Using Sea Turtle Carcasses to Assess the Conservation Potential of a Turtle Excluder Dredge

Abstract

Fisheries observers have documented interactions between sea turtles in the family Cheloniidae and the Atlantic sea scallop Placopecten magellanicus fishery. Sea turtle injuries resulting from interactions with scallop dredges are being mitigated through shifts in fishing effort and modifications to fishing gear. The standard New Bedford dredge can trap objects and crush them as they pass between the dredge frame and sea floor, so a modified turtle excluder dredge has been designed to reduce the likelihood of a turtle's passing under the frame when the dredge fishes on the seafloor. The key elements of the modified design are a forward cutting bar (which results in a sloping rather than a vertical face), a reduced number of bale support bars (just the center and outer bales), extension of the outer bale bars before tapering to the gooseneck (hauling point), and a reduction in the sources of entrapment between the depressor plate and the cutting bar via reduced spacing of struts. We evaluated the ability of the modified dredge to cause live sea turtles to pass over it by using loggerhead sea turtle Caretta caretta carcasses as a proxy. The carcasses were placed on the seafloor in the path of a towed dredge equipped with video cameras. Nine interactions between carcasses and the modified dredge were documented on video recordings. In each of the interactions, the carcass hit the dredge and passed over the dredge frame with little or no physical damage to the recovered carcasses. These carcass studies suggest that the turtle excluder dredge reduces sea turtle injuries associated with interactions between sea turtles and scallop dredges fishing on the seafloor.