Sea turtles

DEFINITION: Large marine reptiles found in all of the world’s oceans except the Arctic

All sea turtle species have long been listed as threatened or endangered, and they have been protected under international law. Nevertheless, their numbers have continued to decline, primarily because of human activities. Conservation efforts have helped stabilize the numbers of some species, but many populations remain at risk of extinction.

The seven extant species of sea turtles—leatherback, Kemp’s ridley, olive ridley, green, hawksbill, loggerhead, and flatback—differ substantially in size, food preferences, and nesting and feeding locations. The smallest, the Kemp’s ridley sea turtle, has a maximum weight of about 45 kilograms (100 pounds) and eats primarily crabs, whereas the leatherback sea turtle can reach 907 kilograms (2,000 pounds) and feeds on jellyfish and various other marine life. All of these species (except the flatback, for which insufficient data are available) are listed as threatened or endangered under the US Endangered Species Act (ESA) of 1973 and exist at a small fraction of their historical population size.

Female sea turtles lay eggs on warm oceanic beaches, and it is there that the animals are most vulnerable. Egg clutches and hatchlings are eaten by natural and introduced predators, and both eggs and adult turtles are poached by humans. Human-made alterations along nesting beachfronts, including buildings, seawalls, beach extensions, and other barriers, pose additional challenges to successful sea turtle reproduction. Further, hatchlings instinctively use reflected starlight or moonlight to find the ocean, and they can become confused by artificial light on land, migrate toward it, and perish.

New threats appear as the animals mature. Cold stunning, a change in temperature that disorients sea turtles, is a natural phenomenon that leaves their immune systems compromised and can lead to beach stranding. Human influences are the most perilous, however. Polluted waters, particularly in oceans with low water turnover, can cause the growth of potentially lethal fibropapilloma tumors on the eyes, skin, and internal organs of sea turtles. Turtles may mistake marine debris for prey, ingesting plastics and other materials that cause digestive failure; leatherback turtles, for example, sometimes ingest plastic bags that they mistake for their primary prey, jellyfish.

Global warming also affects the turtles, as the temperature of the sand in which eggs are laid strongly influences the sex of the developing turtles, with warmer temperatures favoring more female offspring. In January 2018, Michael P. Jensen and colleagues reported that as a result of rising temperatures, the Pacific green sea turtles that nest in the northern Great Barrier Reef region—one of the world's largest sea turtle populations—had been producing primarily female hatchlings for over two decades, with the result that the population was approximately 99 percent female (99.1 percent of juveniles, 99.8 percent of subadults, and 86.8 percent of adult turtles), and that "the complete feminization of this population is possible in the near future." Of the sea turtles originating in the cooler waters of the southern Great Barrier Reef, the sex disparity was less extreme but still showed a majority female population (approximately 65–69 percent). The discovery raised significant concerns that these important sea turtle populations will soon no longer be able to sustain themselves. The feminization of sea turtle populations due to global warming is a trend that researchers continued to identify as problematic in the early 2020s, in addition to other population challenges including decreased areas for marine foraging and decreased overall reproductive success.

Sea turtles must surface regularly to breathe, and they often drown when they are trapped in fishing nets or hooked as they take long-line fishing bait. Some efforts have been made to reduce sea turtle bycatch, including the use of turtle excluder devices in shrimp-trawling nets, but such endeavors are not required by all governments. In fact, several nations still have active sea turtle fisheries in spite of these species having long been listed as endangered by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

Sea turtles are also poached for their meat and even for their body parts. The shells of hawksbill turtles are used to make decorative items such as hair combs, jewelry, and handbags. The skin of some species is turned into shoes and purses. In many instances, unknowing tourists buy these illegal items only to have them confiscated when they return home.

All of these factors have contributed to a drastic decline in sea turtle numbers, from historical millions to as little as a few thousand (a greater than 99 percent reduction) by the early twenty-first century. Conservation efforts—including international programs aimed at reducing the accidental taking of turtles during fishing operations and at preserving, restoring, and monitoring nesting sites—have reversed this trend for some populations. For example, the numbers of Kemp’s ridley sea turtles in the wild, while still extremely low, have increased since the early 1990s, and local enforcement efforts in the Dominican Republic have almost eliminated the once-prevalent sale of turtle shell items there. Sea turtle products are still in high demand in many Asian countries, however, most notably Indonesia and Vietnam, and millions of turtles continue to be caught and killed as fishing bycatch. Given the global distribution of sea turtles, a worldwide effort will be required to stem and reverse the decline of their population numbers.

In 2014, after years of investigation, undercover officials in Vietnam discovered warehouses containing approximately seven thousand corpses of sea turtles that had been killed for sale; despite further efforts, no one was ever prosecuted for the crimes. In November 2017, it was reported that between three hundred and four hundred dead sea turtles had been discovered floating off of the coast of El Salvador, with the total estimated to be between three and four hundred; the olive ridley species seemed to be the most impacted. Similar events had occurred in that area in 2006 and 2013, and in both of those cases, it was concluded that the turtles had been killed by what is known as "red tide," a phenomenon in which chemical runoff such as pesticides leads to an overabundance of algal blooms that can be toxic to the turtles. A week after the 2017 discovery, scientists revealed that these deaths, too, were a result of red tide algal blooms; specifically, the turtles had consumed microalgae that contained saxitoxin, a potent paralytic neurotoxin. A surge of these red tide microalgae had been brought to the area by Tropical Storm Selma, which struck El Salvador in late October 2017. Because red tide is a naturally occurring phenomena, preventing it from happening is generally not an option. Scientists have posed options for treating its effects, including treating affected waters with natural microorganisms that would counter the negative effects of red tide. However, until future research provides plausible mitigation solutions, red tide will continue to remain a major threat to the sea turtle population.

Bibliography

Gibbens, Sarah. "Hundreds of Sea Turtles Found Dead." National Geographic, 3 Nov. 2017, www.nationalgeographic.com/animals/article/sea-turtle-hundreds-die-off-el-salvador-spd. Accessed 22 Aug. 2024.

"Hundreds of Sea Turtles Killed by Microalgae in El Salvador." DW, Deutsche Welle, 11 Nov. 2017, www.dw.com/en/hundreds-of-sea-turtles-killed-by-microalgae-in-el-salvador/a-41336854. Accessed 22 Aug. 2024.

Jensen, Michael P., et al. "Environmental Warming and Feminization of One of the Largest Sea Turtle Populations in the World." Current Biology, vol. 28, no. 1, pp. 154–59, doi:10.1016/j.cub.2017.11.057. Accessed 22 Aug. 2024.

Nuwer, Rachel. "Huge Haul of Slain Sea Turtles Tests Vietnam." National Geographic, 5 Aug. 2016, news.nationalgeographic.com/2016/07/wildlife-trafficking-sea-turtles-raid-vietnam/. Accessed 6 Dec. 2017.

Patrício et al. "Climate Change and Marine Turtles: Recent Advances and Future Directions." Endangered Species Research, vol. 44, pp. 363–95., doi.org/10.3354/esr01110. Accessed 22 Aug. 2024.

Safina, Carl. Voyage of the Turtle: In Pursuit of the Earth’s Last Dinosaur. Henry Holt, 2006.

"Sea Turtle." WWF, World Wildlife Fund, www.worldwildlife.org/species/sea-turtle. Accessed 22 Aug. 2024.

Spotila, James R. Sea Turtles: A Complete Guide to Their Biology, Behavior, and Conservation. Johns Hopkins UP, 2004.

Welch, Craig. "Sea Turtles are Being Born Mostly Female Due to Warming—Will They Survive?" National Geographic, 4 Apr. 2019, www.nationalgeographic.com/environment/article/sea-turtle-sex-ratio-crisis-from-climate-change-has-hope. Accessed 22 Aug. 2024.