Scientists have published what is likely to be the first-ever scientifically recorded birthing migration for the critically endangered scalloped hammerhead shark, tracking the individual as it travelled between the Galapagos Islands, the coast of Panama, and international waters to the west of the Galapagos.

Displaying what the researchers called a ‘clearly distended abdomen’, strongly suggesting that this was a pregnant mother, the satellite-tagged shark was tracked for nearly seven months as she journeyed almost 6,000km – the furthest distance a scalloped hammerhead has been tracked to date.

The study was published this week in the special issue ‘Frontiers in Elasmobranch Biology’ of the journal Environmental Biology of Fishes.

To track the mother, researchers used Closed Circuit Rebreathers (CCR) to closely approach the elusive species when the sharks visited the numerous reef fish cleaning stations around Darwin Island – the northernmost island in the Galapagos Marine Reserve.

Scalloped hammerhead sharks are known to be very shy to the bubbles and sounds produced by traditional SCUBA diving gear, and to be extremely sensitive to handling stress produced when captured. Using silent CCR (which produce no bubbles) scientists were able to approach within two metres of the sharks to deploy minimally invasive, towed satellite transmitters near the base of the sharks’ dorsal fin with a modified speargun.

Similar to a GPS device, towed satellite transmitters provide accurate location data in near-real time whenever the shark swims near the ocean’s surface. The tags are designed to resemble remora fish swimming next to the shark, allowing researchers to follow the movements of the nearly nine-foot-long female shark.

Nicknamed Alicia, the female scalloped hammerhead was tagged on February 11th 2023 at Darwin Island where it lingered for two months. In early May, the shark travelled 1,300km to the Gulf of Chiriqui on the Pacific coast of Panama – a known nursery area for this species. 

After six days in Panama’s coastal waters – where researchers believe Alicia gave birth to somewhere between 15 to 30 pups – the shark initiated a 3,000km westerly migration, settling in an area in international waters more than 1,800km west of the Galapagos Marine Reserve.

“It’s hard to believe how little we still know about the basic life history of most shark species, including this one critically threatened with extinction,” said Dr Pelayo Salinas de León, senior marine scientist at the Charles Darwin Foundation.

“Alicia’s clearly distended abdomen at tagging, combined with her brief visit to known birthing grounds in Panama coastal areas during the peak time of newborn shark occurrence, made us conclude this published satellite track represents the first documented birthing migration recorded for this species.

“Importantly, it provides critical insights on the complex life cycles and long-range movements scalloped hammerhead sharks undertake to give birth to their young, and underscores the need to further protect endangered sharks beyond already established Marine Protected Areas.”

Despite their critical conservation status, pregnant hammerheads continue to be fished while migraine, and newborn sharks are fished daily within most coastal nurseries. So severe is the threat that in 2019, the scalloped hammerhead was categorised as Critically Endangered by the Red List of Threatened Species issued by the International Union for Conservation of Nature.

Noting just how long this individual was tracked for within international waters to the west of the Galapagos Marine Reserve, researchers have urged for international collaboration and cooperation to reduce fishing mortality in the high seas to revert ongoing population declines for the species.

Professor Mahmood Shivji, director of the Guy Harvey Research Institute and Save our Seas Foundation Shark Research Centre at NSU Florida, said: “Getting this unprecedented view of the longest distance recorded journey by this scalloped hammerhead shark provides new knowledge not only on the reproductive behaviour but also extensive migratory capabilities of this species.

“Such new knowledge should aid the planning of where to focus additional conservation actions in the Eastern Tropical Pacific to preserve this highly endangered shark.”

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