For these reasons, the most common sea turtle population assessments have been made at nesting beaches (Schroeder and Murphy 1999). In addition, the oceanic habitat of juveniles is a major obstacle to studying immature stages of sea turtles (NRC 2010). They are difficult to study and monitor since they are broadly distributed, with nesting aggregations in various locations of the Gulf, have wide-ranging migrations, have long generation times and long life spans, and spend the majority of their lives at sea (Holder and Holder 2007 Witherington et al. Sea turtles that occur in the Gulf of Mexico are not randomly or evenly distributed spatially or temporally. The natural and anthropogenic threats that affect sea turtles in the Gulf of Mexico are also discussed, including sea turtle stranding, fisheries bycatch, and other types of less common but important impacts, such as boat strikes. The types of information summarized for sea turtles that use the Gulf of Mexico for at least some portion of their life cycle includes life history, distribution, and abundance location of nesting beaches and nesting numbers and habitat use and foraging area locations for the various life stages. This chapter describes Gulf of Mexico sea turtle populations prior to the Deepwater Horizon incident that occurred on April 20, 2010, especially with regard to abundance and distribution. The eastern half is influenced strongly by Caribbean inflow and has relatively clear water, while the western half is influenced by the turbid Mississippi River, incurs significant shrimp trawling pressure, and has thousands of oil and gas production structures (Hopkins-Murphy et al. The northern Gulf of Mexico can be divided oceanographically into the eastern half and the western half. 2012), and the nearshore waters of the Gulf provide critical foraging habitat for juvenile and adult sea turtles, as well as important mating and internesting habitat (Musick and Limpus 1997 Bolten et al. Sea turtles often spend their post-hatchling and early juvenile years in the pelagic Gulf of Mexico (Witherington et al. For example, protected beaches in Rancho Nuevo, Mexico and at Padre Island National Seashore (PAIS), Texas, are the major nesting beaches for the Kemp’s ridley, and loggerheads and green sea turtles nest on beaches at Dry Tortugas and Everglades National Parks in Florida. The Gulf of Mexico provides important sea turtle nesting habitat, and many Gulf of Mexico beaches where sea turtles nest have been protected as refuges and parks. While individuals of some species of sea turtles may nest on beaches and spend nearly their entire lives in the Gulf of Mexico, such as the Kemp’s ridley, others may only use the Gulf to nest, as a foraging area, or as part of their migration routes. Keywordsįive species of sea turtles are found in the Gulf of Mexico: the Kemp’s ridley ( Lepidochelys kempii), loggerhead ( Caretta caretta), green ( Chelonia mydas), leatherback ( Dermochelys coriacea), and hawksbill ( Eretmochelys imbricata). Threats to hawksbills in the Gulf of Mexico include the destruction of nesting habitat, their dependence on coral reefs-one of the world’s most endangered ecosystems-for food and shelter, and the continued illegal trade in hawksbill products. Large numbers of leatherbacks are captured each year in the Gulf as bycatch in pelagic longline fisheries. Leatherback sea turtles use the Gulf of Mexico as a foraging area and are often found in areas containing an abundance of jellyfish. Annual loggerhead nesting on Peninsular Florida beaches in both the Gulf of Mexico and Atlantic Ocean increased from 1979 through 2000 but declined from 2001 through 2009 however, loggerhead nesting on Florida Gulf and Atlantic coast beaches in 20 was similar to 2000 levels, indicating that the nesting population may undergo periods of variability that may affect long-term trend predictions. Kemp’s ridley has made a remarkable recovery from the brink of extinction in the early 1980s. Nesting, distribution, abundance, habitat, and life history information has been reviewed for each sea turtle species in the Gulf prior to the Deepwater Horizon oil spill in April 2010. Five species of sea turtles occur in the Gulf of Mexico: Kemp’s ridley ( Lepidochelys kempii), loggerhead ( Caretta caretta), green ( Chelonia mydas), leatherback ( Dermochelys coriacea), and hawksbill ( Eretmochelys imbricata).
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