University of New England

Otter Trawl Bycatch Research

The mortality rate of fish discarded after capture is one of the most significant questions affecting marine fisheries management today and is listed by the Nation Marine Fisheries Service (NMFS) as a priority research area.  However, the discard mortality rates of most commercially important fish in New England waters have received little investigation following otter trawl capture.  THis presents a problem because bycatch mortality rates are obviously needed to assess total mortality, to understand population dynamics, and to arrive at correct management strategies.  Thus, the determination of discard mortality rates is essential in order for stock assessments and ultimately the successful management of fish species in the Gulf of Maine.  The objective of our bycatch research is to quantitatively determine the short-term (48-72 hours post trawl) discard mortality rates and the behavioral factors influencing the observed mortality during normal trawling operations.  For these investigations, we have developed a unique open ocean net pen system.  In contrast to previous studies that have employed cages and on deck holding tanks, these studies utilize innovative net pens with a design that extends from the surface down to 20 fathoms.  More conducive to normal discard conditions, the spacious open-net system enables the monitoring of discarded fish in a manner significantly closer to what would be experienced under actual commercial fishing conditions.  Such a development reduces interferences from holding tanks/cages (e.g. forced recompression), accounts for factors such as avain predation at the surface, and strengethens the accuracy of discard mortality estimates for both target and non-target fish species.