Researchers from the University of Chester and partners in the Philippines have highlighted the extreme vulnerability of thresher shark populations in the Central Visayas Sea. Their study, which used a remotely operated stereo-camera system, shows that even small losses through fishing can have serious consequences.
Pelagic thresher sharks in the Central Visayas Sea, a hotspot for shark-diving tourism at Monad Shoal and Kimud Shoal, could suffer a potentially catastrophic decline at an annual fishing mortality rate of only 5.3%. The removal of just 15 to 18 female sharks per year would be enough to push the population into a downward trend.
Threatened species and tourism
Over the past five decades, oceanic shark populations worldwide are estimated to have declined by 71%. In the Philippines, thresher sharks are especially important for the regional tourism economy, which depends strongly on shark diving.
Although targeted shark fishing is banned, the sustainability of the population is not guaranteed. Bycatch, meaning accidental capture in fishing gear, and illegal fishing remain major threats. The research team deployed a stereo-camera system for four months to measure sharks underwater without capturing them. Significantly more females from all maturity groups were observed than males.
