Communication among grey nurse sharks is not well understood. Sharks in general are sensitive to electrical and chemical cues.
Grey nurse sharks, and other species of sharks, have pores on their ventral surface. These pores are instrumental in detecting electrical fields, which help them to detect and locate prey and may help in navigating using the earth's magnetic field.
Perception Channels: visual ; tactile ; chemical ; electric
Grey nurse sharks were the first shark species to be protected by law. Grey nurse sharks are cited as being critically endangered in the Commonwealth Legislation (Australia). They are also considered endangered in New South Wales. The Queensland Government is hoping to provide a listing in the Nature Conservation Act of 1992 which will give these sharks additional protection. The National Marine Fisheries service in the United States prohibits hunting of these sharks. The IUCN lists grey nurse sharks as a vulnerable species on the red list (last evaluated in 2000). CITES does not have a listing for them, and is the most recently updated (2005). The fact that these sharks live in shallow, accessible waters, have a fierce appearance, and have a low reproductive rate, has contributed to declines in populations. Population declines worldwide are estimated at 20% in the last 10 years.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: critically endangered
It takes a grey nurse shark pup between 6-9 months to develop in the uterus of a female. Young nurse sharks develop a jaw and teeth very early their development and some eat their siblings while still developing within their mother, a phenomenon known as intra-uterine cannibalism. It is uncertain how long it takes grey nurse sharks to reach maturity, but maturity is estimated at between 5 and 13 years. Sharks continue to grow throughout their lives.
Development - Life Cycle: indeterminate growth
Grey nurse sharks are known for their fierce appearance and have gained an undeserved reputation as a man-eater in Australia. These sharks are not generally aggressive, but have been known to bite. Their bites can inflict serious damage because of their size and their dangerous teeth. They are sometimes tangled in fishing nets.
Negative Impacts: injures humans (bites or stings)
Shark teeth are lost frequently and are prized gifts in many regions of the world. Shark is a delicacy that is eaten in many areas.
Positive Impacts: food ; body parts are source of valuable material; ecotourism ; research and education
Grey nurse sharks help to regulate prey populations. Different species of lampreys (Petromyzontidae) prey on these sharks in a parasitic relationship, whereby the lamprey attaches to the shark, and extracts blood and other nutrients through a wound. These sharks also have mutualistic relationships with pilotfish (Naucrates ductor), which clean their gills and, in exchange, get to eat the scraps of food left behind in the gills.
Mutualist Species:
Commensal/Parasitic Species:
Grey nurse sharks have a range of prey, including bony fish, rays, lobsters, crabs, squid, and other small sharks. Grey nurse sharks sometimes hunt cooperatively, chasing fish into small groups and then attacking them. Grey nurse sharks, like other sharks, have been known to attack at random during feeding frenzies, where a large number of prey is found together. In feeding frenzies sharks rely heavily on their electroreceptors, attacking everything in close vicinity.
Animal Foods: fish; mollusks; aquatic crustaceans
Primary Diet: carnivore (Piscivore , Eats non-insect arthropods)
Grey nurse sharks, also called sand tiger sharks, can be found in the Atlantic, Indian, and Pacific Oceans in temperate and tropical waters. They are found in warm seas, except for the eastern Pacific. They occur from the Gulf of Maine to Argentina in the western Atlantic, the coast of Europe to north Africa in the eastern Atlantic, in the Mediterranean sea, from Australia to Japan in the west Pacific, and off the coasts of South Africa.
Biogeographic Regions: indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )
Grey nurse sharks are found in temperate and tropical waters. They are typically found in shallow waters, such as shallow bays, surf zones, and near coral or rocky reefs. They have been sighted in waters as deep as 191 meters, but will most likely be seen in the surf zone to a depth of 60 meters. They are usually found near the bottom of the water column.
Range depth: 2 to 191 m.
Average depth: 60 meters m.
Habitat Regions: temperate ; tropical ; saltwater or marine
Aquatic Biomes: reef ; coastal
Other Habitat Features: estuarine
Little is known about the lifespan of ocean dwelling grey nurse sharks, however those held in captivity live to an average age of thirteen to sixteen years. It is believed that those in the wild live longer still.
Range lifespan
Status: wild: 35 (high) years.
Range lifespan
Status: captivity: 16 (high) years.
The dorsal side of grey nurse sharks is grey, the underside is a dirty white color. These are stout-bodied sharks with metallic brown or reddish colored spots on the sides. When a grey nurse shark pup is born it is typically between 115 and 150 cm. As they mature, grey nurse sharks can reach 5.5 meters, but an average size is 3.6 meters. Females are generally larger than males. Average weight is from 95 to 110 kg. A distinguishing characteristic of grey nurse sharks is that the anal fin and both dorsal fins are the same size. The tail is heterocercal, with a long, upper lobe and a shorter, lower lobe. These different lobes allow for great movement. The mouth bears razor like teeth and is long and slender, with pointed snout. Their elongated teeth are visible even when the mouth is closed, giving these sharks a menacing appearance. This has led many to believe that these are dangerous sharks, a reputation they don't deserve.
Range mass: 50 to 300 kg.
Average mass: 95-110 kg.
Range length: 6 (high) m.
Average length: 3.6 m.
Range basal metabolic rate: <190 to 311 cm3.O2/g/hr.
Average basal metabolic rate: 239 cm3.O2/g/hr.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: female larger
The only know predators of adult grey nurse sharks are humans. Human hunting has caused population declines, both as a result of shark fishing and persecution because their fierce appearance has caused them to be mistaken for other, more dangerous, species of sharks. They are also accidentally caught in commercial fishing nets. Young sharks are eaten by other sharks.
Known Predators:
Males outnumber females by a 2:1 ratio and multiple males will copulate with a single female. A dominance hierarchy has only been observed in captivity, with the oldest males copulating first.
Mating System: polygynandrous (promiscuous)
Mating occurs in November and October. The gestation period will take anywhere from six to nine months. Females give birth in early spring near coastal, rocky reefs. Caves inhabited by these sharks are also used as breeding grounds and, if disrupted, their breeding may be interrupted. Female sharks bear young once every two years, with a maximum of two shark pups at birth, one from each uterus. Grey nurse sharks are ovoviviparous which means that eggs develop inside of the female in each uterus. Young hatch from the eggs and are retained in the uteri until they are fully developed. Females have hundreds of eggs inside the uterus. When an egg is fertilized the shark pup begins to grow and, at 55 mm, develops a jaw and teeth. This shark then eats the other developing embryos during its 6 to 9 month gestation (intra-uterine cannibalism).
Males mature at a length of 1.95 meters, or 4-5 years in age, and females mature at 2.2 meters, or 6 years in age.
Breeding interval: Grey nurse sharks bear young once every two years.
Breeding season: Shark pups are usually born in early spring (March and April).
Range number of offspring: 1 to 2.
Average number of offspring: 1.
Range gestation period: 6 to 9 months.
Range age at sexual or reproductive maturity (female): 5 to 13 years.
Average age at sexual or reproductive maturity (female): 7-8 years.
Range age at sexual or reproductive maturity (male): 5 to 13 years.
Average age at sexual or reproductive maturity (male): 7-8 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); ovoviviparous
A pup will be born approximately 115-150 cm in length. This shark is able to fend for itself and live without parental care. Intra-uterine cannibalism ensures plenty of energy to the developing pup, resulting in a well-fed and well-developed offspring.
Parental Investment: no parental involvement; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female)
