The Influence of Recreational Crabbing Regulations on Diamondback Terrapin By-Catch

Abstract

Malaclemys terrapin terrapin (Northern Diamondback Terrapin) is susceptible to drowning in commercial-style pots used for the Callinectes sapidus (Blue Crab) fishery. Regulations to reduce by-catch mortality vary by state. We compared three different regulatory strategies with respect to crab catch and their relative effectiveness at reducing terrapin by-catch. To mimic their possible use by recreational crabbers, we grouped and fished together ten unbaited crab pots with no by-catch reduction devices (BRDs), ten with large BRDs, and ten with small BRDs in a tidal creek in southeastern Virginia. Over 24 sampling days, the total legal crab catch (crabs ≥ 12.7 cm) in pots with no BRDs (29.9 ± 10.0 SD crabs pot-1) and large BRDs (27.9 ± 6.2 crabs pot-1) was significantly greater than catch in pots with small BRDs (14.0 ± 5.8 crabs pot-1). Legal crabs varied in average size from 14.1 ± 1.2 cm, 14.0 ± 1.2 cm, and 13.7 ± 1.0 cm from pots with no BRDs, large BRDs, and small BRDs, respectively, but these differences were not significant. Of a by-catch of 71 terrapins, 69 were from pots with no BRDs, 2 from pots with large BRDs, and none from pots with small BRDs. The potential mortality of terrapins in pots without BRDs would have reduced the population in this tidal creek by 42% in just 24 days. Based on these results, regulations requiring the use of large BRDs come closest to the objective of reducing by-catch mortality of terrapins without a large effect on crab capture in Virginia. Both recreational crabbing and commercial crabbing with no BRDs on pots in terrapin habitat can contribute to declines in local terrapin populations.