Kemp’s Ridley: Biology, Natural History, and Conservation in Cape Cod

Despite their status as the rarest species of sea turtle (superfamily ​Chelonioidea​), the critically endangered Kemp’s ridley (​Lepidochelys kempi) strands by the hundreds and even thousands each winter on the beaches lining the Cape Cod Bay in Massachusetts. Weakened by cold stunning after being trapped in the cooling waters of the hooked bay, the appearance of so many Kemp’s ridleys every winter is no surprise to rehabilitation facilities in the American Northeast, including the National Marine Life Center in Buzzards Bay. The sea turtles which end up at New England facilities for intensive care associated with cold stunning are overwhelmingly juvenile sea turtles that did not migrate to southern waters before the winter brought rapidly dropping temperatures. Though almost all Kemp’s ridleys hatch on eastern Mexican beaches in the Gulf of Mexico, scientists attribute their presence in North Atlantic Ocean waters to the warm and powerful currents of the Gulf Stream, which may sweep juvenile sea turtles out to nutrient-rich northern feeding and nursery waters. This reflects a transitionary period between the pelagic hatchling stage, and the coastal juvenile and adult stage of their lifetimes (Ruckdeschel et. al, 2006, p. 69-70). Researchers remain largely uncertain about the distribution, population, life history, and behavior of the Kemp’s ridley sea turtle due to their small population and the inability to satellite tag hatchlings.

The Kemp’s ridley is the smallest extant sea turtle in the world, with adults typically growing no heavier than 45 kg, and no longer than 65 cm at the straight carapace length (U.S. Fish and Wildlife Service: South Florida Ecological Services Field, 1999, p. 1). The lifespan of the Kemp’s ridley is believed to be around 30 to 50 years, in accordance with other sea turtles; the ridley may reach sexual maturity between 10 and 17 years (Snover et al., 2007, p. 22). They are unique in shape compared to other sea turtle species due to their circular caparace: the Kemp’s ridley is generally as wide as it is long (U.S. Fish and Wildlife Service: North Florida Ecological Services Office, 2018). Between hatching and adulthood, the carapace and plastron of the Kemp’s ridley changes in color from a deep gray-black, to a paler gray-olive and creamy yellow, respectively (U.S. Fish and Wildlife Service, 1999). The geographic range of the Kemp’s ridley is principally limited in scope, as they tend to remain in warm waters along the eastern coasts of North and Central America, and the northern coast of South America (Seney, 2011, p. 241-242). Nesting females will migrate to the western Gulf of Mexico to lay their eggs, while hatchlings are rarely seen before the ages of two to 15 and are thought to inhabit miles-long sargassum lines in the open ocean, returning to coastal waters as juveniles once they have reached a larger size (Putnam et. al, 2013, p. 1). Up to 25% of juveniles are thought to migrate up the Atlantic coast using the Gulf Stream, while the rest remain in the Gulf of Mexico (Musick et. al 1997). Adults return to or remain in the Gulf, spending their life nearshore in shallow waters with muddy, sandy, and grassy bottoms and preying on swimming crabs, fish, jellyfish, and mollusks (National Wildlife Federation, n.d.). Their migration patterns, especially regarding breeding and feeding grounds, are inconsistent, individualistic, and unclear, and some juveniles have been found as far as the Iberian Peninsula (Covelo, et. al, 2016, p. 3-4).

The Kemp’s ridley was first recognized as a distinct species in 1880 after a long period of misidentification: for years, scientists believed it was a sterile hybrid between other species, a subspecies of the olive ridley, or simply a variety of loggerhead (Bowen et. al, 1991, p. 709). Yet the most significant discovery regarding the Kemp’s ridley was not its official nineteenth-century recognition, but footage filmed in Mexico forty years later, not to be seen by scientists until the 60s: over 40,000 sea turtles swarming onto a single beach in the state of Tamaulipas, Mexico in the middle of the day to nest (Taubes, 1992). The Kemp’s ridley is the only species known to nest at a single site by the thousands; the olive ridley also participates in mass-nesting events but will lay eggs solitarily, as well as globally in warm waters as far as India, Australia, and Vietnam (NOAA Fisheries, n.d.). A synchronous nesting phenomenon of this size, called an ​arribada – ‘arrival’ in Spanish – would not be seen again for the Kemp’s ridley, as fishing deadly gear, frequent poaching, and fossil fuel operations resulted in a “devastating decline with a 99.4% reduction in numbers of nests,” (U.S. Fish and Wildlife Service, 2020). In 1985, fewer than 250 observed females laid nests in Tamaulipas, a stunning fall off of their once abundant ​arribadas​ (1992, Kemp’s Ridley Recovery Team, p. 5).

The near-extinction of the Kemp’s ridley led to joint U.S. and Mexican efforts to conserve the species through a controversial head start program, effective nest protection efforts, and mandatory turtle excluder devices on fishing boats (Taubes, 1992). While the population is still critical, the number of nests laid in Mexico has increased to between 7,000 and 16,000 each year since 2005 (National Marine Fisheries Service Office and U.S. Fish and Wildlife Service, 2015, p. 18-19). The trend has not been steadily positive, however, as the years between 2010 and 2017 showed a sharp decline in nests at Tamaulipas. In 2018, the Chelonian Research Foundation and Turtle Conservancy published a study positing that this nesting setback was the result of declining carrying capacity in the Gulf of Mexico due to “degradation of the GoM [Gulf of Mexico] ecosystem, the exponentially increasing Kemp’s ridley population, and declining per capita availability of neritic (i.e., postpelagic) Kemp’s ridley food, including natural prey and scavenged discarded bycatch from shrimp trawling,” (Caillouet et. al, 2018, p. 123).

In spite of the discouraging results from this seven-year period, conservation efforts have continued and even improved, with the exception of the Texas-based head-start program, which was terminated in 1993 after 15 years due to uncertain results and rising costs (Houston Chroncile, 1993). Today, the National Park Service in Padre Island, Texas collects and incubates eggs laid on the island until they are ready for hatch and release. While 95% of Kemp’s ridley nesting takes place in Tamaulipas, solitary females have been observed nesting on Padre Island and in Veracruz, Mexico, with their hatchlings consequently imprinting on this secondary nesting site (National Park Service: Padre Island, 2018). The rescue and rehabilitation of each Kemp’s ridley is crucial in the struggle for the species’ survival. Facilities such as the National Marine Life Center, the New England Aquarium, and the Pittsburgh Zoo respond to hundreds of cold-stunning Kemp ridley strandings each year in the hopes of stabilizing and improving the odds of survival for this critically endangered species.

References

Bowen, B. & Meylan, A. & Avise, J. (1991). Evolutionary distinctiveness of the endangered Kemp’s Ridley sea turtle. ​Nature,​ p. 352. doi: 10.1038/352709a0.

Caillouet, C.W. & Raborn, S.W. & Shaver, D.J. & Putman, N.F. & Gallaway, B.J. & Mansfield K.L. (2018). Did Declining Carrying Capacity for the Kemp’s Ridley Sea Turtle Population Within the Gulf of Mexico Contribute to the Nesting Setback in 2010−2017? ​Chelonian Conservation and Biology.​ doi: 10.2744/CCB-1283.1

Covelo, P., Nicolau, L. & López, A. (2016). Four new records of stranded Kemp’s ridley turtle Lepidochelys kempii in the NW Iberian Peninsula. ​Mar Biodivers. doi: 10.1186/s41200-016-0079-5

Houston Chronicle Archives. (1993). U.S. Terminates “Head-Start” for Kemp’s Ridley Turtles. ​The Houson Chronicle.

Musick, J.A. & Lutz, P.L. (1997). Habitat Utilization and Migration in Juvenile Sea Turtles. The Biology of Sea Turtles, Vol 1.​ CRC Press.

National Marine Fisheries Service & U.S. Fish and Wildlife Service. (2015). Kemp’s Ridley Sea Turtle (Lepidochelys Kempii) 5-Year Review: Summary and Evaluation. repository.library.noaa.gov/view/noaa/17048

National Marine Fisheries Service & U.S. Fish and Wildlife Service. (2015). Olive Ridley Sea Turtle (Lepidochelys Olivacea) 5-Year Review: Summary and Evaluation. repository.library.noaa.gov/view/noaa/17036

National Park Service: Padre Island. (2018). The Story of the Kemp’s Ridley. nps.gov/pais/learn/nature/kempsridleystory.htm

National Wildlife Federation. (n.d.). Kemp’s Ridley Sea Turtle.

nwf.org/Educational-Resources/Wildlife-Guide/Reptiles/Sea-Turtles/Kemps-Ridley-Sea-Turtle

Putman, N. & Mansfield, K. & He, R. & Shaver, D. & Verley, P. (2013). Predicting the distribution of oceanic-stage Kemp’s ridley sea turtles. ​Biology Letters. ​doi: 10.1098/rsbl.2013.0345.

Ruckdeschel, C., Shoop, C., Hoyle, M., & Spotila, J. (2006). Kemp’s Ridley. ​Sea Turtles ofthe Atlantic and Gulf Coasts of the United States. U​ niversity of Georgia Press.

Seney, E. & Jr, A. (2011). Movement patterns of immature and adult female Kemp’s ridley sea turtles in the northwestern Gulf of Mexico. ​Marine Ecology Progress Series.​ doi: 10.3354/meps093

Snover, M. & Hohn, A. & Crowder, L. & Heppell, S. (2007). Age and growth in Kemp’s ridley sea turtles: Evidence from mark-recapture and skeletochronology.

Taubes, G. (1992). A Dubious Battle to Save the Kemp’s Ridley Sea Turtle. ​Science​.

U.S. Fish and Wildlife Service. (2020). News Release: Sea Turtle Nesting Season Begins on the Texas Coast. ​fws.gov/news/ShowNews.cfm?ref=sea-turtle-nesting-season-begins-on-the- texas-coast-&_ID=36537

U.S. Fish and Wildlife Service & National Marine Fisheries Service. (1992). Recovery Plan for the Kemp’s Ridley Sea Turtle. ​fws.gov/kempsridley/pdfs/kempsrid.pdf

U.S. Fish and Wildlife Service: South Florida Ecological Services Field Office Southwest Region. (1999). Kemp’s Ridley Sea Turtle Fact Sheet. ​South Florida Multi-Species Recovery Plan​.fws.gov/northflorida/SeaTurtles/Turtle%20Factsheets/kemps-ridley-sea-turtle.htm

NOAA Fisheries. (n.d.). Olive Ridley Turtle. ​fisheries.noaa.gov/species/olive-ridley-turtle

Research review paper written by summer intern, Sabrine B. Sabrine is a student at Williams College studying Environmental Science.