Whitemargin Smoothhound

Whitemargin Smoothhound, Mustelus albipinnis

The Whitemargin Smoothhound, Mustelus albipinnis, whose common Spanish name is cazón hacat, is a species in the Hound Shark or Triakidae Family, known collectively as cazones in Mexico. This fish is also known as the White-tipped Smoothhound. Its common Spanish name, hacat, is the word for shark in the dialect of the Seri Indians from Tiburon Island. It was introduced to science as recently as 2005 and is therefore poorly documented and poorly studied. Globally, there are twenty-two species in the genus Mustelus, eight of which are found in Mexican waters, three in the Atlantic and five in the Pacific.

The Whitemargin Smoothhounds have elongated slender bodies. They are uniform gray-brown dorsally and transition to yellowish-white ventrally with conspicuous white tips and white at the trailing edges of their anal, caudal, dorsal, and pectoral fins. They have a short narrow head with a pointed snout. Their eyes are large horizontal ovals with ventral nictitating membranes. They have a short mouth equipped with eight rows of curved teeth. Their upper jaw teeth are cuspidate and asymmetric with low rounded blunt cusps and a small basal point and their lower central bottom teeth are wide, low, and without points. Their teeth are periodically shed and replaced. Their upper jaw folds are longer than their lower folds. They have five gill slits, the last two located over their pectoral fin base. Their anal fin originates a little behind the middle of the second dorsal fin and is smaller than the second dorsal fin. Their caudal fin is strongly asymmetric and semi-lunar; the upper caudal lobe is notched and elongated with a concave rear margin; the lower caudal lobe has not point and a concave rear margin. Their first dorsal fin is large and its center is nearer the base of the pectoral fins than the base of the pelvic fins; their second dorsal fin is smaller than the first; and their pectoral fins are large and curved with round pointed tips. The pelvic fins in juveniles and females are asymmetrical with the left fin being smaller and more concave than the right fin. They have numerous triangular and pointed skin denticles along most of their body.

The Whitemargin Smoothhounds are found offshore demersal on the continental shelf at depths between 350 and 900 feet. Females are larger than males and reach a maximum of 1.18 meters (3 feet 10 inches) in length; males reach a maximum of 1.09 meters (3 feet 7 inches) in length. Reproduction occurs via aplacental viviparity with young being nourished by the yolk and hatching inside the uterus. Litter sizes range from three to twenty-three pups measuring 30 cm (12 inches) to 35 cm (14 inches) in length. Their feeding habits, prey, predators, and lifespan have been poorly studied and very little is known about their behavioral patterns.

In Mexican waters the Whitemargin Smoothhounds have a poorly documented limited range but have been found north of Angel de la Guarda Island in the northern Sea of Cortez, west of Santa Cruz and Montserrat Islands and in Bahia de La Ventana in the southern Cortez, and along the southwest coast of the Baja.  The major problem is that they are exceedingly difficult to recognize and almost always identified as the very common Gray Smoothhound, Mustelus californicus.

The Whitemargin Smoothhound can be confused with the Brown Smoothhound, Mustelus henlei (slightly asymmetric, high, sharp, and cusped teeth), the Gray Smoothhound, Mustelus californicus (molarform and slightly asymmetric upper teeth; jaw folds of equal length), the Sharptooth Smoothhound, Mustelus dorsalis (slightly asymmetric, high, sharp, and cusped teeth; upper jaw fold slightly longer than lower fold), the Sicklefin Smoothhound, Mustelus lunulatus (molarform and slightly asymmetric upper teeth; upper jaw fold shorter than bottom fold), and the Whitetip Reef Shark, Triaenodon obesus (white tips only on caudal and dorsal fins).

The Whitemargin Smoothhounds are caught by artisanal fishermen and deepwater trawlers targeting hake, and thus are poorly documented. Their distribution and abundance are virtually unknown. From a conservation perspective, they are listed as of Least Concern. They are considered quality food for human consumption.

Whitemargin Smoothhound, Mustelus albipinnis. Fish caught from coastal waters off Point Palmilla, Baja California Sur, January 2017. Length: 66 cm (26 inches).

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f675-whitemargin-smoothhound-3aWhitemargin Smoothhound, Mustelus albipinnis. Fish caught from coastal waters of Bahia de los Angeles, Baja California, August 2016. Length: 92 cm (36 inches). Catch, photo, and identification courtesy of Chris Wheaton, Fullerton, CA.