Nearly 200 Kemp's ridley (Lepidochelys kempii), green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtles washed up along the Louisiana, Mississippi and Alabama coasts in April, the most deaths in one month since record keeping began in 1986. And 100 green sea turtles were found dead on the coast of Uruguay in the first three months of this year. The latter group died from ingestion of trash, primarily plastic. Most of the former showed signs of drowning in trawl nets.

Both events are the latest pointing to a larger trend in which pollution and fisheries practices pose significant obstacles worldwide to these endangered animals' recovery. Scientists who have been sounding the alarm for decades see these latest tragedies as the tipping point that may finally translate science into action.

Kemp's ridleys, which live primarily in the Gulf of Mexico, are listed as endangered under the Endangered Species Act. In the recently ended 2011 season, U.S. National Park Service scientist Donna Shaver recorded 192 ridley nests on the Texas coast (95 percent of ridley nests occur in northern Mexico, where a record high of 12,143 nests were recorded in 2006). Green turtles, also endangered in the U.S., range widely in tropical and subtropical waters, generally between 30 degrees north and 30 degrees south latitude, with an estimated 200 to 1,100 nesting annually in Florida. Loggerheads, currently listed as threatened, are found throughout temperate and tropical regions of the Atlantic, Pacific and Indian oceans, with an estimated 60,000 to 90,000 nests per year and declining. The four other species of sea turtles worldwide—leatherback, hawksbill, olive ridley and flatback—all are listed as either endangered or threatened, and the first three are also found in U.S. waters.

Deadly Seas
Sea turtles die of drowning or injury when caught on hooks, entangled in fishing line or trapped in fixed nets or trawls. For instance, the National Marine Fisheries Service estimates commercial shrimping in the Gulf of Mexico killed 5,365 turtles in 2009. And mid-Atlantic trawl fisheries capture an average of 770 sea turtles each year, says Elizabeth Wilson, a marine wildlife scientist at the nonprofit Oceana.

Sea turtles and commercially targeted fishes frequently gather in the same places, which results in turtles being caught as bycatch, says biologist Larry Crowder of Duke University. In fact, a 2004 paper Crowder and his colleagues published in Ecology Letters suggests that loggerhead and leatherback (Dermochelys coriacea) sea turtles face between a one half and two thirds chance of encountering longline gear every year. Sea turtle species also spend time near shore, where they can become bycatch of subsistence or artisanal fishers. A 2007 case study led by biologist Hoyt Peckham at University of California, Santa Cruz, suggests that these small-scale fisheries also represent a significant threat.

Turtles that elude hooks, nets and lines still face the risk of ingesting or becoming entangled in plastic debris floating at the sea surface or lower in the water column. Plastic washed up on beaches can interfere with nesting and hatching.

The Algalita Marine Research Foundation has documented plastic in all five of the Earth's large ocean gyres, says Marcus Eriksen, director of project development. In the North Pacific, foundation scientists have measured plastic particles at up to six times the volume by weight of zooplankton. Ingested plastic is also now found in the bodies of most marine organisms, where it can cause injury, nutritional deficiency and death, primarily by blocking their intestinal tracts—the fate of many of those Uruguay turtles.

Plastics can become a problem even before they are ingested. They start off containing potentially toxic chemicals such as nonylphenol and bisphenol A (BPA) and pick up more in seawater. A study in 2010 by Marc Ward of Sea Turtles Forever  and researchers from Algalita, Hokkaido University in Japan and the Woods Hole Oceanographic Institution identified regional patterns in the concentrations of some chemicals taken up by marine plastic. For example, PCB concentrations were greatest in Japanese and U.S. urban coastal areas, reflecting the chemicals' higher past usage in those areas. Plastic particles act as pseudo-plankton, introducing these chemicals into the food chain, where they work their way right up to humans.

Calls to Action
These threats to turtles have been known for decades. Research published in Nature more than 10 years ago warned that current fisheries activities would doom Pacific sea turtles, and a paper in Science in 1972 identified the threat of microplastics in the ocean. (Scientific American is part of Nature Publishing Group.) Both problems have relatively clear-cut solutions, including reducing single-use plastics, cleaning up debris and developing and requiring turtle-safe fishing gear.

Yet translation of this knowledge into policy and concrete action remains limited and often controversial. Whereas a few U.S. fisheries require the use of devices to allow turtles to escape trawl nets, the majority of trawl fisheries worldwide do not, and even in the U.S. their use is not always enforced. U.S. longliners must use circle hooks, which cause less injury to turtles, and fish as bait, rather than more turtle-attracting squid. Enforcement remains spotty here, too, though, and the U.S. fleet, Crowder points out, represents, at most, about 10 percent of total longlining efforts worldwide.

Other possible protections have yet to get even that far. In March the federal government issued a six-month extension to its deadline for a final ruling on whether to change the status of loggerhead sea turtles from "threatened" to "endangered"—an effort first spurred by legal petitions back in 2007. The listing has proved controversial, in part because of its potential effects on fisheries, particularly those in the North Atlantic. "There has not been widespread acceptance of gear fixes by the fishing community, which generally resists any type of regulation," says Catherine Kilduff, an attorney at the Center for Biological Diversity (CBD).

Court Cases
Organizations are also seeking to catalyze action through the courts. In April the CBD, Oceana and Turtle Island Restoration Network (TIRN) sued the U.S. government for missing another deadline, this one to designate more than 70,000 square miles of waters off the West Coast as critical habitat for leatherbacks. As of June the parties were negotiating a settlement that would set another deadline for designation of the protected area, Kilduff says--this one technically enforceable by the court. Even if the designation is made, restrictions on fishing practices there will not necessarily follow.

On May 31 the CBD, TIRN, Sea Turtle Conservancy and Defenders of Wildlife filed a 60-day notice of intent to sue the National Marine Fisheries Service and the states of Louisiana, Mississippi and Alabama for violations of the Endangered Species Act. Acting in direct response to those sea turtles deaths along the Gulf Coast—which as of June 1 totaled 320 for these three states—the groups also asked for emergency closure of the Gulf shrimp trawl fishery. Kilduff says it is unlikely that anything will happen before the end of the 60 days.

Nor is the scientific community twiddling its thumbs. Ward pays locals in Costa Rica $2 an hour to remove plastic from the reef and plans to seek more funding to pay fishers to net plastic. Eriksen, in addition to publicizing research on plastic pollution, also plugs existing technology that uses plastic waste to make literal building blocks and technology used by PyroGenesis Canada, which uses waste (including plastic) to generate power. In 2009 the United Nations Environment Program called for a worldwide ban on plastic bags, and more than nine countries, including the Congo, had banned or taxed plastic bags as of June 2011.

Meanwhile, some scientists point out that individuals can make a difference by changing the way they use and dispose of plastics and demanding sustainably caught seafood. Individuals can also call on industry and policy makers to respond, helping to turn these most recent tragedies deaths into action. Then they may yet prove to be that tipping point.

View a slide show of the threatened turtles.