California horn shark  (Heterodontus francisci)

Classified as Data Deficient (DD) on the IUCN Red List (1).

In contrast to the conventional image of sharks as a sleek, dynamic predators, the California horn shark is a sluggish species with an enlarged blunt-nosed head, featuring pronounced ridges above the eyes and a pig-like snout (3) (4). The pectoral fins are broad and muscular, allowing this species to clamber along the sea-bed, while the two dorsal fins each bear a sharp spine, which help to deter predators (2) (4). The overall colouration is dark to light grey or brown on the upperparts, with numerous small, dark brown or blackish spots all over (2).

The California horn shark occupies warm temperate and sub-tropical waters along the Pacific continental shelf, occurring off the west coast of the U.S.A., from Monterey Bay south to California, and off Mexico, where it occurs around Baja California and in the Gulf of California. A population has also been recorded off the coasts of Ecuador and Peru, although it is thought that this may represent a separate species (1) (2).

A bottom-dwelling species, the California horn shark is typically found around rocky bottoms, reefs, kelp beds, sandy areas, deep crevices, small caves and large caverns. It occurs from the intertidal zone to depths of 152 metres, but is most commonly found between 2 and 11 metres, moving offshore in the winter to waters over 30 metres deep (1) (2).

Generally nocturnal and solitary, during the day the California horn shark conceals itself amongst rocks, kelp or within crevices or caves, and emerges at dusk to feed (2) (5). This species takes a variety of bottom-dwelling marine invertebrates, including sea urchins, crabs, gastropods, shrimp, squid, sea stars and probably abalone; it will also take small fish (1) (5). Prey is captured by rapidly protruding the upper jaw, which bears pointed teeth at the front that act like a chisel to chip the victim away from the substrate. The rapid opening of the mouth then creates a powerful suction that pulls the prey inside, where it is crushed by the flattened, molar-like teeth at the rear of the jaws. In order to aid the removal of strongly attached prey, the California horn shark will also use its body as a lever, performing a headstand in the water, grasping the prey in the jaws and pulling the rear of the body down while bracing against the pectoral fins, which are in contact with the substrate (6). The adult California horn shark hunts within a relatively small home range, usually no larger than 1000 square metres and may occupy the same site for many years (1).

The California horn shark mates in December or January. After one or two weeks, the female starts laying eggs, producing two eggs at 11 to 14 days intervals for around four months. The egg is roughly conical in shape with a spiral flange running around the outside, which enables the female to wedge it into a crevice, thereby making it difficult for predators to access. The embryos take between 6 and 8 months to develop according to water temperature, and emerge measuring between 15 and 17 centimetres in length (1). After hatching, the young sharks shelter in areas of shallow water, on sandy bottoms near kelp or rock, or in feeding holes excavated by bat rays (Myliobatis californica) (2). When the immature sharks reach between 35 and 49 centimetres in length, they migrate to deeper waters, between 40 and 150 metres, eventually migrating back to relatively shallow water when mature. Such segregation of age classes helps to reduce competition for food and habitat. Sexual maturity is reached at lengths of around 58 centimetres and the maximum recorded lifespan is 25 years (1).

While the California horn shark is of no commercial value, it is taken as bycatch by some fisheries, particularly during bottom trawls for shrimp off the coast of Mexico. Owing to a lack of monitoring, it is currently unclear what effect this is having on the population. Nevertheless, there is concern that if the Mexican gillnet fishery, which captures fish by entangling them in a net set in the water, shows a significant expansion, it could pose a threat to this species. The California horn shark is also commonly caught by divers for sport, and populations have apparently shown a decline in areas of intense diver activity in Southern California (1).

A hardy species, the California horn shark can often survive capture in trawl and drift nets, hence it has been recommended that individuals should be returned to the water after capture, rather than left to die on the beach, as sometimes occurs in Mexico. Further information about this species should be gathered to ensure that it is properly managed and conservation measures implemented where necessary (1)

View information on this species at the UNEP World Conservation Monitoring Centre.

To learn more about the conservation of sharks and rays visit:

• Save Our Seas Foundation:
  www.saveourseas.com
• IUCN Shark Specialist Group:
  www.iucnssg.org
• Shark Research Institute:
  www.sharks.org
• Shark Trust:
  www.sharktrust.org