Mexican Horn Shark

Mexican Horn Shark, Heterodontus mexicanus

The Mexican Horn Shark, Heterodontus mexicanus, whose common Spanish name is tiburón perro, is a species in the Bullhead Shark or Heterodontidae Family, known collectively as tiburones cornudos in Mexico. This fish is named after its dorsal fin spines. Globally, there are only eight species in the genus Heterodontus, of which two are found in Mexican waters, both in the Pacific.

The Mexican Horn Sharks have rectangular blocky bodies and are easy to identify. They are gray-brown dorsally and transition to white ventrally with black spotting on their fins and body. They have a pale bar between their eyes and one or two indistinct blotches below their eyes. Their head is conical and elevated with a pig-like round blunt snout and a small mouth that opens anteriorly. They have a low bony ridge above each eye that ends abruptly at the rear; the space between their eyes is deeply concave. Their teeth morphology varies: it is sharp at the front for grasping prey and flat at the back for crushing shellfish. They have five gill slits, the first of which is enlarged and the second and third of which are over their pectoral fins. Their caudal fin is asymmetric. They have two virtually identical dorsal fins, each with a spine at the front (a key to identification). Their first dorsal fin originates before the pectoral fin base and their second dorsal fin originates behind the pelvic fins. They have small denticles on their flank that are rough to the touch.

The Mexican Horn Sharks are a coastal species found in both rocky and sandy areas from close inshore to depths up to 220 feet. They reach a maximum length of 70 cm (28 inches). They prefer water temperatures in excess of 21oC (70oF). They are elusive, slow, and sluggish fish that spend their days hiding under ledges, in caves, and in kelp beds. They emerge at night to feed on seafloor benthic invertebrates including abalone, crabs, oysters, polychaete worms, shrimp, and occasionally small fish. They are poor swimmers and use their strong pectoral fins to crawl along rocks. Reproduction is oviparous with females laying spiral egg cases that they wedge into crevices; pups hatch and emerge as 14 cm (5.5 inch) miniature adults. Very little known about the biology of this species including maturity, longevity, reproduction age, gestation period, reproduction periodicity, litter size, growth rate, and lifespan.

In Mexican waters the Mexican Horn Sharks are found in all waters of the Pacific with the exception that they are absent from Magdalena Bay northwards along the central and northwest coasts of Baja. They are most common in the greater Magdalena Bay area and in the northern portions of the Sea of Cortez.

The Mexican Horn Shark can be easily confused with the Horn Shark, Heterodontus francisci (black spots on fins and body measuring less than one third the eye diameter).

The Mexican Horn Sharks are considered a poor food fish and are not of commercial value. They are normally a catch and release except for subsistence fishermen. They are caught fairly frequently as a by-catch in bottom gill nets and by trawlers and are processed into fishmeal when retained. From a conservation perspective they are currently listed as Data Deficient being poorly monitored with undocumented populations. They are also often confused in the field with the Horn Shark, with whom they co-exist. Due to their low resiliency, long regeneration cycles, restricted range, and catch frequency, they are considered threatened. They are also targeted by spearfishermen and their spines are retained to make jewelry. They are considered harmless and will only attack humans if provoked.

Mexican Horn Shark, Heterodontus mexicanus. Fish caught within the coastal waters of Magdalena Bay, Baja California Sur, May 2017. Length: 41 cm (16 inches). Catch, photo, and identification courtesy of Jimmy Camacho, Jimmy’s Sportfishing, Puerto Adolfo Lopez Mateos, Baja California Sur (jimmyhcamacho@gmail.com; 613-114-0761; 612-204-1960).