Researchers have discovered a location in a marine park off the coast of Perth where juvenile scalloped hammerheads (Sphyrna lewini) gather in large groups. These sharks, one of ten species in the hammerhead family, prefer warm waters but have become regular visitors to the waters off Perth in summer. They are not considered dangerous to humans but are among the world’s most threatened species due to over-fishing.
Despite their populations falling by 80% in 55 years, they are still legally fished in Australia. Scalloped hammerheads are skilled long-distance swimmers and exceptional free divers, able to hunt in dark waters 500 meters below the surface. Oceanic wayfarers, slow-growing and living up to 55 years, face challenges in studying due to their long distances and deep dives.
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Surf lifesavers observed hammerhead sharks off Perth beaches during helicopter shark patrols. Researchers used drones to track scalloped hammerheads in the Shoalwater Islands Marine Park, observing them as they aggregated. They found juveniles, not adults, in a small area during the full moon. The aggregated organisms would swim in formation, moving in winding patterns through the shallow waters.
The juveniles were likely seeking a place to rest and recover, as sharks often hunt more on nights with a full moon, taking advantage of better light to see prey. The shallow waters are likely important shelter for scalloped hammerheads.
The research highlights the urgent need to strengthen protection of scalloped hammerheads in the Shoalwater Islands Marine Park. A code of conduct should be in place to prevent water users from disturbing the animals, similar to those protecting whale sharks and humpback whales. Boat speed limits and bans on chasing animals are essential for protecting these endangered animals.
Stopping fishing at aggregation sites is crucial for hammerhead sharks, who are vulnerable to capture and unlikely to survive “catch and release” fishing. The marine park should be a safe spot for the sharks to rest and shelter. Strengthening protections in the park from multiple use status to highly protected status is necessary.
The federal government is reviewing the status of these sharks, assessing them as endangered due to ongoing fishing pressure. Australia hosts remarkable and endangered species like hammerhead sharks, and simple steps can be taken by the state and federal government to safeguard their future and maintain healthy marine ecosystems.
