Tortuga Gazette 29(3): 1-3, March 1993
Diamondback terrapin,
Malaclemys terrapin
by Mimi Loutrel and Marvin Cornett
Today, diamondback terrapins (Malaclemys terrapin) are fairly common along the east coast United States. They were practically eaten out of existence earlier this century, but fortunately these heavily exploited turtles have made a good recovery and have re-established themselves over much of their former range.
Few people in Southern California keep diamondback terrapins, but we've been keeping these turtles for eight years. Our first diamondback terrapin, a female, came from our veterinarian and was quickly named Terry by the kids. A mate for Terry was obtained through a CTTC member, and was probably from a commercial wholesaler. Later, we acquired a second younger male from New Jersey and a second female that had been raised from a hatchling by another Club member.
Diamondback terrapins show a wide morphological variation. Seven subspecies are recognized that vary in their coloration, markings and behavior as well as their ranges. For instance, there is a Florida form of the diamondback terrapin which is slate-black in color with a widened head and jaw for eating barnacles off the roots of mangrove trees. Diamondback terrapins may change in appearance as they get older. For example, our female Terry was very dark when she was young; now her shell color has lightened up a lot. Because these turtles were collected and transported to be commercially raised for food in the past, specimens of some subspecies derived from escaped or released captives may be found outside their expected range and may have influenced the appearance of local populations.
Diamondback terrapins have a wide tolerance of salt in their water, and are the only North American turtles native to brackish (salty, but not as salty as the ocean) waters. They live in salt marshes as far north as Cape Cod, all the way down to the Florida Keys and around the Gulf Coast from Florida to Texas. Salt concentrations in their wild habitats have been measured at 28 parts per 1000. Some of their marshes are totally tidal while some are fed by freshwater springs. Wild hatchlings may spend their first years upstream in creeks. These creeks are sometimes brackish and sometimes relatively fresh water. As the hatchlings age, they seem to move down to the salt marshes where nutrients are plentiful and there are good nesting sites. Surfers have found grown terrapins swimming beside them in the Atlantic Ocean.
Our terrapins are housed indoors in large aquariums with basking areas, filter systems, incandescent lights and Vitalites. We add salt to their water, 1/4 cup salt to 20 gallons water, and slightly acidify it (to pH 6.8) using commercial kits available at tropical fish stores. Terry, our egg-laying female, behaves oddly when it's time for her to lay her eggs. At the appropriate time of year, when she claws and scratches at the glass wall of the aquarium we place her outside in our box turtle enclosure so she can dig her nest and lay eggs. She lays her first clutch in January, with up to 3 more clutches laid about a month apart.
In years past, our incubation method was very casual. We would put the eggs on a damp paper towel in a margarine tub and simply leave them in a cupboard over the refrigerator. Last year (1992) was the first year that we used an incubator for our turtles' eggs. The incubator was a 10-gallon aquarium heated with 15 and 25 watt incandescent light bulbs to keep the temperature at 80°-83°F (26.6°-28.3°C). The eggs were placed on moistened paper towels in margarine tubs with tight fitting lids with no holes. A dish of water was placed in the incubator for added humidity. The containers were checked regularly to ensure that the paper towels remained damp.
Two clutches of five eggs were incubated for about 90 days. Two eggs hatched from the first clutch; all five eggs hatched from the second clutch. Two other clutches were found too late to incubate. While cleaning up in the box turtle yard one day, we were surprised to find a tiny live terrapin among a clutch of dried out eggs! I brought it inside and put it in water. It started to swim right away, and has thrived. We named it Serendipity.
We start the hatchlings on live brine shrimp and then switch them to Tetra Reptomin. The older terrapins eat Purina trout chow and turtle "meat-loaf".
We've had few health problems with the terrapins. Shell rot showed up in a couple of animals obtained through wholesalers. This was treated fairly aggressively. First, the affected areas were gently scraped with dental tools to remove all signs of rot. Then concentrated Gentian Violet was painted onto the affected spots. They were kept dry for few days, then put them back in the water. Their shells healed perfectly. We had two females which were lost when they became egg-bound. Once a juvenile terrapin had a broken leg, found after an X-ray by the veterinarian. The fracture probably occurred during a fight with its brother.
Overcrowding can pose a definite problem. Chewed toes and tails can result when turtles are provided with insufficient space. The relative size of cage-mates is a concern as well. We've had situations where we put hatchlings in with older terrapins, and after about five minutes of not being sure whether the older terrapins were just curious or being aggressive, we've had to take the hatchlings out for fear that they would be bitten.
Generally, diamondbacks are sweet, gentle but curious turtles. They have a very habitual nature, and learn quickly what times people are normally around. They seem very sociable except when their cage is too small. They enjoy basking together, often on top of one another, and it isn't always the largest one on the bottom. Our female, Terry, will threaten to bite her mate when she has had enough of his attentions. They're only aggressive to people when they think we're something good to eat, and may occasionally mistake fingers for food.
Cape Cod, Massachusetts, is the northern end of the terrapin's range. At Wellfleet Bay, the Audubon Society is studying the wild diamondback terrapin. They weigh, measure and mark female terrapins captured as they crawl out of the water to nest in June and early July. There is a tremendous variety of food in the salt marshes and in the spring the wild terrapins feed well and often. The females are very dense by the time they are ready to lay their eggs.
The Wetlands Institute at Stone Harbor, New Jersey, is head-starting terrapins. In this program, researchers retrieve eggs from female terrapins killed by road traffic. The researchers incubate and hatch the eggs, and raise the hatchlings until they are yearlings. The yearling terrapins are then released back into the wild. The yearlings are much larger and stronger and, hopefully, have a better chance of surviving than hatchlings. Researchers at the Wetlands Institute have incubated diamondback terrapin eggs at various temperatures. They have found that at 26°C (78.8°F) the hatchlings are predominately male. At 32°C (89.6°F) the hatchlings are all females, although at this high temperature some scute abnormalities occur.
Research on terrapins is going on in the Carolinas and elsewhere up and down the East Coast. An unusual method for getting through the coldest part of the year has been found in New Jersey, where terrapins have been found congregating in sinkholes in mud during February. Terrapins may hibernate in their northerly ranges but do not seem to hibernate in their warmer southerly ranges.
Although terrapins are recovering from the exploitation of earlier this century, there are several threats to them. Crab nets cause many terrapin deaths by drowning. Seaside development has led to the loss of nesting beaches. Tire tracks from vehicles used on the sand pose a hazard to hatchlings: they get trapped in the tire tracks and can die before reaching water. Diamondbacks are protected in several states. Interestingly, in some places the native beachgrass is now also protected and removal of it is against the law. Researchers have found that the presence of the beachgrass lowers the temperature of the nesting areas and can affect the sex of the hatchlings.
We would like to part with this suggestion: do not buy terrapins in a pet store. This is a great way to end up with sick animals which will only be of grief to you. Let's kill the demand for pet store turtles and tortoises by not buying them. Through clubs such as CTTC learn how to take good care of your animals. Get new animals from other club members that have bred them or kept them for a long time. The result will be healthier and well cared for turtles.