Reducing the Capture of the Flatfish Complex in Small Mesh Bottom Trawls Using the 30.5 cm Drop Chain Trawl Net Design

Several species of flatfish in the Southern New England (SNE) area have been targeted as overfished and in need of rebuilding.  Many are targeted species in directed fisheries; others are bycatch/discard species, especially in the small mesh fishery in SNE. These include summer (Paralichthys dentatus), winter (Pseudopleuronectes americanus), yellowtail (Limanda ferruginea) and windowpane (Scophthalmus aquosus) flounders. All of these species can be potentially caught in the squid (Loligo pealeii), scup (Stenotomus chrysops) and butterfish (Peprilus triacanthus) small mesh fishery.  A modified fishing net (MFN) was designed using a standard bottom trawl squid net (SFN) with the addition of a 30.5 cm (12 inch) drop chain to create space between the sweep and the footrope.  This net was laboratory and field tested for its ability to reduce the capture of flatfish.

A total of 42 successful comparative paired tows (84 total tows) were completed over 7 sampling days using the SFN and MFN in Block Island and Rhode Island Sound.  After testing for vessel effects, a paired t-test was used to test for differences between the combined mean weight in kilograms per tow for flatfish (summer, yellowtail and windowpane flounders) and target species (squid, scup and butterfish) in the SFN and MFN.   Results show a significant difference between mean weights per tow for all flatfish species.  There was no significant difference between mean weights per tow of target species.

Results were as follows: summer flounder, paired t(36) = 4.87, p = <.01; yellowtail flounder,  paired t(7) = 2.06, p = <.01 and windowpane flounder, paired t(35) = 4.63, p = <.01.  A paired t-test was also used to test for differences between the mean catches of the two nets for each potential target species (butterfish, squid and scup).  There was no significant difference between mean weights for all three species of interest. Results were as follows: butterfish, paired t(42) = .473, p = .11; squid, paired t(42) = .119, p = .23 and scup, paired t(36) = .132, p = .72.   These results indicate that the use of 30.5 cm (12 inch) drop chain net will reduce the capture of flatfish while retaining target species in the small mesh bottom trawl fishery in SNE.