One of the first shark species to be protected was the grey nurse shark (Carcharias taurus). The biology, distribution and conservation of this species are dealt with in the following paragraphs with a main focus on Australia as it was here it first became protected.
The grey nurse shark, Carcharias taurus, also called the ragged-tooth shark, is an elasmobranch and belongs to the odontaspididae (ragged-tooth) shark family. It can easily be recognized by its characteristic conical snout and under hung jaw. Both jaws are laden with sharp, long and pointed teeth. The head is flattened and it has a large and stout body, which ranges up to 3.2 m and may weigh up to 300 kg. The body is grey to grey-brown dorsally and off-white on the belly. The juveniles (young sharks) usually have dark spots on the upper two-thirds of the body. The first and second dorsal fins are of similar size and the caudal fin is asymmetric. Once believed to be a man-eater, it is now known that this shark rarely attacks humans and if it does it is only in defense, or if it is baited.
Sharks are the top predators in our oceans, and as such they are important for the marine ecosystems as important regulators of other species. They eat the weak, the old and the dead animals. The grey nurse sharks eat mainly lobsters, crabs, smaller sharks, fish, rays and squid.
Grey nurse sharks live near the coast in sub-tropical to cool-temperate waters near most continental land masses (not found in the eastern Pacific Ocean off North and South America). They have a preference for some places resulting in an uneven distribution. For example, there are few Grey nurse sharks found in north Australia while they are relatively abundant in the southern part of the eastern and western Australian waters.
They are usually found swimming slowly, just above the sea floor, in sandy-bottomed gutters or in rocky underwater caves near inshore rocky reefs and islands. They can be found at depths ranging from 10 m (near the coastline) to 200 m (on the continental shelf). They are generally solitary but at times small schools of Grey nurse sharks are found swimming and feeding together.
The grey nurse shark is one of the most critically endangered shark species and believed to be the first protected shark in the world. It was declared 'vulnerable' in the waters of New South Wales (Australia) in 1984 and later throughout the world. In 1996 the species was listed globally 'vulnerable' by the International Union for Conservation of Nature (IUCN) and declared 'vulnerable' in Commonwealth waters of Australia. According to the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act 1999) it is believed that there are two separate populations of Grey nurse shark in Australia. The population in the east coast is listed as 'critically endangered' whereas the west coast population is listed as 'vulnerable' under the EPBC Act (1999) [1] The grey nurse sharks are also protected under the Fisheries Legislation in New South Wales, Western Australia, Victoria, Tasmania and Queensland. In the Northern Territory the species is classified as 'data deficient' by the Territory Parks and Wildlife Conservation Act (2000)NTG.
The population has declined dramatically in recent decades, especially in the 1960s and 1970s. After 20 years of protection the population is still declining and there are approximately 1000-1500 grey nurse sharks left in Eastern Australia. [2]
Every year, millions of sharks are killed by driftnets, by-catch, revenge actions, beach protective shark meshing, commercial-, recreational- and spear-fishing. [1] [3] The main risk is from by-catch of indirect methods of line fishing and particularly bottom-set commercial fishing lines targeting wobbegong sharks.[ citation needed ] The grey nurse sharks are particularly vulnerable to these threats due to their late maturation and low breeding success. They reach sexual maturity at the age of three months and give birth to one or two young every second year; thus, the population grows very slowly. Furthermore, their limited distribution and specific habitats [4] make it difficult for them to migrate to other areas. Beach nets cause the death of hundreds of shark that are caught in the nets and cannot escape. [5] This also occurs in trawling and fishing nets. Another threat for the sharks is finning.
The increased public awareness has led to the development of methods that reduce the unintentional killing of elasmobranch (sharks and rays), turtles and marine mammals. An inexpensive method to reduce by-catch is by using tunnel excluders. These enable sharks, turtles and rays to escape and survive. A prototype used by the Dutch achieved a 40-100% reduction of the by-catch of the most vulnerable species. [6]
The size and texture of nets are also of great importance for the survival of larger vulnerable species. Often smaller nets have been shown to catch the same amount of target fish and reduce the by-catch greatly, especially of the mature sharks. [7]
Foundation of protected marine areas is particularly valuable for protecting sharks [8] and a new method, taggingCSIRO, can reveal their preferred forage and breeding areas. A good example of managed marine areas is to be found in Jervis Bay, NSW. [9] Jervis Bay has been divided into time zones, some for fishing and some for diving, and the strategy has been approved by both fishermen and divers. However, “Divers that regularly dive at places like South West Rocks in New South Wales will tell you that up to 70 per cent of the sharks there are trailing hooks from line fishing.” says Nicola Beynon from the Humane Society International (HSI). Another widely used method for preserving sharks is eco-tourism such as scuba diving, [10] cage-diving and feeding of sharks. However, it is crucial that this is strictly managed, [1] and that the sharks' behaviour is monitored. Feeding and touching of marine animals should be strictly discouraged since it can alter their behaviour, and result in long lasting and severe stress to the animals. Divers have noticed sharks altering their behaviour due to increased hierarchy behaviour around killing areas. The lowest in the hierarchy become stressed and exhibit unpredictable behaviour, which could result in attacks on humans.
The great white shark, also known as the white shark, white pointer, or simply great white, is a species of large mackerel shark which can be found in the coastal surface waters of all the major oceans. It is the only known surviving species of its genus Carcharodon. The great white shark is notable for its size, with the largest preserved female specimen measuring 5.83 m (19.1 ft) in length and around 2,000 kg (4,410 lb) in weight at maturity. However, most are smaller; males measure 3.4 to 4.0 m, and females measure 4.6 to 4.9 m on average. According to a 2014 study, the lifespan of great white sharks is estimated to be as long as 70 years or more, well above previous estimates, making it one of the longest lived cartilaginous fishes currently known. According to the same study, male great white sharks take 26 years to reach sexual maturity, while the females take 33 years to be ready to produce offspring. Great white sharks can swim at speeds of 25 km/h (16 mph) for short bursts and to depths of 1,200 m (3,900 ft).
Bycatch, in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juveniles of the target species. The term "bycatch" is also sometimes used for untargeted catch in other forms of animal harvesting or collecting. Non-marine species that are caught but regarded as generally "undesirable" are referred to as rough fish or coarse fish.
Dall's porpoise is a species of porpoise endemic to the North Pacific. It is the largest of porpoises and the only member of the genus Phocoenoides. The species is named after American naturalist W. H. Dall.
A shark net is a submerged section of gillnets placed at beaches designed to intercept large marine animals including sharks, with the aim to reduce the likelihood of shark attacks on swimmers. Shark nets used are gillnets which is a wall of netting that hangs in the water and captures the marine animals by entanglement, however only around 10% of catch is the intended target shark species. The nets in Queensland, Australia, are typically 186m long, set at a depth of 6m, have a mesh size of 500mm and are designed to catch sharks longer than 2m in length. The nets in New South Wales, Australia, are typically 150m long, set on the sea floor, extending approximately 6m up the water column, are designed to catch sharks longer than 2m in length. Shark nets do not create an exclusion zone between sharks and humans, and are not to be confused with shark barriers.
The sand tiger shark, gray nurse shark, spotted ragged-tooth shark or blue-nurse sand tiger, is a species of shark that inhabits subtropical and temperate waters worldwide. It inhabits the continental shelf, from sandy shorelines and submerged reefs to a depth of around 191 m (627 ft). They dwell in the waters of Japan, Australia, South Africa, and the east coasts of North and South America. The sand tiger shark also inhabited the Mediterranean, however it was last seen there in 2003 and is presumed extinct in the region. Despite its common names, it is not closely related to either the tiger shark or the nurse shark.
Cetacean bycatch is the accidental capture of non-target cetacean species such as dolphins, porpoises, and whales by fisheries. Bycatch can be caused by entanglement in fishing nets and lines, or direct capture by hooks or in trawl nets.
The great hammerhead is the largest species of hammerhead shark, belonging to the family Sphyrnidae, attaining an average length of 4.6 m (15 ft) and reaching a maximum length of 6.1 m (20 ft). It is found in tropical and warm temperate waters worldwide, inhabiting coastal areas and the continental shelf. The great hammerhead can be distinguished from other hammerheads by the shape of its "hammer", which is wide with an almost straight front margin, and by its tall, sickle-shaped first dorsal fin. A solitary, strong-swimming apex predator, the great hammerhead feeds on a wide variety of prey ranging from crustaceans and cephalopods, to bony fish, to smaller sharks. Observations of this species in the wild suggest that the cephalofoil functions to immobilize stingrays, a favored prey. This species has a viviparous mode of reproduction, bearing litters of up to 50 pups every two years.
Sand sharks, also known as sand tiger sharks, gray nurse sharks or ragged tooth sharks, are mackerel sharks of the family Odontaspididae. They are found worldwide in temperate and tropical waters. The three species are in two genera.
Ghost nets are fishing nets that have been abandoned, lost or otherwise discarded in the ocean, lakes and rivers. These nets, often nearly invisible in the dim light, can be left tangled on a rocky reef or drifting in the open sea. They can entangle fish, dolphins, sea turtles, sharks, dugongs, crocodiles, seabirds, crabs, and other creatures, including the occasional human diver. Acting as designed, the nets restrict movement, causing starvation, laceration and infection, and suffocation in those that need to return to the surface to breathe. It's estimated that around 48,000 tons of ghost nets are generated each year, and these may linger in the oceans for a considerable time before breaking-up.
Shark cage diving is underwater diving or snorkeling where the observer remains inside a protective cage designed to prevent sharks from making contact with the divers. Shark cage diving is used for scientific observation, underwater cinematography, and as a tourist activity. Sharks may be attracted to the vicinity of the cage by the use of bait, in a procedure known as chumming, which has attracted some controversy as it is claimed to potentially alter the natural behaviour of sharks in the vicinity of swimmers.
Drift netting is a fishing technique where nets, called drift nets, hang vertically in the water column without being anchored to the bottom. The nets are kept vertical in the water by floats attached to a rope along the top of the net and weights attached to another rope along the bottom of the net. Drift nets generally rely on the entanglement properties of loosely affixed netting. Folds of loose netting, much like a window drapery, snag on a fish's tail and fins and wrap the fish up in loose netting as it struggles to escape. However, the nets can also function as gill nets if fish are captured when their gills get stuck in the net. The size of the mesh varies depending on the fish being targeted. These nets usually target schools of pelagic fish.
The gulper shark is a long and slender dogfish usually about three feet in length generally found in deep, murky waters all around the world. It is a light grayish brown, paler ventrally, with a long snout and large greenish eyes. This deep water shark has two dorsal fins with long, grooved spines and the second dorsal fin smaller than the first. Its upper teeth are blade-like and lower have finely serrated edges. This tertiary consumer feeds on mainly fish such as bony fish, but also cephalopods such as squid and other invertebrates like crustaceans. The gulper shark is currently an endangered species mainly because of exploitation by humans and their abnormally long gestation period and low fecundity, preventing their population from recovering.
The dusky shark is a species of requiem shark, in the family Carcharhinidae, occurring in tropical and warm-temperate continental seas worldwide. A generalist apex predator, the dusky shark can be found from the coast to the outer continental shelf and adjacent pelagic waters, and has been recorded from a depth of 400 m (1,300 ft). Populations migrate seasonally towards the poles in the summer and towards the equator in the winter, traveling hundreds to thousands of kilometers. One of the largest members of its genus, the dusky shark reaches more than 4 m (13 ft) in length and 350 kg (770 lb) in weight. It has a slender, streamlined body and can be identified by its short round snout, long sickle-shaped pectoral fins, ridge between the first and second dorsal fins, and faintly marked fins.
The Caribbean reef shark is a species of requiem shark, belonging to the family Carcharhinidae. It is found in the tropical waters of the western Atlantic Ocean from Florida to Brazil, and is the most commonly encountered reef shark in the Caribbean Sea. With a robust, streamlined body typical of the requiem sharks, this species is difficult to tell apart from other large members of its family such as the dusky shark and the silky shark. Distinguishing characteristics include dusky-colored fins without prominent markings, a short free rear tip on the second dorsal fin, and tooth shape and number.
The smalltooth sand tiger or bumpytail ragged-tooth is a species of mackerel shark in the family Odontaspididae, with a patchy but worldwide distribution in tropical and warm temperate waters. They usually inhabit deepwater rocky habitats, though they are occasionally encountered in shallow water, and have been known to return to the same location year after year. This rare species is often mistaken for the much more common grey nurse shark, from which it can be distinguished by its first dorsal fin, which is larger than the second and placed further forward. It grows to at least 4.1 m (13.5 ft) in length. They have also been recently sighted in Irish and English waters.
Oophagy sometimes ovophagy, literally "egg eating", is the practice of embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek ᾠόν and classical Greek φᾱγεῖν. In contrast, adelphophagy is the cannibalism of a multi-celled embryo.
Shark tourism is a form of eco-tourism that allows people to dive with sharks in their natural environment. This benefits local shark populations by educating tourists and through funds raised by the shark tourism industry. Communities that previously relied on shark finning to make their livelihoods are able to make a larger profit from diving tours while protecting the local environment. People can get close to the sharks by free- or scuba diving or by entering the water in a protective cage for more aggressive species. Many of these dives are done by private companies and are often baited to ensure shark sightings, a practice which is highly controversial and under review in many areas.
The environmental impact of fishing includes issues such as the availability of fish, overfishing, fisheries, and fisheries management; as well as the impact of industrial fishing on other elements of the environment, such as bycatch. These issues are part of marine conservation, and are addressed in fisheries science programs. According to a 2019 FAO report, global production of fish, crustaceans, molluscs and other aquatic animals has continued to grow and reached 172.6 million tonnes in 2017, with an increase of 4.1 percent compared with 2016. There is a growing gap between the supply of fish and demand, due in part to world population growth.
The Australian grey smooth-hound or also known as the grey gummy shark is a species of houndshark classified under the large family Triakidae. It is one of the twenty-eight species belonging to the genus Mustelus, which are often small in length. While members of the genus Mustelus may be found globally in tropical and temperate waters, the grey gummy shark in particular is native to the Pacific Ocean and Indian Ocean waters surrounding Australia and is particularly widespread in deep coastal waters. The grey gummy shark is known to be a viviparous species and gives birth to live young. With little data available, it is regarded to have a relatively stable population and possesses little threat to humans.
Cape Byron Marine Park is one of four marine parks in New South Wales, Australia, and is the most recently sanctioned. The Cape Byron Marine Park is located in Northern NSW and extends 37 kilometres (23 mi) from the Brunswick River to Lennox Head. The marine park extends out to 3 nautical miles which dictates the border between state and federal jurisdiction. The marine park covers an area of 220 square kilometres (85 sq mi) and includes a variety of marine terrain including beaches, rocky shores, open ocean and the tidal waters of the Brunswick River and its tributaries, the Belongil Creek and Tallow Creek. The Cape Byron Marine Park was declared in 2002 and the zoning plan was implemented in April 2006. Of the 15 distinct marine ecosystems identified within the Tweed-Moreton bioregion, the Cape Byron Marine Park supports 10 of these.
