Terrapins Break Out in the Navesink River

By Joe Reynolds
​www.nyharbornature.com

​It was the first weekend after Labor Day. The sky was sunny and blue, the air was breezy with a northwest wind. Air temperatures were chilly for this time year, reaching only into the lower 70s.
 
I was spending part of the weekend kayaking in the Naveisnk River, an approximately eight mile long tidal river in Monmouth County, New Jersey. It was a beautiful day paddling near the mouth of the river, not far from where the Navesink River meets the Shrewsbury River and drains into Sandy Hook Bay.
 
On a small sandy island is where I discovered a break-out event.
 
Several Northern Diamondback terrapins had newly hatched out of eggs.  The little reptiles must have emerged from their sandy nest only a few days before. 

​Diamondback Terrapins are unique among the turtle world. Most turtles live exclusively in either freshwater or saltwater. Diamondback terrapins, however, are the only turtle known to live its entire life-cycle within brackish or tidal waters. It is truly an estuarine loving creature.
 
During late spring and early summer, female Diamondbacks will wait in estuarine waters for a high tide to reach its highest point in order to find a nesting place that is above the high tide line and covered with very small amounts of beach grass, since it can be difficult to dig in the sand with too many roots. Females will dig their nests up to 6 inches deep and lay about 8 to 12 eggs per nest. Since Diamondbacks do not have X or Y chromosomes like humans do to determine a baby's sex, the gender of a young terrapin is determined by temperature during nest incubation. Eggs that are sustained at high temperatures above 86 degrees give birth to girls, and eggs incubated at lower temperatures hatch boys.

​Come late summer, young terrapins are hatching out from eggs laid along the sandy coast during the spring or summer. Generally, it takes about 60 to 120 days for eggs to hatch.
 
Unfortunately, it's not easy being a small diamondback terrapin. People often refer to these miniature turtles, which are only about the size of a quarter, as "Sea Gull Potato Chips." Birds, such as gulls and crows, and small mammals, such as foxes and raccoons can often be seen moving about the coastline and lower dunes to seek out nesting terrapin sites and hatchlings. A baby terrapin then has to quickly crawl with its small legs to advance into the water and escape being gobbled up. As you can imagine, a good percentage of hatchlings don't survive. I have seen one study in Cape May County, NJ that reported up to 40 percent of nest sites were destroyed by predators.
 
I’m hoping most if not all of the little terrapin hatchlings from the Navesink River will make it. They will not have much time, though, to get used to their surroundings. The little turtles will have to hurry up and eat and eat, and get ready for winter. Terrapins hibernate in the winter. The first cold temperatures of the season are a signal for these turtles to bury themselves in mud. Body functions will slow down to the point where terrapins do not need to come up to breathe until the arrival again of spring. 

For more information about Northern Diamondback Terrapins, check out the book entitled, Diamond in the Marsh, A Natural History of the Diamondback Terrapin by Barbara Brennessel, published by the University of New England, 2006.
 
Also, check out the website devoted Diamondback Terrapin conservation from the Wetlands Institute in Stone Harbor, NJ: wetlandsinstitute.org/conservation/terrapin-conservation/20-years-of-terrapin-conservation-and-research/