A species-selective trawl for demersal gadoid fisheries

Abstract

Engås, A., Jørgensen, T., and West, C. W. 1998. A species-selective trawl for demersal gadoid fisheries. -ICES Journal of Marine Science, 55: 835-845.Experiments were carried out during two cruises in 1995 to test a prototype species-selective bottom trawl for separating cod from haddock and saithe, in the Norwegian bottom trawl fisheries in the Barents Sea. A sorting system incorporating a horizontal square mesh panel (150 mm bar length) dividing the trawl's body and extension sections into upper and lower compartments, leading aft to verticallyoriented trouser codends, was installed in a commercial roundfish trawl. During the first cruise approximately 90% of the haddock and 70% of the saithe were caught in the upper codend, with 70% of the cod in the lower codend. During the second cruise 90% of the haddock and 60% of the saithe were caught in the upper codend, with 65% of the cod caught in the lower codend. In situ video observations showed that fish, apparently haddock, entered the trawl at all levels, but subsequently many of those in the lower half attacked upwards and through the separating panel along its length as they passed towards the trouser codends. The differences in the results by species and season are discussed, along with the applicability of the sorting system to commercial fisheries.1998 International Council for the Exploration of the Sea

Separation of fish from Nephrops norvegicus into a two-tier cod-end using a selection grid

“…Some species, such as Nephrops, fall back under the separating panel and continue into the lower portion of the trawl. Others, such as haddock and whiting, tend to rise as they become exhausted, passing over the panel and into the upper portion of the trawl (Main and Sangster, 1981;Engås et al, 1998). However, the separator trawl is ineffective for improving the size selection of cod and flatfish (Galbraith and Main, 1989;Main and Sangster, 1985;Arkley et al, 1995;Dunlin, 1998), which do not rise in the trawl mouth, passing under the separating panel to be retained in the lower cod-end.…”

Understanding the Size Selectivity of Redfish (Sebastes spp.) in North Atlantic Trawl Codends

“…Fish behaviour can be important in the capture process of some fish, especially in the trawl mouth (Engås et al, 1998), but our method does not explicitly account for behavioral aspects of redfish. However the strong similarity found regarding the effect of codend mesh size between the FISHSELECT predictions and the different sea trial results (Fig.…”

Escapement of gadoid fish beneath a commercial bottom trawl: Relevance to the overall trawl selectivity

“…Cod have been observed to swim very close to the bottom as they tire from swimming in front of an approaching trawl, while haddock display upward escape reactions (Main and Sangster, 1981). This difference has been utilized to design species-selective trawls by the use of horizontal separator panels Sangster, 1982, 1985;Engås et al, 1998). The length-dependent escapement may be due to size-related differences in swimming ability and greater tendency of smaller fish to make escape attempts through the narrow spaces between the rockhopper discs.…”