Product Code Database
The smalltail shark ( Carcharhinus porosus) is a species of requiem shark, and part of the family Requiem shark. It is found in the western Atlantic Ocean, from the northern Gulf of Mexico to southern Brazil. It inhabits shallow waters close to shore, particularly over bottoms around estuaries. It tends to swim low in the water column and forms large aggregations segregated by sex. A slim species generally not exceeding in length, the smalltail shark has a rather long, pointed snout, a broad, triangular first dorsal fin, and a second dorsal fin that originates over the midpoint of the anal fin base. It is plain gray in color, without prominent markings on its fins.
The diet of the smalltail shark consists mainly of such as Sciaenidae, while , , and smaller elasmobranch may also be consumed. It is viviparous, meaning the developing are sustained by a connection. Females bear litters of two to 9 young on a biennial cycle, following a roughly 12-month gestation period. The smalltail shark is often caught as bycatch and may be used for meat, fins, liver oil, shark cartilage, and fishmeal. It seems to have declined significantly since the 1980s. Therefore, the International Union for Conservation of Nature has listed it as critically endangered.
The evolutionary relationships of the smalltail shark are uncertain. Based on morphology, Jack Garrick in 1982 and Leonard Compagno in 1988 tentatively placed it in a group defined by the whitecheek shark ( C. dussumieri) and the blackspot shark ( C. sealei). This grouping was equivocally supported by Gavin Naylor's 1992 allozyme-based phylogenetic analysis. Alternately, a 2011 phylogenetic study by Ximena Vélez-Zuazoa and Ingi Agnarsson, based on nuclear DNA and mitochondrial , found close relationships between the smalltail shark, the daggernose shark ( Isogomphodon oxyrhynchus), the blacknose shark ( C. acronotus), and the finetooth shark ( C. isodon). The Pacific smalltail shark ( C. cerdale) was once mistakenly synonymized with C. porosus, until 2011 when José Castro resurrected it as a distinct taxon. An undescribed species closely similar to C. porosus is known from Southeast Asia.
The small are falcate (sickle-shaped) with relatively pointed tips. The first dorsal fin is broad, forming nearly an equilateral triangle in adults, with a blunt apex; it originates over the pectoral fin rear tips. The second dorsal fin is small and originates over the midpoint of the anal fin base. No ridge exists between the dorsal fins. The are small with pointed to narrowly rounded tips, and the anal fin has a deep notch in its trailing margin. The asymmetrical caudal fin has a strong lower lobe and a longer upper lobe with a ventral notch near the tip. The mostly do not overlap; each has three to five horizontal ridges leading to posterior teeth, with the central one the longest. This shark is plain gray to slate above and whitish below, with a faint lighter stripe on the flanks. The pectoral, dorsal, and caudal fins may darken toward the tips. The smalltail shark reaches a maximum known length of , though is typical. Females grow larger than males.
Like other members of its family, the smalltail shark is viviparous: once the developing exhaust their supply of yolk, the yolk sac develops into a connection through which the mother delivers nourishment. Females produce litters of two to 9 (typically four to six) young every other year; litter size increases with the size of the female. The gestation period lasts around 12 months. Reproduction occurs throughout the year, with a peak in birthing from September to November. Known nursery areas occur in shallow, murky waters off northern Brazil and Trinidad, where many and estuaries provide shelter and food. The newborns measure long and grow an average of per year in their first four years of life. Males and females sexual maturity at and long, respectively, corresponding to six years of age for both sexes. The average growth rate slows to per year after maturation. The maximum lifespan is at least 12 years.
|
|
