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Diamondback Terrapins in the Chesapeake Bay – 2002 Beach Survey


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Results Summary

Timing. Total field effort for the May-August survey is estimated at over 2,220 hours.

Sites surveyed. We stopped at 1401 sites; findings presented here are based on 1367 sites. Sites were visited based on their apparent beach-like or open sand areas visible from the water. Once on land, several sites were re-evaluated with the high probability of being submerged at high tide.  Any nests present would be considered lost/unsuccessful.

Terrapin activity. Presence/absence of turtle activity (1/0) was based on turtles , crawls or tracks for both adults and hatchlings, nests (new, hatched, or predated), egg-shards and shells, turtles observed swimming close to the shoreline of the site, as well as reports from local residents that terrapins have been using the site. In cases when packets of eggs shards were found associated to no specific nest, if clustered, we assigned them to that site rather than randomly transported by waves or wind. Based on this classification of 1/0,  62% of the stopovers showed some sign of activity, and  51% of the stopovers (or 95% of the activity) were based on "predated" nests. Given the geographic scope and limited time frame for the survey, no steps were taken to identify specific predators. 

Relative Density. Based on 746 sites in which we observed terrapin nesting-related activity, relative densities ranged from 0 to 1.8 counts/m with a mean of 0.103/m of shoreline.

Evaluations. Evaluations are based on notes and comments transcribed on site by the observer with respect to overall quality and availability of the site for nesting.  A sign of good nesting habitat was based on previously defined attributes: sandy soils in areas either open or with low vegetative cover, sandy beach-like or high dune habitat, and located above the mean high tide level (Burger and Montevecchi, 1975; Burger 1977; Roosenburg 1994; Pfau and Roosenburg, 2010).  Access to a marsh or tidal creek is critical to the survival of the emerging hatchling therefore proximity to these water resources were also considered when evaluating what constituted a good nesting habitat. 

Observations. Summary of observations recorded in the dataset.

Females on beach:
12 females actively nesting
20 females walking, running, or basking on the beach
2 females observed climbing over rip rap
Hatchlings presence:
A dead, probably newly emerged hatchling was found 5/30. 
Tracks were positively identified as belonging to emerging hatchlings starting from July 1st.  
Basking behavior:
1 terrapin was observed basking on logs near shore 5/30
A group of 12-15 terrapins were observed basking along a bank – 6/24
Terrapins swimming near the shoreline
33 incidences of single terrapins
20 groups of 2 terrapins
6 groups of 3 terrapins
7 groups of 4 terrapins
2 groups of 5 terrapins
6 groups of 10 terrapins
1 groups of 25-40
7 adult empty plastron and carapace
40 dead adult/sub adult terrapins


Recommendations: while recommending a standardized strategy for a new terrapin survey are beyond the scope of this document, we feel that an improved survey used to assess distribution and population parameters would benefit from:

  • repeated surveys, e.g. three visits in a week, to estimate detectability, and hence adjusted counts that could produce a more robust nest density estimate.
  • taking into account how the different signs used to detect terrapins (eggshells, spotting heads in the water, and so on) are correlated differently with the adjusted counts.


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Last updated: website – April 2012; data collected 2002.


Terrapin nest with eggs A Diamondback Terrapin nest with eggs. Photo: USGS.


Burger, J. 1977. Determinants of Hatching Success in Diamondback Terrapin, Malaclemys terrapin.  The American Midland Naturalist 97(2): 444-463.

Burger, J. and W A. Montevecchi. 1975.  Nest Site Selection in the Terrapin Malaclemys terrapin. Copeia 1975 (1): 113-119.

Maryland Diamondback Terrapin Task Force, Findings and Recommendations. Final Report to the Secretary of the MD DNR, September 20, 2001.

Pfau, B and W. M. Roosenburg. 2010. Diamondback terrapins in Maryland: Research and conservation. Radiata 19(1): 2-34.

Roosenburg, W. M. 1994. Nesting Habitat Requirements of the Diamondback Terrapin: A geographic Comparison. Wetland Journal 6(2):8-11.


The following posters summarize the data resulting of these surveys.

Maps & data - see the Maps & data page to view & download the data resulting from this survey. results map thumbnail



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