Snapping Turtles
by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station
What Nantucket visit or idyllic summer is complete without a trip down to Second Bridge off Madaket Road to catch a snapping turtle? All you need is string, a chicken leg, and a large net, plus some bravery. There are some big snapping turtles in there! For a while there was even a geocache (find out what that is at www.geocaching.com) located under the water at that spot, aptly named “Snap!”
What precisely are these denizens of the depths and what is their role in the ecology and ecosystem of the island? First, we should mention that we have three different species of turtles on Nantucket who all love to be near freshwater, the spotted turtle (Clemmys guttata), the painted turtle (Chrysemys picta), and the common snapping turtle (Chelydra serpentina). There is some discussion as to whether we have any of the states’ other species (ten in total) such as the eastern box turtle. The Nantucket Conservation Foundation has conducted several years of very interesting telemetry research on the spotted turtle which has recently been delisted from the Commonwealth's List of Endangered, Threatened and Special Concern Species. A video of their research is at www.plumtv.com/videos/nantucket-ncf-scientific-research/index.html. They are checking out the range and behavior of the snapping turtle's much cuter yellow polka-dotted cousin, but that does not mean that the snapping turtle is a boring creature at all. I know for students paddling around the freshwater pond at the Field Station, that the mere mention of the monstrous snappers keeps them in the rowboat and probably has contributed to more than a couple of nightmares.
Turtles, a generic name for the group of reptiles which includes tortoises and terrapins, are reptiles most of whose body is shielded by a special bony shell developed from their ribs. All extant, or living, turtles are members of the order Testudines, which includes both living and extinct varieties of turtle.
The etymology of the Order name Testudines and the Family Chelydridae are intertwined in a strange chicken versus the egg fashion. The term “chelys” is Greek (Latin: “testudo”) for “turtle” and was originally known as a stringed musical instrument that had a convex back of tortoiseshell or of wood shaped like the shell. The word “chelys” was used to specifically refer to the oldest lyre of the Greeks, which was said to have been invented by Hermes. According to the Homeric Hymn to Hermes (475), he was attracted by sounds of music while walking on the banks of the Nile, and found they were coming from the shell of a tortoise across which were stretched tendons which vibrated in the wind. The word “chelys” continued to be used for a variety of stringed instruments. The term Chelydra was formed by combining “chelys” with “hydros” for “ water serpent” and “serpentina” is Latin for “snake-like” referring to the snake-like neck.
There are two major groups of turtles: sea turtles, which grow to large sizes and live in the oceans in the temperate and tropical regions of the earth, and fresh-water turtles. Fresh-water turtles which spend the majority of their time on the land are generally called tortoises. In the United Kingdom, aquatic fresh-water turtles are known as terrapins. Fresh-water turtles are generally much smaller, ranging in size from a few centimeters to a few feet long. All turtles have a protective shell around their bodies. The top part of their case is called the carapace, the underside is the plastron, and the two are connected by the bridge. Even though they spend large amounts of their lives underwater, turtles are air-breathing reptiles, and must surface at regular intervals to refill their lungs with fresh air. They also spend part of their lives on dry land.
The common snapping turtle is not the same critter as the alligator snapping turtle (Macrochelys temminckii), which is even more primordial in appearance and larger. Both species are endemic to the Northern hemisphere and are in the same family, the Chelydridae. The oldest snapping turtle fossil relatives were previously thought to be approximately 65-70 million years old. Those ancient species living in the Paleocene and Late Cretaceous eras had thicker carapaces (top shells) to help ward off the attacks of turtle-eating relatives of the crocodile. Just a few months ago, an article that maps the discover of the missing link for turtles was published in the scientific journal “Nature” (November 27, 2008) by Li et al. The researchers discovered a primitive turtle from the Late Triassic, some 220 million years ago, which was about 40 cm in length and preserved in sedimentary deposits in what is now southwestern China. These fossils are examples of a new species of a very early turtle, named Odontochelys semitestacea. This discovery is helping to answer how turtle shells developed because prior to that, all fossils were essentially intact with the whole armored shell already formed. Now we can start to understand how turtles developed their amazingly protective shell.
Wikipedia tells us that the common snapper's natural range extends from southeastern Canada, west to the Rocky Mountains, and south through Mexico, and as far south as Ecuador. Snapping turtles are noted for their powerful beak-like jaws and belligerent disposition. They have a muscular build with ridged shells that may measure from 35 cm long in Chelydra species to some 66 cm long in the alligator snapping turtle (Macroclemys temmincki). The latter species is the largest freshwater turtle in the world, weighing up to 100 kg. The common snapping turtle (Chelydra serpentina serpentina) and its subspecies are much smaller, weighing up to 17 kg in weight. The alligator snapping turtle has a much spikier head and body while the common snapping turtle's body is more smooth and less “dinosaur-ish”. In some areas, alligator snapping turtles are hunted for their meat, which is a popular ingredient in turtle soup. Both species can survive for close to 50 years in captivity, while the lifespan of wild individuals is estimated to be around 30 years.
Snapping turtles have long spiked tails and necks which can reach two thirds the length of their shells, making handling dangerous. They cannot fully retract their head and appendages, relying on fierce displays when aggravated. Their snapping jaws and sharp claws are capable of inflicting serious injury: these turtles are best left alone. They are poorly suited to terrestrial locomotion, spending most of their time in ponds, shallow lakes, and streams; they forgo regular basking. Rare forays onto land occur in June and July when females lay their spherical eggs. Some may inhabit brackish environments, such as estuaries.
All snapping turtles are important scavengers, but will also actively hunt fish, frogs and small mammals. The alligator snapper has a flesh-red, worm-like tongue which it uses to lure fish into its mouth. Young turtles tend to forage actively, while adults tend to lie in ambush. Many individuals can be found within a small range; snapping turtle density is normally related to the amount of available food. The diet of wild young snappers consists mainly of snails, worms, leeches, insects, larvae, small fish and water plants. Adult snappers eat larger prey such as frogs, fish, newts, tadpoles, toads, crayfish, and even snakes, small turtles, small mammals, and young waterfowl like ducklings and goslings. We have seen several “peg-leg” seagulls at the field station, which shows you exactly how dangerous the snappers lurking underwater can be; sometimes a simple dip in fresh water is just not worth it for the birds!
This species mates from April through November, with their peak laying season in June and July. Male snapping turtles are larger than females, and hence courtship is not elaborate (no need for roses or convincing, I guess). The female can hold sperm for several seasons, utilizing it as necessary, which you think would teach the males to be more elaborate in their courtship. There is some “dancing” involved because they tend to communicate to mates with leg movements while facing each other. Females travel over land to find sandy soil in which to lay their eggs, often some distance from the water, up to a mile away has been recorded in some instances. After digging a hole, the female typically deposits 25 to 80 eggs each year, guiding them into the nest with her hind feet and covering them with sand for incubation and protection. Incubation time is temperature-dependent, ranging from 9 to 18 weeks. In cooler climates, hatchlings may overwinter in the nest, although that doesn't always insure survival in a frigid winter.
Females produce, at most, one clutch per year, with some females apparently skipping some years. They lay spherical, hard-shelled eggs that average 1.1 in (2.8 cm) in diameter and 0.4 oz (11 g) in mass. Egg size does not seem to increase significantly with female size. Clutch size is highly variable, ranging from six to 109, averaging about 32 across the range, and is positively correlated with female body size, latitude, longitude, and elevation (the largest clutches are laid in western Nebraska). Incubation in nature requires 55–125 days (more typically 75–95) depending on nest temperature (development being faster at higher temperatures) and geography (incubation times being longer in the south). Hatchling snapping turtles usually emerge from the nest in the late summer and fall (August to October) and move directly to the water. Hatchlings in northern populations that do not emerge in the fall before the onset of cold weather almost never survive the winter, probably because of their low tolerance of subfreezing body temperatures. High and low incubation temperatures result in the production of all-female offspring, and intermediate temperatures produce all males. Because their clutches are so large, eggs in different parts of the same nest may produce different sex ratios, e.g., all females at the top and all males at the bottom.
The picture shows a female at the field station laying eggs along the roadside. The process took about two hours. The “choice” nesting locations for the typical Nantucket snapper are somewhat unfortunate as they tend to be near pedestrians and cars and give the new hatchlings a boatload of obstacles to overcome when they hatch and make their way to the water. Sad to say, I have found more than a fair share of tiny pancaked and dessicated hatchlings. Now, when possible, we mark the nest site and keep an eagle eye out for the hatchling's emergence. Of course, many predators are doing the same thing and hawks and snakes are the main predators who would most enjoy a crunchy snack. The eggs and hatchlings of snapping turtles may be eaten by other large turtles, great blue herons, crows, raccoons, skunks, foxes, bullfrogs, water snakes, and large predatory fish. However, once snapping turtles become larger, there are few animals that prey on them. Snapping turtles may be active at any time of day or night, but nocturnal activity is rare in northern populations. These turtles hibernate at temperate latitudes, but presumably are active year-round at more tropical sites. They occasionally bask out of water.
This Massachusetts Division of Fisheries and Wildlife site has some tips for handling turtles including the infamous finger nabbing snapping turtle (www.mass.gov/dfwele/dfw/nhesp/conservation/herps/turtle_tips.htm). It is important to note that many turtles can exhibit a behavior called “site fidelity,” which is actually relatively common in many species and simply means that the mother will come back to the same location to lay her eggs each year. They caution that if you must move a snapping turtle, use a broom and plastic tub (or box) to capture them, by sweeping them into the tub. This is the best method because snapping turtles are fast and have very powerful jaws (can sever fingers). An alternative method is to pick them up by grabbing the tail and then sliding one hand underneath the turtle to support the body. Lift it like a platter, steering with the tail. A snapping turtle can reach your hands if you lift it by the sides of its shell, but they cannot reach your hand directly under the shell. Do not lift them only by the tail; that can injure their spine. Once captured take them to the nearest body of water (e.g. vernal pool, pond, stream, etc.). For some reason, a very large (1 foot in diameter and at least 30 pounds) snapping turtle showed up in my family's backyard in Northeastern Oklahoma one summer. That was one severely lost turtle. I learned quickly that a shovel was a great way to move a turtle that big although a large stick works too. You can wave the stick in front of the jaws, they will snap at it and grab it, then hold on for dear life while you drag them to a safer spot (well, safer for you).
There are some human interactions that can reduce snapping turtle populations, namely, elimination or fragmentation of wetland areas, over-harvesting the alligator snapping turtles for food, road construction and the associated automobile carnage, and capturing turtles for pets (or releasing them in areas they should not be in which has caused them to pop up in California). So admire them down at Second Bridge, at the Field Station, or while crossing the road (and gently help them across); your fingers and the population will thank you! To learn more, check out this cool website that is also fun for kids: www.chelydra.org/index.html
