TAWNY NURSE SHARK
One of the strongest suctioning sharks
The Tawny Nurse shark (Nebrius ferrugineus) is a species of shark belonging to the family Ginglymostomatidae. They are currently the only extant member of the genus Nebrius. It is found widely along coastlines in the Indo-Pacific, preferring reefs, sandy flats, and seagrass beds from very shallow water to a depth of 230 feet. Nocturnal and social, the large Tawny Nurse shark is vulnerable currently.
Family: Ginglymostomatidae – Nurse Sharks
Common Name– Carpet Sharks
Common Name– Nurse Sharks
Average Size and Length: They are born between 40-60 cm/1.3-1.9 feet. Mature Tawny Nurse sharks have been measured around 250 cm/8.2 feet. The maximum recorded has been between 314-320 cm/10.3-10.5 feet.
Current Rare Mythical Sightings: The Tawny Nurse shark was first described by French naturalist René-Primevère Lesson as Scyllium ferrugineum, based on a 1.4 m/4.7-foot-long specimen from New Guinea. His short account was published in 1831 in Voyage au tour du monde, sur la corvette La Coquille. A more detailed description, along with an illustration, was published by German naturalist Eduard Rüppell in 1837 as Nebrius concolor, based on a specimen from the Red Sea. Both names were retained, often in separate genera (Ginglymostoma and Nebrius), until they were synonymized by Leonard Compagno in 1984. Compagno recognized that the tooth shape differences used to separate these species were the result of differences in age. There are a number of other names that this shark is sometimes referred to as, but the most commonly known name is the Tawny Nurse shark.
Fossil teeth belonging to the Tawny Nurse shark have been found in the Pirabas Formation of northern Brazil, dating back to the Lower Miocene (23–16 Ma). The presence of these fossils indicates that the range of the Tawny Nurse shark once extended to the tropical Atlantic Ocean, prior to the formation of the Isthmus of Panama. (dos Reis, M.A.F. (2005). “Chondrichthyan Fauna from the Pirabas Formation, Miocene of Northern Brazil, with Comments on Paleobiogeography“. Anuário do Instituto de Geociências. 28: 31–58).
Teeth and Jaw: The mouth is small and terminal, with the lower lip divided into three lobes. There are 29–33 tooth rows in the upper jaw and 26–28 tooth rows in the lower jaw. They are compresses and arranged in an imbricate (overlapping) pattern with the outermost 2–4 functional rows separated from the rest by a narrow space. Each tooth is small and comb-like and resembles a fan, with a broad base rising to a small, sharp central point flanked by 3 or more smaller cusps on both sides. As the shark ages, the teeth become relatively taller and thicker. They are osteodont with the pulp cavity filled with osteodentine.
Head: The head of the Tawny Nurse shark is flat and broad and square-ish. There are fairly long barbels. The mouth is in front of the lateral eyes. There are tiny spiracles behind the eyes. The small eyes have prominent ridges. It is suggested that the young have white lower eyelids, but this is not confirmed.
Denticles: The dermal denticles are diamond-shaped or rounded-rhomboid in shape, having 4–5 faint ridges radiating from a short, blunt point.
Tail: The caudal fin is fairly long. It is greater than 25% of the total length. The caudal fin has a shallow upper lobe and barely present lower lobe.
Demographic, Distribution, Habitat, Environment and Range: The Tawny Nurse shark has a wide range. In the tropical Indo-Pacific it can be found in KwaZulu-Natal, South Africa to the Red Sea and the Persian Gulf and India, including Madagascar, Mauritius, the Chagos Archipelago, the Seychelles, and the Maldives. In east Asia north to Japan, Australia to the Marshall Islands and Tahiti (36°N – 27°S, 32°E – 136°W). They are found on or near the bottom in sheltered areas such as lagoons (juveniles particularly love lagoons), in channels, crevices, and in caves in the outer coral and rocky reef edges, in seagrass and sand on and near reefs and off beaches. They stay in the intertidal zone to greater than 330 feet, but stay mainly between 16-98 feet. There home range is limited and they often return to the same resting place.
Diet: They feed on corals, crustaceans, cephalopods, reef fish, sea urchins, and sometimes even sea snakes.
Ram-Suction Index: Nurse sharks are obligate suction feeders capable of generating suction forces that are among the highest recorded for any aquatic vertebrate to date. They may also shake their head violently to rip off smaller, digestible sizes of prey, or suck and spit. They suck prey in rapidly with their very small mouths and large pharynx.
Aesthetic Identification: The Tawny Nurse shark is quite similar in appearance to the Nurse shark (Ginglymostoma cirratum). Some differences include its pointed-tipped dorsal fins and narrow, falcate shaped pectoral fins. The body is large and cylindrical in shape. The fourth and fifth pairs of gill slits are placed close together. The color of the Tawny Nurse shark may slowly change between different shades of browns and brownish-greys depending on its habitat. Sometimes they appear to have a reddish or yellowish hue. They are off-white ventrally. The large first dorsal fin base is over the pelvic fin bases. The fins are angular. It has sickle-shaped pectoral fins. There are 2 spineless dorsal fins, and the first is larger than the second one.
Biology and Reproduction: The Tawny Nurse shark is ovoviviparous. The young feed inside the uterus on large infertile yolky eggs. This is called oophagy. The litter size is not confirmed, but research suggests 1-4 pups depending upon completion in the uterus. The Tawny Nurse shark is known to mate from July to August off Madagascar.
There are five species of tapeworms (Pedibothrium sp.) documented from the spiral intestines of the Tawny Nurse shark taken from the waters off Australia and French Polynesia.
Many tawny nurse sharks found off the coasts of Japan, Taiwan, and the Ryukyu Islands lack a second dorsal fin. This physical abnormality has been speculated to result from pregnant females being exposed to water of unusually high salinity and/or temperature, possibly from human activity. In 1986, 9.6-foot-long adult male with both a missing dorsal fin and partial albinism (in the form of white body color with gray-brown eyes) was captured off Wakayama Prefecture, Japan. This anomalous individual is the largest albino shark known to date, having survived for a long time in the wild despite its lack of camouflage.
(Teshima, K.; Kamei, Y.; Toda, M. & Uchida, S. (December 1995). “Reproductive Mode of the Tawny Nurse Shark Taken from the Yaeyama Islands, Okinawa, Japan with Comments on Individuals Lacking the Second Dorsal Fin“. Bulletin of the Seikai National Fisheries Research Institute. 73: 1–12.)
Behavioral Traits, Sensing and Intelligence: They are mainly nocturnal. They are known to stalk reefs at night searching for prey to suck out of crevices. They will aggregate and rest in piles in shelters by day.
The Tawny Nurse shark has a more placid disposition than the Nurse shark.
The Tawny Nurse shark has been observed to make a noise or grunt when captured. There isn’t enough research to confirm if this is intentional or not, and if it is strictly defensive in nature.
Speed: The Tawny Nurse shark is much more streamlined than other Nurse sharks. It is believed that they are more active swimmers and less benthic. The characteristics of its body, head, fins, and teeth are comparable to other active reef sharks sharing its range, such as the Sicklefin Lemon shark.
Tawny Nurse Shark Future and Conservation: They are considered vulnerable. They are fished through most of its range. There have been local extirpations reported. Since litter sizes are small and there is limited dispersion, this will prevent rapid recovery from overfishing.
Commercial fisheries off the coast of Pakistan, India, Thailand, and the Philippines take the Tawny Nurse shark. In Australia they are just taken as bycatch. They are caught using demersal trawls, floating and fixed bottom gill nets, and on hook-and-line. The meat is sold fresh or dried and salted, the fins are used for shark fin soup, and the offal processed into fishmeal. In addition, the liver is a source of oil and vitamins, and the thick, tough skin is made into leather products. It is also valued by anglers as big game.
Tawny Nurse Shark Recorded Attacks on Humans: Typically, they are docile, but will bite divers if threatened or caught. They have strong suction, and do not let go so their bites can pack a lasting and powerful punch. If caught, they may spit water and spin on the line when hooked. One of the most recent encounters was in 2018 in Australia. A woman was bitten while hand-feeding them. They are popular among dive tourism and ecotourism. They are hardy in public aquaria.