Design, Evolution, and Assessment of a Sea Turtle Deflector Dredge for the U.S. Northwest Atlantic Sea Scallop Fishery: Impacts on Fish Bycatch

Abstract

AbstractBetween May 2006 and November 2009 we tested five sequential dredge modifications during 37 trips on 13 different sea scallop fishing vessels. The testing evaluated the impacts of these modifications on the catch of sea scallops Placopecten magellanicus, the bycatch of fish and sea turtles in the families Cheloniidae and Dermochelyidae, and frame durability. We tested the modified dredges and an original New Bedford dredge (control) by conducting paired, side‐by‐side tows using identical tow parameters. A total of 4,059 paired tows were conducted in which tow data, scallop catch, and bycatch were recorded; data from 44% of the tows were sufficiently sampled for comparisons of bycatch. The dredge catches showed a significant 3% increase in sea scallop catch and significant decreases in the bycatch of many species, including yellowtail flounder Limanda ferruginea (46%), winter flounder Pseudopleuronectes americanus (69%), barndoor skate Dipturus laevis (18%), and winter skate Leucoraja ocellata (20%). The final design, the CFarm turtle deflector dredge, proved effective at guiding turtle carcasses over the top of the dredge by eliminating most of the bale bars and forming a ramp with a forward‐positioned cutting bar and closely spaced struts leading back at a 45° angle. The final design also proved effective in reducing bycatch for a number of nontarget fish species. Flow characterizations in a flume tank provided insight into the cutting bar and frame hydrodynamics that may explain the field trial results.Received February 2, 2011; accepted November 2, 2011