Ecology of the Northeast US Continental Shelf
Protected Species: Sea Turtles
Sea turtles are distributed throughout the world ocean except in polar regions. Sea turtles are one of the few groups of marine reptiles. Like other reptiles, they are cold blooded and breathe air. Sea turtles are extremely well adapted to life in the marine environment and are capable of undertaking extensive migrations. They live most of their lives in the ocean but adult females must return to beaches for nesting and laying their eggs.
Five species of sea turtles can be found in the Northeast U.S. Continental Shelf Large Marine Ecosystem (NES LME) including green, hawksbill, Kemp’s Ridley, leatherback, and loggerhead turtles. Observed distribution patterns of sea turtles in the NES LME for these species (except for hawksbill) are depicted in Figure 1. All five of the species occurring off our coast are listed under the Endangered Species Act as Threatened or Endangered (Table 1). Important threats to sea turtles include disruption of nesting sites, incidental capture in fishing gear, and ship collisions (described further below). The latter two impacts are of special concern for species occurring in the NES LME.Table 1. Endangered Species Act (ESA) listing status for sea turtles found in the NES LME and in adjacent offshore waters.
|Common name||Scientific name||ESA status|
|Loggerhead turtle||Caretta Caretta||Threatened|
|Kemp's ridley turtle||Lepidochelys kempii||Endangered|
|Leatherback turtle||Dermochelys coriacea||Endangered|
|Green turtle||Chelonia mydas||Endangered/Threatened|
|Hawksbill turtle||Eretmochelys imbricate||Endangered|
In the following, we focus on the Loggerhead turtle (Caretta caretta (Figure 2) to illustrate important aspects of the biology and ecology of sea turtles and to highlight some of the special conservation concerns for this important taxonomic group.
Loggerhead turtles can attain a shell length of nearly one meter and weigh over 100 kg. They are long lived and do not reach maturity until approximately 20-30 years. Loggerheads mate during late March through early June with egg laying taking place on beaches throughout the summer in nesting areas. Loggerheads have a reddish-brown upper shell. Scales on the top and sides of the head and top of the flippers are also reddish-brown with yellow borders. The neck, shoulders and limb bases are dull brown on top and medium yellow on the sides and bottom. The lower shell is also medium yellow.
Range and population level
Loggerhead turtles are found throughout temperate and tropical regions of the Atlantic, Pacific, and Indian Oceans, inhabiting continental shelves, bays, estuaries, lagoons. as well as off the continental shelf. In the Atlantic, the loggerhead turtle's range extends from Newfoundland to as far south as Argentina. However, loggerhead nesting sites are concentrated on the western Atlantic and Indian oceans. Only two loggerhead nesting beaches are reported to have greater than 10,000 females nesting per year and one of these is located in South Florida. Smaller nesting concentrations (1-10 thousand females) are found from Florida through North Carolina (U.S.) and it is individuals from these breeding groups that are found seasonally north of Cape Hatteras in the NES LME. Adult loggerheads may undertake long distance migrations between foraging areas on our shelf and their nesting beaches.
Adult and older juvenile loggerhead turtles feed principally on bottom dwelling invertebrates (notably mollusks and crustaceans). Jellyfish and squids are also eaten by larger turtles but these invertebrates are especially favored by early juvenile stage loggerheads. Post-hatchling loggerheads feed on larger plankton species associated with floating algae (including Sargassum weed).
In the United States, the nesting season extends from about May through August. Nesting occurs primarily at night. Adult females return to nest every 2-3 years (although the range is 1-7 years). Loggerheads are known to nest from one to seven times within a nesting season (averaging 4.1 nests per season) at intervals of approximately 14 days. The average number of eggs laid is about 100 to 126 along the southeastern United States coast and the eggs can take from 45 to 95 days to hatch, depending on incubation temperatures (averaging from 55 to 60 days for most batches of eggs in Florida). Hatchlings generally emerge at night.
Loggerhead sea turtles (and other sea turtles) are threatened by impacts on nesting sites, due to natural processes such as beach erosions and to human alteration of beach habitats including placement of breakwaters, beach armoring and beach nourishment, and beach cleaning. Nesting and hatching is adversely affected by artificial lighting on beaches, including increasing the risk of predation on hatchlings. Increased human activity (beach use by bathers, recreational vehicle use and traffic) are exacting a toll on sea turtles in many areas. Poaching of eggs by humans remains a problem in some areas. Changes in beach ecosystems through the introduction of exotic dune and beach vegetation disrupt nesting as well.
Sea turtles, including loggerheads, are vulnerable to impacts in the marine environment ranging from oil and gas operations, dredging activities, pollution, fishing operations, boat strikes, power plant entrapment, underwater explosions, and offshore artificial lighting to ingestion of marine debris and poaching. Collisions with boats (recreational and commercial) are a significant problem with up to 9% of stranded sea turtles showing evidence of propeller injuries or ship strikes.
Because sea turtles require air to breathe, they are vulnerable to drowning if they are caught by or otherwise entangled in fishing gears of various types including dredges, trawls, seines, hooks, and gill nets, pound nets, and traps. They may also be entangled in discarded or lost fishing gear (so-called ghost gear).
National Research Council. 2010. As Assessment of Sea-Turtle Status and Trends: Integrating Demography and Abundance. The National Academies Press, Washington, D.C. 162 pp.
Shoop, R. 1987. Sea turtles. Chapter 33. In: (Backus, RH, ed.) Georges Bank. Cambridge, MA: MIT Press; pp. 357-358.
Shoop, R. and R. Kenney (1992) “Seasonal distributions and abundances of loggerhead and leatherback sea turtles in waters of the Northeastern United States”, Herpetological Monographs, vol 6.
Thompson, N. (1988) “The status of loggerhead, Caretta caretta, Kemp’s ridley, Lepidochelys kempi, and green, Chelonia mydas, sea turtles in US waters”, Marine Fisheries Review, vol 50, no 3.