Mexican Horn Shark.
Stout body. Blocky, buntly rounded head with prominent ridges above eyes. Two dorsal fins, each with a spine at its origin. Small gap between dorsal spines and leading edge of dorsal fins. First dorsal fin origin over pectoral fin insertion. Second dorsal fin origin anterior to pelvic fin free rear tip. Pectoral fins much larger than first dorsal. Pelvic fins about the same size as first dorsal fin. High, short anal fin. Well developed caudal fin with square terminal lobe.
Dorsal coloration light brown with scattered black spots that are half of eye diameter or bigger. Subtle pale vertical bar behind eye. Spots may be vague on larger animals. Juveniles may have more prominent light and dark areas and more noticeable spots.
Maximum length at least 70cm.
Subtropical seas. Present on rocky terrain, coral reefs and sand. From inshore to at least 50m.
The Mexican horn shark is found in the eastern Pacific from the Sea of Cortez, southern Mexico, Guatemala, Colombia and Panama and possibly Ecuador and Peru.
The Mexican hornshark is not of commercial value, but is taken as bycatch in bottom gillnets and shrimp trawling operations in the Gulf of California and Mexican coastal lagoons. Catches are discarded or sometimes retained for human consumption or fishmeal. Hornsharks are hardy species and can survive capture if returned to the water; however, catches in Mexico are often left to die on beaches. Eggs are laid in rocky areas unlikely to be impacted by fisheries. Insufficient information is available at present to assess the species beyond Data Deficient, however, the species is of potential concern due to its restricted disjunct distribution and artisanal and industrial fishing pressure.
Citations and References
Garayzar, C.V. 2006. Heterodontus mexicanus. The IUCN Red List of Threatened Species 2006: e.T60235A12331644. https://dx.doi.org/10.2305/IUCN.UK.2006.RLTS.T60235A12331644.en. Downloaded on 27 November 2020.
Oviparous. the Mexican horn shark lays auger shaped egg cases with short tendrils on the widest end. Cases measure 6-8cm in length. Egg cases may be found laying on the substrate, in crevices, or entangled on corals.
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. It is possible that the Mexican horn shark employs a similar technique.
The Mexican horn shark consumes crustaceans (crabs) and bottom dwelling fishes.
Reaction to divers
Probably easy to approach. Most heterodontids remain motionless unless molested, at which point they usually retreat deeper into crevices or caves where possible.
I have only come across the egg cases of this species. On multiple visits, I have seen egg cases suspended from corals in 25-40m on the wall at Coronado Island near Loreto in the Sea of Cortez.
I have heard that Mexican horn sharks are spotted fairly regularly on liveaboard dive trips to the Midriff Islands. During my only trip there, I spent a lot of time searching for this species but did not see any evidence of it.
Please email any recent information on sightings to sharkandrayinfo(at)gmail.com