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Mortality of Lingcod Towed in a Net as Related to Fish Length, Seawater Temperature, and Air Exposure: A Laboratory Bycatch Study

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  • The mortality of discarded bycatch is a critical problem in the management of fisheries worldwide. Little is known about the key principles involved in the mortality of discarded bycatch. These principles are best elaborated under controlled conditions in the laboratory where the actions and interactions of stressors found in fishing practices can be investigated independently. The goal of this study was to investigate the principles involved in the mortality of lingcod Ophiodon elongatus by testing hypotheses concerning the factors that may control trawl bycatch mortality. Lingcod were towed in a net and exposed to increased seawater temperature and to air, two stressors that occur during the processes of trawl capture, retrieval through a thermocline, and landing on deck. Mortality occurred after exposure to more than 45 min in air, after exposure to 4 h towing in a net followed by more than 30 min in air, or after 4 h towing followed by exposure to seawater above 16.0degreesC for 30 min and air for 15 min. In treatments of equal stressor intensity, smaller fish (41-51 cm total length) had higher rates of mortality than larger fish (52-67 cm). The effects of net towing and air-as well as of towing, increased seawater temperature, and air-were additive. Lingcod bycatch mortality may be reduced by decreasing trawling times and exposure to increased seawater and air temperatures during warmer seasons or by restricting fisheries that produce bycatch to seasons of cooler temperatures. The sorting, handling, and release of bycatch on deck after capture may be conducted in a manner that would probably enhance survival if fish are released within 30 min of capture. Because smaller lingcod had higher rates of mortality, further information about the mortality rates of relevant size-classes of fish is needed to validate the assumptions of management rules for released, undersized bycatch that are designed to enhance recruitment.
  • Keywords: Ophiodon elongatus, mortality, bycatch
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  • Davis, M. W., & Olla, B. L. (2002, November). Mortality of lingcod towed in a net as related to fish length, seawater temperature, and air exposure: A laboratory bycatch study. North American Journal of Fisheries Management, 22(4), 1095-1104.
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  • 22
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