By Stacey Venzel
Hunting, habitat destruction, food shortage, global warming, pollution, litter, boating, fishing and tourism are the main concerns facing today’s turtles. These are almost solely human-related causes, an unsettling truth but also suggestive that altering human practices could drastically improve worldwide turtle survival.
“The consensus among turtle conservation biologists is that the Asian turtle trade is the primary threat to the world’s turtles,” cautioned ecologist and turtle biologist Whit Gibbons.
While turtle commerce is decimating Asian species, other factors are contributing to the global decline of turtle populations.
Revered for their unproven medicinal properties and food qualities, mature turtles and their eggs are being hunted by humans, drawing these reptiles closer to extinction. Annually, more than 12 million turtles are sold in China alone, thousands illegally imported from the United States. Vietnam exports anywhere from 2 to 18 tons of turtles every day.
In 2011, the IUCN reported a 90 percent increase in endemic Asian turtle species listed as critically endangered over a 10-year period. Species like Zhou’s box turtle were first discovered among stalls at Asian markets but since have never been found in the wild. Without the collaborative intervention of conservation organizations, species like the Yangtze giant softshell would already be extinct. As of 2011, only four individuals were left in the entire species, only one of which is female. Breeding to date has not been successful, possibly due to old age and a history of poor nutrition.
Globally, turtles are bought and sold for their commercial properties, including the popular hawksbill tortoise shell used in jewelry and oil from leatherbacks used to shellac boats. Though these species are now protected in many regions, hunting still occurs under the radar.
Turtles are losing feeding, resting and nesting habitats from natural and human-related activities. Wetland destruction for highways not only creates habitat loss but also confuses nesting females who now have a busy road to cross. Dredging—the process of mechanically clearing aquatic areas by digging harbors or canals—creates noise pollution, physically alters habitat, adds a geographic barrier and can injure shoreline and swimming turtles. Other forms of coastal alteration affecting turtles include building development, sea wall construction and artificial lighting. These can diminish nesting sites and prey availability, disorient turtles or change sand temperature that will alter sex ratios within a nest. In 2013, 38 loggerhead hatchlings in a nest of 120 hatched eggs were reportedly disoriented from a tennis court light in the Florida Keys, with 31 surviving hatchlings taken to the Turtle Hospital for recovery.
The rapid rate of global warming makes it difficult for animals to keep up with adaptations. Because temperature surrounding most turtle eggs determines if the hatchling is a boy or girl, rising temperatures could skew the sex ratio, creating an unsustainable population balance. Global warming also causes coral bleaching, with reefs being an important habitat for many sea turtles. Extreme weather patterns from drought to flood to severe hurricanes limits resources and destroys habitat.
Oil spills pose physiological and ecological dilemmas for turtles. Ingestion can cause organ damage while oil accumulation on the shell results in drag. Prey can die off and habitats can be destroyed, leading to displaced turtles and decreased growth rates—even death. After the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, hundreds of critically endangered sea turtles were taken to rescue facilities while others died at sea.
Toxic chemicals also suppress the immune system. An ugly, debilitating tumor disease called Fibropapillomatosis is found in sea turtles, predominantly greens. Studies link the ailment to nitrogen run-off accumulating in coastal sea grass beds, causing the toxin to infiltrate the turtle’s body upon ingestion of the contaminated algae.
Turtles are curious individuals who investigate with their mouths, often mistaking floating debris or brightly colored plastics for food. In addition to fishing gear, cigarette butts, plastic bags, balloons, soda rings and shoe soles have found their way into turtle digestive tracts, leading to infections and blockages. Turtles also get tangled in litter resulting in starvation, drowning, deformities and injuries.
BOATING AND FISHING
Propellers from boats and the hull strikes from joy-riding jet-skiers send many turtles to wildlife rescue centers with sometimes fatal or non-releasable injuries. Fishing gear causes flipper entanglements and hook ingestions from wayfaring or curious turtles. Drowning occurs when turtles are accidentally caught underwater in nets.
Prior to the 1994 federal law mandating the use of Turtle Excluder Devices (TEDs) in all commercial shrimping nets, an estimated 50,000 loggerheads and 5,000 critically endangered Kemp’s ridley sea turtles drowned annually in U.S. waters. It is estimated that it will take up to 70 years for these species to recover from the population blow.
Overfishing is depleting the food supply for aquatic turtles. This allows untargeted species to overpopulate, resulting in increased hatchling predation. Capture of fish is not the only threat to turtles. Lobster, crabs and algae are also collected commercially, creating competition that is hard to beat.
Harassment from snorkelers, divers and sunbathers deters sea turtles from entering into nesting, feeding or resting habitats. Tire tracks from ATVs are deep enough to trap a hatchling sea turtle on its journey to the open ocean. Even sandcastles create a barrier for baby turtles! Beach towels, chairs and umbrellas left on the beach block a nesting or hatching turtle’s path and can cover up undetected nests.
OTHER THREATS AND CONCLUSION
This list is, of course, not all-inclusive. For example, invasive species, weather events and cars also affect turtle populations. Overall, human interaction is easily the worst threat to turtles.
“Despite the number of eggs and turtles eaten by predatory mammals,” turtle biologist Carl Franklin summarized, “humans consume more turtles than any other vertebrate predators.”
As sea turtle biologists David Gucko and Karen Eckert wrote: “An animal that existed for 100 million years before dinosaurs walked the earth is now severely threatened by man.”
T Blanck, BD Horne, R Hudson, Et. Al., “Turtles in trouble: The world’s 25+ most endangered tortoises and freshwater turtles—2011,” MTC Printing, Inc., February 2011, http://cmsdata.iucn.org/downloads/top_25__turtles_in_trouble_2011_1.pdf
Meghan L Dailer, Migiwa Kawachi, Celia M Smith, Et. Al., “Eutrophication and the dietary promotion of sea turtle tumors,” PeerJ, September 30, 2014, https://peerj.com/articles/602.pdf.
Stephen Divers, Doug Mader, Current Therapy in Reptile Medicine & Surgery, (St. Louis, Elsevier Saunders, 2014), 296-301.
Karen Eckert, David Gulko, Sea Turtles: An Ecological Guide (Honolulu, Mutual Publishing, 2004), 68, 84-101.
Carl J Franklin, Turtles: An Extraordinary Natural History 245 Million Years in the Making (St. Paul, Voyageur Press, 2007), 38-40.
Whit Gibbons, “Are we really losing the world’s turtles?” Savannah River Ecology Laboratory, October 24, 2010, http://srel.uga.edu/outreach/ecoviews/ecoview101024.htm.
Whit Gibbons, Judy Greene, Turtle: The Animal Answer Guide (Baltimore, The John Hopkins University Press, 2009),100-107.
Stacey Venzel, “Lobster mini season brings 31 mini turtles,” The Turtle Hospital, July 26, 2012, http://www.turtlehospital.org/news/lobster-mini-season-brings-31-mini-turtles/.