ANIMALS
Hammerhead sharks have seemingly disappeared from two underwater mountains in the southwestern Gulf of California, and fishing is likely to blame. Researchers looked at observations from divers over the last 50 years and found that scalloped hammerhead sharks (Sphyrna lewini) experienced a 97 per cent decline at the El Bajo seamount and a 100 per cent decline at the Las Ánimas seamount, both off the coast of Mexico, between the 1970s and 2010s.
Scalloped hammerhead sharks are a critically endangered species threatened by fishing, according to the International Union for Conservation of Nature’s Red List of Threatened Species. The sharks are targeted for their large fins, which are used in shark fin soup. Researchers don’t know how many of these sharks are left globally. “Scalloped hammerhead sharks, and most shark species in general, are vulnerable to extinction as they produce few offspring, have long gestation periods and are slow growing,” said Kathryn Ayres, a research scientist at organisation Beneath The Waves. The El Bajo and Las Ánimas seamounts were once hotspots for large schools of hammerhead sharks; one survey carried out in the late 1970s and 1980s recorded 225 hammerhead sharks at El Bajo, according to the study. Ayres said the sharks use seamounts as a refuge during the day, where strong currents force oxygenated water over their gills so they don’t have to use energy swimming around.
To learn more about hammerhead shark decline at the seamounts, the authors sent a questionnaire to divers between 2017 and 2020. All of the people who participated – 50 for El Bajo and 32 for Las Ánimas – were either diving guides, experienced recreational divers, researchers or photographers. However, their responses were still based on memories from up to 50 years ago. Ayres said she believes human memories are reliable enough for studies like this with such
