Lifespan, longevity, and ageing

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Maximum longevity: 12 years (wild)
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Conservation Status

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Horn sharks are not an endangered species. Therefore, they have no special status. They have been known to vacate certain areas with a high number of divers. But as long as divers don't drastically increase all along the Eastern Pacific Coast horn sharks should remain off the endangered species list.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: data deficient

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Herstein, M. 2000. "Heterodontus francisci" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Heterodontus_francisci.html
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Matt Herstein, University of Michigan-Ann Arbor
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Benefits

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Horn sharks do not have any negative effect on humans. They will not even attack humans, prefering to flee if a person comes near (Stevens 1987).

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Herstein, M. 2000. "Heterodontus francisci" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Heterodontus_francisci.html
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Benefits

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The horn shark does not have a great deal of commercial value. Some people catch them "for sport and for its large fin spines, which are made into jewelry" (Compagno 1994, p. 157). However the most important value of Heterodontus francisci comes from research. These sharks have been known to survive in captivity for as many as twelve years where scientists study them (Castro 1983). This is important because most sharks die shortly after they are placed into captivity; usually because they stop eating. Therefore, the horn shark proves quite valuable to scientists wishing to study sharks (Compagno 1984; Castro 1983; Stevens 1987).

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Herstein, M. 2000. "Heterodontus francisci" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Heterodontus_francisci.html
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Trophic Strategy

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The diet of horn sharks consists mainly of small fishes and invertebrates. Heterodontus francisci have been known to eat many types of small fish; however, their chief staples are mollusks, sea urchins, and crustaceans. Since horn sharks are fairly inactive they prefer to wait for their prey to swim by before attacking it and feasting. But they won't necessarily lie still waiting for food to come by (Compagno 1984; Castro 1983; Stevens 1987).

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Herstein, M. 2000. "Heterodontus francisci" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Heterodontus_francisci.html
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Matt Herstein, University of Michigan-Ann Arbor
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Distribution

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Heterodontus francisci lives in warm-temperate and subtropical regions of the eastern Pacific. It is mainly found inhabiting the coastal areas from Southern California to the Gulf of California and also areas around Ecuador and Peru (Compagno 1984).

Biogeographic Regions: pacific ocean (Native )

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Herstein, M. 2000. "Heterodontus francisci" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Heterodontus_francisci.html
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Habitat

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Horn sharks live in temperate waters in the Eastern Pacific. They dwell along the water bottom frequently in kelp beds laying 8-12 meters deep. Horn Sharks have been found in caves as deep as 200 meters, but usually they remain at much shallower depths (Castro 1983).

Aquatic Biomes: coastal

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Herstein, M. 2000. "Heterodontus francisci" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Heterodontus_francisci.html
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Life Expectancy

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Average lifespan
Status: captivity:
12 years.

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Herstein, M. 2000. "Heterodontus francisci" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Heterodontus_francisci.html
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Matt Herstein, University of Michigan-Ann Arbor
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Morphology

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The horn shark gets its name because it has a short, blunt head with high ridges above the eyes (Castro 1983). Heterodontus francisci range in size from approximately 97cm to 120cm (Compagno 1984). They are a brownish color covered in black spots and their underbellies have a yellowish tint (Compagno 1984; Castro 1983).

Range mass: 0 to 0 kg.

Average mass: 10 kg.

Other Physical Features: bilateral symmetry

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Herstein, M. 2000. "Heterodontus francisci" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Heterodontus_francisci.html
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Reproduction

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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" (Compagno 1984). A few weeks after copulation, the female will deposit the fertilized eggs amongst the rocks where they will hatch anywhere from 6-9 months later. The young sharks, when first born, will be roughly 15-17cm in length (Castro 1983; Compagno 1984; Stevens 1987).

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Herstein, M. 2000. "Heterodontus francisci" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Heterodontus_francisci.html
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Diagnostic Description

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fieldmarks: Dorsal fins with spines, anal fin present, colour pattern of small dark spots less than one-third eye diameter on light background, no light bar on interorbital space between supraorbital ridges, first dorsal-fin origin over pectoral-fin bases. Supraorbital ridges moderately low, abruptly truncated posteriorly; interorbital space deeply concave, depth between ridges less than one-fourth eye length.

Anterior holding teeth with a cusp and a pair of cusplets in adults, posterior molariform teeth strongly carinate and not greatly expanded and rounded.

Pre-first dorsal-fin length 22 to 27%, and anal-caudal space 4 to 8%, of total length.

Lateral trunk denticles small and smooth, area behind first dorsal fin with about 200 denticles per cm² in adults.

Propterygium separate, not fused to mesopterygium.

First dorsal-fin spine directed obliquely posterodorsally in juveniles and adults; first dorsal-fin origin anterior to pectoral-fin insertions, over or slightly behind midbases of pectoral fins and well posterior to fifth gill openings; first dorsal-fin insertion well anterior to pelvic-fin origin and well behind pectoral-fin insertion; first dorsal-fin free rear tip opposite or somewhat anterior to pelvic-fin origins; first dorsal fin moderately high and semifalcate in adults, height 9 to 14% of total length, slightly larger than pelvic fins. Second dorsal-fin origin over or slightly in front of pelvic-fin rear tips, second dorsal fin somewhat falcate and nearly as large as first dorsal fin. Anal fin subangular and weakly falcate, with apex reaching lower caudal-fin origin when laid back; anal-caudal space about equal to anal-fin base.

Total vertebral count 103 to 123, precaudal count 65 to 76, monospondylous precaudal count 30 to 38, diplospondylous precaudal count 32 to 46, pre-first dorsal-fin spine count 12 to 16, count from diplospondylous transition to second dorsal-fin spine 7 to 16.

Egg cases with flat thin spiral flanges diagonal to case axis and no tendrils on case apices; flanges with five turns. A large species, mature between 59 and 122 cm.

Background colour of dorsal surface dark to light grey or brown with dark brown or black spots on body and fins, spots generally less than one-third eye diameter; body without a dark harness pattern; head without a light bar on interorbital surface; small dark spots present below eye on a dusky patch; fins without abrupt dark tips and white dorsal-fin apices; hatchlings without whorls on fins and body, colour pattern as in adults although brighter.

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Sharks of the world An annotated and illustrated catalogue of shark species known to date. Volume 2 Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Leonard J.V. Compagno 2001.  FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO. 2001. p.269.
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Distribution

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Warm-temperate and subtropical waters of the eastern Pacific: USA (Central and southern California), Mexico (Baja California, Gulf of California), and probably Ecuador and Peru. Off the USA it is most common off southern California but ranges to Monterey Bay and may occasionally penetrate as far north as San Francisco Bay (where it is not resident) during northern influxes of warm water.
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Sharks of the world An annotated and illustrated catalogue of shark species known to date. Volume 2 Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Leonard J.V. Compagno 2001.  FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO. 2001. p.269.
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Size

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Maximum 122 cm but most adults are below 97 cm. Egg cases 10 to 12 cm long and 3 to 4 cm wide at broad end (not over flanges); length at hatching 15 to 16 cm; males maturing at about 58 to 59 cm and adult at 59 to 84 cm; females mature above 58 cm.
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Sharks of the world An annotated and illustrated catalogue of shark species known to date. Volume 2 Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Leonard J.V. Compagno 2001.  FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO. 2001. p.269.
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Brief Summary

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A common benthic and epibenthic shark, found on the eastern Pacific continental shelf,most abundantly at depths from 2 to 11 m but ranging from the intertidal down to at least 150 m. Found on rocky bottoms including reefs, kelp beds, sandy draws between rocks, and on sand flats. On rocks it often occurs in deep crevices and small caves, and ventures far into large underwater caverns. Juveniles shelter on sandy bottom, often near algae, rocks, detritus, or in feeding holes excavated by bat rays (Myliobatis californica). The horn shark is sluggish, nocturnal, and mostly solitary, though small aggregations have been seen by divers. It is seldom seen moving during the daytime but commonly has its head in a crevice. Shortly after dusk this shark becomes active and apparently feeds mostly at night, but ceases activity after dawn. Adults tend to return to the same resting place every day, but range at night over a small home range of roughly 0.1 hectare.According to Michael (1993) these sharks migrate into deeper water in winter, but it is uncertain if this occurs in the tropical part of their range.Experimentation with captive horn sharks indicates that their diel activity pattern is controlled by light intensity. The broad, muscular paired fins of the horn shark are used as limbs for clambering on the bottom, and are highly mobile and flexible. Swimming is slow and sporadic. Courtship and copulation have been observed in captivity. The male horn shark chases the female until the latter is ready, then both drop to the 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 min. One to two weeks later eggs are laid by captive females, one of which laid two eggs per day at 11 to 14 day intervals for four months. In nature these sharks mate in December or January and females drop eggs in February to April. Females normally deposit eggs under rocks or in crevices between them, but in captivity they drop eggs on the bottom where the contents of egg cases may be subsequently sucked out and eaten by these sharks. Eggs can be readily hatched in aquaria and take 7 to 9 months to hatch; the young begin to feed a month after hatching.

The horn shark feeds on benthic invertebrates, including sea urchins (echinoids), crabs, shrimp, isopods, sipunculid worms, anemones, bivalves, gastropods (possibly abalone), cephalopods (octopuses), but less commonly on small fish including pipefish (Syngnathidae) and blacksmith (Chromis punctipinnis, Pomacentridae). According to Michael (1993), the active diurnal blacksmith is eaten at night by the horn shark while it is resting on the bottom.Predators are little known: a Pacific angelshark (Squatina californica) has been filmed as swallowing small horn sharks and spitting them out alive, possibly because of their strong spines.

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Sharks of the world An annotated and illustrated catalogue of shark species known to date. Volume 2 Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Leonard J.V. Compagno 2001.  FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO. 2001. p.269.
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Benefits

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Interest to fisheries minimal, probably utilized or formerly utilized for fishmeal as a bycatch of the shrimp fishery and other bottom trawling operations in Pacific Mexican waters. It has been captured by divers for sport and for its large fin spines, which are made into jewellery; decreases in numbers of horn sharks have been noted in areas with intense diver activity in southern California.
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Sharks of the world An annotated and illustrated catalogue of shark species known to date. Volume 2 Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Leonard J.V. Compagno 2001.  FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO. 2001. p.269.
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Life Cycle

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Oviparous (Ref. 205). Distinct pairing with embrace (Ref. 205). Courtship starts when the male chases the female, then when both are ready, they drop to the bottom (Ref. 43278). During courtship and prior to copulation, the male bites and wraps its body to the female pectoral fin, body, tail, and gills (Ref. 51127, 49562). The male then inserts a single clasper in the female's cloaca; copulation lasts 30 to 40 min. After one or two weeks later, the eggs are laid in about 11 to 14 intervals for 4 months which were deposited under rocks or in crevices, as was observed in nature. In captivity, the female drops the eggs on the bottom where the contents of the egg cases maybe eaten by these sharks; the eggs are hatched in 7 to 9 months. The young begin to feed one month after hatching (Ref. 43278).
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Recorder
Susan M. Luna
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Trophic Strategy

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Sluggish, nocturnal, and mostly solitary species. Inhabits rocky bottoms, kelp beds, sandy draws between rocks, on sand flats, deep crevices and small caves and also large underwater caverns. Adults tend to return to the same resting place every day (Ref. 43278). Feeds on benthic invertebrates, especially sea urchins, crabs and probably abalone, also fishes. Also in Ref. 9137.
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Biology

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Sluggish, nocturnal, and mostly solitary species. Inhabit rocky bottoms, kelp beds, sandy draws between rocks, on sand flats, deep crevices and small caves and also large underwater caverns. Adults tend to return to the same resting place every day (Ref. 43278). Feed on benthic invertebrates, especially sea urchins, crabs and probably abalone, also fishes. Oviparous (Ref. 50449). May bite back when harassed. Has broad muscular paired fins used as limbs for clambering on the bottom. Catch reduced to fish meal; fin spines used in production of jewels.
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Importance

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fisheries: minor commercial; aquarium: public aquariums; price category: unknown; price reliability:
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Horn shark

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The horn shark (Heterodontus francisci) is a species of bullhead shark, in the family Heterodontidae. It is endemic to the coastal waters off the western coast of North America, from California to the Gulf of California. Young sharks are segregated spatially from the adults, with the former preferring deeper sandy flats and the latter preferring shallower rocky reefs or algal beds. A small species typically measuring 1 m (3.3 ft) in length, the horn shark can be recognized by a short, blunt head with ridges over its eyes, two high dorsal fins with large spines, and a brown or gray coloration with many small dark spots.

Slow-moving, generally solitary predators, horn sharks hunt at night inside small home ranges and retreat to a favored shelter during the day. Their daily activity cycles are controlled by environmental light levels. Adult sharks prey mainly on hard-shelled molluscs, echinoderms, and crustaceans, which they crush between powerful jaws and molar-like teeth, while also feeding opportunistically on a wide variety of other invertebrates and small bony fishes. Juveniles prefer softer-bodied prey such as polychaete worms and sea anemones. The shark extracts its prey from the substrate using suction and, if necessary, levering motions with its body. Reproduction is oviparous, with females laying up to 24 eggs from February to April. After laying, the female picks up the auger-shaped egg cases and wedges them into crevices to protect them from predators.

Horn sharks are harmless unless harassed, and are readily maintained in captivity. They are not targeted by either commercial or recreational fisheries, though small numbers are caught as bycatch. In Mexico this species is used for food and fishmeal, and in California its spines are made into jewelry. The International Union for Conservation of Nature (IUCN) does not yet have enough information to determine the horn shark's conservation status. It faces few threats off the coast of the United States.

Taxonomy

The French biologist Charles Frédéric Girard published the first scientific description of the horn shark under the name Cestracion francisci in 1855, in the Proceedings of the Academy of Natural Sciences of Philadelphia.[2] This species was later placed in the genus Gyropleurodus, which was eventually synonymized with the genus Heterodontus. The specific epithet francisci is a reference to San Francisco, although the range of the horn shark does not extend that far north.[3] The type specimen from Monterey Bay has since been lost. The scientific name for this species has been given erroneously as Heterodontus californicus.[2]

Description

Like other bullhead sharks, the horn shark has a short, wide head with a blunt snout and prominent supraorbital ridges over the eyes. The horn shark's supraorbital ridges are low and terminate abruptly; the space between them on top of the head is deeply concave. Each eye lacks a nictating membrane and is followed by a tiny spiracle. The nostrils are split into inflow and outflow openings by a long flap that reaches the mouth. The inflow openings are encircled by a groove, while another groove connects the outflow openings to the mouth. The mouth is small and curved, with prominent furrows at the corners. There are 19–26 tooth rows in the upper jaw and 18–29 tooth rows in the lower jaw. The teeth at the front of the jaws are small and pointed, with a central cusp flanked by a pair of lateral cusplets; those at the sides of the jaws are much larger, elongated lengthwise, and molar-like.[2][3]

The body is cylindrical, with two high, somewhat falcate (sickle-shaped) dorsal fins bearing stout spines at the front.[2] The fin spines of reef-dwelling horn sharks are shorter than those living in algal habitats, as their spines become worn down on rocks from the sharks' movements.[3] The first dorsal fin originates over the bases of the large pectoral fins, while the second dorsal fin originates slightly anterior to the free rear tips of the pelvic fins. The caudal fin has a short lower lobe and a long, broad upper lobe with a strong notch near the tip. The horn shark's dermal denticles are small and smooth, numbering some 200/cm2 on the back in adults.[2] The dorsal coloration consists of various shades of gray or brown with many small dark spots, though these may be absent in older sharks; the underside is yellowish. There is a dark patch of small spots below the eye.[2][3] This species may reach a length of 1.2 m (3.9 ft), though most individuals do not exceed 1 m (3.3 ft).[4]

Distribution and habitat

 src=
A horn shark off Santa Catalina, California.
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Unlike the adults, juvenile horn sharks prefer a flat, sandy habitat.

The horn shark inhabits the continental shelf of the eastern Pacific Ocean, occurring off the coasts of California and Baja California from Monterey Bay southward, and in the Gulf of California. Uncommon influxes of warm water northward may bring it as far as San Francisco Bay.[2] There are unconfirmed reports of this species off Ecuador and Peru, which may be misidentifications of other species.[1]

For most of the year, horn sharks are most common at a depth of 2–11 m (6.6–36.1 ft). At the onset of winter, they migrate to water deeper than 30 m (98 ft).[3] This species has been found in caves as deep as 200 m (660 ft). Juvenile horn sharks between 35–48 cm (1.15–1.57 ft) long prefer sandy flats with low vertical relief, in water 40–150 m (130–490 ft) deep. They often take advantage of large feeding pits excavated by the bat ray (Myliobatis californica) for shelter and food. As they mature, horn sharks shift into shallower water and their preferred habitat becomes structurally complex rocky reefs or algae beds.[4] This strongly benthic species seldom ventures more than 2 m (6.6 ft) above the substrate.[3]

The relative abundances of the horn shark and the swellshark (Centroscyllim ventriosum), which shares the same habitat, are negatively correlated because horn sharks prefer temperatures warmer than 20 °C (68 °F) while swellsharks are more cold-tolerant. At Santa Catalina Island, a 20-year warming trend has resulted in an increase in the horn shark population and a decrease in the swellshark population. Horn sharks are less common than swellsharks in the northern Channel Islands, where the water is cooler.[3]

Biology and ecology

 src=
Horn sharks rest during the day and only become active at night.

The horn shark is a 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.[2] 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.[5] 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.[3] The longest documented movement for an individual horn shark is 16 km (9.9 mi).[4]

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.[5]

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.[6] 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.[2] 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.[7][8][9][10]

Feeding

 src=
Sea urchins are a favored prey of the horn shark.

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).[11] 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.[11] 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.[3]

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.[3][6] Horn sharks hunt mainly using their sense of smell.[4] Although electroreception certainly plays a role in locating prey, this species has only 148 ampullae of Lorenzini. This is much fewer than in most other sharks, which may have over 2,000.[12] Like other sharks, the horn shark's teeth are regularly replaced; it takes 4 weeks for a dropped tooth to be replaced.[13]

The horn shark captures prey via suction, created by expanding its buccal cavity. Its labial cartilages are modified so that the mouth can form a tube, facilitating the suction force. Once the prey is drawn into the mouth, it is secured with the sharp front teeth and then ground into pieces by the flat lateral teeth. To extract buried or affixed prey, the horn shark grips it and adopts a vertical posture with the head and pectoral fins against the substrate and the tail arched above. The shark then acts as a lever with its pectoral fins as the fulcrum: with a downward stroke of the tail, it forces its head upwards and pulls the prey loose; this mode of feeding has not been observed in any other shark. The horn shark is also capable of protruding its upper jaw up to 15% the length of its head; this motion takes only 20 milliseconds to accomplish and allows the shark to use its upper jaw like a chisel to dislodge firmly attached prey.[14]

Life history

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The spiral-flanged egg case of a horn shark; the shape allows the egg to be secured within crevices.

Mating in the horn shark occurs in December or January, on a possibly annual reproductive cycle.[15] The male chases the female to indicate interest; once she is ready both sharks settle on the bottom, where the male grips the female's pectoral fin in his teeth and inserts one of his claspers into her cloaca. After 30–40 minutes of copulation, the pair disengages and the female spins with her snout in the sand for another 30 minutes.[6] From February to April, the females lay a maximum of 24 eggs two at a time once every 11–14 days, in water 2–13 m (6.6–42.7 ft) deep.[1] The egg case has two flanges spiraling around it, and thus may take the female several hours to deposit.[16] At first the case is soft and light brown, and over a few days it hardens and darkens in color. Not including the flanges, the case measures 10–12 cm (3.9–4.7 in) long and 3–4 cm (1.2–1.6 in) wide; sharks from the Channel Islands produce longer egg cases than those from mainland California, suggesting that they are separate populations.[2][3]

One of the few sharks to exhibit parental care, female horn sharks in the wild pick up their eggs in their mouths and wedge them into crevices.[3] However, in captivity the eggs are simply dropped on the bottom and may later be cannibalized.[2] The eggs hatch in 6–10 months; at emergence the young measure 15–17 cm (5.9–6.7 in) long.[1] Newly hatched sharks are provisioned with an internal yolk sac and do not have to feed until they are a month old, though they are capable of feeding and will accept food during this period. Horn sharks grow slowly and at a highly variable rate that does not correspond to their size; this has frustrated attempts to determine their aging process.[3] Males mature at a length of 56–61 cm (22–24 in) and females at a length of at least 58 cm (23 in).[1] Individual sharks have lived to over 12 years old in captivity, and there exists an unconfirmed report of a shark reaching 25 years of age.[3]

Human interactions

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Horn sharks are innocuous towards humans.

Under normal circumstances, horn sharks are harmless to humans and can readily be approached underwater.[3] However, they can be provoked into biting, and some pugnacious individuals have been known to chase and bite divers after being harassed.[6] These sharks should be handled with care as their fin spines can inflict a painful wound.[3] The horn shark adapts well to captivity and has been maintained and bred in many public aquariums across the United States.[2] In July 2018, three people were arrested after stealing a juvenile horn shark from the San Antonio Aquarium. The shark was smuggled out of the aquarium in a stroller under a blanket. It was returned unharmed two days later.[17]

The horn shark has no commercial value in California, where it is captured unintentionally in traps and trawls and by recreational anglers. The shark's hardiness ensures that it can often be returned to the water alive.[1] This species benefits from general restrictions placed on coastal fishing gear by the State of California. The average annual bycatch off California is 1,800 kg (4,000 lb), though historically it has varied from 2.5 kg (5.5 lb) in 1976 to 9,500 kg (20,900 lb) in 1979.[15] Divers sometimes kill them for sport or to make jewelry out of their fin spines, which may be the cause of a decline in the numbers of horn sharks in the most intensely dived areas of southern California. Off Mexico, this species is caught incidentally in shrimp trawls and demersal gillnets, and used for human consumption and fishmeal. The expansion of Mexican gillnet fisheries may pose a conservation concern in the future. At present, the International Union for Conservation of Nature (IUCN) does not have sufficient information to assess the overall conservation status of this species; its status in United States waters is likely Least Concern.[1]

References

  1. ^ a b c d e f g Carlisle, A.B. (2015). "Heterodontus francisci". IUCN Red List of Threatened Species. 2015: e.T39333A80671300. doi:10.2305/IUCN.UK.2015-4.RLTS.T39333A80671300.en.
  2. ^ a b c d e f g h i j k l Compagno, L.J.V. (2002). Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date (Volume 2). Rome: Food and Agriculture Organization. pp. 36–37. ISBN 978-92-5-104543-5.
  3. ^ a b c d e f g h i j k l m n o p Ebert, D.A. (2003). Sharks, Rays, and Chimaeras of California. University of California Press. pp. 81–86. ISBN 978-0-520-23484-0.
  4. ^ a b c d Buch, R. Biological Profiles: Horn Shark. Florida Museum of Natural History Ichthyology Department. Retrieved on June 18, 2009.
  5. ^ a b Nelson, D.R.; Johnson, R.H. (December 12, 1970). "Diel Activity Rhythms in the Nocturnal, Bottom-Dwelling Sharks, Heterodontus francisci and Cephaloscyllium ventriosum". Copeia. 1970 (4): 732–739. doi:10.2307/1442315. JSTOR 1442315.
  6. ^ a b c d Martin, R.A. Kelp Forests: Horn Shark. ReefQuest Centre for Shark Research. Retrieved on June 19, 2009.
  7. ^ Appy, R.G.; Dailey, M.D. (October 1973). "Two New Species of Acanthobothrium (Cestoda: Tetraphyllidea) from Elasmobranchs of the Eastern Pacific". The Journal of Parasitology. 59 (5): 817–820. doi:10.2307/3278414. JSTOR 3278414.
  8. ^ Caira, J.N.; Zahner, S.D. (November 2001). "Two new species of Acanthobothrium Beneden, 1849 (Tetraphyllidea: Onchobothriidae) from horn sharks in the Gulf of California, Mexico". Systematic Parasitology. 50 (3): 219–229. doi:10.1023/A:1012241913722. PMID 11590308.
  9. ^ Deets, G.B.; Dojiri, M. (March 1989). "Three species of Trebius Krøyer, 1838 (Copepoda: Siphonostomatoida) parasitic on Pacific elasmobranchs". Systematic Parasitology. 13 (2): 81–101. doi:10.1007/BF00015217.
  10. ^ Anderson, R.C. (2000). Nematode Parasites of Vertebrates: Their Development and Transmission. CABI. p. 389. ISBN 978-0-85199-421-5.
  11. ^ a b Huber, D.R., Eason, T.G., Hueter, R.E. and Motta, P.J. (2005). "Analysis of the bite force and mechanical design of the feeding mechanism of the durophagous horn shark Heterodontus francisci". Journal of Experimental Biology. 208 (Pt 18): 3553–3571. doi:10.1242/jeb.01816. PMID 16155227.CS1 maint: multiple names: authors list (link)
  12. ^ Bullock, T.H., Hopkins, C.D., Popper, A.N. and Fay, R.R. (2005). Electroreception. Birkhäuser. p. 49. ISBN 978-0-387-23192-1.CS1 maint: multiple names: authors list (link)
  13. ^ Reif, W. (1976). "Morphogenesis, pattern formation and function of the dentition of Heterodontus (Selachii)". Zoomorphologie. 83: 1–47. doi:10.1007/BF00995429.
  14. ^ Edmonds, M.A., Motta, P.J. and Hueter, R.E. (2001). "Food capture kinematics of the suction feeding horn shark, Heterodontus francisci". Environmental Biology of Fishes. 62 (4): 415–427. doi:10.1023/A:1012205518704.CS1 maint: multiple names: authors list (link)
  15. ^ a b Fowler, S.L., Cavanagh, R.D., Camhi, M., Burgess, G.H., Cailliet, G.M., Fordham, S.V., Simpfendorfer, C.A. and Musick, J.A. (2005). Sharks, Rays and Chimaeras: The Status of the Chondrichthyan Fishes. International Union for Conservation of Nature and Natural Resources. pp. 237–238. ISBN 978-2-8317-0700-6.CS1 maint: multiple names: authors list (link)
  16. ^ Martin, R.A. Heterodontiformes: Bullhead Sharks. ReefQuest Centre for Shark Research. Retrieved on June 19, 2009.
  17. ^ "Shark returned to San Antonio aquarium after being stolen in baby stroller".

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Horn shark: Brief Summary

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The horn shark (Heterodontus francisci) is a species of bullhead shark, in the family Heterodontidae. It is endemic to the coastal waters off the western coast of North America, from California to the Gulf of California. Young sharks are segregated spatially from the adults, with the former preferring deeper sandy flats and the latter preferring shallower rocky reefs or algal beds. A small species typically measuring 1 m (3.3 ft) in length, the horn shark can be recognized by a short, blunt head with ridges over its eyes, two high dorsal fins with large spines, and a brown or gray coloration with many small dark spots.

Slow-moving, generally solitary predators, horn sharks hunt at night inside small home ranges and retreat to a favored shelter during the day. Their daily activity cycles are controlled by environmental light levels. Adult sharks prey mainly on hard-shelled molluscs, echinoderms, and crustaceans, which they crush between powerful jaws and molar-like teeth, while also feeding opportunistically on a wide variety of other invertebrates and small bony fishes. Juveniles prefer softer-bodied prey such as polychaete worms and sea anemones. The shark extracts its prey from the substrate using suction and, if necessary, levering motions with its body. Reproduction is oviparous, with females laying up to 24 eggs from February to April. After laying, the female picks up the auger-shaped egg cases and wedges them into crevices to protect them from predators.

Horn sharks are harmless unless harassed, and are readily maintained in captivity. They are not targeted by either commercial or recreational fisheries, though small numbers are caught as bycatch. In Mexico this species is used for food and fishmeal, and in California its spines are made into jewelry. The International Union for Conservation of Nature (IUCN) does not yet have enough information to determine the horn shark's conservation status. It faces few threats off the coast of the United States.

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Habitat

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A common benthic and epibenthic shark, found on the eastern Pacific continental shelf most abundantly at depths from 2 to 11 m but ranging from the intertidal down to at least 150 m. Found on rocky bottoms including reefs, kelp beds, sandy draws between rocks, and on sand flats. On rocks it often occurs in deep crevices and small caves, and ventures far into large underwater caverns
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bibliographic citation
Compagno, L.J.V. (2001). Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Volume 2. Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). <em>FAO Species Catalogue for Fishery Purposes.</em> No. 1, Vol. 2. Rome, FAO. 269p. Compagno, L.J.V. (2001). Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Volume 2. Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). <em>FAO Species Catalogue for Fishery Purposes.</em> No. 1, Vol. 2. Rome, FAO. 269p.
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