Second International Congress on Chelonian Conservation
Barton, Meredith and William Espenshade. 2003. Using telemetry to study the distribution of northern diamondback terrapins (Malaclemys terrapin terrapin) within their salt marsh habitat.
Herlands, Rosalind, Roger C. Wood, and Tom Mohrman. 2003. Conservation of northern diamondback terrapins (Malaclemys terrapin terrapin) in southern New Jersey, USA: Comparison of artificial incubation with natural incubation.
Mohrman, Tom and Roger C. Wood. 2003. Habitat partitioning by different age classes of northern diamondback terrapins (Malaclemys terrapin terrapin) in salt marshes of the Cape May Peninsula, New Jersey, USA.
Watters, Christina and Roger C. Wood. 2003. Large scale mortality of diamondback terrapins (Malaclemys terrapin terrapin) as the result of drowning in commercial crab traps.
Woerner, Joanna and Roger C. Wood. 2003. An analysis of northern diamondback terrapin (Malaclemys terrapin terrapin) roadkills on the Cape May Peninsula in New Jersey, USA: 19922002.
Wood, Roger C. 2003. Observations on the natural history of the side-necked turtle Pelusios broadlyi (Pleurodira; Pelomedusidae) in Lake Turkana, Northern Kenya.
Using Telemetry to Study the Distribution of
Northern Diamondback Terrapins (Malaclemys terrapin terrapin)
within their Salt Marsh Habitat
Meredith Barton1,2 and William Espenshade1,3
Diamondback terrapins (Malaclemys terrapin terrapin) are uniquely adapted to brackish water coastal environments (salt marshes and mangrove forests) along the Atlantic and Gulf Coasts of the United States. Although very closely related to the widely distributed freshwater turtle Graptemys, terrapins never occur naturally in freshwater. Very little is known about the distribution and movements of individual terrapins within their range. We have studied a population of northern diamondback terrapins in salt marshes on the Cape May Peninsula of southernmost New Jersey, USA, in order to determine: (1) whether adult terrapins have a definable home range and (2) whether adult and juvenile terrapins routinely occupy different areas within the salt marsh. Two techniques have been used: (1) sonic telemetry for adults and (2) radio telemetry for head-started hatchlings. Preliminary results show that adult female terrapins tend to occupy discreet home ranges within relatively small areas of the salt marsh. However, nesting females may travel distances of several kilometers in order to find suitable nesting habitat. Two incidental discoveries about nesting behavior were made: (1) females show signs of nesting ground fidelity and (2) females can lay as many as three clutches in one season. Limited work with radio tracking suggests that hatchlings do not move as far or as fast as adults and also that they tend to be restricted in distribution to fringes of the marsh.
Conservation of Northern Diamondback Terrapins (Malaclemys terrapin terrapin)
in Southern New Jersey, USA:
Rosalind Herlands,1,2 Roger C. Wood,1,2 and Tom Mohrman2
For the past 14 years, we have recovered potentially viable eggs from road-killed diamondback terrapins during the nesting season in June and July. These eggs are then placed in artificial nests (clean plastic storage boxes containing sterile, moist vermiculite), which are incubated under controlled conditions in the laboratory. In a typical year we will incubate 750 to 1000 eggs with a 30 to 45 % hatching success. The resultant hatchlings are head started for 9 to 10 months and then returned to the wild population in the local salt marsh from which their mothers emerged the previous year. We have established the critical temperatures for producing female and male hatchlings. Because these efforts are part of a larger conservation project, we intentionally produce mostly females to replace those lost on the local salt marsh roads; however, the replacement is only partial because each year we return far fewer hatchlings than the number of adult females killed. We are currently tagging the hatchlings with microchips just before release in an effort to determine their long-term survival in the wild.
We have recently started to compare artificial incubation with natural incubation. Nests laid along the nature trail at the Wetlands Institute have been protected with predator exclosures (21 nests in 2001 and 30 nests in 2002). Temperature probes were placed in several of the nests. We have documented the emergence of hatchlings from these natural nests, as well as the number of eggs in the nest that hatch and the location of these nests (in shade vs. in full sun) versus the length of the incubation period. Preliminary data from our first year of observations show: (1) unlike the eggs in our artificial incubated nests, most of the eggs in these protected natural nests did complete development; (2) hatchlings in several of the nests overwintered; and (3) hatchlings from the nest do not emerge simultaneously. During summer 2002 we have also placed potentially viable eggs from roadkills into 20 natural nest sites near the exclosures of natural nest in order to compare the hatching success and the size of the hatchlings with those from our artificially incubated nests.
Habitat Partitioning by Different Age Classes of
Northern Diamondback Terrapins (Malaclemys terrapin terrapin)
in Salt Marshes of the Cape May Peninsula, New Jersey, USA
Tom Mohrman1 and Roger C. Wood1,2
Continuing fieldwork has shown that adult populations of northern diamondback terrapins along the Atlantic coast of southern New Jersey, USA, are not uniformly distributed throughout an apparently homogeneous Spartina salt marsh. The densest terrapin populations occur in creeks and marsh banks along the fringes of open sounds (= shallow bays within coastal salt marshes). Within sounds themselves, adult diamondback terrapins appear to be more dispersed, based on comparative catch effort using commercial-type crab traps. Terrapins trapped in all of these areas are, for the most part, mature females or, less commonly, adult males. Subadult terrapins of either sex are rarely caught, which accords with the theoretical reverse pyramid structure typical of any turtle population. However, in the summer of 2002, we discovered a relatively small creek on the mainland margin of the marsh which, based on the large number of small diamondback terrapin heads breaking the waters surface, appeared to be populated largely if not entirely by subadults. Trapping here resulted in capture of 64 terrapins, only one of which was an adult female. Thus, for reasons not yet clear, this creek appears to be a refugium for immature terrapins of both sexes. Further field work will be required to determine how common these refugium creeks may be and what selectively attracts immature terrapins to them.
Large Scale Mortality of
Diamondback Terrapins (Malaclemys terrapin terrapin)
as the Result of Drowning in Commercial Crab Traps
Christina Watters1,2 and Roger C. Wood2,3
Lost or abandoned commercial crab traps are called "ghost traps." These traps are no longer tended by their owners and continue to catch a variety of marine organisms not only crabs, but also various species of fish, conchs, and diamondback terrapins (Malaclemys terrapin terrapin). Terrapins breathe using lungs, rather than gills, and they will drown in a ghost trap within a few hours of being caught unless they can find a means to escape. The geographic range (= Atlantic and Gulf Coasts of the United States) of the blue crab (Callinectes sapidus) for which commercial crab traps were designed coincides almost exactly with the range of diamondback terrapins. It has been estimated that more than 2 million traps are annually deployed in coastal waters within this range. A recent study indicates that as many as 25% of these commercial crab traps become ghost traps each year. Thus, in any given year, there are tens of thousands, perhaps even hundreds of thousands, of ghost traps that can potentially capture terrapins. Over the last few years, studies at the Wetlands Institute have shown that a single ghost trap can drown as many as 15 terrapins, representing sub-adults and adults of both sexes. In our study area, an average of one terrapin is caught for each ghost trap recovered. The implication of our research is that tens of thousands, potentially even hundreds of thousands, of terrapins are drowned in ghost traps annually throughout the range of this species. These needless deaths could easily be prevented by implementing fisheries regulations, which require the use of terrapin excluder devices on the entrance funnels of all commercial crab traps.
An Analysis of Northern Diamondback Terrapin
(Malaclemys terrapin terrapin) Roadkills on the
Cape May Peninsula in New Jersey, USA: 19922002
Increased motor vehicle traffic on the causeways between the mainland and the barrier islands of coastal southern New Jersey are a growing threat to diamondback terrapins. During the nesting season (typically from late May or early June to mid July), females leave the protection of the marsh in search of nesting grounds. Development on the barrier beach islands has destroyed most of the sand dunes that originally served as the primary nesting site for these animals. With the disappearance of these dunes, female diamondback terrapins have had to find alternate nesting grounds, which have proven to be the embankments of causeways crossing the marshes. Thus, the shoulders of these causeways have become a dangerous substitute for sand dunes, resulting in hundreds of terrapin road kills annually. Every year during the nesting season, researchers at the Wetlands Institute have patrolled a 38-mile transect on the Cape May Peninsula of southernmost New Jersey in order to collect road killed terrapins and remove potentially viable eggs. Since terrapins nest around the clock, patrols were conducted both day and night. The potentially viable eggs are incubated and hatchlings are cared for until they grow large enough after ten months to deter most predators. The head start program typically releases 250 hatchlings each summer. However, 400 to 700 adult female terrapins are killed on the roadways each year. Thus, the terrapin population suffers a net loss of at least several hundred adult females every year. Data collected over that past ten years indicate that: 1) the number of road kills per nesting season is increasing; 2) the start of the nesting season is occurring progressively earlier each year; and 3) the mean length of the nesting seasons is 51 days but varies as much as thirty days between the longest and shortest nesting seasons over the past decade.
Observations on the Natural History of the
Side-Necked Turtle Pelusios broadlyi (Pleurodira; Pelomedusidae)
in Lake Turkana, Northern Kenya
Roger C. Wood
Only two genera of side-necked turtles occur in Africa, the monotypic Pelomedusa and several species of Pelusios. Both are found only in sub-Saharan regions of the continent in aquatic habitats. Relatively little is known about the ecology and behavior of any African pelomedusid species. Pelusios broadlyi is found along the margins of Lake Turkana, the largest by far of the Eastern Rift Valley lakes of Africa (approximately 270 km long and no more than 50 km at its greatest width). Fishermen who venture out into the deeper waters of the lake in small boats regularly net soft-shelled (trionychid) turtles but evidently never catch specimens of broadlyi, suggesting that this species is in fact restricted in its distribution only to the margins of the lake. P. broadlyi is a cryptic species, spending the daytime shallowly buried under shoreline sediments covered only by a thin veneer of water, presumably an adaptive response to intense equatorial heat. Turtle tracks found in the early morning on several occasions leading from and returning to the lake indicate nocturnal nesting activity, though no actual nests were located. The distribution of this species around the shoreline of the lake appears to be patchy, but factors determining the distribution of P. broadlyi populations are not yet at all clear. Human consumption of this species seems to be minimal, with occasional specimens being eaten by subsistence pastoralists of the Dassenatch tribe along the northeastern shores of the lake. Members of the tiny El Molo tribe on the lakes southeastern shore may also dine on an occasional specimen of P. broadlyi. Human impacts on this species (both for food and in terms of habitat alteration) appear at present to be minimal. But as this still remote region becomes increasingly accessible to the growing human population of Kenya, the possibility of unsustainable utilization of this species is likely to increase.