In response to diamondback terrapin bycatch reduction requirements in North Carolina, crab fishers have proposed a gear modification called a narrow funnel design (NFD), which narrows the funnel entry without altering the continuity of the surface of the trap. NFDs also are installed at the manufacturing stage, eliminating the need to purchase and install traditional BRDs. A second modification proposed by fishers is to make existing funnels more rigid so that it is more difficult for terrapins to enter the pot. This is done through a reinforced funnel design (RFD), where rigid wire is placed on the outside perimeter of the entrance funnel.
Fisheries-independent trials found no significant impact of BRD use on legal-sized crab catch. In addition, there was a 74% reduction in terrapin bycatch in NFD traps, and a 49% reduction in RFD traps compared to controls. In fisheries-dependent observer trips, NFD pots had significantly higher crab catch compared to standard crab pots, and also caught larger crabs. 25 terrapins were captured in standard pots compared to 11 in NFD pots.
However, site had a strong effect on both blue crab size and catch, and terrapin bycatch throughout the study. In addition, smaller adult males and juvenile terrapins could still successfully enter the NFD pots, meaning that the use of gear modifications alone may not be sufficient to prevent terrapin bycatch. BRDs should be used in conjunction with other regulatory strategies that prioritize spatial and temporal restrictions to minimize overlap between areas with high densities of terrapins and commercial fishing operations.