The Ecology of Sea Turtles in Virginia

The Ecology of Sea Turtles in Virginia

From the time Jack Musick started at the Virginia Institute of Marine Science (VIMS) in 1967, he has noted the large number of turtles stranded along the Chesapeake Bay, especially in the Tidewater area. After about 10 years at VIMS and because of special interest from a student, Jack became very involved in finding out why strandings occurred and joined the campaign to save these endangered turtle species. In 1960, there were an estimated 60,000 turtles in the Chesapeake Bay. By the 1980s, there were only 300. The recovery effort has now increased numbers to 15,000. Strandings are mostly juvenile males after a long hard migration. They become sick and starve and are found along the Chesapeake Bay. Some level of stranding is a natural occurrence.

The Chesapeake Bay is the northernmost range for turtles such as Loggerheads, Leatherbacks, and Hawksbills. They enter the bay when the temperature of the water rises to about 18 degrees Celsius. Turtles winter in North Carolina, Florida, the Caribbean, and Mexico. Some species, like the Kemp's Ridley, travel very infrequently north into the Chesapeake Bay. This is the smallest, most endangered species that weighs 60 lbs at maturity. The Hawksbill turtle, the source of tortoise shell, lives mostly in tropical coral reefs. Researchers are studying this turtle at the Buck Island Reef National Monument in St. Croix.

The Leatherback turtle, largest of the turtles, was found stranded five times this year. The average weight found was 500 to 800 lbs. The largest found weighed 2000 lbs. Loggerhead turtles are the most abundant species found stranded. Most of the turtles found were juvenile males about 70 centimeters in diameter and weighing about 100 pounds. Loggerhead turtles used to feed on horseshoe crabs along the shallows of the Bay. Since the population of horseshoe crabs has been drastically reduced, loggerheads now feed on fish, which are harder to catch.

During the last 20 years of conservation, scientists have learned the main causes of turtle deaths are due to the fishing industry and reduction of safe beaches for nesting. Netting from shrimp trawlers and pound enclosures have caused the greatest mortality of juvenile and adult turtles. Turtles often die when caught in the larger mesh nets. When the turtles first arrive and the water is still cold, turtles swim close to the surface and tend to swim into pound enclosures. They are trapped like fish into smaller net enclosures. Improved fishing practices are helping turtles recover. Since 1989 trawling within three miles of the coast has been eliminated in the Chesapeake Bay. Fisherman still need to be aware of ways to reduce mortality in pound nets. Turtles are frequently found in pound nets in part because it provides easy food. Some 'trap happy' turtles have found their way into pound nets 7 or 8 times.

VIMS researchers have been studying the number, size, and habits of turtles in the Bay. Radio/sonic tracking devices are attached with epoxy to the shells of turtles to determine how much time they spend on the surface and deep in the water. Tracking found that turtles spend 95% of their time underwater. Small planes are used to sight large turtles swimming on the surface. Using trigonometry, the number of turtles were estimated at 5,000 to 10,000 in the Chesapeake Bay in the summer.

Turtles have been tracked to North Carolina, Florida, and the Gulf of Mexico. It takes a migrating turtle about 26 days to swim from Yorktown to Cape Hatteras. One female turtle has been tracked for 3 years traveling back and forth from North Carolina to Tangier Island and the mouth of the Potomac River.

Turtles grow slowly and mature at about 25 years of age. Females lay about 120 eggs in a nest on the beach at night. Eggs hatch in 60 days. Along the beaches at Back Bay Virginia, US Fish and Wildlife Service personnel move eggs into cylinder cages to prevent raccoons from digging them up. Beach traffic scares turtles from nesting and tire ruts catch hatchlings on their way to the water. Hatchlings navigate by light to the water. The sea reflects light at night. Lights from buildings have confused hatchlings and so one measure of conservation in Florida has been to limit lights near beaches. Only 3 % of hatchlings survive the first year of life.

Hatchlings in warmer areas such as Florida have a much better chance of survival than do those is cooler water like in Virginia. The temperature of the sand determines survival and determines sex of the hatchlings. 29 degrees C. produces 50% males and 32 degrees produces females.

Editor’s note: Dr. Musick is on staff in the Fisheries Science Department of the VIMS of the College of William and Mary. He has a Phd. from Harvard University and is an expert on the ecology of sharks and turtles. From the September general meeting presentation. Reported by Adrienne Frank.