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Tracking Pelagic Thresher Sharks in Central Indonesia: Exciting Discoveries for Local Conservation

A thresher Shark
Thresher Shark Photo by Elisa Chan.

The pelagic thresher shark (Alopias pelagicus), a globally endangered species, faces significant threats from bycatch and targeted fishing in Indonesia's industrial and artisanal fisheries. Unfortunately, our limited understanding of their ecology, particularly regarding their movements and habitat use, hampers the development of effective conservation strategies. 

Recent research, spearheaded by an international team from the USA, New Zealand, and Indonesia, marked a groundbreaking first in the study of pelagic thresher sharks. This pioneering study employed a combination of satellite and passive acoustic telemetry to investigate the movements and residency of these sharks in Indonesian waters, particularly in regions significantly affected by local fisheries.

In this study, 24 sharks were tagged in the Selat Pantar Marine Protected Area (MPA) using archival satellite tags (9 sharks), internal acoustic tags (10 sharks), and both types of tags (5 sharks). The tagged sharks, primarily females (71%), ranged in size from 125 to 180 cm in fork length. Data from seven of the fifteen acoustically tagged sharks and twelve of the fourteen satellite-tagged sharks were successfully recorded. The satellite tags remained attached for 81 to 181 days, while acoustic tag detection periods varied from 44 to 175 days. It is vital to monitor individuals due to different behaviours and/or defects.

A thresher with a defect in its dorsal fin
Photo By Padraig O'grady. Notice the Defect in the Dorsal Fin

Horizontally, the satellite-tagged sharks exhibited broad movements, predominantly offshore, approximately 90km from the tagging locations. They ventured to regions between Banda, Flores, and the Savu Sea, areas known for unregulated and unreported longline and gillnet fisheries. Conversely, the acoustically tagged sharks displayed distinct diel patterns around the coastal waters of Selat Pantar MPA, suggesting potential philopatric behaviour. Vertically, these sharks spent significantly more time in deeper waters during the day, moving to shallower waters at night, with the deepest dive recorded at 1,889.5 m - the deepest ever documented for this species.

The findings indicate that area-based protection could be an effective conservation tool nearshore, as the sharks tend to remain in relatively restricted areas within the Selat Pantar MPA for extended periods. However, regulation of fisheries, particularly targeting illegal longline and gillnet fishing, is crucial to protect these sharks when they move offshore. The insights gained from this research have been communicated to relevant governmental bodies, resulting in increased political will and new legislation to protect pelagic thresher sharks within the Selat Pantar MPA and the broader waters of East Nusa Tenggara.

A thresher shark swimming in mid water
Thresher Shark Photo by Elisa Chan.

Recently, Liz, the director of Shark Guardian, returned from an exciting expedition to Malapascua, (Indonesia) dedicated to thresher sharks. The adventure was not just about observing these magnificent creatures in their natural habitat but also about educating her group on their behaviour, ecology, and the urgent need for their conservation.

The trip was packed with thrilling dives with Evolution Diving, where participants had the chance to witness the grace and beauty of thresher sharks up close. Between dives, Liz held engaging educational sessions, sharing her extensive knowledge and passion for shark conservation. The group learned about the unique characteristics of thresher sharks, the threats they face, and what can be done to protect them.

“Losing the opportunity to witness these majestic creatures up close would be tragic. It's imperative that dive centres prioritise the protection of thresher sharks and their habitat, especially at Kimud Shoal. By restricting access to experienced divers and encouraging data collection through platforms like EOceans, we can contribute to their conservation. Let's not just witness their beauty but actively work to preserve it." - Liz at Shark Guardian

This blend of adventure and education made the expedition a memorable and enriching experience for all involved, fostering a deeper understanding and appreciation of thresher sharks and the marine environment.

Get ready for a journey of a lifetime with our upcoming expeditions! Do you want to be part of an educational, fun adventure? Do you want to see an array of different marine life - not just sharks? Drop us a line at to get more information. 



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