Small shark, large aggregations
The Smalltail shark (Carcharhinus porosus) is a species of requiem shark, and part of the family Carcharhinidae. It can be found from southern Brazil to the northern Gulf of Mexico. It stays close to shore and prefers estuaries and muddy bottoms. They are known to form large aggregations.
Family: Carcharhinidae – Requiem sharks
Common Name– Ground Sharks
Common Name– Requiem Sharks
Status: IUCN Red List DATA DEFICIENT
Average Size and Length: The Smalltail shark reaches a maximum length of 4.9 feet. The average length 3.0–3.6 feet. Females grow larger than males.
Teeth and Jaw: The mouth of a Smalltail shark has short furrows at the corners and contains 13–15 tooth rows on either side of both jaws, but typically 14 upper and 13 lower tooth rows. The upper teeth are tall and triangular with strong serrations, becoming increasing oblique towards the sides. The lower teeth are comparatively narrower and more upright, with finer serrations.
Head: The Smalltail shark has a long, pointed snout. The leading margin of each nostril is enlarged into a narrow, pointed lobe. The Smalltail shark has large circular eyes with nictitating membranes. Just behind the eyes are a series of prominent pores.
Denticles: The dermal denticles are mostly non-overlapping; each has 3–5 horizontal ridges leading to posterior teeth, with the central one the longest.
Tail: The asymmetrical caudal fin has a strong lower lobe and a longer upper lobe with a ventral notch near the tip.
Demographic, Distribution, Habitat, Environment and Range: The Smalltail shark lives from the northern Gulf of Mexico to southern Brazil, excluding the Caribbean islands. They do live in Trinidad and Tobago.
The Smalltail shark is most abundant oof the northern Brazilian coast, off Pará and Maranhão. Historically over 50 years ago, there once was reported a nursery area just east of the Mississippi river, however there hasn’t been a sighting in 50 years.
The Smalltail shark can usually be found close to the bottom in inshore waters no deeper than 118 feet. Off northern Brazil, its environment is characterized by tides up to 23 feet high and reaching 7.5 knots; the salinity fluctuates between 14 ppt in the rainy season and 34 ppt in the dry season, and the temperature ranges from 25 to 32 °C (77 to 90 °F). It favors estuarine areas with muddy bottoms.
Diet: The Smalltail shark eats mainly bony fishes, including sea catfish, croakers, jacks, and grunts. Shrimp, crabs, and squid are a secondary food sources, while adults are also capable of taking young Sharpnose and Hammerhead sharks, and stingrays.
The Smalltail shark may potentially be preyed upon by larger sharks.
Aesthetic Identification: The Smalltail shark has a slender body, with 5 pairs of short gill slits. The Smalltail shark is plain gray to slate above and counter-shaded whitish below, with a faint lighter stripe on the flanks. The pectoral, dorsal, and caudal fins may darken toward the tips.
The small pectoral fins are falcate 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. There is no ridge between the dorsal fins. The pelvic fins are small with pointed to narrowly rounded tips, and the anal fin has a deep notch in its trailing margin.
Biology and Reproduction: The Smalltail shark is viviparous. Females produce litters of 2 to 9, but typically 4 to 6 pups 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. There are known nursery areas in shallow, murky waters like bays or estuaries off northern Brazil and Trinidad.
The newborns measure 12–13 inches long and grow an average of 2.8 inches per year in their first four years of life. Males and females mature sexually at 28–37 inches and 28–33 inches long. The maximum lifespan of a Smalltail shark is at least 12 years.
Behavioral Traits, Sensing and Intelligence: The Smalltail shark forms large aggregations segregated by sex, with the males generally found deeper than the females.
Smalltail Shark Future and Conservation: The Smalltail shark is caught incidentally by gillnet and longline fisheries. The meat is sold fresh, frozen, or dried and salted. The dried fins are exported for use in shark fin soup, the liver oil and cartilage are used medicinally, and the carcass is processed into fishmeal.
In Trinidad, its richness makes it the most economically important shark. Off northern Brazil, substantial numbers are caught by gillnet fisheries targeting the Serra Spanish mackerel.
Smalltail Shark Recorded Attacks on Humans: The Smalltail shark is considered harmless to humans, with no reported attacks.