Reactions of cod (Gadus morhua L.) in the pre-vessel zone to an approaching trawler under different light conditions

Behavior-dependent selectivity of yellowtail flounder (Limanda ferruginea) in the mouth of a commercial bottom trawl

“…The mean density at the start of an observation, as well as standard errors (SE), 95% confidence intervals (CI), and ranges, are calculated for all observations (Overall) and for escaped and caught fishes. In contrast to findings in earlier flatfish studies (Walsh, 1992;Godø et al, 1999;Gibson, 2005), results from our study indicate that neither fish size nor fish density in the trawl mouth influenced the response or capture of yellowtail. Walsh (1992) collected high numbers of small flatfishes (<31 cm) under the trawl with the use of bags.…”

“…In Walsh's (1992) study, the small flatfishes may not have reacted to the footgear but could have reacted to the small bag itself after they passed under the footgear. The lack of a density effect in our study may be explained by density counts that were lower in our study than in the study by Godø et al (1999). Furthermore, we modeled fish size and density along with other variables to establish which factors influenced herded individuals the most, and both fish size and density were not among those factors.…”

“…Likewise, some of the fish in peripheral locations could have maintained an inward orientation without having reacted to the gear. One solution to this conundrum may be the use of electronic tagging of individual fishes (Engås et al, 1998;Winger, 2004), an approach that could provide information about gear encounters by recording the position of an individual fish in relation to the sweeps before it enters the mouth of a trawl. Another potential bias in our analysis is the undercounting of fish that did not react to the footgear and were passed over by the trawl.…”

“…Once they are in the trawl mouth, escapement under the footgear is a particular problem (Albert et al, 2003;Ryer and Barnett, 2006). Consequently, the mouth of the trawl is a critically important area when considering how to improve gear efficiency (Engås and Godø, 1989;Walsh, 1992).…”

“…Then we examined the behavior of yellowtail in the central part of the trawl mouth during commercial bottom trawling operations. The influence of fish size (Walsh, 1992;Peake and Farrell, 2004), swimming endurance and gait (Winger et al, 1999(Winger et al, , 2004, orientation (Beamish, 1966), and density (Godø et al, 1999) on general flatfish behavior have been examined in these studies; however, each factor was examined separately. In contrast, we conducted an in-depth, quantitative study and applied statistical models to simultaneously assess all of the above factors and explain what drives the behavior of individual fish and overall outcome for yellowtail in the mouth of the trawl.…”