Unique long-distance migration documented
Scientists have likely, for the first time, scientifically documented the birth migration of the scalloped hammerhead (Sphyrna lewini), a critically endangered species. An adult female, whose visibly swollen belly indicated pregnancy, traveled 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, the shark traveled almost 6,000 kilometers – the longest documented migration of a scalloped hammerhead to date. The animal, affectionately named “Alicia,” spent over two months near Darwin Island before covering 1,300 kilometers to the Gulf of Chiriquí in Panama in early May, a well-known birthing area for the species.
Minimally invasive satellite technology
The researchers used specialized closed-circuit rebreathers (CCR) to observe the extremely shy sharks at cleaning stations for reef fish. With an almost silent CCR, they were able to approach within two meters and attach a satellite-supported tow tag near the dorsal fin – minimally invasive and stress-reducing for the animal.
The tags work similarly to GPS and provide precise position data almost in real time as soon as the shark swims near the surface. This allowed the movements of the 2.7-meter-long, likely pregnant shark to be tracked accurately over the seven months.
Birth and further migration
Only six days after arriving in the Gulf of Chiriquí, the researchers estimated that Alicia gave birth to between 15 and 30 pups. She then embarked on a 3,000-kilometer westward migration, reaching an international zone about 1,800 kilometers west of the Galapagos Reserve by the end of July. She remained there until the device’s battery life ended on September 3.
Dr. Pelayo Salinas de León of the Charles Darwin Foundation stated: “These data provide the first scientifically documented insights into the birth migration of the scalloped hammerhead and highlight the importance of international protection measures beyond existing marine protected areas.”
Threats and need for protection
The scalloped hammerhead was classified as critically endangered by the IUCN in 2019, with an estimated global population decline of over 80 % within three generations. Despite this 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 that 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, emphasizes: “These insights help to plan targeted conservation measures in the eastern tropical Pacific and safeguard the reproduction and migration of the scalloped hammerhead.”
