IMPACT OF A BYCATCH REDUCTION DEVICE ON DIAMONDBACK TERRAPIN AND BLUE CRAB CAPTURE IN CRAB POTS

Abstract

Bycatch in fisheries is receiving attention because of its impact on ecological diversity and resource sustainability. Male and juvenile female diamondback terrapins, Malaclemys terrapin, frequently drown as bycatch in crab pots, removing individuals with high reproductive value from the population and possibly skewing sex ratios. We tested a wire bycatch reduction device (BRD) to determine its ability to reduce terrapin entrapment and to examine any effects the BRD has on the size and number of blue crabs, Callinectes sapidus, caught in crab pots. We tested three sizes of BRDs, a 4 × 10 cm BRD in 1996, and 4.5 × 12 cm and 5 × 10 cm BRDs in 1997. We equipped both standard crab pots and modified (tall) crab pots with BRDs, the latter were used to prevent terrapin mortality in areas of high terrapin density. Traps were checked and baited daily. In 1996, we caught no terrapins in 14 crab pots equipped with the 4 × 10 cm BRDs and 21 terrapins in 14 crab pots without BRDs. In 1997, the 4.5 × 12 cm BRD reduced terrapin bycatch by 82%, whereas the 5 × 10 cm BRD reduced terrapin bycatch by 47%. The 4 × 10 cm BRDs, however, reduced the size and number of large “Number One” and mature female crabs. Catch rate for standard crab pots with 4 × 10 cm BRDs was 2 crabs·pot−1·day−1 lower than standard crab pots fished without BRDs in 1996. Neither the 5 × 10 cm BRD nor the 4.5 × 12 cm BRD affected crab size or the number of crabs caught in crab pots. Standard crab pots with a 4.5 × 12 cm BRDs had the highest catch per unit effort (2.69 crabs·pot−1·day−1), followed by standard crab pots without BRDs (2.55 crabs·pot−1·day−1) and standard crab pots with 5 × 10 cm BRDs (2.39 crabs·pot−1·day−1). The largest crab caught in 1997 was in a crab pot with a 4.5 × 12 cm BRD. We stress the importance of using the 4.5 × 12 cm BRD on crab pots fished commercially and recreationally to reduce terrapin mortality and the need to integrate the use of BRDs on crab pots with other conservation practices such as protection of critical terrapin habitat, particularly nesting beaches.