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The hammerhead sharks are a group of sharks that form the family Sphyrnidae, named for the unusual and distinctive form of their heads, which are flattened and laterally extended into a cephalofoil. The shark's eyes are placed one on each end of this T-shaped structure, with their small mouths directly centered and underneath. Most hammerhead species are placed in the genus Sphyrna, while the winghead shark is placed in its own genus, Eusphyra. Many different—but not necessarily mutually exclusive—functions have been postulated for the cephalofoil, including sensory reception, manoeuvering, and prey manipulation. The cephalofoil gives the shark superior binocular vision and depth perception.
The grey reef shark or gray reef shark is a species of requiem shark, in the family Carcharhinidae. One of the most common reef sharks in the Indo-Pacific, it is found as far east as Easter Island and as far west as South Africa. This species is most often seen in shallow water near the drop-offs of coral reefs. It has the typical "reef shark" shape, with a broad, round snout and large eyes. It can be distinguished from similar species by the plain or white-tipped first dorsal fin, the dark tips on the other fins, the broad, black rear margin on the tail fin, and the lack of a ridge between the dorsal fins. Most individuals are less than 1.88 m (6.2 ft) long.
The silky shark, also known by numerous names such as blackspot shark, gray whaler shark, olive shark, ridgeback shark, sickle shark, sickle-shaped shark and sickle silk shark, is a species of requiem shark, in the family Carcharhinidae, named for the smooth texture of its skin. It is one of the most abundant sharks in the pelagic zone, and can be found around the world in tropical waters. Highly mobile and migratory, this shark is most often found over the edge of the continental shelf down to 50 m (164 ft). The silky shark has a slender, streamlined body and typically grows to a length of 2.5 m. It can be distinguished from other large requiem sharks by its relatively small first dorsal fin with a curving rear margin, its tiny second dorsal fin with a long free rear tip, and its long, sickle-shaped pectoral fins. It is a deep, metallic bronze-gray above and white below.
Umkomaas, also known by its official name eMkhomazi, is a small coastal village on the subtropical South Coast of KwaZulu-Natal, South Africa was formed when a harbour was built in 1861 to export sugar. The village rests beside the mouth of the navigable uMkhomazi River, also known as the Mkhomazi or Umkomaas. With the successful dredging of Durban harbour's sandbar and arrival of the railway, like Port Shepstone, the harbour fell into disuse, but the village came to life. It is administered as eMkhomazi Area, together with the nearby areas of Craigieburn, Clansthal, Ilfracombe, Crowder, Amahlongwa and Hull Valley as part Ward 99 in the eThekwini Metropolitan Municipality
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 6.2 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.
The smooth hammerhead is a species of hammerhead shark, and part of the family Sphyrnidae. This species is named "smooth hammerhead" because of the distinctive shape of the head, which is flattened and laterally extended into a hammer shape, without an indentation in the middle of the front margin. Unlike other hammerheads, this species prefers temperate waters and occurs worldwide at medium latitudes. In the summer, these sharks migrate towards the poles following cool water masses, sometimes forming schools numbering in the hundreds to thousands.
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.
The silvertip shark is a large species of requiem shark, in the family Carcharhinidae, with a fragmented distribution throughout the tropical Indian and Pacific Oceans. It is often encountered around offshore islands and coral reefs, and has been known to dive to a depth of 800 m (2,600 ft). The silvertip shark resembles a larger and bulkier grey reef shark, but can be easily identified by the prominent white margins on its fins. It attains a maximum length of 3 m (10 ft).
The Aliwal Shoal is a rocky reef which is the remains of an ancient sand dune approximately 5 kilometres (3.1 mi) off the coast of KwaZulu-Natal, South Africa. The reef is inhabited by many kinds of hard and soft corals and other marine invertebrates, and a variety of tropical and subtropical fish species. Aliwal Shoal was named after the near-sinking in 1849 of the three-masted vessel Aliwal, captained by James Anderson. There are two wrecks near the reef that are popular recreational dive sites. The Norwegian bulk carrier MV Produce sank in 1974, and SS Nebo sank in 1884. Aliwal Shoal has diverse marine life, including large predators, and is popular as a recreational scuba diving destination. The Shoal is known especially for its abundance of Grey nurse sharks between July and November when the sharks congregate there to mate.
One of the first shark species to be protected was the grey nurse shark. 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.
Holdfast Bay is a small bay in Gulf St Vincent, next to Adelaide, South Australia. Along its shores lie the local government area of the City of Holdfast Bay and the suburbs of Glenelg and Glenelg North The colonial settlement at Holdfast Bay was the first seat of government of South Australia.
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 scalloped hammerhead is a species of hammerhead shark in the family Sphyrnidae. It was originally known as Zygaena lewini. The Greek word sphyrna translates into "hammer" in English, referring to the shape of this shark's head, which is its most distinguishing characteristic. The shark's eyes and nostrils are at the tips of the extensions. It is a fairly large hammerhead, but is still smaller than both the great and smooth hammerheads.
Pescador Island is a small limestone island located in the Tañon Strait, a few kilometres from the western coast of the island of Cebu in the Philippines. It is under the jurisdiction of the municipality of Moalboal.
Sodwana Bay is a bay in South Africa on the KwaZulu Natal north coast, between St. Lucia and Lake Sibhayi. It is in the Sodwana Bay National Park, and the Maputaland Marine Reserve, and is a popular recreational diving destination. The term is commonly used to refer to both the marine reserve and the terrestrial park, as well as the geographical bay.
Richelieu Rock is a dive site in Thailand in the Andaman Sea about 45 kilometres (28 mi) from the mainland. It is part of the Mu Ko Surin National Park although being about 18 km (11 mi) east of Ko Surin Tai. There are no islands in the immediate vicinity of the reef.
The Aliwal Shoal Marine Protected Area is a coastal and offshore marine protected area between the Lovu and Mzimayi estuaries, off the KwaZulu-Natal South Coast, South Africa. The MPA contains the popular scuba diving destination Aliwal Shoal
The Tstsikamma Marine Protected Area is a marine protected area on the south coast of South Africa, in both the Western Cape and Eastern Cape. It is on the coast of the Tsitsikamma National Park, and is one of the oldest MPAs in the country. The MPA provides protection for marine habitat and wildlife, including birds and threatened and endangered fish species.
The Protea Banks Marine Protected Area is a marine conservation area on the continental shelf edge off the South Coast of KwaZulu-Natal in South Africa.
References
- ↑ "Diving Protea Banks". www.afridive.com. Retrieved 15 July 2019.
- ↑ "Protea Banks - Shelly Beach - Aqua Planet Dive Centre". www.aquaplanet.co.za. Retrieved 15 July 2019.
- ↑ "Protea Banks". Marine Protected Areas South Africa. Retrieved 15 July 2019.
- ↑ "Scuba diving, protea banks with African Dive Adventures". Proteabanks.co.za.
- ↑ "About African Odyssea". africanodyssea.co.za.
- ↑ "Ragged-tooth shark". Aqua Planet. Retrieved 15 July 2019.
- ↑ "Protea Banks-Northern Pinnacle". www.afridive.com. Retrieved 15 July 2019.
- ↑ "Protea Banks". south-africa.greatestdivesites.com. Retrieved 15 July 2019.
- ↑ Coles, Russell J. (7 May 1919). "The Large Sharks of Cape Lookout, North Carolina. The White Shark or Maneater, Tiger Shark and Hammerhead". Copeia (69): 34–43. doi:10.2307/1436356. ISSN 0045-8511. JSTOR 1436356.
- ↑ "The yearly sardine migration attracts many predators". south-africa.greatestdivesites.com. Retrieved 15 July 2019.
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