Thunderbird: the turtle that was captured twice by fishing gears

The story of a turtle that was taken twice by different fishing gears reveals a

The story of a turtle that was taken twice by different fishing gears reveals a dual threat for many marine animals: Photo: Save The Med

Thunderbird is the name of a female loggerhead turtle (Caretta caretta) that was entangled in July 2020 by abandoned fishing gears near the island of Majorca. After this accident, the foundation Save the Med could save the trapped turtle and took it to the rescue centre Palma Aquarium Foundation. Once it recovered, Thunderbird was put a satellite tag from the Balearic Islands Coastal Observation and Prediction System (ICTS-SOCIB) and freed in the Mediterranean on August 11.

The turtle was monitored while it swam on the Gibraltar Strait and moved south along the African coast. "Most of the tagged turtles in the Mediterranean stay in that marine area for longer periods and when they enter the Atlantic, they swim to America. Thanks to the telemetry monitoring, we could follow Thunderbird’s epic journey over more than 6,000 kilometres in the western Mediterranean and the western African waters", notes the expert David March, member of the Faculty of Biology and the Biodiversity Research Institute of the UB (IRBio).

"This turtle surprised us when crossing the Gibraltar Strait, a challenging area due to strong currents and high density of marine traffic, which could result in a high risk of boat collision", notes March, also member of the Centre for Ecology and Conservation (CEC) of the University of Exeter (United Kingdom).

"The fact that Thunderbird went to western Africa could be because a few turtles in the western Mediterranean come from the Cape Verde archipelago, where they return to when they are adults", notes Lluís Cardona, lecturer at the Faculty of Biology of the University of Barcelona and IRBio.

A long tour around the Mediterranean

The satellite tag on Thunderbird provided data on the depth the chelonian was, so the team could see the turtle spent most of the time on the shallows while swimming in the Mediterranean, and then dived near the seafloor when it was under western African waters.

The daily updates provided by the device on Thunderbird disappeared in February 2021. Then, on March 17, the team received the last signal with a position on land, near the main harbour of Dakar (Senegal). "This suggested Thunderbird would have been accidentally caught by a fishing vessel, probably a trawler", notes March.

"It is never easy to know why the device stops sending data, so we checked telemetry data to get more information on potential causes", continues the expert. "After checking that the battery and its sensors worked correctly, we used the Global Fishing Watch portal to compare the turtle’s journey to that of fishing vessels".

"We do not know whether Thunderbird was released alive after its capture or whether it died as a result of the bycatch event".

A dual threat for the population of sea turtles

Currently, the team of this project uses satellite data on the movement of the vessels and works with collaborative entities in Senegal to try to find the boat that took the turtle, in order to get more information on Thunderbird’s final destination.

"There is a lot of unregulated or illegal fishing in western Africa and we are working with local agents and fisher communities in order to adapt the equipment and methods for fishing to minimize the bycatches of marine turtles", comments expert Ahmed Diame, from Birdlife International. "We are also working I order to identify the main points of interest in bycatches, such as the place where this turtle was captured".

"Thunderbird’s epic journey illustrates two of the major threats many marine species face: entanglement in ghost fishing gears and bycatch in industrial fisheries".

For this reason, the University of Barcelona and Birdlife International launched a project on to assess and reduce turtle and seabird bycatches in western Africa. "The marine current of the Canary Islands is a key upwelling for many seabird and turtle species, and for many seabirds that breed in Europe, spend the winter in western African waters and die entangled in fishing gears, sometimes from European fishing fleet", highlights the director of the project, Jacob González-Solís, professor of Zoology and member of the Department of Evolutionary Biology, Ecology and Environmental Sciences and IRBio.

Thunderbird was tagged as part of the program of Oceanographic Turtles, a jointly initiative by ICTS-SOCIB, Alnitag NGO, Palma Aquarium Foundation and the University of Exeter, with the support from the National Service of Marine Fishing from the National Oceanic and Atmospheric Administration of the United States (NOAA-NMFS).

The journey of these turtles can be followed through the ICTS-SOCIB website viewer.

Vídeo (Save The Med)

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