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Title: Crab trapping causes population decline and demographic changes in diamondback terrapins over two decades

Abstract

Diamondback terrapins (Malaclemys terrapin) are thought to be declining throughout their range. Although many factors have been proposed to contribute to terrapin declines, including increased predation of nests and adults, habitat loss and degradation, road mortality, commercial harvest for food, and mortality as bycatch in crab traps, few studies have provided evidence linking these agents to population declines. Because male and small female terrapins are most susceptible to mortality in crab traps, population declines should coincide with shifts in the age and size distributions of the population and a shift to a more female-biased sex ratio. We used twenty-one years of mark-recapture data (>2800 captures of 1399 individuals) from a declining diamondback terrapin population in South Carolina to test the prediction that the decline is the result of mortality in crab traps. Since the 1980s, the modal size of both male and female terrapins has increased substantially and the proportion that are females is higher than in earlier samples. Additionally, the population now contains more old and fewer young individuals than before. The changes in demography and sex ratio we observed suggest that this terrapin population has declined as a result of selective mortality of smaller individuals in crab traps.more » The use of bycatch-reduction devices on crab traps may help prevent terrapins from entering the traps, but current models are too large to prevent mortality of males and many females in this population. Future research should focus on design and testing of effective bycatch-reduction devices for specific regions and other methods to prevent terrapin mortality in crab traps.« less

Authors:
Publication Date:
Research Org.:
Savannah River Ecology Laboratory (SREL), Aiken, SC
Sponsoring Org.:
USDOE
OSTI Identifier:
908666
Report Number(s):
SREL-3035
Journal ID: ISSN 0006-3207; BICOBK; TRN: US200722%%742
DOE Contract Number:
DE-FC09-07SR22506
Resource Type:
Journal Article
Resource Relation:
Journal Name: Biological Conservation; Journal Volume: 137
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; ADULTS; CRABS; FEMALES; FOOD; HABITAT; MALES; MORTALITY; SEX RATIO; SOUTH CAROLINA; TURTLES; POPULATION DYNAMICS

Citation Formats

Dorcas, M.E., J.D. Willson and J.W. Gibbons. Crab trapping causes population decline and demographic changes in diamondback terrapins over two decades. United States: N. p., 2007. Web. doi:10.1016/j.biocon.2007.02.014.
Dorcas, M.E., J.D. Willson and J.W. Gibbons. Crab trapping causes population decline and demographic changes in diamondback terrapins over two decades. United States. doi:10.1016/j.biocon.2007.02.014.
Dorcas, M.E., J.D. Willson and J.W. Gibbons. Mon . "Crab trapping causes population decline and demographic changes in diamondback terrapins over two decades". United States. doi:10.1016/j.biocon.2007.02.014.
@article{osti_908666,
title = {Crab trapping causes population decline and demographic changes in diamondback terrapins over two decades},
author = {Dorcas, M.E., J.D. Willson and J.W. Gibbons},
abstractNote = {Diamondback terrapins (Malaclemys terrapin) are thought to be declining throughout their range. Although many factors have been proposed to contribute to terrapin declines, including increased predation of nests and adults, habitat loss and degradation, road mortality, commercial harvest for food, and mortality as bycatch in crab traps, few studies have provided evidence linking these agents to population declines. Because male and small female terrapins are most susceptible to mortality in crab traps, population declines should coincide with shifts in the age and size distributions of the population and a shift to a more female-biased sex ratio. We used twenty-one years of mark-recapture data (>2800 captures of 1399 individuals) from a declining diamondback terrapin population in South Carolina to test the prediction that the decline is the result of mortality in crab traps. Since the 1980s, the modal size of both male and female terrapins has increased substantially and the proportion that are females is higher than in earlier samples. Additionally, the population now contains more old and fewer young individuals than before. The changes in demography and sex ratio we observed suggest that this terrapin population has declined as a result of selective mortality of smaller individuals in crab traps. The use of bycatch-reduction devices on crab traps may help prevent terrapins from entering the traps, but current models are too large to prevent mortality of males and many females in this population. Future research should focus on design and testing of effective bycatch-reduction devices for specific regions and other methods to prevent terrapin mortality in crab traps.},
doi = {10.1016/j.biocon.2007.02.014},
journal = {Biological Conservation},
number = ,
volume = 137,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}