Turtles and Tires: The Impact of Roadkills on Northern Diamondback Terrapin, Malaclemys terrapin terrapin, Populations on the Cape May Peninsula, Southern New Jersey, USA

Abstract

A century ago overhunting of the northern diamondback terrapin, Malaclemys terrapin terra- pin, nearly extirpated populations in many parts of its range. More recently, coastal development has led to considerable habitat destruction, especially of traditional nesting sites on barrier beach islands. Along the Atlantic coast of New Jersey, the search for alternative nesting sites on highway embankments has resulted in large numbers of roadkills every nesting season. We have documented the annual mortality of nesting diamondback terrapins on the Cape May Peninsula of southern New Jersey from 1989 through 1995. A total of 4,020 roadkills were recorded on roads crossing or adjacent to our study area. Potentially viable eggs were recovered from carcasses and 32% were success- fully incubated. Since 1991 hatchlings have been headstarted for ten months and 782 (an 81% hatchling sur- vivorship) have been released into the salt marshes of the parents' origin. Roadkill mortality of adult females remains considerably higher than their rate of replacement, and we have noted a substantial decrease in num- bers of mature female terrapins in our study area. Diamondback terrapins, Malaclemys terrapin, include several subspecies within a unique genus and species of emy- did turtles. The terrapin is the only one of more than 270 extant species of turtles whose habitat is confined to coastal brackish (as opposed to fresh or truly oceanic) waters. The species' range is several thousand miles long but never more than a few miles wide, extending from the north-temper- ate zone into the subtropics, from Cape Cod, Massachusetts, through the Florida peninsula and Keys, to the Gulf Coast of the United States. The western terminus of its range has not been precisely deter- mined, but probably lies near Corpus Christi, Texas. Malaclemys terrapin ter- rapin (the focus of this report) is the northernmost of the seven described sub- species. It ranges from Cape Cod, Massachusetts, to Cape Hatteras, North Carolina.