The story of a female loggerhead turtle caught twice in fishing gear reveals a dual threat facing many marine animals.
Thunderbird was entangled in fishing gear in the Mediterranean off the coast of Mallorca last year, and was subsequently fitted with a satellite tag and freed. Researchers tracked the turtle as it swam through the Strait of Gibraltar and headed south along the coast of Africa, however signals then became erratic before a final position from the tag showed the turtle on land near a major fishing port in Dakar, Senegal, suggesting it was unintentionally caught by a fishing vessel - probably a trawler.
The turtle was found entangled in ghost fishing gear during one of Save the Med Foundation's research expeditions in July 2020, off the waters of Dragonera Island. The team initiated a rescue protocol together with Palma Aquarium Foundation’s rescue centre and within hours the turtle was transported to the rescue centre in Mallorca.
Thunderbird was not the only turtle rescued by Save The Med Foundation in 2020 - another three were found entangled in abandoned fishing gear in different parts of the Balearic Sea, and last season even proved to be a record year in turtle strandings in the Balearic Islands.
The satellite tag attached to Thunderbird before her release on 11 August allowed researchers to track her epic journey of 6,000 km through the Western Mediterranean and the waters off West Africa. Data from the satellite tag is analysed within the framework of the “Turtle Oceanographers” programme, and the trajectories of the tagged turtles can be followed on SOCIB’s website.
"Thunderbird surprised us in November 2020 by crossing the strait of Gibraltar,” explained Dr March from the Balearic Islands Coastal Observing and Forecasting System (SOCIB). “Instead of swimming west to Florida or the Caribbean, where most turtles from the Mediterranean go, she swam south along the West African coast. In February we stopped receiving regular updates from Thunderbird’s tag, with a final signal on 17th March on land, near the main harbour in Dakar.” This suggests the turtle was caught by accident by a fishing vessel and taken back to the port. “We don’t know if Thunderbird was released alive after capture, or died as consequence of the bycatch event.”
Entanglement in abandoned or lost fishing gear has become the major threat for sea turtles in the Balearic Islands, and off the coast of West Africa, unregulated or illegal fishing is not uncommon and migratory animals such as turtles may face the same threats over and over again on their journeys.
Dr March added: "The journey of this turtle illustrates two of the major threats that many marine species face on a daily basis at sea – entanglement in abandoned fishing gear, and bycatch in industrial fisheries. We must urgently address both issues to limit their impact on a wide range of marine species and ecosystems."