Pacific Sharpnose Shark, Rhizoprionodon longurio
The Pacific Sharpnose Shark, Rhizoprionodon longurio, whose common Spanish name is cazón bironche, is a member of the Requiem Shark or Carcharhinidae Family, known collectively as tiburónes gambuso in Mexico. This fish is named after its long snout. Globally, there are seven species in the genus Rhizoprionodon, three of which are found in Mexican waters, two in the Atlantic and one in the Pacific.
The Pacific Sharpnose Sharks are medium-sized with slender bodies. They are grayish-brown dorsally and transition to white ventrally. The rear margin and upper tip of their caudal fins are broadly black. Their dorsal fins have dusky tips and their pectoral fins have light margins. Their caudal fin is strongly asymmetrical and has a large lower lobe and a top lobe notched under the tip. Their anal fin is smaller than the second dorsal fin; their first dorsal fin is large with its origin over the rear margin of the pectoral fins; their second dorsal fin is slightly smaller than and originates behind the anal fin origin; and their pectoral fins are broad and triangular. Their head has a long pointed snout which is longer than the width of the mouth. They have long labial furrows at the corner of their mouth, large round eyes, widely spaced nostrils, and 26 to 29 rows of narrowly triangular, oblique, and smooth to finally serrated teeth. They have five gill slits, the last two being over the pectoral fins.
The Pacific Sharpnose Sharks are a relatively common inshore shark often found in shallow estuaries over sandy and muddy bottoms. At certain times of the year, they can be locally abundant. They are known to move to deeper waters during the summer and autumn being found from the surface to depths up to 330 feet. They are known to migrate up to 600 miles. Females are larger than males reaching a maximum length of 1.54 meters (5 feet 6 inches) versus 1.10 meters (3 feet 7 inches). They consume small fish, cephalopods, and crustaceans. In turn they are preyed upon by numerous large carnivorous fish including large sharks. They reach sexual maturity within three years. Reproduction is viviparous and follows either an annual or biannual cycle with gestation periods of six to twelve months. Litter sizes range from one to twelve pups measuring 30 cm (12 inch) to 37 cm (16 inch). Larger females produce larger litter sizes but their pups are smaller in stature. Females reside in deeper waters most of the year and return to coastal waters in large sexually segregated schools to give birth. Nursery areas are inshore in enclosed bays and sounds with the coastal waters of Sonora being documented as an important pupping area. They have a lifespan of up to nine years.
In Mexican waters the Pacific Sharpnose Sharks are found in all waters of the Pacific.
The Pacific Sharpnose Shark is most likely confused with the Smalltail Shark, Carcharhinus porosus (second dorsal fin origin over middle of anal fin) and the Whitenose Shark, Nasolamia velox (large nostrils set close together). It is the only requiem shark in the eastern Pacific with long labial furrows.
The Pacific Sharpnose Sharks are seasonally abundant and caught primarily as a by-catch in trawls with gill nets, longlines, and traps set by inshore artisanal fishermen. They provide the basis for an important seasonal inshore artisanal fishery, however, are overfished in some locations with significantly diminishing populations. Their meat is sold for human consumption and also used as chunk bait targeting other larger sharks. Their fins are small and not in demand for shark fin soup. In United States waters they are regulated with daily bag limits for recreational anglers and annual quotas for commercial fishermen. From a conservation perspective they are currently listed as Data Deficient as catch levels within their range have been poorly documented. They are considered one of the most resilient sharks. As their nursery areas are located inshore, they are vulnerable to exploitation and human-induced habitat degradation. They pose a moderate threat to humans due to their inshore habitat bringing them in close contact with humans, however, their bites are normally not serious. They can be found in several public aquariums.
Pacific Sharpnose Shark, Rhizoprionodon longurio. Provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, May 2012. Length: 72 cm (2 feet 4 inches).