Researchers Tracking Pelagic Thresher Sharks Lose Signal from Two Tagged Specimens
30 July 2020
A confidential source in the Galápagos Islands has reported that two sharks marked with research tracking monitors have recently gone missing. This source studies fisheries in the Galápagos Islands and has chosen to remain anonymous.
Of the four pelagic thresher sharks that were being tracked, 2 of the 4 tracking monitors have appeared on shore in Panama in the Punta Arena area.
This species is under threat from both accidental bycatch and due to its status as a prized species in commercial fisheries.
This news comes after the suspicious timing of the disappearance of Esperanza, or “Hope,” the whale shark in May 2020. Hope was a young whale shark who had been tagged and tracked by researchers from the Galápagos Whale Shark Project (GWSP) since September 2019.
Her signal was lost after entering an area of high fishing pressure on the western edge of the archipelago and her speed and distance travelled are highly suggestive of capture and transit by boat. Her story was recently featured in the August 6th coverage in the Guardian in an interview with a GWSP researcher.
Pelagic threshers are valued by commercial fisheries for their meat, skin, liver oil, and fins, and are also pursued by sport fishers.
Though often captured as bycatch, the Pelagic Thresher Shark is also considered a prized game fish and has numerous human applications. The meat is sold for human consumption, the skin is made into leather, and the fins are used for shark fin soup in Asia. The squalene oil in the liver of the pelagic thresher can comprise 10% of its weight, and is used in the manufacture of cosmetics, health foods, and high-grade machine oil.
Little is known about their feeding ecology, but stomach content analysis reveals that pelagic threshers feed mainly on inhabitants of the mesopelagic zone, such as barracudinas (family Paralepididae), lightfishes (family Phosichthyidae) and escolars (family Gempylidae)(EN) As in other thresher sharks, pelagic thresher sharks may swim in circles to drive schooling prey into a compact mass, before striking them sharply with the upper lobe of their tails to stun them. Because of this behavior, pelagic threshers are often hooked on longlines by their tails. They are also frequently caught in driftnets meant for other species, such as tuna.
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