an important component. Species composition of the catch was depth dependent. Comparative trawl and longline surveys of the eastern and southern slopes of the Rockall Trough (west and north of Ireland) were used to examine size-selectivity. Trawls and longlines selected for significantly different size frequency distributions of Centroscymnus coelolepis and Deania calceus, though not for Centrophorus squamosus. These data highlight some important aspects of behavior of the species studying relation to fishing gears. Smaller C. coelolepis were selected by longlines than trawls, suggesting that smaller sharks were present at a considerable height above the seabed, out of reach of trawls, but attracted to baited hooks. In the case of D. calceus, larger females were selected by hooks, but were not present in trawl catches, possibly indicating their ability to escape towed gears. Trawl selectivity ogives were constructed for D. calceus and ogives for C. coelolepis and C. squamosus were simulated, using available data. Results suggest that longlines are not as selective for C. coelolepis as trawls. Selectivity ogives for D. calceus were similar in form, but longlines selected bigger individuals. Life history studies suggest that these species cannot sustain high fishing pressures. The implications of these results for the management of fisheries taking elasmobranchs are discussed.
Key words: catches, deepwater, longline, Ireland, shark, squalids, trawl