Unique long-distance migration documented
Scientists have likely documented for the first time the birth migration of the scalloped hammerhead shark (Sphyrna lewini), a critically endangered species. An adult female, showing a visibly swollen abdomen indicating pregnancy, covered a remarkable distance: from the Galapagos Islands along the coast of Panama to international waters west of the Galapagos.
During the nearly seven-month tracking period, the shark covered almost 6,000 kilometres – the longest documented migration of a scalloped hammerhead shark to date. The animal, affectionately named “Alicia,” initially spent over two months near Darwin Island before travelling 1,300 kilometres back to the Gulf of Chiriquí in Panama in early May, a known birthing area for the species.
Minimally invasive satellite technology
Researchers used special closed-circuit rebreathers (CCR) to observe the highly elusive sharks at reef fish cleaning stations. With an almost silent CCR, they could approach within two metres and attach a towed satellite tag near the dorsal fin – minimally invasive and low-stress for the animal.
The tags function similarly to a GPS, providing precise location data almost in real-time when the shark swims near the surface. This allowed the movements of the 2.7-metre-long, likely pregnant shark to be tracked accurately over the seven months.
Birth and further migration
Just six days after arriving in the Gulf of Chiriquí, researchers estimated that Alicia gave birth to between 15 and 30 pups. She then embarked on a 3,000-kilometre westward migration, reaching an international zone about 1,800 kilometres west of the Galapagos Reserve by late July. She remained there until the tag’s battery expired on 3 September.
Dr. Pelayo Salinas de León from the Charles Darwin Foundation stated: “This data provides the first scientifically documented insights into the birth migration of the scalloped hammerhead shark and underscores the importance of international protective measures beyond existing marine protected areas.”
Endangerment and need for protection
The scalloped hammerhead shark was classified as critically endangered by the IUCN in 2019, with an estimated global population decline of over 80% in three generations. Despite its critical status, pregnant females and juveniles continue to be heavily fished, particularly in the coastal waters of the eastern tropical Pacific.
The nearly 77 days Alicia spent in international waters highlight the urgent need for international cooperation to reduce mortality from high-seas fishing and halt the decline of this iconic species.
Professor Mahmood Shivji, Director of the Guy Harvey Research Institute, emphasises: “These findings help target protective measures in the eastern tropical Pacific and secure the reproduction and migration of the scalloped hammerhead shark.”
