Sphyrnidae

Bonnethead

Sphyrna tiburo

A half moon head grazing seagrass after dark

• Gray
• White
• Tropical
• Nearshore
• Globally widespread
• Marine fish
• Fusiform
• Large
• Tropical fish

Distinguished by a semicircular shovel-like head and an astonishing omnivorous diet, the bonnethead is the smallest and most ecologically eccentric member of the hammerhead shark family. Its smooth, rounded cephalofoil resembles an arching bonnet or gardener's spade, entirely lacking any front notches or lobes. The compact body is washed in pale grey-brown or greenish-grey with scattered faint dark spots along the upper flanks, shading into a clean white underside. Ranging through subtropical and tropical coastal waters of the western Atlantic from North Carolina to Brazil, and the eastern Pacific from California to Ecuador, it inhabits shallow estuaries, seagrass meadows, and muddy flats down to twenty-five meters depth. In a groundbreaking revelation for elasmobranch biology, seagrass has been documented to comprise up to sixty percent of its stomach contents, which it digests with specialized carbohydrate-cleaving enzymes alongside blue crabs, mantis shrimps, and small molluscs. Viviparous with placental nourishment, its recorded maximum total length reaches one hundred and fifty centimetres.

Sources: Florida Museum — Bonnethead, Sphyrna tiburo