Over half of sea turtles accidentally caught suffer from gas embolism

A study carried out by the Fundación Oceanogràfic in collaboration with the Institut de Ciències del Mar (ICM-CSIC) of Barcelona and recently published in the journal Conservation Physiology provides new information on the risk of gas embolism for sea turtles accidentally caught in trawls or gillnets.

The results of the study, in which researchers from the National Oceanic and Atmospheric Administration (NOAA) and Texas A&M University Corpus Christi also participated, showed that over half of the studied turtles (54%) suffered from the disease after being captured. Furthermore, the severity and likihood of surfering from the disease was greatly increased in larger turtles as well as those caught at deeper depths.

the study showed that a turtle caught with by a trawl net at a depth of 100 meters had approximately a 50% probability of mortality and this depth decreased to 45 m for turtles caught in gillnets.

The study also provides information on other risk factors associated with the accidental capture of turtles from fisheries in the Valencian Community.

The study focused on the species Caretta caretta, commonly known as loggerhead turtle, and classified as "vulnerable" in the Red List of the International Union for Conservation of Nature (IUCN). The authors stress the importance of understanding all the risk factors associated with the accidental capture of these turtles to reduce the mortality associated with fishing activities.

"Knowing the risk factors that lead to the onset of the disease in loggerhead turtles, as well as the consequences of suffering from gas embolism, is central to developing management and mitigation strategies to conserve turtles.  We are able to uncover this information from the animals that are sent for treatment at our center thanks to our extensive network of collaborators", says Daniel García-Párraga, technical director of the Fundacion Oceanogràfic.

Nathan Robinson, a researcher at ICM-CSIC and co-author of the study, highlights "the great threat" posed by the accidental capture of sea turtles. In the case of gas embolism, if turtles are not properly treated, they can die within days of being captured," he says. For this reason, Robinson adds, "it is essential to know the probability of a turtle dying after being accidentally caught to understand the real effect of fishing on these animals and to take this into account in management and conservation policies".

Diver's disease in sea turtles

Until a few years ago, there was no evidence that sea turtles could suffer from diving-induced gas embolism. A condition similar to gas embolism suffered by divers, but from which turtles were thought to be totally immune.

When researchers at the Oceanogràfic Foundation discovered in 2014 that turtles accidentally caught in fishing nets were suffering from this disease it opened up a whole new field of study  and had a great impact on the conservation of these species, as it implies that many of the turtles caught in the netswere dying within days of being returned to the sea.

Since then, studies have confirmed that this issue is not exclusive to loggerhead turtles and affects all seven sea turtle species. This highlights the need to study the disease better discover ways to reduce the risk of decompression in turtles caught by fisheries and also to develop methods for treating afflicted individuals in facilities such as those of the Oceanogràfic of the Ciutat de les Arts i les Ciències de València (Valencia's City of Arts and Sciences).

"The fact that turtles caught by gillnets have a higher risk of gas embolism to those caught by tralws as similar depths is likely to gillnets spending longer in the water. We therefore recommend setting nets for shorter times and trying to avoid key habitats for adult turtles”, says Robinson.

This work has been possible thanks to the extensive collaboration between fishers, researchers, veterinarians, local and international groups that, hand in hand with good governance, make it possible to study these endangered species to guarantee both their conservation and the sustainability of fishing activity".

"To make progress in science we need society, and the collaboration between research institutions such as the Oceanogràfic Foundation, ICM-CSIC, NOAA and Texas A&M University Corpus Christi has been fundamental in developing the work and making its results available to the whole planet," concludes Andreas Fahlman.