Gibbons, J. W., J. E. Lovich, A. D. Tucker, N. N. Fitzsimmons and J. L. Greene. 2001. Demographic and ecological factors affecting conservation and management of diamondback terrapins (Malaclemys terrapin) in South Carolina. Chelonian Conservation and Biology 4:66-74.

A complete discussion of current threats to terrapin populations; also references studies on Maryland's terrapins and their own declines:

 

"Diamondback terrapins show extraordinarily high home range site fidelity, most individuals remaining from year to year in the same tidal creek, with little or no interchange among the adult populations of adjoining creeks...Consequently, extirpation of terrapins in a particular section of marsh habitat could take a generation or more of recruitment time to fill. And, unless the source of extirpation is removed, terrapins might never return."

“Roosenburg (1991) found a single unattended crab pot in Maryland that contained the entire shells of 49 turtles and the remains of others, or approximately 1.6-2.8% of the entire population in his study area. Hoyle (1997) calculated that recreational crab trapping typical of the region could remove individuals from a tidal creek similar to Fiddler Creek at a rate that would not be sustainable"

"As if this were not enough, a market for consumption of terrapins is recrudescing, particularly in Chinese restaurants of New York City. Some vendors sell as many as 2000-3000 terrapins in a single year. Most are collected in Virginia, the Carolinas, Maryland or New Jersey with some coming from nearby areas...Continued exploitation, coupled with all the other problems terrapin face in a modern world [see full article], bodes poorly for the future of the species unless prudent management recommendations are implemented immediately."

Note: Maryland, New Jersey and New York are the only states in the above list that allow a commercial terrapin fishery. In 2001 when this article was published the MD DNR's dealer reports reflect a take of "no reports" and 80 pounds the previous year. As of 2004 this figure soared to 14,664.5 pounds.

"Several recent and comprehensive studies have demonstrated the susceptibility of long-lived species like turtles to population decline when subjected to levels of mortality associated with commercial harvest (Congdon et al., 1993, 1994; Galbraith et al., 1997)"

 

Hart and Lee, "The Diamondback Terrapin: The Biology, Ecology, Cultural History, And Conservation Status Of An Obligate Estuarine Turtle", a chapter within Studies In Avian Biology—Tidal-Marsh Vertebrates, in press; Academic Press

 

"Despite limited protected status in some regions, populations of this long-lived turtle species generally have not recovered from past episodes of direct harvest (Seigel and Gibbons 1995)."

" The work by Dunham et al. (1989) on life-history modeling and Congdon et al. (1993) on Blanding’s turtles (Emydoidea blandingii) focused attention on the life-history and demographic constraints of long-lived organisms. Recent work by Heppell (1998), Heppell et al. (2000), and Sæther and Bakke (2000) examined relationships among age at sexual maturity, adult survivorship, and juvenile survivorship within life histories of long-lived organisms. Results from their studies indicate that all long-lived vertebrates have coevolved life-history traits that limit their ability to respond to increased mortality imposed on any age group (Congdon et al. 1993)."

Please also see the informative tables within. Reference List

 

Hoyle, M. E. and J. W. Gibbons. 2000. Use of a marked population of diamondback terrapins (Malaclemys terrapin) to determine impacts of recreational crab pots. Chelonian Conservation and Biology 3:735-737.

 

"Characterized by life history traits in which individuals are slow to mature and have extended longevity, terrapin populations cannot absorb chronic adult mortality (Congdon et al., 1994) caused by crab pots."

"In the Chesapeake Bay area, local terrapin populations can be extirpated in 3 to 4 years due to mortality in crab pots (Roosenburg et al., 1997)."

 

Mitro, M. G. 2003. Demography and viability analysis of a diamondback terrapin population. Can. J. Zool. 81:716-726.

 

Figure 5 (pp. 722) shows that even in a terrapin population that was otherwise increasing, an increase in mortality rates of 5% resulted in a declining population at a rate of about 3% per year.

"...large-scale declines over a number of years have been observed (e.g., Seigel 1993). Recovery from such events would be hindered by the demography and life history of this species, including low reproductive rates, low recruitment rates, and low dispersal rates (Roosenburg et al. 1999; Gibbons et al. 2001; this study)."

 

"The low probability of clutch success (<10%) was largely attributable to predation by raccoon and striped skunk. These small carnivores have thrived in fragmented habitat (Crooks and Soule 1999) and urban environments (Broadfoot et al. 2001)."

 

Roosenburg, W. M. 1991. The diamondback terrapin: Habitat requirements, population dynamics, and opportunities for conservation. New Perspectives in the Chesapeake System: A Research and Management and Partnership. Proceedings of a Conference. Chesapeake Research Consortium Pub. No 137. Solomons, Md. pp. 237 - 234.

 

 

Roosenburg, W. M., W. Cresko, M. Modesitte, and M. B. Robbins. 1997. Diamondback terrapin (Malaclemys terrapin) mortality in crab pots. Conservation Biology 5:1166-1172.

 

"Our estimates of the capture rates of terrapins by crab pots indicate that crab pot fisheries can have a severe effect on local terrapin populations. We estimated that between 15-18% of the patuxent population dies annually as a result of this fishery."

 

Seigel, R. A. and J. W. Gibbons. 1995. Workshop on the ecology, status, and management of the diamondback terrapin (Malaclemys terrapin) Savannah River Ecology Laboratory, 2 August 1994: final results and recommendations. Chelonian Conservation and Biology 1:241-243.

 

"...there is sufficient evidence that populations in some areas are declining as a result of the factors described above....Thus action needs to be taken before the species declines to the point where only dramatic interventions will help."

 

Szerlag, S. and S. P. McRobert. 2006. Road occurrence and mortality of the northern diamondback terrapin. Applied Herpetology. 3:27-37.

 

"Simply looking at individual numbers of road kills may conceal the effects of traffic mortality of local populations. Fewer mortalities seen on the road may give the appearance that there is no real problem. However, if the number of terrapins utilizing an area is relatively small, the outcome may actually be quite detrimental."

 

Tucker, A. D., J. W. Gibbons, and J. L. Greene. 2001. Estimates of adult survival and migration for diamondback terrapins: conservation insight from local extirpation within a metapopulation. Can. J. Zool. 79:2199-2209.

 

"Terrapins showed high fidelity to each subpopulation [i.e., they exist in localized populations] and low migration rates were insufficient for recolonizing a creek that had suffered extirpation [removal from a local area]."

"The results emphasize that incidental mortality of terrapins in crab pots is a conservation concern."

"Our empirical estimates of survival establish that mortality in crab pots is a detriment to the long-term persistence of terrapins in zones of high-fishing pressure. The case study at Terrapin Creek proves that population declines can be sudden and that recolonization will be uncertain as long as a population sink persists nearby."

 

Wood, R. C. 1997. The impact of commercial crab traps on northern diamondback terrapins, Malaclemys terrapin terrapin. Pages 21-27. In J. Van Abbema editor. Proceedings: Conservation, Restoration, and Management of Tortoises and Turtles--An International Conference. New York Turtle and Tortoise Society, New York, USA.

 

"Commercial crab traps kill subadult and adult diamondback terrapins of both sexes. From the most conservative estimates, it is clear that large numbers are drowned annually in New Jersey's coastal waters, during the time of year when terrapins are officially protected by state laws.

Trap-induced mortality is also common throughout much or all of the rest of the range of diamondback terrapins; the cumulative annual drownings are having a drastic impact on the species as a whole (Seigel and Gibbons 1995; Mann, 1995; G. S. Grant, pers. comm.)"

 

Wood, R. C. and R. Herlands. 1997. Turtles and tires: the impact of road kills on northern diamondback terrapin, Malaclemys terrapin terrapin, populations on the Cape May peninsula, southern New Jersey. Pages 46-53. In J. Van Abbema editor. Proceedings: Conservation, Restoration, and Management of Tortoises and Turtles--An International Conference. New York Turtle and Tortoise Society, New York, USA.

 

"The unsustainable exploitation of terrapins at the turn of this century raised such concern for their well-being that protective legislation was enacted by most of the states where terrapin are found (Donnelly and Owens, 1988). These regulations vary widely from state to state, and while penalties for violating these laws may be imposing, they appear to be largely unenforceable and do not address issues of habitat degradation."

"Our results clearly show that our terrapin conservation efforts, however well-intentioned and well-publicized, are the equivalent of waging a losing battle. We simply lack the capacity to replace adult road-killed terrapins with headstarted juveniles as fast as adults are killed by vehicles. After seven years of extremely labor-intensive efforts, we have released nearly 800 head-started terrapins. Unfortunately, during these same seven years, 4,020 adult female roadkills have been documented....Under current circumstances, therefore, we can neither reverse nor even stabilize the precipitous population decline now taking place."

 

The following article may be the one reference that at first glance seems to indicate harvesting has little effect, Gamble, T. and Simons, A. M. 2004. Comparison of harvest and nonharvested painted turtle populations. Wildlife Society Bulletin 32 (4): 1269-1277. However, the below discussion as to how this article compares to terrapin population demographic studies finds that:

 

"Even with a 2 year study the authors are not sure what the results say, this is because turtles live so long and it's hard to take such a short study period and assume it's reflective of the whole story over time.

Northern painted turtles lay up to 5 clutches per season (Moll 1973. Herpetological 29:307-318), thus they can rebound faster. They are not as size dimorphic so catch, bycatch, and other selective factors would not favor increased mortality of one sex or the other. They also grow faster as a species.

While these turtles would face all the natural mortality factors that terrapins do, they would not have problems associated with loss of nesting areas, drowning in crab traps, nets, etc. Lakes are not closed populations, painted turtles move from one to another and their young disperse, this could cloud studies and comparisons to terrapins that exhibit little migration. They also have no real baseline for a healthy population. The non harvested lakes may have been not harvested that year or even decade but who knows what went on before. Also if they are having unreported harvesting, how do they know that no one is removing turtles from their control lakes?

Turtles removed for biological supply houses and pet trade assume a finite number. Only so many would be used a year, once you have a pet or two and once a biology class has a turtle to dissect for that year, that's it; demand for terrapins soars for the food market.

However, the main point is that this study is inclusive and all the other studies quoted showed a harvest can not be sustained."