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‘Resilient’ leatherback turtles can survive fishing rope entanglements. Mostly

Leatherback turtle nesting on a beach

Leatherback turtle nesting on a beach

  • Leatherback turtles are highly vulnerable to getting entangled in lobster pot fishing gear off the coast of Massachusetts.
  • A new study now shows that they can largely survive these entanglements — if they’re reached by rescuers in time, and their injuries are treatable.
  • However, researchers say the lobster fishery must move toward a ropeless model to ensure that leatherbacks, and other marine animals, can survive over the long term.

Leatherback sea turtles run a gantlet of fishing lines and other human impacts during their annual migratory loop from Caribbean nesting grounds to the eastern coast of North America and back. One of the leatherback turtle’s biggest obstacles is entanglement in ropes from lobster pot traps deployed by commercial fisheries in the waters of New England. A recently published report in Endangered Species Research found that while turtles can survive entanglement if reached by rescuers, new approaches in fisheries are needed for them to survive over the long term.

“I was surprised and encouraged by how many of the cases [showed] that the turtles were able to survive these events,” said lead author Kara Dodge, from the New England Aquarium in Massachusetts, who analyzed 15 years’ worth of data collected by the Center for Coastal Studies (CCS) based in Provincetown, Massachusetts.

The CCS played the dual role of collecting data and coming to the rescue during turtle entanglements with its Marine Animal Entanglement Response Program. Between 2005 and 2019, the CCS saved more than 100 leatherback turtles. The world’s largest sea turtle, the leatherback, Dermochelys coriacea, is currently listed as vulnerable on the IUCN Red List, and is threatened by fisheries, destruction of beaches and climate change.

“We did a categorization based on behavior and the injuries,” Dodge said. “We found that 88% of the turtles had a low to intermediate risk of mortality based on that categorization and the tagging data also supported that.”

A leatherback sea turtle entangled in the buoy lines of pot/trap gear in Cape Cod Bay. One of the leatherback turtle’s biggest obstacles is entanglement in ropes from lobster pot traps deployed by commercial fisheries in the waters of Cape Cod. Image courtesy of Center for Coastal Studies.

Still, the researchers suggest the best way to mitigate turtle entanglement is to minimize the culprit itself: the fishing ropes.

In 2018, according to the paper, lobster fishers in Massachusetts deployed some 82,000 vertical buoy lines, at the end of which sits a pot trap to catch a lobster. But as they sit in the water column, stretching from the sea floor all the way up to the surface, the lines can unintentionally entangle leatherback sea turtles or other marine animals. The highest entanglement reports happen from May to November, peaking in August.

Since the early 2000s there has been a noticeable increase in reports of leatherbacks becoming entangled in such fixed-gear fisheries — either pot trap or gillnet — prompting the collection of data, beginning in 2005. The CCS confirmed 272 leatherback turtle entanglement cases throughout the 15-year study period; 92% of the study’s leatherback entanglements were due to pot trap fishing.

Of these, the CCS found forty-seven entangled turtles dead on arrival, while 149 cases were deemed “actionable,” according to the study. In other words, the turtle was still alive and rescuers could reach it. Of those 149, CCS successfully freed 137.

A diver records a sea turtle unintentionally entangling itself in a fishing line off the coast of Martinique.

The study also reviewed data on callers to the CCS emergency hotline. Only 12% of calls came from commercial fishers, while recreational boaters made 62% of the calls.

“Lobster fishermen in our area set out their traps and then check them once a week,” said Scott Landry, director of the Marine Animal Entanglement Response Program at the CCS, who has worked as an on-call disentanglement professional for 25 years. “The time that the fisherman has with the gear is actually relatively small.”

A co-author on the paper, Landry takes calls along with five to six other workers day and night to rescue turtles and other marine animals, even whales.

Turtles are most commonly entangled around their flippers and neck. Determined to continue migrating and foraging, the turtles continue to swim, exacerbating the entanglement and potentially leading to serious injuries or choking to death. The study reported that one turtle dragged its gear 48 kilometers (29 miles).

Landry and Dodge agree that using less rope, or removing rope entirely from the lobster fishery, would save turtles.

“The whole coast is going to have to agree upon how we’re going to rejigger how we go fishing,” Landry said, “and this is not an easy discussion as fishing in this form has been going on for generations and generations.”

A leatherback turtle entangled in fishing gear. Image courtesy of Sean Whelan.
A CCS crew works to disentangle a leatherback turtle from the fishing rope caught around its neck. Image by Amy Kukulya.

Dodge said she wants to see ropeless gear become an economic reality.

“There’s been a lot of research and a lot of funding put into [creating] ropeless fishing gear, which is being tested now,” she said. “[This is] the ideal solution, because not only would that help leatherback sea turtles and North Atlantic right whales, but there are other marine species that get entangled that see less attention.”

Dodge cited species like basking sharks (Cetorhinus maximus), as well as humpback whales (Megaptera novaeangliae) and northern minke whales (Balaenoptera acutorostrata), all of which commonly suffer from entanglements.

“It is incredibly gratifying to free these individual animals and see them swim away,” Dodge said. “They are a very resilient species. I feel like we’re [continuing to] expand on the post-release part of the work over the next couple of years.  I’m hopeful we’re going to see a high survival rate.”

Banner image: Leatherback turtle nesting on a beach. Image by Jordan Beard via Wikimedia Commons (CC BY-SA 4.0).

Citation:

Dodge, K. L., Landry, S., Lynch, B., Innis, C. J., Sampson, K., Sandilands, D., & Sharp, B. (2022). Disentanglement network data to characterize leatherback sea turtle Dermochelys coriacea bycatch in fixed-gear fisheries. Endangered Species Research, 47, 155-170. doi:10.3354/esr01173