Sep 15

The number of sea turtles accidentally captured and killed in U.S. coastal waters has declined by an estimated 90% since 1990, according to new research.

Photo of a green turtle

An estimated 300 green turtles died in U.S. waters each year after being caught by fisheries.

In a study published in the journal Biological Conservation, researchers analysed bycatch data from 20 fisheries operating in Atlantic and Pacific waters between 1990 and 2007, looking at the number of different turtle species accidentally caught and killed in fishing gear.

The results showed that the number of turtles being killed each year was around 4,600, down from an estimated 70,000 in 1990. Overall, the total number of turtles caught, including those that were not killed, fell by about 60% from 300,000 a year in 1990.

Photo of a loggerhead turtle caught in a fishing net

Loggerhead turtle caught in fishing net. An estimated 1,400 loggerhead turtles died each year due to fishing activities.

The researchers put the decline in bycatch down to regulations put in place over the last 20 years to protect turtles, together with overall declines in U.S. fishing activity.

Reducing turtle deaths

Regulations put in place by the National Marine Fisheries Service (NMFS) have included the use of circle hooks in longlines, as well as removing hooks from equipment to reduce the severity of injuries to turtles. Special ‘turtle excluder devices’ have also been used in shrimp trawl nets to allow turtles to escape.

There have also been measures to keep fishing activities and turtles separate in places and at times that turtles are likely to be present in large numbers.

The authors of the study say that these mitigation measures could also be effective in reducing sea turtle deaths in other countries.

According to Elena Finkbeiner, the lead author of the study, “The reduction of bycatch and mortality shows important progress by NMFS, which serves as a model for reducing sea turtle bycatch in other parts of the world. Our findings show that there are effective tools available… to reduce sea turtle bycatch, as long as they are implemented properly and consistently.”

Photo of Kemp's ridley turtle hatchlings

Kemp’s ridley turtle hatchlings. This species suffered the highest mortality from bycatch in U.S. waters, with around 2,700 killed every year.

Still work to be done

However, the researchers also noted that there are shortcomings in the current approach. Sea turtles are managed on a fishery-by-fishery basis, which does not take into account the impacts on overall turtle populations. This may mean that the total amount of bycatch exceeds what sea turtle populations can sustain.

The study also found that the Gulf of Mexico shrimp trawl fishery, which accounts for 98% of sea turtle deaths, does not consistently comply with regulations. A lack of onboard observers recording bycatch makes enforcing regulations difficult.

Photo of a leatherback turtle on nesting beach

Leatherback turtle on nesting beach. Around 40 leatherbacks were killed each year in U.S. waters.

We commend the successful efforts of fishers and NMFS managers to reduce sea turtle bycatch, but there is still important work to be done,” said Bryan Wallace, one of the authors of the study.

Bycatch limits must be set unilaterally across all U.S. fisheries with overall impacts to populations in mind, much as it’s done for marine mammals. This would ensure that these bycatch reductions are successful in recovering sea turtle populations.”

Baseline for monitoring

Six species of sea turtle occur in U.S. waters. The olive ridley turtle is classified as Vulnerable by the IUCN, while the green turtle and loggerhead turtle are classified as Endangered. The leatherback turtle, Kemp’s ridley turtle and hawksbill turtle are classified as Critically Endangered. All six species are listed as ‘Threatened’ or ‘Endangered’ on the U.S. Endangered Species List.

The researchers noted that the actual levels of turtle bycatch in U.S. waters are likely to be higher than those recorded in the study, due to the lack of onboard observers in many fisheries. However, the study does provide a baseline from which scientists can examine which measures are working and what can be improved to better protect sea turtle species.

Read more on this story at Science Daily and Mongabay.

View photos and videos of turtles on ARKive.

Liz Shaw, ARKive Species Text Author