Sicklefin Smoothhound, Mustelus lunulatus
The Sicklefin Smoothhound, Mustelus lunulatus, whose Spanish common name is cazón segador, is a species in the Hound Shark or Triakidae Family, known as collectively as cazónes in Mexico. 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 Sicklefin Smoothhounds have elongated slender bodies. They are gray or brown on their backs and sides transitioning to white ventrally. Their fins have no distinguishing marks. Their head has a pointed snout, large horizontal oval eyes, and a large mouth. Their teeth are distinctive and only feature small nubs. They have prominent short spiracles behind each eye. Their anal fin is smaller than and originates under the middle of the second of the two dorsal fins. Their caudal fin is strongly asymmetrical; the lower lobe is expanded with a concave rear edge. Their first dorsal fin is slightly larger than the second dorsal fin with a concave rear edge and a base midway between the pectoral and pelvic fins. The origin of the second dorsal fin is well before the origin of the anal fin. They have five gill slits with the last two being over the pectoral fins. They have skin denticles shaped as pointed ovals with a single point.
The Sicklefin Smoothhounds are a coastal schooling pelagic species found demersal over the continental shelf and within enclosed bays and shallow muddy bottoms at depths up to 655 feet. They reach a maximum length of 1.75 meters (5 feet 9 inches). They feed on crabs, isopods, polychaetes worms, shrimp, squid, and a wide variety of small fish. In turn they are preyed upon by larger predatory bony fish including sharks. Reproduction is viviparous with embryos being nourished by yolk-sac placenta. Litter sizes are small with pups born live. They are a poorly studied species and very little is known about their behavioral patterns.
In Mexican waters the Sicklefin Smoothhounds are found in all waters of the Pacific.
The Sicklefin Smoothhound Shark is most likely confused with the Brown Smoothhound, Mustelus henlei (first dorsal fin with a fibrous edge), the Gray Smoothhound, Mustelus californicus (broadly triangular dorsal fin), the Sharptooth Smoothhound, Mustelus dorsalis (sharp pointed teeth), and the Whitemargin Smoothhound, Mustelus albipinnis (fins with white edges).
The Sicklefin Smoothhound are considered marginal food fish and normally a “catch and release”. They are marketed fresh, frozen, and smoked on a limited basis for human consumption. However, things have changed dramatically in Mexico over the last year. A shark in the possession of a local fishermen can be a real problem since a moratorium has been put in place banning the retention of all sharks taken in Mexican waters. This species is considered harmless to humans. The Sicklefin Smoothhounds have not been evaluated from a conservation perspective. They most likely have had population declines due to extensive commercial fishing pressures, low birth rates, and low resiliency.