© Joseph Dougherty. All rights reserved.
Heterodontus francisci (Girard, 1855)
Some 95% of the adult horn shark's diet consists of hard-shelled molluscs (e.g. bivalves and gastropods), echinoderms (e.g. sea urchins) and crustaceans (e.g. crabs, shrimp, and isopods). To crack their shells, the horn shark generates the highest known bite force relative to its size of any shark, well in excess of other measured species such as the spiny dogfish (Squalus acanthias) and the blacktip shark (Carcharhinus limbatus). One study found the average bite force for this species in the wild to be 95 N with a maximum of 135 N, while under experimental conditions sharks could be induced to bite with over 200 N of force. Large horn sharks that feed mainly on sea urchins (particularly the short-spined purple urchin, Strongylocentrotus purpuratus) have their teeth and fin spines stained purple.
Other prey items of adults include peanut worms, sea stars, cephalopods, and small bony fishes. Juveniles feed primarily on polychaete worms, sea anemones, and small clams, and have been known to "pounce" on anemones to bite off tentacles before they can be retracted. Off southern California, horn sharks are known to take advantage of seasonal opportunities. In the summer, diurnally active fishes, in particular the blacksmith (Chromis punctipinnis), are especially abundant and are easily captured at night when they lie dormant. In the winter, the sharks scavenge on market squid (Loligo opalescens), which die by the tens of thousands after their mass spawning event. Horn sharks hunt mainly using their sense of smell. Although electroreception certainly plays a role in locating prey, this species has only 148 ampullae of Lorenzini. This is much fewer than in most other sharks, which may have over 2,000. Like other sharks, the horn shark's teeth are regularly replaced; it takes 4 weeks for a dropped tooth to be replaced.