If you’re an avid scuba diver, you’re probably all too familiar with decompression sickness (DCS)—more commonly known as the bends—a disease that can strike astronauts, divers, and others, and arises after inadequately recompressing after changes in pressure gradients. In the marine environment, scientists long thought that many diving vertebrates—like sea turtles and marine mammals—were immune to DCS through various adaptations. That all changed when scientists discovered that beaked whales exhibited DCS conditions, similar to humans, after stranding years ago in association with military activity. And now, for the first time, new research shows that the bends can strike sea turtles, too.
In a new study recently published in Diseases of Aquatic Organisms, a team of international researchers found that sea turtles can in fact experience DCS after being brought to the water’s surface too quickly after incidental capture in fishing gear, commonly known as bycatch. The researchers studied 67 loggerhead sea turtles caught as bycatch in trawl and drift gillnets off Spain’s east coast, and discovered that nearly half (29 individuals) showed DCS symptoms of varying severity—including unconsciousness, inability to move their flippers, or death.
“This study is unique in many aspects. It is actually the first time that DCS is demonstrated in sea turtles, and actually the first time this pathological entity is confirmed (not just suspected) in any breath-holding diver through the clinical reversion of symptoms and gas re-absorption under hyperbaric treatment,” lead study author Dr. Daniel García Párraga told Oceana. “So, first we demonstrate that the condition can occur—when it was previously unclear if this animal could really decompress—and second we demonstrate we can treat affected individuals and make them survive.”
After sea turtles are brought aboard after becoming caught in fishing gear—such as on the hooks of longlines or in the nets of trawling vessels—they are typically released back into the ocean if they appear healthy. But, this study shows that sea turtles can suffer from DCS symptoms after being thrown back overboard—indicating that there is yet another threat to sea turtles beyond capture in fishing gear, say the authors.
“Even if they are surfaced alert and active after hours of immersion, the turtles could be forming bubbles as a consequence of gas off,” says Dr. García Párraga. “This brings up another potential cause of death for this animal, revealing that certain fisheries could be causing higher mortality rates than previously estimated and that certain protocols recommending direct release of awake and active by caught turtles captured in certain fisheries should be revised.”
Bycatch in commercial fishing activity is one of the greatest threats to sea turtles. Some estimates say that 63 million pounds of marine life are caught as bycatch each year—a figure that includes sea turtles, according to Oceana’s Wasted Catch report. In fact, the Monterey Bay Aquarium’s Seafood Watch program reports that as many as 200,000 loggerhead sea turtles and 50,000 leatherbacks are caught each year. Because bycatch can often go unreported if there is not an observer on vessels, assessing cumulative mortality and injury rates from bycatch is difficult.
Since sea turtles are now found to be susceptible to the bends after capture in fishing gear—adding another element to preexisting effects of bycatch like death or outward injury from fishing gear—this study opens the door for modifications to fisheries and sea turtle management, as well as future studies on this topic.
“Now is the time to determine the real impact of DCS on the different fisheries, how many animals are affected, how many of them develop lesions, and how many die as a consequence of the interaction. This will allow us to propose mitigation measurements in order to minimize lethal interactions, limiting total times or depths of submersion for instance, or empowering the use of Turtle Excluder Devices (TEDs),” says Dr. García Párraga.
Oceana is working to reduce bycatch of sea turtles and other marine life through a number of outlets. Oceana advocates for fishing gear modifications—such as the inclusion of TEDs that allow sea turtles to escape from fishing nets after being caught—as well as switching to more sustainable fishing gear. Oceana also pushes for fisheries activities to be halted when sea turtles are present in the area, as well as urging for fishery managers to adopt the Oceana approach to reducing bycatch: count all catch (including bycatch), cap bycatch using science-based limits, and control bycatch through effective management. Click here to learn more.