By: Jacob Causey
My lifelong interest in turtles has taken me to some fantastically beautiful places. I’ve swam after sliders in the Ichetucknee River, tracked box turtles in the hills of Tennessee, and currently I’m tagging sea turtles and capturing diamondback terrapins for research projects in northwest Florida. As I work with a species I develop an interest in their natural history and biology. Recently, the focal point of my fascination has fallen on diamondback terrapins – a species like no other, with a harrowing past and an uncertain future.
Diamondback terrapins are named for the concentric diamond-shaped growth marks found on the costal scutes (large scales) of their carapace (top portion of their shell). The color of their skin varies between individuals and can range from shades of white, yellow, grey, and brown. When compared to other turtles, terrapins are relatively small as adults. Males have an average length of 13 cm (5.1 in) and females grow to 19 cm (7.5 in). They are part of the pond turtle family (emydidae), but are unique in that they live their entire lives in saltwater marshes. Terrapins have several adaptations to help them survive in these habitats. Much akin to sea turtles (to whom terrapins are distantly related), terrapins have a gland in the orbital of their eye which allows them to excrete excess salt from their bodies. To find drinking water, terrapins can differentiate between salinity levels in water and will drink from the layer of freshwater that accumulates on top of saltwater during a rainstorm. Interestingly, they’ve also been observed raising their heads, mouth open to the sky, to catch falling rain. Terrapins feed on marine snails and small crabs living in salt marshes. They have strong jaws that allow them to bite through the hard shells of their prey.
Terrapins are listed as vulnerable by the International Union for the Conservation of Nature. Their habitat covers most of the eastern coast and the Gulf of Mexico, and terrapin populations across their range are declining. Factors influencing this decline include the collection of wild terrapins, habitat loss, road mortality, and incidental drowning in fishing gear. Terrapins were historically collected from the wild for food (and considered a delicacy) until the early 20th century. At that time, captive breeding programs were enacted in order to meet the needs of the public and reduce the stress on wild populations across the entire range. A more modern problem for terrapins is the conversion of large portions of their habitat for coastal development – particularly, the draining of salt marshes and loss of nesting sand dunes on barrier islands. As loss of habitat continues to increase, female terrapins will often travel far and wide to find nesting sites. Their journeys can lead them across busy roadways where they are frequently struck and killed by cars. Researchers at the Wetlands Institute in New Jersey have recorded over 10,000 terrapin road mortalities between 1989 and 2011. Females are not the only group at risk; it is also sometimes necessary for hatchlings to cross roads to reach bodies of water.
Traps intended to catch blue crabs (Callinectes sapidus) often attract and kill terrapins as bycatch. Males and small females crawl into the traps to feed on bait intended for the crabs and, unable to escape, drown within a few hours. Abandoned or lost traps, poignantly called ghost traps, are of considerable interest to terrapin conservation groups. These traps will perpetually kill through a sinister cycle where each organism drowned by the trap becomes bait for the next. This cycle continues until the traps are removed from the habitat.
Conservationists have made headway in mitigating some of the causes of widespread terrapin declines. The invention and distribution of Bycatch Reduction Devices (BRDs) for use in crab traps has reduced the number of terrapins and other non-target species killed as bycatch. Notably for commercial blue crab harvesting, the BRDs have been shown to increase the overall number of marketable crabs caught in the traps. The Wetlands Institute has placed barrier fencing along roadways and enacted a terrapin road patrol program to reduce the number of vehicle-related fatalities. The road patrol is active during nesting season, assisting turtles across roadways and transporting injured animals to a veterinarian. Headstarting programs are also in place to supplement declining populations with individuals raised in captivity.
Terrapins are delightfully fascinating little turtles. Holding them and looking into their eyes, you feel a longing for untamed saltwater and hot summer days. Turtles have always been my favorite animal but I had never been inspired by them the way that I am now. These creatures are special and we all must do our part to guarantee they are around to inspire those who will follow in our footsteps. Through solid conservation and stewardship practices, we can ensure these little diamonds will remain in the rough.
(Photo of various terrapin color morphs found in the same habitat.)
“I believe our biggest issue is the same biggest issue that the whole world is facing, and that’s habitat destruction.” ~ Steve Irwin