REDUCING DISCARDS OF FLATFISH IN THE SEA SCALLOP DREDGE FISHERY BY DREDGE PAUSE

摘要

Flatfishes are routine bycatch in the Atlantic sea scallop Placopecten magellanicus (Gmelin) dredge fishery but must be discarded at sea. Despite release, a 90% mortality rate is assumed for overfished species such as yellowtail flounder Limanda ferruginae and windowpane Scophthalmus aquosus. When the scallop fishery exceeds the annual catch limit for yellowtail flounder, accountability measures may be triggered and seasonal closures of the scallop fishery can occur in specific areas. Flatfish bycatch is potentially reduced by stopping the scallop dredge in midwater to allow escape. This technique has been voluntarily practiced, but not widely adopted, owing to a lack of knowledge about its efficacy relative to collateral scallop loss. In a test of 122 scallop dredge tows on a commercial vessel using otherwise standard procedures, pausing the dredge during retrieval significantly reduced flatfish bycatch relative to pause length (0, 5, 10, or 15 min) but also allowed some scallop escapement. Flatfish were more likely to escape from paused dredges if there were fewer scallops in the dredge. Video provided evidence that flatfish do escape through the tickler chains and over the lip during pauses, and also showed the benefit of time in allowing them to work free of the suspended scallop load. During rough weather, vessel heave winnowed the dredge contents, increasing scallop loss. Captains can judge the practice as a cost-benefit calculation to avoid loss of revenue from early closure, but it appears to offer only a weak return on the time investment. Escaped fish may still suffer mortality.