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Fisheries Behavioral Ecology - Abstracts

Olla, B.L., M.W. Davis, and C. Rose. 2000. Differences in orientation and swimming of walleye pollock Theragra chalcogramma in a trawl net under light and dark conditions: concordance between field and laboratory observations. Fisheries Research 44:261-266.


The success of modifications to fishing gear in reducing or eliminating bycatch mortality requires in many cases that escaping fish be able to use vision for volitional guiding out of gear. Light adequate for vision is often not present as fishing operations are commonly conducted at depths or at night when light quantity is below visual capability. Previous observations of walleye pollock behavior in the laboratory indicated that darkness inhibited their ability to respond and orient to trawling gear. The goal of the present study was to test this result in situ by comparing swimming and orientation capabilities of walleye pollock under light and dark conditions in commercial type trawl gear using infrared illumination and video cameras to monitor these behaviors. Under light conditions, fish swam actively and were oriented parallel to the principle axis of the trawl. In contrast, under dark conditions there was little or no active swimming and the fish showed a significant degree of deviation from the principle axis of the trawl. These results showed that vision plays a major role in trawl gear interactions for walleye pollock and points out the importance of measuring light quantity in field studies of bycatch processes and mortality.


Last updated 30 March, 2009

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