Bonnethead Shark

The Bonnethead Shark (Sphyrna tiburo) is the smallest member of the hammerhead family, Sphyrnidae, distinguished by its smoothly rounded, shovel-shaped head rather than the angular hammer of larger relatives. It ranges through warm coastal waters of the western Atlantic and eastern Pacific, from the eastern United States to Brazil. Notably, the Bonnethead is the only shark documented to digest plant material, regularly consuming seagrass alongside its animal prey. It is a common, fast-swimming inhabitant of shallow bays and estuaries and is frequently studied by scientists researching shark reproduction and cognition due to its small size and abundance. It is not considered a threat to humans.

Key field marks:

• Smooth, rounded shovel-shaped head, not scalloped like other hammerheads
• Slender, gray to grayish-brown body, pale belly
• Tall, curved dorsal fin
• Small size, typically under 1 m for males, up to 1.5 m for females
• Lacks the pronounced lateral head indentations of the Scalloped or Great Hammerhead

The rounded head shape alone reliably separates this species from every other hammerhead.

Inhabits shallow, warm temperate to tropical coastal waters of the western Atlantic, from North Carolina to southern Brazil including the Gulf of Mexico, and parts of the eastern Pacific. Commonly found in bays, estuaries, seagrass meadows, and over sandy or muddy bottoms at depths generally less than 25 m. Highly tolerant of variable salinity and often moves into very shallow water on flooding tides. Seasonal migrations track water temperature, with individuals moving to deeper or more southern waters in winter.

Bonnetheads are active, schooling sharks often seen in groups segregated by sex and size, foraging over seagrass beds and sand flats primarily during the day. They use their wide head to pin and manipulate crabs and other invertebrates while feeding, and studies show they digest significant amounts of seagrass, making them functionally omnivorous. They are viviparous, giving birth to litters of 4-16 pups after roughly a 4.5-5 month gestation, typically in shallow nursery bays. Their small size and abundance make them an important mesopredator linking invertebrate and larger predator food webs.