WHY SOME HAMMERHEADS AGGREGATE
If you’ve ever seen hundreds of hammerheads gliding together in perfect formation, you’ve witnessed one of the ocean’s most stunning sights. But why do they gather?
Across the globe, scalloped hammerheads (Sphyrna lewini) form massive groups - at places like Cocos Island (Costa Rica), Galápagos (Ecuador), and Mikomoto (Japan). Scientists think they aggregate for three main reasons:
💬 Social behaviour: Helps individuals communicate or maintain social hierarchies.
💞 Mating opportunities: Some aggregations happen seasonally, possibly for reproduction.
🛡️ Safety in numbers: Reduces predation risk when juveniles.
In Western Australia, a unique coastal aggregation was recently documented at Point Peron, near Perth (López et al., 2022; López et al., 2023). Unlike deep-ocean sites elsewhere, this aggregation happens in shallow coastal waters, close to shore - and mainly involves juvenile scalloped hammerheads.
Drone and BRUVS surveys led by Dr. López at the Marine Futures Lab (UWA) revealed these gatherings occur mostly during peak summer, suggesting the area may be a refuge for juveniles hammerheads to rest. This finding reminds us that scalloped hammerhead aggregations occur beyond remote tropical waters and highlights the importance of local coastal habitats.
Protecting these aggregation sites is vital for hammerhead conservation - and thanks to citizen scientists contributing sightings through Hammerhead Hub, we’ll be able to uncover new insights every season.
Scalloped hammerhead (Sphyrna lewini) - By julianluna; CC BY-NC 4.0
Watch: “Scalloped Hammerhead Aggregation at Point Peron” - drone footage from our research team