The Impact of Crab Pot Fisheries on Terrapin (Malaclemys terrapin) Populations: Where Are We and Where Do We Need to Go?

In the Atlantic and Gulf states, the crab pot fishery overlaps with much of the habitat of the diamondback terrapin, Malaclemys terrapin. The exclusively estuarine terrapin can be found throughout the coastal bays and creeks of the eastern and Gulf coasts of the United States. Terrapin populations can incur considerable mortality of males and juveniles when crab pots are fished in terrapin habitat. Terrapin catch rates in crab pots vary from 0.0 to 0.49 terrapins/crab pot/day. Depending on the extent of the fishery and the assumed mortality rates, between 15% and 78% of a local terrapin population may be removed annually (Roosenburg et al. 1997). Several solutions have been tested with varying degrees of success and feasibility as techniques to reduce terrapin mortality in both recreational and commercial crab pot fisheries. The most feasible mechanism is a by-catch reduction device (BRD) developed by Wood (1997), a rigid rectangular structure placed in the funnel entrance to the crab pot that prevents terrapins from entering but has no effect on the size or number of crabs caught. Several studies have evaluated different BRD sizes throughout the terrapin’s range resulting in different size requirements and use regulations in different states. Herein, I review studies of crab pots, terrapins and BRDs, I summarize the current terrapin safe technologies for crab pot fisheries, and I suggest future research needs for terrapins and their interaction with crab pots and other similar fisheries. The capture of turtles and other non-target species as by-catch in fishing gear is a tremendous problem that confronts both fisheries managers and conservationists. Determining the impact of fishing practices and developing techniques to reduce by-catch mortality without affecting fishing effectiveness has recently attracted considerable legal, political and environmental attention. One widespread example of a by-catch problem is the capture of diamondback terrapins, Malaclemys terrapin, in commercial and recreational crab pots. Davis (1942) first identified the potential problem of terrapin mortality in crab pots when they were introduced as a commercial fishing gear. This concern prompted the Maryland Department of Natural Resources, at that time, to restrict the use of crab pots to a commercial fishery in deeper water areas where the impact on shallow water by-catch species such as terrapins would be minimal. Over the years, the use of crab pots has become more widespread throughout the Atlantic and Gulf coasts, and many states have permitted their use by recreational crabbers. The conflict between crab pots and terrapin populations has been reported in several states including New York (Garber 1988, 1990a, 1990b), New Jersey (Burger 1989, Burger and Garber 1995, Wood 1995a, 1997a and 1997b), Delaware (Wood 1995b), Maryland (Davis 1942, Roosenburg et al. 1997, Roosenburg and Green 2000), North Carolina (Grant 1997, Hart, 1999), South Carolina (Bishop 1983, Hoyle and Gibbons 2000, Gibbons et al. 2001), Florida (Seigel 1993, Butler 2000), Louisiana (Guillory and Prejean 1998) and Mississippi (Mann 1995). Additionally, a diamondback terrapin workshop in August of 1994 concluded that terrapin mortality as by-catch in crab pots is the single largest threat to terrapin populations throughout their range (Seigel and Gibbons 1995, Nemec 1995). The diamondback terrapin is an obligate estuarine species that lives in coastal and brackish bays and inlets along the eastern seaboard and the Gulf of Mexico of the United States (Carr 1952). Throughout much of its range, its habitat overlaps with that of the blue crab, Callinectes sapidus. The blue crab is an important commercial and recreational species throughout coastal regions of the Atlantic and Gulf States and is the primary commercial fishery in inland waters of the mid-Atlantic region. Crab pots are the primary method used to catch crabs in both the commercial and recreational fisheries. Crab pots are 60 cm by 60 cm by 60 cm wire mesh structures with four funnellike openings that allow crabs to enter. Crabs are attracted to the pots by bait (usually menhaden, chicken or razor Department of Biological Sciences, Ohio University, Athens, Ohio 45701, USA. Email: [email protected] CONSERVATION AND ECOLOGY OF TURTLES 24 OF THE MID-ATLANTIC REGION 25 clams) and enter through one of the four funnels. The openings of the funnels vary in size and are flexible. In addition to blue crabs, a variety of other animals are caught in crab pots including spider crabs, conch, various species of fish, muskrat, otter and diamondback terrapins. Because crab pots remain submerged while set and are checked every 24 hours or less frequently, the air-breathing animals that get caught in the pots frequently drown. Several states including New Jersey, Maryland, Delaware, North Carolina, South Carolina, Florida, Mississippi and Louisiana have recognized that terrapins are caught in crab pots, and most of these states have indicated that substantial decreases in terrapin populations are the result of drowning in crab pots (Seigel and Gibbons 1995). Because of the pervasive habitat overlap between terrapins and blue crabs, research has been undertaken to determine both the impact of crab pots on terrapin populations and potential solutions to reduce terrapin and other by-catch in crab pots. Bishop (1983) first studied the problem and estimated that 285 terrapins died daily in South Carolina crab pots, concluding that the impact on terrapin populations was minimal. However, more recent work has suggested that the impact of crab pot mortality on terrapin populations is substantial and could quickly result in extirpating local populations (Roosenburg et al. 1997). Interestingly, the catch rates of terrapins per crab pot in these two studies were very similar. Two viable solutions to the crab pot by-catch problem have been developed and tested to various degrees. In this manuscript, I review the studies that to date have investigated the impact crab pots have on terrapin populations and the potential mechanisms for reducing by-catch in crab pots. I summarize the current BRD regulations and suggest the research needed to further reduce terrapin mortality in crab pots and other fisheries that drown terrapins.