Fisheries Behavioral Ecology - Abstracts
Davis, M.W. and B.L. Olla. 2002. 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 22:1095-1104.
Abstract
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 16.0°C 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.
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26 April, 2007
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