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Biological Profiles




HORN SHARK
Order - Heterodontiformes
Family - Heterodontidae
Genus - Heterodontus
Species - francisci
Horn Shark

Taxonomy

The horn shark belongs to the family Heterodontidae (bullhead sharks). The genus was described by Blainville in 1816. The species was described by Girard in 1855. The current valid scientific name for the horn shark is Heterondontus francisci. This comes from the Greek word "heteros", meaning different; and the Greek word "odont", meaning teeth. One synonym used in past scientific literature referring to this species is Gyropleurodus francisci (Girard, 1854). Heterodontus californicus (Herald 1961) was used in apparent error for H. francisci.


Common Names

Common names for Heterodontus francisci throughout English-speaking countries are the horn shark, bullhead shark, pig shark, and horned shark. Other names include Californische stierkophaai (Dutch), Californisk hornhaj (Danish), dormilón cornudo (Spanish), gata (Spanish), kalifornský žralok plochozubý (Czech), requin dormeur cornu (French), sarvihai (Finnish), stierkopfhai (German), tiburón cabeza de toro (Spanish), tiburón cornudo (Spanish), tiburón gato (Spanish), and tiburón puerco (Spanish).


Geographical Distribution

The horn shark, Heterodontus francisci, occurs in warm-temperate and subtropical regions of the eastern Pacific Ocean from central California to the Gulf of California. The literature also suggests that this species may occur off the coasts of Ecuador and Peru (however these records are unconfirmed and may have been misidentifications of other species).


map
World distribution map for the horn shark


Habitat

The horn shark is common in warm-temperate to subtropical waters. The horn shark is a benthic shark, and is found on the continental shelf at a depth of 25-40 ft (8-12 m) to the intertidal zone at a depth of 656 ft (200 m) or more. It is most common at a depth of 7-36 ft (2-11 m). Horn sharks have been found in caves as deep as 656 ft (200 m), but usually they remain at much shallower depths. During the winter, horn sharks migrate into deeper waters, usually below 98 ft (30 m). Horn sharks exhibit a high degree of segregation corresponding to their life history. Adolescent horn sharks, between 1-1.6 ft (35-48 cm) total length (TL), tend to remain in deeper water, usually between 131-492 ft (40-150 m), and as they mature they migrate back into relatively shallow water. This segregation of habitat by size and stage of maturity reduces competition for food and habitat between younger and older sharks. Habitat choice also changes ontogenetically, with juveniles inhabiting sandy bottoms with little vertical relief and adults inhabiting rocky reefs with caves and crevices, or areas of thick algae cover. Juvenile horn sharks also use bat ray (Myliobatis californica) feeding pits in sandy areas as shelter and foraging areas. Horn sharks show a distinct diel pattern of activity, which is influenced by light intensity. Adult horn sharks are relatively inactive during the day, but are very active nocturnally. Horn sharks are site specific, returning to the same resting place at dawn and remaining there until the evening. Horn sharks have a small home range, usually no larger than 3,300 ft² (1,000 m²), and they exhibit long-term site fidelity (horn sharks have been recovered in their tagging locations after as much as 11.25 years at liberty). The furthest distance a horn shark has been documented as traveling is 10 miles (16.3 km). Water temperature is an important factor controlling the relative abundance of the horn shark, as they prefer water over 70°F, or 20 °C.


Biology

Horn shark
courtesy National Oceanic and Atmospheric Administration
horn shark
· Distinctive Features
The horn shark gets its name because it has a short, blunt head with high ridges above the eyes. This shark possesses spines on its 1st and 2nd dorsal fins and has an anal fin. The horn shark has broad muscular paired fins that are used as limbs for clambering on the bottom, and have a first dorsal-fin which originates over the pectoral-fin bases.

The supraorbital ridges on the horn shark are moderately low, and are abruptly truncated posteriorly. The interorbital space of the horn shark is deeply concave (the depth between ridges is less than one-fourth the eye length). The pre first dorsal-fin length is 22 to 27% of TL, and the anal-caudal space is 4 to 8% of total length (TL). The first dorsal-fin spine in the horn shark is directed obliquely posterodorsally in juveniles and adults; the first dorsal-fin origin is anterior to pectoral-fin insertions, over or slightly behind midbases of pectoral-fins and well posterior to fifth gill openings; the first dorsal-fin insertion is well anterior to pelvic-fin origin and well behind pectoral-fin insertion The first dorsal-fin free rear tip of the horn shark is opposite or somewhat anterior to pelvic-fin origins, and the first dorsal-fin is moderately high and semifalcate in adults, with heights of 9 to 14% of TL, and are slightly larger than the pelvic-fins. The second dorsal-fin origin is over or slightly in front of the pelvic-fin rear tips, and the second dorsal-fin is somewhat falcate and nearly as large as the first dorsal-fin. The anal-fin in horn sharks is subangular and weakly falcate, with the apex reaching the lower caudal-fin origin when laid back; the anal-caudal space is about equal to the anal-fin base. Total vertebral count in an adult H. francisci is from 103 to 123, the precaudal count is from 65 to 76. Egg cases of the horn shark have flat thin spiral flanges diagonal to the case axis and have no tendrils on case apices; the flanges have five turns.


· Coloration
The background color of the dorsal surface on the horn shark is dark to light grey or brown with dark brown or black spots, which are generally less than one-third eye diameter, on the body and fins. Small dark spots are also present below the eye on a dusky patch; and the fins are without abrupt dark tips and white dorsal-fin apices.


Horn shark jaw
© Doug Perrine
horn shark jaw
·Dentition
As the name of the genus implies, the dentition of the horn shark includes more than one type of tooth and serves a clutching-grinding function. The frontal holding teeth of this shark possess a cusp, and a pair of cusplets are present in adults. These teeth are small, the cusp is broad and deep, and lateral cusplets are usually present. The anterior-most teeth are symmetrical, becoming less symmetrical in more distal positions. The lateral teeth are molariform, are strongly carinate, and are not greatly expanded and rounded. The lateral teeth are significantly larger. These teeth have a low root, are laterally elongated, have a transverse depression on the basal lingual face, and may be weakly curved.


·Denticles
The horn sharks lateral trunk scales, or denticles, are small and smooth. The area behind the first dorsal fin of the horn shark has about 200 scales per cm² in adults.


·Size, Age, and Growth
Maximum total length of the horn shark is 4 ft (122 cm), with most adults reaching lengths of 3.2 ft (97 cm). Male horn sharks are sexually mature at 2-2.3 ft (58-71 cm); females mature at lengths greater than 2 ft (58 cm). The size of the hatchlings is 6-6.3 in (15-16 cm).


Horn sharks feed on benthic invertebrates including octopi
© Pasquale Pascullo
octopus
· Food Habits
The horn shark feeds primarily on benthic invertebrates, and small fishes. Adults prey upon gastropods, crabs, shrimp, squid, sea urchins, sea stars, and small fishes. Juvenile horn sharks feed on polychaetes, small clams, and sea anemones in addition to opportunistically feeding on squid and small fishes. Juveniles with their smaller, more pointed teeth seem to take more soft-bodied prey than adults. Food items in stomachs are usually broken into small pieces, indicating that the sharks actively grind their food with their powerful jaws and heavy molariform teeth. Olfactory cues are thought to be important in horn shark feeding, but electrosense and lateral line sense may also play a role.


· Reproduction
Horn sharks are oviparous, and females lay eggs (usually two) every 11-14 days, usually between February and April, depositing up the 24 eggs in a single season. Egg cases are usually laid in shallow water between 7-43 ft (2-13 m) deep. Development of embryos lasts 6-10 months, depending on water temperature. At hatching, the young measure 5.9-6.3 inches (15-16 cm) total length. The young begin to feed about a month after hatching.

Horn sharks mate in the months of December and January. "The male horn shark chases the female until the latter is ready, then both drop to the (ocean) bottom. The male grabs the female's pectoral fin with his teeth and inserts a single clasper in her cloaca; copulation lasts 30 to 40 minutes" according to Compagno in a 1984 publication. A few weeks after copulation, the female will deposit the fertilized eggs.

The egg cases of horn sharks are auger-shaped: more-or-less conical and surrounded by two broad spiral flanges. This shape enables a mother horn shark to wedge her eggs (which are usually laid two at a time) into crevices. This helps to prevent removal by most would-be predators.


· Predators
Other sharks and large fish are potential predators on horn sharks.


Importance to Humans

The horn shark's significance is mostly with recreational fisheries. Heterodontids are not consumed by humans on a regular basis. Horn sharks are caught as bycatch in bottom trawls and usually discarded, but they may be occasionally consumed or used as fishmeal. Various species of Heterodontids are commonly kept in public and private aquaria, where they can be maintained successfully for more than a decade.


Danger to Humans

Horn sharks may bite when harassed. According to the International Shark Attack File, there is one recorded instance of a shark bite involving a horn shark.


Conservation

The horn shark is listed as "Data Deficient", and as such has no special conservation status. This species is currently assessed as "Data Deficient" by the World Conservation Union (IUCN) because although horn sharks are taken as bycatch (primarily off Mexico), insufficient information exists to classify it differently. The IUCN is a global union of states, governmental agencies, and non-governmental organizations in a partnership that assesses the conservation status of species. If the gillnet fishery in Mexico expands significantly in the future, the population could potentially face problems.


Prepared by:
Robert Buch