Avoidance of an approaching net by juvenile walleye pollock Theragra chalcogramma in the laboratory: the influence of light intensity

Fisheries management strategies often rely upon regulation of mesh sizes or the use of exclusion/escape structures to reduce the bycatch of undersize fish or non-target species. Design and evaluation of fishing gears to reduc e bycatch should be based upon knowledge of fish behavior and sensory capab ilities. The response of juvenile walleye pollock Theragra chalcogramma to an approaching panel made of 8 cm square mesh netting was compared under a range of laboratory illuminations, from <1 x 10(-8) (darkness) to 1.7 x 10( -3) mu moles photons m(-2)s(-1). Fish in darkness struck the net more frequ ently and swam closer to the net than fish at the highest illumination. The se results, along with those of other laboratory and field studies, suggest that trawl bycatch reduction strategies which rely upon undersize or non-t arget fish using vision to guide them out of the net may be less effective at night or at depths where ambient light levels fall below critical levels . (C) 2000 Elsevier Science B.V. All rights reserved.