at night may stop swimming and sink to the bottom. The horn shark is preyed upon by larger fishes and the northern elephant seal (Mirounga angustirostris), which consumes adults, juveniles, and egg cases. In addition, they are captured and eaten by bald eagles (Haliaeetus leucocephalus) at Catalina Island, and large marine snails are able to drill into their egg cases to extract the yolk. The tough skin and spines of this species confer some protection; a Pacific angelshark (Squatina californica) has been filmed engulfing a juvenile horn shark, only to spit it out due to its spines. Known parasites of this species include the tapeworms Acanthobothrium bajaensis and Acanthobothrium puertecitense, the copepod Trebius heterodonti, and the nematode Echinocephalus pseudouncinatus, which spends its larval stage inside potential prey such as scallops and sea urchins. Feeding 95% of the adult horn shark's diet consists of hard-shelled mollusks (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