The night-stalking shark
The Night shark (Carcharhinus signatus) is a species of requiem shark, in the family Carcharhinidae, found in the temperate and tropical waters of the Atlantic Ocean. It prefers depths from 160 to 1,970 feet deep. Night sharks are schooling sharks and are primarily active nocturnally.
Family: Carcharhinidae – Requiem sharks
Common Name– Ground Sharks
Common Name– Requiem Sharks
Status: IUCN Red List VULNERABLE
Average Size and Length: The Night shark is 6.6 feet long on average but reaches a length of 9.2 feet.
Average Weight: The Night shark reaches a weight of 169 pounds.
Teeth and Jaw: The mouth of the Night shark doesn’t have conspicuous furrows at the corners. It usually has 15 tooth rows on either side of both jaws, plus 1–2 upper and 1 lower symphysial tooth rows. Each upper tooth has a smooth to serrated edge, a narrow cusp becoming more oblique towards the corner of the mouth, and 2–5 coarse serrations at the base of the trailing margin. The number and size of serrations on the leading margin of the tooth cusp increase relative to those on the trailing margin as the Night shark grows. The lower teeth are upright and smooth-edged.
Head: The Night shark has a pointed, elongated snout. The nostrils have developed skin flaps. The Night shark has large circular eyes with irregular shaped pupils and nictitating membranes. The Night shark has green eyes when it is alive.
Denticles: The Night shark has diamond-shaped dermal denticles with horizontal ridges leading to marginal teeth, the number increasing from 3 in juveniles to 5–7 in adults.
Demographic, Distribution, Habitat, Environment and Range: The Night shark is mostly found in deep waters and has been documented as far down as depths of 1.2 miles. The Night shark has been seen as shallow as 85 feet from the surface. Off the southeastern United States, it is usually caught at a depth range of 160–1,970 feet. Off northeastern Brazil, the Night shark is most commonly found near the summits of seamounts ranging from 125 feet to 1,210 feet deep. Off West Africa, it occurs at depths of 295–935 feet. The temperature range is between 52–61 °F, the salinity is 36 ppt, and the dissolved oxygen level is 1.81 ml/l.
The Night shark can be found along the outer continental shelves and upper continental slopes of the Atlantic Ocean, from the U.S. state of Massachusetts to Argentina in the west, including the Gulf of Mexico and the Caribbean Sea, and from Senegal to northern Namibia in the east. In United States, it is relatively common off North Carolina and Florida (particularly the Florida Straits). It is possible that there have been sightings off the coast of Panama.
Diet: The Night shark feeds primarily on small, active bony fishes like mackerel, mullet, butterfish, sea basses, and flyingfish. On occasion, they will eat shrimp and squid.
Most feeding activity occurs at night with peaks at dawn and dusk.
Catch records and data indicate that the Night shark is usually found in schools and conducts a diel vertical migration, spending the day at a depth of 902–1,201 feet and moving up to shallower than 600 feet at night.
Ovulating and gravid females are rarely ever caught, suggesting that during this period they may stop feeding or segregate themselves from others of their species.
Aesthetic Identification: The Night shark is long and slender, and they have 5 pairs of short gill slits. They are grayish blue or brown above and counter-shaded whitish below, without fin markings. There is a faint band on each side and sometimes small black spots scattered over the back.
The pectoral fins are less than a fifth as long as the total body length of the Night shark, and taper towards a rounded tip. The first dorsal fin is small, triangular, and pointed, originating over the free rear tips of the pectoral fins. The second dorsal fin is much smaller than the first and originates over or slightly ahead of the anal fin. There is a ridge running between the dorsal fins.
Biology and Reproduction: Known parasites of the Night shark include an unknown usopod, the copepods Kroyeria caseyi, which attach to the gills, Pandarus bicolor and P. smithii, which infest the skin, and the tapeworms Heteronybelinia yamagutii, H. nipponica and Progrillotia dollfusi, which are found in the spiral valve intestine.
The common remora, Remora remora, may be found attached to the Night shark.
The Night shark is viviparous. After a year-long gestation period, females give birth to 4–18 but usually 12 or more) pups. Parturition may take place over several months.
One known nursery area is believed to exist at the continental shelf break at 34°S latitude, near the southern extreme of this species’ range.
The newborn young measure 20–28 inches long. They have a fast growth rate to start, which slows down once they reach the thresholds of adulthood. Males mature sexually at a length of 5.9–6.2 feet, which is about an age of 8 years, and females at a length of 6.6–6.9 feet, about 10 years.
The oldest known Night sharks are 17 years old; based on growth curves the maximum lifespan has been estimated at 28 years for males and 30 years for females.
Behavioral Traits, Sensing and Intelligence: The Night shark is fast an energetic and is nocturnal or most active at night. They do school and during diel vertical migrations.
Speed: The Night shark is a fast an energetic swimmer.
Night Shark Future and Conservation: This Night shark is prized for its large fins, which are exported for use in shark fin soup, and is also utilized as a source of meat, liver oil, and fishmeal. It has been included a part of the bycatch of pelagic longline fisheries targeting swordfish and tuna in the western Atlantic. Eating only 0.22 pounds of Night shark meat per day could result in the ingestion of several times the daily mercury content judged safe by the World Health Organization.
Despite its high value, new data suggest that the populations off the Untied States are stabilizing and even increasing. This isn’t the case in other regions.
Night Shark Recorded Attacks on Humans: The Night shark is a deep-water shark, and does not pose a threat to humans.