Featured Elasmobranch-Smalltail Shark
Category : Featured Elasmobranch
Carcharhinus porosus (Ranzani, 1840)
Family Carcharhinidae (Requiem Sharks)
Identification: This is a small requiem shark, with a slender fusiform body, a moderately long, well-rounded snout, and large circular eyes. Five short gill slits located anterior to the pectoral fin. Labial furrows are weakly developed and inconspicuous. Teeth of upper jaw broad and triangular, with high cusps and heavy serration; upper teeth display a distinct notch along the outer margin; lower teeth obliquely set, with wide bases, and narrow cusps. Large first dorsal fin originates over posterior margin of pectoral fin and curves back to a blunt sickle shaped apex. Second dorsal fin is low and positioned over or slightly behind the base mid-point of the anal fin. The interdorsal ridge absent. Pectoral fins short and broad, and curve to slightly rounded tips. Anal fin notched. Caudal fin approximately one-fourth total length of body. Coloration is grey to bluish-grey above, becoming white ventrally; a white bands sometimes appears on flanks; tips of pectoral, dorsal, and caudal fins may have slightly dusky markings.
Size: Average length of adult smalltail sharks ranges from 90-110 cm. (3 – 3.6 ft) with females being slightly larger than males. Maximum reported total length is 130 cm (4.4 ft). Size at birth ranges between 30-40 cm. (0.9 – 1.3 ft).
Distribution: The smalltail shark is found in the shallow coastal waters of the eastern Pacific from the Gulf of California south to Peru, and in the western Atlantic Ocean from the northern Gulf of Mexico to southern Brazil, with the exclusion of the Caribbean Sea. The highest population density of smalltail sharks has been found to be in estuaries and mangroves in northern Brazil, coinciding with the species’ nursery grounds. These regions are known for their high tidal range.
Habitat: This is an inshore, demersal (down to a depth of 35 m) shark found over continental shelves as well as in the brackish waters of shallow, muddy bottom estuarine habitats.
Biology: The smalltail shark is an opportunistic predator, with a diet consisting of small bony fishes and benthic invertebrates. Adults often prey on the young of other sharks, skates, and rays. Males reach reproductive maturity at 75 cm (2.5 ft) and females at 84 cm (2.8ft), coinciding with an average age of six years. This shark is viviparous, with a yolk-sac placenta. After a 10-month gestation period, two to nine pups per litter are born during the spring and summer.
General interest: Although there is a small market for its flesh and liver oil, the smalltail shark has little significant commercial value. It is commonly caught as bycatch in the gillnets of other fisheries, notably fisheries targeting Spanish mackerel off the coast of Brazil. The smalltail shark is currently listed as “Data Deficient” by the IUCN. In Brazil, due to its slow growth rate, late maturity and low reproductive rate, along with an overall lack of management this species is considered vulnerable. Virtually nothing is known of this species in the eastern central Pacific. This shark is considered to be harmless to humans.
By Paul J. Clerkin
Pacific Shark Research Center
Moss Landing Marine Laboratories
8272 Moss Landing Road, Moss Landing, CA 95039