Great Hammerhead sharks are slow to grow and reproduce, making them highly vulnerable to extremes – worldwide populations are shrinking and dangerously low in genetic diversity. Identifying the habitats they use and when they use them is critical to protecting these sharks. Science and Tracking with Andros Island in the Bahamas Tagging and Tracking Although the Bahamas travel to the east coast of the United States, others prefer to stay closer to home, returning to the same sites year after year.
New research suggests that some large hammerhead sharks are homes. Scientists studying great hammerheads around Andros in the Bahamas have found that some individuals migrate while others prefer to stay at home. This information can help protect critically endangered species. “The global population of Great Hammerheads is thought to have declined by more than 80% in the last three generations and genetic analysis has revealed low genetic variation and inbreeding,” said Dr Tristan Guttridge. Blue savingsThe guidance of the author of the article Frontiers in Marine Science. “Understanding the movement patterns of great hammerheads is critical to improving conservation efforts. Some great hammerheads show year-round residency in the Bahamas, protecting them from fishing pressures.”
Fishing for information
The great Hammerhead shark has been recorded traveling 3,000 km. In addition, they are also particularly favorable in regions, including the Bahamas, to the summer of large hammerheads, but leave in the summer. But the potential importance of sharks from other Bahamian islands, the role of local food products and the lack of long-term stay there are less well known. Scientists began to investigate this, focusing on the island of Andros, the largest in the country.
“When we started this study, there was no information about large hammerheads in the central Bahamas and no information about their habitat on Andros, one of the largest fry reefs in the world and the most practical habitat in the wider Caribbean,” Guttrigh said. “Didn’t we answer simple questions like what is this shark?”
Using tags and support from Discovery’s Shark Week, the team captured 22 sharks between June 2020 and June 2024. He placed there sites depicting the usual habitats of the Great Hammerheads. He measured, sexed, and took small muscle biopsies from each shark and attached satellite trackers to seven sharks. As the stress of capture took a serious toll on the great hammerheads, so did the health of each shark.
Data from shark catches were combined with records of opportunistic sightings, totaling 78 between 2018 and 2024, mostly large juveniles and adults. Half of what was seen between January and March, a significant number was seen between June and July. The two scenes showed evidence of recent mating, implying that the region may be important for reproduction. Several sharks were seen again in the same places and some were captured in the same places several years apart.
The shark prefers only northern and central Andros for long-term use, especially the relatively small 400 km2 area. However, there are patches of increased use elsewhere around the island: outlying habitats near reef openings rich in prey species were particularly popular.
The sharks passed through the southern or northern tip of the island and continued further in transit. The shark that left the Bahamas headed for the east coast of the United States, suggesting that it may be part of the Western Atlantic population of large hammerheads.
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A huge hammerhead menu
Isotope analysis of the biopsies revealed that barracuda and stingrays made up two-thirds of the sharks’ diet, with the rest being small sharks. But different sharks had different preferences. One individual had a diet that was almost two-thirds silky shark. Combined with access to deep waters that remain cooler during the summer wet season, this shark may be able to survive in the Bahamas, as opposed to Hammerheads near Bimini. “Resource availability is the main driver of space utilization, but why doesn’t everyone stay when food is so plentiful?” Guttridge said. “We found evidence of individual variation in their diets, so we decided whether to stay or go might depend on what they were doing.”
“For other species, why or if migration is linked to environmental conditions, body size, food availability, competition and predation,” Guttrigh. “Maybe, like salmon, there’s a genetic component to it? We need to investigate this phenomenon further.”
“Our research demonstrates the importance of Bahamian waters and their conservation measures,” said Guttridge. “Furthermore, while some individuals live year-round in protected waters, others do not see how these hammerheads fit into the broader northwest Atlantic population, highlighting the need for international cooperation on conservation efforts for this mobile species.”
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