Summary:

Mordecai Island, a brackish water marsh habitat located in Barnegat Bay, has recently undergone conservation efforts, which included pumping of dredge material, shoreline stabilization, and shellfish development. In May 2017, an area of sandy substrate located on slightly higher ground of the southwest corner of the island, and with a gently sloping sandy bay beach access, was cleared of dense vegetation. On June 25, 2017, three Northern Diamondback Terrapin clutches totaling 38 eggs were transported to Mordecai for renesting. Since terrapins possess high nesting site fidelity, it was the hope that the development and emergence of the hatchlings would reestablish the area as a natural nesting site for future generations of this recently protected NJ species. Terrapins are regularly seen swimming in the cove adjacent to the island as well as basking on its shores.

The site however was less then optimal for natural nesting and required care and maintenance. Due to an abundance of spring rains, the prospective nesting site had become overgrown with marsh plants/grasses and there was evidence of flooding in the area. The site was also a high predation area. Predated nests (7 holes with 49 eggshells), false attempts and depressions (20) were observed and recorded (Table 1). Similar predation findings were observed and recorded for the entire Mordecai site (see Table 2: 150 eggshells among 21 nests). Fresh mammalian tracks were photographed and positively identified as mink by Fish & Wildlife personnel. Crows and gulls, and their tracks, were also routinely observed at the nesting site and around existing predated holes.

Prior to renesting, the area chosen for each nest had to be recleared of vegetation as well as the extensive root systems. Anchored nest exclosures (17” wide x 22” high with 1”x 2” openings) were used to protect each nest from predators. The nests were monitored weekly and their periphery cleared of vegetation throughout the incubation period. Hatchling emergence occurred from Day 60 through Day 67, with a 68% hatchling success rate (Table 3). Hatchling mortality within the nest cavity occurred at 21% due to maggot infestation. Mortality results would have been higher if the larvae had not been removed and the nest cavity replaced with clean sand. Egg mortality at 11% was due to undeveloped eggs, which may have been the result of multiple flooding of the nest cavity. Hatchling emergence from these nests was observed on 3 occasions, with directional movement of hatchlings toward the western bay marsh. Live hatchling emergence and their directional movement, plus fresh track prints, indicated a 75% western movement after emergence (Table 4). Hatchlings were also observed resting under marsh plants on the west side of the nesting site. There was no evidence of successful hatchling emergence from any other natural nesting areas on Mordecai.

Conclusion:

Mordecai would appear to be a desired natural nesting area for the Northern Diamondback Terrapins of LBI, since Mordecai’s cove is home to this indigenous species. Unfortunately, Mordecai is subject to substantial and multiple flooding, erosion, dense vegetative growth and natural predators, which prohibit successful natural nesting for terrapins. Since extensive care and monitoring was required to achieve a 68% hatchling success rate and because of the continued threat of nest flooding and predation, future renesting of Northern Diamondback Terrapin eggs is not recommended for this site unless the site conditions improve.

Recommendations for this site:

The following recommendations are made, which would attract natural nesting by Northern Diamondback Terrapins and allow for successful nesting, incubation and hatchling emergence:

  • Clearing of vegetation at the Southwest natural nesting site.
  • Addition of sand or dredge material to a nesting site, in order to create a higher elevation and dryer nesting area.
  • Ongoing vegetative maintenance of the site should occur prior to any future renesting of eggs since excess rains encouraged new growth and extensive root systems into the area. Regular maintenance of the area would also attract natural nesting.
  • Mammalian predators should be humanely removed.
  • Nests should be protected from predation by using exclosures with 1 x 2 openings to allow for movement of hatchlings following emergence.
  • Identify and maintain another location as a natural nesting site, possibly on the north end beach, where a terrapin was seen nesting, or on a higher south western location.

Acknowledgements:

I am indebted to the crew members of ReClam the Bay for travel to/from the nesting site. This project would not have been possible without their cooperation and assistance. This project was conducted under Scientific Collecting Permit NO: SC 2017109, issued to Turtle Conservancy and Terrapin Nesting Project, by the NJ Division of Fish and Wildlife.

Table 1: Mordecai Nesting Summary
 

# Predated

Avg Predated

 

# False

Avg False

 

Site

Natural Nests

Hole Depth (inches)

# Eggshells

Holes

Hole Depth (inches)

# Depressions

Nest Site-West

5

3.5

37

2

3.5

8

Nest Site-East

2

4.25

12

0

0

12

 

 

 

 

 

 

 

Average/Totals

7

3.88″

49

2

3.5″

20

Table 2: Mordecai Site Summary

 

# Predated

Avg Predated

 

# False

Avg False

 

Site

Natural Nests

Hole Depth (inches)

# Eggshells

Holes

Hole Depth (inches)

# Depressions

Terrapins

Nest Site-W

5

3.5

37

2

3.5

8

0

Nest Site-E

2

4.25

12

0

0

12

0

North Side

5

4.4

30

2

3.75

4

4

Tidal Pool

4

4.25

25

2

3.75

0

0

South West

5

4.5

34

4

3.5

0

2

SW Wrack

 0

12

0

0

 0

East Side

 0

0

0

1

 

 

 

 

 

 

 

 

Avg/Totals

21

4.18″

150

10

3.63″

24

7

Table 3: Mordecai Nest/Hatchling Summary

Nest

# Eggs

Emerged

Dead

Egg Failures

A

12

7

4

1

B

14

11

2

1

C

12

8

2

2

 

 

 

 

 

Total

38

26

8

4

Percentage  

68%

21%

11%

Table 4: Mordecai: Hatchling Directional Movement

 

 

 

North

South 

East

West

Live Hatchling Emergence

 0

 0

 3

Tracks

 

 

1

 3

0

12

 

 

 

 

 

 

 

Total

 

 

1

 3

1

15

Percentage

 

 

5%

 15%

5%

75%

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