Horn Shark - Biology and Ecology

Biology and Ecology

The horn shark is a clumsy, sporadic swimmer that prefers to use its flexible, muscular pectoral fins to push itself along the bottom. It is usually solitary, though small groups have been recorded. During the day, horn sharks rest motionless, hidden inside caves or crevices, or within thick mats of algae, though they remain relatively alert and will swim away quickly if disturbed. After dusk, they roam actively above the reef in search of food. Horn sharks maintain small home ranges of around 1,000 m2 (11,000 sq ft), which they may remain faithful to for over a decade, returning to the same shelter every day. The shelter is usually located at the edge of the resident shark's foraging area. The longest documented movement for an individual horn shark is 16 km (9.9 mi).

Unlike most fishes, the daily activity pattern of the horn shark is under exogenous control, meaning that it is regulated by environmental factors rather than by an internal physiological cycle. Observations of captive horn sharks show that the relevant cue is light intensity: the sharks become active immediately after the lights are turned off, and stop as soon as they are turned back on. In one experiment where the sharks were kept in darkness, they remained continuously active for 11 days before slowing, possibly from fatigue. In nature, horn sharks exposed to a bright light 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.