Horn sharks (Heterodontus francisci), aptly named for the spines preceding their two dorsal fins and the ridges above their eyes, are small, bottom-dwelling sharks also recognized for their distinctive spiral-shaped egg cases. Photo credit: Ed Bierman.
Description
Horn sharks can reach nearly four feet in length and weigh up to twenty pounds at full maturity. They possess short, blunt heads featuring a pronounced ridge above each eye. Along their slender bodies are two dorsal fins, each preceded by a cartilaginous spine. Their coloration varies from dark to light grey or brown, adorned with brown or black spots on their bodies and fins, while their bellies exhibit a lighter yellow hue. They have a pectoral fin on each side of their bodies, vertically positioned tail fins, and smaller pelvic fins closer to the center of their bodies, which they can use to walk along the sea floor.
Within their mouths, they have two distinct types of teeth: pointed front teeth for grasping prey and larger, wider teeth along the sides for crushing the hard shells or exoskeletons of their prey. Despite their small size, horn sharks possess a remarkable bite force, the greatest known among sharks relative to their size. Horn sharks have 19-26 tooth rows of teeth in the upper jaw and 18-29 tooth rows in the lower. Front teeth are small and pointed, sporting a central cusp with a pair of lateral cusplets.
These sharks are easy to identify by their blunt head, curved snouts, long mouths, and sharp spines. They also have a brown or gray back with white spots and a yellowish underside to provide camouflage amid the dirt and rocks.
Key physical characteristics include:
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- Stout body.
- Large square head with prominent ridges above eyes.
- Two large dorsal fin, each with a spine at its origin.
- First dorsal fin origin anterior to pectoral fin insertion.
- Second dorsal fin origin level with pelvic fin free rear tip.
- Pectoral fins much larger than first dorsal.
- Pelvic fins about the same size as dorsal fins.
- High, short anal fin.
- Dorsal coloration may be light brown, dark brown, or patches of both, with scattered small black spots.
- Spots may be absent on larger animals.
- Maximum length 120cm.
Diet and Habitat
Horn sharks are carnivorous, consuming mollusks, echinoderms, and crustaceans, with a particular fondness for the purple sea urchin. As slow-moving, nocturnal predators, they utilize their teeth to seize, trap, and crush prey found along the sea floor. Horn sharks move along the bottom of the sea bed, sucking up prey into its mouth. Adults feed almost exclusively on mollusks, echinoderms, and crustaceans. In order, the crush its well-armored prey these sharks bite down with the highest known bite force relative to size of any shark. Ranging from 95 to 200 N. The largest adults feed on the short-spined purple urchin, (Strongylocentrotus purpuratus) which stains their teeth and fin spines purple. A new study shows that these bottom-dwelling sharks use powerful suction to slurp up their prey, even when it’s tucked into tight spaces. Their jaw movements stay the same no matter how tricky the meal, but when food is stuck, they get creative-leveraging their fins, doing little headstands, and using their whole bodies to yank it free.
They inhabit warmer temperate and subtropical regions of the eastern Pacific Ocean, ranging from central California down to the Gulf of California in Mexico, including Channel Islands National Marine Sanctuary. Horn sharks tend to reside on the continental shelf along the coasts of California and Mexico, including the Gulf of California. It is sometimes found as far north as San Francisco and almost as far south as Guadalajara. Young horn sharks reside in deeper offshore waters, gradually migrating to shallower waters as they mature. Adults inhabit the sea floor, favoring rocky reefs where they can conceal themselves among kelp, caves, and crevices. Each day, horn sharks return to the same hidden site to rest, avoiding predators such as seals, predatory birds like eagles, and larger sharks.
Horn sharks dwell among kelp beds or rocky outcrops in shallow waters around 26 to 40 feet deep. Present on rocky reefs and in kelp forests. La Jolla Cove is a well known shore dive north of San Diego where horn sharks are frequently sighted. If the swell is not too problematic, try searching for juveniles under rocks in the sea grass zone very close to the entry point. Adults tend to be in slightly deeper water e.g. The beach in front of the commercial laundry near Avalon on Catalina Island is another great spot to see juvenile horn sharks at night.
Life History
Horn sharks belong to the bullhead shark family and can live up to 25 years, although the oldest observed horn shark is estimated to have been approximately 50 years old. Based on observations from its life in captivity, the horn shark is known to have a life expectancy of at least 12 years.
They are oviparous sharks, meaning females lay eggs that hatch outside the mother’s womb. Mature females can lay two eggs every 11 to 14 days, with each egg protected by a spiralized egg case. The female wedges these cases into small cracks and crevices to protect them from potential predators. Every egg case contains one shark pup, which takes between six and nine months to hatch, depending on environmental conditions and genetics. Although egg cases sometimes found laying on the sand, they are usually found securely screwed into tight crevices between rocks. Although their installation has not been witnessed, Port Jackson Sharks in Australia have been documented holding their egg cases in their mouths and rotating their bodies to literally screw the eggs into cracks. Eggs usually laid 2-13 m (7-43 ft.) deep. As many as 24 eggs may be laid in a single season.
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Horn sharks are generally solitary, living near other individuals but not gathering in social groups except for hunting and breeding. These sharks have an annual mating season in December or January. The male chases the female to indicate his interest. Once the female signals she is ready, the male grabs her pectoral fin with his teeth and mates with her. A few weeks later, the female will begin laying a litter of up to 24 eggs. She only lays two of her litter at a time, so it takes her a few months to fully produce them all. These eggs are encased in a spiral-shaped substance with the same color as the surrounding kelp so they can be safely deposited in crevices and kept hidden from predators. The horn shark is one of the few species of shark to actually invest a great deal of time into parental care. The young litter of pups emerges from the eggs after some six to nine months, usually measuring no more than 7 inches in size. The sharp spines serve as the main means of protection against hungry predators like angel sharks and sea bass. The juveniles begin to feed on the yolk sac for the first month until they are old enough to hunt on their own. Then they graduate to soft-bodied prey such as worms and sea anemones. Only once their teeth and bodies are more developed do they finally begin to feed on hard-shelled creatures. Each individual shark grows at a highly different rate, which makes it difficult to say anything consistent about its life stages.
Interestingly this species segregates by age. Adolescents between 35-48 cm (1-1.6 ft.), are normally seen in 40-150 m (131-492 ft.) on sandy bottoms. As the sharks age, they move closer and closer to shallower habitats, thus reducing competition between age groups. Adults live on rocky reefs in caves and crevices. They are nocturnal, resting in the same site from dawn till dusk every day, hunting a small area of 1,000 m² (3,300 ft²).
Threats and Conservation
Horn sharks are not commercially valuable in California and are not targeted by fishing, although they are often accidentally caught in fishing gear like traps and trawls during recreational and commercial activities. This shark has almost no value to fishers except as a sport for the most dedicated recreational fishers. The only real danger from humans is when it’s accidentally caught in shrimp trawls or gill nets. When the shark is caught deliberately, it is almost always for scientific purposes.
The species is desirable for display in aquariums due to their hardy nature, ease of care, and ability to breed regularly in human care. This shark can survive at least 12 years in captivity, while other sharks die from starvation because they stop eating.
There is still a need for more information to understand how horn shark populations are changing over time, but larger-scale threats to the ocean like climate change, ocean acidification, habitat destruction, and overfishing will likely affect them in the future. Not much is known about the number of horn sharks left in the wild. The IUCN Red List considers it to be data deficient, but the species appears to be fairly common throughout its natural habitat. The horn shark (Heterodontus fransisci) population in California is probably stable. This species has no commercial value and is discarded when caught incidentally.
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The IUCN is a global union of states, governmental agencies, and non-governmental organizations in a partnership that assesses the conservation status of species. This species is currently listed as “Data Deficient” by IUCN.
Behavior
The horn shark is a slow-moving and lethargic species that spends most of the day camouflaged among the rocks and only comes out at night to feed. But don’t mistake this lethargy for indolence. Once it spots a predator or prey, the horn shark is ready to move at fast speeds in an instant. This species is mostly ignored by humans because it has little value to recreational and commercial fishers. The shark with horns maintains a territory of approximately 10,000 square feet in which it roams and feeds. This shark is very sensitive to light. Horn sharks are primarily nocturnal and are behaviorally sensitive to environmental light levels.
Horn sharks are sluggish swimmers that rest during the day in deep crevices or under overhangs.
The horn shark is completely harmless to humans because it has evolved to instinctively run away at the first sign of danger. Horn sharks may bite when harassed.
Unlike many other shark species, the horn shark does not rely as heavily on electroreception. In comparison to other species that have over 2,000 ampullae of Lorenzini, this species only has 148.
Sharks with horns are one of the top predators in their ecosystem, but they are not apex predators. A full-grown adult horn shark only has a few natural predators, among them other sharks.
Taxonomy
The horn shark, scientifically known as Heterodontus francisci, belongs to the Heterodontidae family and is a species of bullhead shark. The horn shark is classified within the Heterodontidae family, known as bullhead sharks. The horn shark belongs to the family Heterodontidae (bullhead sharks). There are ten living species in this genus, including the crested bullhead shark and the Port Jackson shark.
The genus was initially described by Blainville in 1816, while the species was later documented by Girard in 1855. The genus was described by Blainville in 1816. The species was described by Girard in 1855. The species was described by Girard in 1855. The current valid scientific name for the horn shark is Heterondontus francisci. There are no subspecies of horn sharks, and they evolved in a similar way to most sharks.
The scientific name of these sharks is Heterodontus francisci. The genus name Heterodontus derives from a combination of two Greek words: heteros, meaning different or other, and odous, meaning teeth. This is perhaps a reference to their molar-like arrangement of teeth in the mouth. 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.
Galapagos Bullhead Shark Distinguished by bolder light and dark pattern and larger, more closely spaced black spots.
Mexican Horn Shark Distinguished by lower brow ridges and pale bar between eyes in adults.
Distribution
The horn shark is common in warm-temperate to subtropical waters. Temperate seas. Normally found along continental shelves, found as deep as 152 m (499 ft.). However, it is most commonly seen at 2-11 m (7-36 ft.), preferring 20 °C (70°F) water. During winter, they migrate to deep water, more than 30 m (98 ft.).
These sharks have a narrow range along the coasts of California and Mexico. Reports indicate that it may appear as far south as Ecuador and Peru, but it’s unclear if these specimens are actually a similar species identified as a horn shark by mistake. This species sticks to the eastern Pacific.
Compagno suggested that the horn shark may also be present in South America but there is no evidence to support this.