Mexican Horn Shark, Heterodontus mexicanus
Mexican Horn Shark, Heterodontus mexicanus. Fish caught within the coastal waters within Magdalena Bay, Baja California Sur, May 2017. Length: 41 cm (16 inches). Catch, photograph, and identification courtesy of Jimmy Camacho, Puerto Adolfo Lopez Mateos, Baja California Sur.
The Mexican Horn Shark, Heterodontus mexicanus, is a member of the Bullhead Shark or Heterodontidae Family, and is known in Mexico as tiburón perro. The common name is derived from its dorsal fin spines. Globally, there are eight species in the genus Heterodontus, of which twi are found in Mexican waters, both in the Pacific Ocean.
The Mexican Horn Sharks has a rectangular blocky body 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 5 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; their 2 dorsal fins are virtually identical, each with a spine at the front (a key to identification) and the first 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 Shark is a coastal species found in both rocky and sandy areas from close inshore to depths up to 67 m (220 feet) preferring water temperatures in excess of 21oC (70oF). They reach a maximum of 70 cm (28 inches) in length. They are an 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. The Mexican Horn Shark has been poorly studied and very little known about the biology of this species including maturity, longevity, reproduction age, gestation period, reproduction periodicity, litter size, growth rate, and lifespan.
he Mexican Horn Sharks is a resident of all Mexican waters of the Pacific Ocean with the exception that they are absent from Magdalena Bay, Baja California Sur, northwards along the central and northwest coasts of Baja. They are most common in the greater Magdalena Bay area, Baja California Sur, and in the northern portions of the Sea of Cortez.
The Mexican Horn Shark is most likely and often confused with the Horn Shark, Heterodontus francisci (black spots on fins and body measuring less than one third the eye diameter) for which the co-exist.
From a conservation perspective the Mexican Horn Shark is currently considered to be Data Deficient with poorly monitored with undocumented populations. They are targeted by spear fishermen in certain locations with their spines being retained to make jewelry. They are also an accidental by-catch in crab traps, gillnets, and trawling nets. They are considered to be of poor food value and no or very limited commercial value are normally a catch and release except for subsistence fishermen. They are consider harmless and will only attack humans if provoked.