Draft Study Plan

Patuxent River Diamondback Terrapin Project

Dr. Roger Wood

The Wetlands Institute and Richard Stockton College of New Jersey

Objective

The objective of the diamondback terrapin injury assessment is to evaluate the hatching 

success of terrapins at nesting beaches that were oiled compared to those unaffected by 

the oil spill. Data from this study will be used to assess the likelihood that injury to the 

eggs or hatching levels occurred, and to assess the magnitude and extent of potential 

injury to the year 2000 cohort that would have hatched in the spill zone.

Background

Terrapins nest on narrow, isolated sandy beaches found along the fringes of salt marsh of 

the Patuxent River. The nesting season starts between mid-May to early June and

continues until late July. Females repeatedly use the same nesting sites and deposit eggs 

above the high tide line. Egg incubation lasts between 60 and 120 days. Average clutch 

size is 13 eggs. Females may lay as many as three clutches per nesting season. Once 

hatchlings emerge from the nest (end of first week of August through 

October/November), they enter the water of the adjacent salt marshes. Hatchlings from 

some nests do not emerge until the following spring. 

Study Approach

Terrapin hatching will be investigated on beaches in the area of the spill, from Swanson 

Creek to Jack Bay, about 8 miles south. This region was selected because it contains the 

beaches where historical studies have been conducted, (Roosenburg 1992), and offers 

other potential nesting beaches for study (Mountford 2000). Study sites will include both 

oiled and unoiled beaches. 

Selection of Study Sites

Oiling level indices for beaches based on SCAT data (April 2000) and observations by 

Mountford (2000) were recorded and entered into a GIS database. In addition, the 22 

known turtle nesting beaches in spill area (Mountford 2000) were recorded and mapped. 

Based on this map and field observations, a total of nine terrapin nesting beaches were 

selected as either “heavily oiled”, “moderately oiled”, or “unoiled” sites. Information 

received subsequent to study initiation has led to the reclassification of some of the 

beaches in terms of their oiling levels:
1. Caney Creek-heavy oiling

2. Golden Beach Playground- heavy oiling

3. Long Point- heavy oiling

4. Hoyer property- moderate oiling

5. Trent Hall- moderate oiling

6. Golden Beach Grandfather’s Pond- moderate oiling

7. Sheridan Point- no oiling

8. Prison Point- no oiling

9. Jack Bay- no oiling

Field Program

A. Exclosure study

Terrapin hatching will be evaluated in beach areas from the beginning of September 

through the end of the fall hatching season (determined by seven consecutive days with 

no hatchlings observed). Plastic fence exclosures will be installed in typical nesting 

habitat to capture emerging hatchlings. Exclosure size is 5 m by 10 m, and about one foot 

in height. Two exclosures will be installed per site in open, sparsely vegetated beaches 

above the mean high tide line (Roosenburg 1992). Each exclosure will be photographed 

showing its proximity to mean high water, mapped using Global Positioning System, and 

entered into GIS database. 

Exclosures will be checked daily for emerging hatchlings through the fall hatching 

season. Hatchlings will be counted, removed from collection devices, and released. 

B. Beach reconnaissance

Teams of three people will walk beaches with suitable habitat (including those without 

exclosures), and record signs of nesting (i.e., scattered egg shells from successful nests or 

nests destroyed by predators). Signs of predators (tracks, scat, etc.) will be identified to 

species when possible and recorded.

Analysis

Nesting beach use will be assessed to determine if terrapins continue to nest successfully 

in the study area (number of successful nests, number of hatchlings).

Terrapin nesting success will be compared between oiled and unoiled beaches (number of 

successful nests, number of hatchlings).

Interpreting Data/Key Results of Damage Assessment
Overall impacts of the oil spill on the use and success of nesting on selected oiled 

beaches will be assessed.

Estimate of impact of spill on year 2000 cohort based on nesting distribution, abundance, 

and nesting success results.

Issues associated with potential levels of hatchling/juvenile mortality related to the spill

will be addressed to the extent possible based on the results of the study.