Ecology of the Northeast US Continental Shelf

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Protected Species: Sea Turtles

sea turtle sighting maps
Green Turtle | Leatherback | Loggerhead | Kemp’s Ridley | Track Lines
Figure 1. Location of track lines and sightings of sea turtles detected during shipboard and aerial line transect cetacean abundance surveys conducted during 06 July to 06 September 1998 (track line length for the plane was 11,640 km and for the ship was 4,414 km), 28 Jul to 31 August 1999 (plane: 5,833 km; ship: 2,563 km), 19 July to 16 August 2002 (plane: 7,461 km), 12 June to 04 August 2004 (plane: 6,936 km; ship: 3,173 km), and 29 July to 25 August 2006 (plane: 10,676 km). The 100 m, 2000 m, and 4000 m depth contours are identified. Mouse over the species' name to see the corresponding map.

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

Loggerhead turtles

loggerhead turtle
Figure 2. Loggerhead sea turtle photographed off New England (photo courtesy of Matthew Weeks)

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.

Feeding

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).

Reproductive biology

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.

Human impacts

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).

Further Readings

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.

 

For more information, contact Heather Haas or visit the Protected Species Branch Webpage

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