Horn shark (Heterodontus francisci) is a species of bullhead sharks, which is native to the Pacific Ocean. Their short, blunt head, with high ridges above the eyes, is the main reason why they are known as horn sharks. They are nocturnal sea creatures, which forage at night and display a comatose behavior during the day. Their genus was described by Blainville in 1816, while the species was described by Girar in 1855.
These sharks are brown in color with black spots all over their body. Adults can reach up to a length of 4 feet and weigh up to 10 kg. Adolescents have been recorded to reach up to a length ranging between 1 to 1.6 feet. Their spines are located in their first and second dorsal fins. That they have five gills, is yet another characteristic feature of this species. More than one type of tooth is present in their dentition; small teeth in the front and crushing molars behind them. This is the primary reason for its genus name; Heterodontus, which is derived from the two Latin words, heteros meaning different and odont meaning teeth.
With whatever records that are available, the geographical range of these sharks can be traced to the waters stretching from California to the Gulf of California, Mexico, along the west coast of North America. Some eminent sea researchers have also suggested the probability of their presence in the seas of Ecuador and Peru.
Horn Sharks don't travel much. The maximum distance that has ever been recorded for a horn shark to have traveled out from its habitat is 10 miles. These sharks inhabit the warm, subtropical waters of the Eastern Pacific. They prefer water with temperature above 68°F (20°C). In contrast to other small sharks, they prefer to stay in the depths of oceans and thus, also fall in the category of 'benthic' sharks. In normal sea water, they stay at depths of 25 to 40 feet from the sea level, while in the inter-tidal zone they go down to a depth of 656 feet. In winter, they prefer to stay at least below 98 feet from the sea level to keep their bodies warm. Adolescent sharks, which are not very large in size, have been observed to stay at depths in the range of 131 to 492 feet from the sea level.
Horn sharks are carnivorous sea creatures. They mainly feed on sea urchins, which is why they have stained purple teeth. They also feed on other benthic invertebrates, mollusks, crustaceans, and sea creatures, like gastropods, crabs, shrimp, squids, polychaetes, small clams, sea anemones, and starfishes.
Horn sharks are oviparous in nature. The females of this species have a very distinctive way of laying their eggs in spiral egg cases, which they wedge into crevices. They mate during the months of December and January and the females start releasing their eggs just a few weeks after mating. The breeding season is generally between the months of February and April, during which the females lay two eggs every 11 to 14 days. Generally 24 eggs are released by a single female in a season. The eggs generally hatch in 7 to 9 months.
Relationship with Humans
Divers often report of coming across horn sharks during night diving. However, seldom do they react to the presence of these divers. They stay inert and do not pose a threat; that's until they are harassed. However, it is always advisable for divers to stay cautious, especially around their dorsal spines. Till date there has just been one recorded incident of a horn shark attack on humans.
Horn sharks are presently listed as "Data Deficient" by the International Union for Conservation of Nature (IUCN). The main problem lies in identifying this species from other varieties with similar features. Though they are not among those species that are hunted primarily for food, they often get caught as by-catch in fishing expeditions. They are only known to inhabit a small area of the ocean world and hence, we know very little about them. It may not be easy to identify them because of the insufficient information available to classify them properly. The need of the hour is to initiate an in-depth study to safeguard them from extinction.