Div­ing by Num­bers

Asian Diver (English) - - Contents - By: Shark Busi­ness

GEO­GRAPH­I­CAL DIS­TRI­BU­TION

This species is wide-rang­ing in the Indo-Pa­cific, oc­cur­ring along the east coast of Africa from South Africa to the Red Sea, In­dian Ocean is­lands, north­ern In­dian Ocean, in­clud­ing In­dia, Sri Lanka, Myan­mar, Viet­nam, the Philip­pines, Aus­tralia, New Guinea and Poly­ne­sia, Me­lane­sia, Mi­crone­sia to the Hawai­ian Is­lands and Pit­cairn group. The species is also found in the eastern Pa­cific, Co­cos Is­lands, Galá­pa­gos and Panama to Costa Rica

BUCCAL PUMP­ING

One of only a few re­quiem sharks that does not have to con­tin­u­ously swim in or­der to breathe, the whitetip reef shark uses a method known as buccal pump­ing to pump wa­ter into its mouth and over its gills, en­abling it to spend long pe­ri­ods of time rest­ing in caves or on the seabed

SITE FIDELITY

In­di­vid­u­als of this species main­tain a small home range for months or even years at a time and of­ten re­turn to the same place day af­ter day to rest

HABI­TAT

Com­monly found rest­ing along the bot­tom in clear, shal­low wa­ter sur­round­ing co­ral reefs, where it is ca­pa­ble of ly­ing mo­tion­less for long pe­ri­ods of time. Will of­ten form groups and rest on sandy patches, un­der ledges or in caves dur­ing the day­time, but at night trans­forms into an ac­tive and ef­fi­cient hunter that pa­trols the reef and rub­ble ar­eas in search of prey. Most com­mon at depths be­tween 8–40 me­tres but has been recorded at 330 me­tres. Rarely seen at the sur­face

TOURISM

A com­mon sight on dives in the Pa­cific, where in­di­vid­u­als are nor­mally easy to spot rest­ing on open sandy ar­eas at depths around 20–30 me­tres. Divers at­tempt­ing to get close to them must move slowly, as they do not like to be ap­proached and will nor­mally move away when dis­turbed. To see this species at its most ac­tive, divers must visit Co­cos Is­land in Costa Rica, where the sharks have learnt to utilise divers’ torches to help them lo­cate their prey, and can be seen in large num­bers at night hunt­ing on the reef

RE­PRO­DUC­TION

Like other mem­bers of its fam­ily, the whitetip reef shark is vi­vip­a­rous, mean­ing the em­bryos are nour­ished via a pla­centa-like like at­tach­ment af­ter ex­haust­ing their ini­tial yolk sup­ply. Af­ter a ges­ta­tion pe­riod of ap­prox­i­mately 5 months, 1–5 pups are born mea­sur­ing 52–60cm in length. Mat­ing has been ob­served in the wild and in cap­tiv­ity and the re­pro­duc­tive cy­cle is bi­en­nial

WHITE TIP

The whitetip reef shark earns its name from its dis­tinc­tive white tips on its first dor­sal and up­per cau­dal fins. These mark­ings some­times cause the species to be mis­taken for the sil­ver­tip shark, although on close in­spec­tion the species are vis­ually quite dif­fer­ent

DIET

This shark is a spe­cial­ist at catch­ing ben­thic prey hid­ing in caves and crevices at night. Its slen­der body en­ables it to wrig­gle into tight spa­ces that are in­ac­ces­si­ble to other reef sharks where it tar­gets bony fishes, oc­to­puses, lob­sters and crabs

PREDA­TORS

Po­ten­tial preda­tors in­clude large sharks such as the tiger shark and Galá­pa­gos shark, while smaller in­di­vid­u­als and ju­ve­niles have also been found in­side the stom­ach of other large fish such as the gi­ant grouper (Epinephelus lance­o­la­tus)

SNOUT, JAWS AND TEETH

The head is flat­tened with a broadly rounded and blunt snout. The mouth has a dis­tinct down­ward slant and the jaws con­tain 42–50 rows of teeth in the up­per jaw and 42–48 rows in the lower jaw. Each tooth has a sin­gle nar­row, smooth-edged cusp at the cen­tre, flanked by a pair of much smaller cus­plets

At­lantic OceanPa­cific Ocean52–60 cen­time­tresNew­born pups mea­sure aroundMouthSpir­a­cleGillWa­ter FlowGill SlitArea of dis­tri­bu­tion

Bony FishCrabSil­ver­tip SharkOc­to­pusLob­sterGi­ant GrouperTiger SharkGalá­pa­gos Shark

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