A Method to Reduce Winter Flounder Retention By Minimizing Variability in Drop Chain Performance in the Inshore Loligo Small Mesh Trawl Fishery off Long Island, NY Within the SNE Winter Flounder Stock Area
(Funded by the Commercial Fisheries Research Foundation Challenge Grant Program for Conservation Engineering Projects - Winter Flounder Bycatch Reduction)
Project Summary
In 2010, Cornell Marine Program conducted a proof of concept project designed to reduce fishing mortality and bycatch of winter flounder in an effort to contribute to the rebuilding of the overfished stock by testing an alternative gear strategy. One direction that shows some promise in achieving these goals is the use of raised footrope trawls. Raising the footrope off the sea bottom is accomplished by using a sweep that is longer than the footrope and attaching this sweep to the footrope using a series of “drop chains”. The strategy we employed was the use of 12 inch drop chains in combination with a lengthened sweep and a series of incremented headrope adjustments. In flume tank testing, it has been shown that lengthening the headrope (making the headrope longer than the footrope) aids in raising the footrope and achieving the full extension of the drop chains.
There are two aspects of longer drop chains that may prove beneficial at reducing winter flounder catch. The first is the increased distance between the sweep and the footrope. This effectively increases the space that is available for avoiding capture below the body of the net. Second, is that by having to use a longer sweep, the sweep is allowed to travel behind the footrope. The importance of this is that with the sweep behind the footrope, the mud cloud created by the sweep occurs behind the footrope. This brief period of increased visibility ahead of the sweep makes the gap between the footrope and the sweep visible for flounders and other species of bycatch offering them a clear path to avoid capture.
The research for this project was conducted using a single vessel (F/V Caitlyn and Mairead) whose home port is Montauk, NY. The vessel was employed to conduct replicate tows comparing a control net to an experimental net. The control net that was used for this study was a four seam, 3 bridle standard otter trawl that is typical of the type of net that is used in the squid fishery along the east coast of the US. The experimental net was the identical net outfitted with a longer sweep and the 12 inch drop chains. The experimental net was also equipped with a length of chain attached to the upper bridle that allowed us to quickly adjust the headrope. Lengthening adjustments were made in 6 inch increments from zero (control net) to 3 feet. We monitored the effects on winter flounder bycatch reduction and retention of the target species (Loligo squid). One hour tow durations were used during this study to maximize the number of tows conducted per trip and still remain within the range of commercial tow durations (1-3 hours). The experimental sampling program consisted of four single day fishing trips. We made a minimum of six tows per trip totaling 24 tows for the entire project.
Our objective during this proof of concept was to maximize drop chain performance relative to bycatch reduction and target species retention. As such, total winter flounder for each tow was accurately weighed. Small catches allowed for all winter flounder to be sampled for length frequency. The total Loligo catch was also weighed on each tow and a length sample obtained. Our goal was to quantify differences in winter flounder and Loligo retention between the control and experimental nets. The total weight of all species in each tow was also recorded by direct weights of the total catch, or for large catches, the entire catch was placed in baskets and a sub-sample of the baskets weighed. Whiting was chosen as an additional priority species relative to its importance to the trawl fishery which may be impacted by winter flounder regulations. Actual total weights of whiting (Merluccius bilinearis) were obtained but whiting catch overall was minimal.