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Marine Turtles in the Southeast


by
C. Kenneth Dodd, Jr.
National Biological Service
Five species of marine turtles frequent the beaches and offshore waters of the southeastern United States: loggerhead (Caretta caretta), green (Chelonia mydas), Kemp's ridley (Lepidochelys kempii), leatherback (Dermochelys coriacea), and hawksbill (Eretmochelys imbricata). All five are reported to nest, but only the loggerhead and green turtle do so in substantial numbers. Most nesting occurs from southern North Carolina to the middle west coast of Florida, but scattered nesting occurs from Virginia through southern Texas. The beaches of Florida, particularly in Brevard and Indian River counties, host what may be the world's largest population of loggerheads.
Marine turtles, especially juveniles and subadults, use lagoons, estuaries, and bays as feeding grounds. Areas of particular importance include Chesapeake Bay, Virginia (for loggerheads and Kemp's ridleys); Pamlico Sound, North Carolina (for loggerheads); and Mosquito Lagoon, Florida, and Laguna Madre, Texas (for greens). Offshore waters also support important feeding grounds such as Florida Bay and the Cedar Keys, Florida (for green turtles), and the mouth of the Mississippi River and the northeast Gulf of Mexico (for Kemp's ridleys). Offshore reefs provide feeding and resting habitat (for loggerheads, greens, and hawksbills), and offshore currents, especially the Gulf Stream, are important migratory corridors (for all species, but especially leatherbacks).
Most marine turtles spend only part of their lives in U.S. waters. For example, hatchling loggerheads ride oceanic currents and gyres (giant circular oceanic surface currents) for many years before returning to feed as subadults in southeastern lagoons. They travel as far as Europe and the Azores, and even enter the Mediterranean Sea, where they are susceptible to longline fishing mortality. Adult loggerheads may leave U.S. waters after nesting and spend years in feeding grounds in the Bahamas and Cuba before returning. Nearly the entire world population of Kemp's ridleys uses a single Mexican beach for nesting, although juveniles and subadults, in particular, spend much time in U.S. offshore waters.
The biological characteristics that make sea turtles difficult to conserve and manage include a long life span, delayed sexual maturity, differential use of habitats both among species and life stages, adult migratory travel, high egg and juvenile mortality, concentrated nesting, and vast areal dispersal of young and subadults. Genetic analyses have confirmed that females of most species return to their natal beaches to nest (Bowen et al. 1992; Bowen et al. 1993). Nesting assemblages contain unique genetic markers showing a tendency toward isolation from other assemblages (Bowen et al. 1993); thus, Florida green turtles are genetically different from green turtles nesting in Costa Rica and Brazil (Bowen et al. 1992). Nesting on warm sandy beaches puts the turtles in direct conflict with human beach use, and their use of rich offshore waters subjects them to mortality from commercial fisheries (National Research Council 1990).
Marine turtles have suffered catastrophic declines since European discovery of the New World (National Research Council 1990). In a relatively short time, the huge nesting assemblages in the Cayman Islands, Jamaica, and Bermuda were decimated. In the United States, commercial turtle fisheries once operated in south Texas (Doughty 1984), Cedar Keys, Florida Keys, and Mosquito Lagoon; these fisheries collapsed from overexploitation of the mostly juvenile green turtle populations. Today, marine turtle populations are threatened worldwide and are under intense pressure in the Caribbean basin and Gulf of Mexico, including Cuba, Mexico, Hispaniola, the Bahamas, and Nicaragua. Subadult loggerheads are captured extensively in the eastern Atlantic Ocean and Mediterranean Sea. Thus, marine turtles that hatch or nest on U.S. beaches or migrate to U.S. waters are under threats far from U.S. jurisdiction. Marine turtles can be conserved only through international efforts and cooperation.
Information on the status and trends of southeastern marine turtle populations comes from a variety of sources, including old fishery records, anecdotal accounts of abundance, beach surveys for nests and females, and trawl and aerial surveys for turtles offshore. Surveys for marine turtles are particularly difficult because most of their lives are spent in habitats that are not easily surveyed. Hence, most status and trends information comes from counting females and nests. Few systematic long-term (more than 10-20 years) surveys have been conducted; the most notable are the nesting surveys at Cumberland Island and adjacent barrier islands in Georgia (T.H. Richardson, University of Georgia, unpublished data), and beaches south of Melbourne in Brevard County, Florida (Ehrhart et al. 1993). Beach monitoring is fairly widespread in many areas of the Southeast, but coverage varies considerably among beaches and field crews. The only long-term sampling of lagoonal or bay populations occurs at Mosquito Lagoon and Chesapeake Bay, although short-duration surveys have sampled Florida Bay, Pamlico Sound, and Laguna Madre. Trawl surveys of inlets and ship channels and aerial surveys of offshore waters have been undertaken periodically.

Loggerhead and Green Turtles
Fig. 1 a. Loggerhead nest totals in south Brevard County, Florida, 1982-93. b. Green turtle nest totals in south Brevard County, Florida, 1982-93. From Ehrhart et al. (1993).
The number of turtles nesting fluctuates substantially from one year to the next, making interpretation of beach counts difficult. The Florida nesting populations of loggerheads and green turtles appear stable based on 12 years of data from east-central Florida (Ehrhart et al. 1993; Fig. 1). The green turtle nesting population may be increasing because of protective measures over the last 20 years or so, although the number of nesting females is still low (assuming 3-5 nests per female). North of Florida, nesting loggerhead numbers are declining 3%-9% a year in Georgia and South Carolina (National Research Council 1990). The main cause of mortality is drowning in shrimp and fish nets (National Research Council 1990), although turtle excluder devices (TEDs; Fig. 2a) have helped reduce mortality (Fig 2b; Henwood et al. 1992). Large juveniles are most susceptible to drowning, and this is a critical life stage in the population dynamics of sea turtles (Crouse et al. 1987).
Few data are available for lagoonal turtles, although similar numbers have been captured in Mosquito Lagoon and Chesapeake Bay from one year to the next. Loggerhead and green turtle populations, both adult and subadult, have undoubtedly declined from historical levels because of beach development and disturbance, the collection of eggs, and destructive fishing practices. Most high-level nesting occurs on the remaining undeveloped or lightly developed beaches. Even there, plans for development and disorientation from lights pose serious and continuing problems.

Kemp's Ridley
At one time, more than 40,000 females nested in a single mass nesting (termed "arribada") in Tamaulipas, Mexico. Several arribadas probably occurred each year. Since 1947 a drastic reduction in the number of nesting females caused the near extinction of this species (Ross et al. 1989). Today only about 400-500 turtles nest each year despite stringent protection of the nesting beach. The principal threat to this species is incidental take during shrimp fishing.

Fig. 2a. Schematic of a turtle excluder device (TED). From Watson et al. (1986).

Leatherback and Hawksbill
The leatherback and hawksbill are rare nesters in the southeastern United States, but offshore waters are important for feeding, resting, and as migratory corridors. The status and trends of these species in U.S. offshore waters are unknown, although they are severely threatened throughout the Caribbean. Leatherbacks are taken by trawlers or are otherwise entangled in nets. Hawksbills are sought, especially in Cuba, for their shell, which is used for jewelry and similar items. The solitary nesting habits of hawksbills make them particularly difficult to monitor.

Fig. 2b. Incidental capture of sea turtles in inshore and offshore waters of the United States before and after regulations requiring the use of TEDs on the U.S. shrimp fleet. From Henwood et al. (1992).

Summary
Sea turtles are threatened by beach development, light pollution, ocean dumping, incidental take in trawl and longline fisheries, disease (especially fibropapillomas), and many other variables. Because sea turtles are long-lived species, trends are difficult to monitor. Present methods of beach monitoring are extremely labor-intensive, expensive, and biased toward one segment of the population. Very little is known about marine turtle life-history and habitat requirements away from nesting beaches, and virtually nothing is known about male turtles. Because the effectiveness of measures aimed at protecting turtles may not be seen for decades, known conservation strategies should be favored over unproven mitigation schemes. Acquiring nesting habitat should be encouraged. One of the most important management measures to protect sea turtles, especially of the juvenile and subadult size class, in the southeastern United States, Caribbean, and western Atlantic Ocean is the use of TEDs to minimize drowning in commercial fisheries. Mature females should also be protected because of their importance to future reproduction. Researchers need to identify migratory routes, feeding and developmental habitat, and ways to minimize adverse impacts during all life-history stages.
For further information:
C. Kenneth Dodd, Jr.
National Biological Service
Southeastern Biological Science Center
7920 N.W. 71st St.
Gainesville, FL 32653
References
Bowen, B., J.C. Avise, J.I. Richardson, A.B. Meylan, D. Margaritoulis, and S.R. Hopkins-Murphy. 1993. Population structure of loggerhead turtles (Caretta caretta) in the northwestern Atlantic Ocean and Mediterranean Sea. Conservation Biology 7:834-844.

Bowen, B.W., A.B. Meylan, J.P. Ross, C.J. Limpus, G.H. Balazs, and J.C. Avise. 1992. Global population structure and natural history of the green turtle (Chelonia mydas) in terms of matriarchal phylogeny. Evolution 46:865-881.

Crouse, D.T., L.B. Crowder, and H. Caswell. 1987. A stage-based population model for loggerhead sea turtles and implications for conservation. Ecology 68:1412-1423.

Doughty, R.W. 1984. Sea turtles in Texas: a forgotten commerce. Southwestern Historical Quarterly 88:43-70.

 Ehrhart, L.H., W.E. Redfoot, R.D. Owen, and S.A. Johnson. 1993. Studies of marine turtle nesting beach productivity in central and south Brevard County, Florida, in 1993. Report to Florida Department of Environmental Protection, Institute of Marine Research, St. Petersburg. 20 pp.

Henwood, T., W. Stuntz, and N. Thompson. 1992. Evaluation of U.S. turtle protective measures under existing TED regulations, including estimates of shrimp trawler related mortality in the wider Caribbean. National Oceanic and Atmospheric Administration Tech. Memorandum NMFS-SEFSC-303. 15 pp.

National Research Council. 1990. Decline of the sea turtles. Causes and prevention. National Academy Press, Washington, DC. 259 pp.

Ross, J.P., S. Beavers, D. Mundell, and M. Airth-Kindree. 1989. The status of Kemp's ridley. Center for Marine Conservation, Washington, DC. 51 pp.

Watson, J.W., J.F. Mitchell, and A.K. Shah. 1986. Trawling efficiency device: a new concept for selective shrimp trawling gear. Marine Fisheries Review 48:1-9.


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