whale shark conservation

8/18/2019 Whale Shark Conservation

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The whale shark

By Brad Norman

The whale shark ( Rhincodon typus ) ( Brad Norman)


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THE WHALE SHARK

By Brad Norman

ECOCEAN Consu ting, 68a Rai way Street, Cottes oe,

Western Austra ia, 6011 Austra ia

Introduction

e w a e s ar R inco on typus s t e argest s ar n t e

ocean, reac ng engt s o 20 metres an a we g t o 20 tonnes

(gure 1). This icon species is often referred to as ‘charismaticegafauna’ and a ‘gentle giant’. With very few defences,

t has become susceptible to exploitation and has a global

conservat on status o ‘vu nera e to ext nct on’ as ste y

e Wor Conservat on Un on n t e Re List o T reatene

pecies.

gure . e w a e s ar inco on typus ra orman).

History

e w a e s ar s a re at ve y recent a t on to t e uman

ecor o t e ocean an ts n a tants. However, t e ancestry

o t s s ar goes ac to t e Jurass c an Cretaceous per o s

245–65 million years ago, when the present groups of sharks

began to appear.

It was not unt 1828 t at t e rst w a e s ar spec men nown

o sc ence was scovere o t e Sout A r can coast.

Dr An rew Sm t orma y escr e t e spec es a ter t at yearas the largest living shark in the ocean.

s spec es s rare. Pr or to t e m -1980s, t ere a een ess

an 350 con rme reports o w a e s ar s wor w e. S nce

t en, cons stent s g t ngs ave een recor e n Austra a. Alucrative ecotourism industry revolving around their annual

appearance at Ningaloo Marine Park (NMP), on the Western

Australian northwest coast, is now well established.

Distribution

W a e s ar s ave a roa str ut on n trop ca an warm-

temperate seas, usua y etween at tu es 30 N an 35ºS gure

2). They are thought to prefer surface sea-water temperatures

of 21–25ºC. Sightings at NMP, however, are most common in

water temperatures around 27 C.

Figure 2. The whale shark is widely distributed through tropical seas

© CSIRO).

W a e s ar s are nown to n a t ot eep an s a ow

coasta waters an t e agoons o cora ato s an ree s.

Austra a s one o t e most re a e ocat ons to n t em.

Regular sightings have also been recorded from many other

regions including India, the Maldives, South Africa, Belize,

Mexico, the Galapagos Islands, Southeast Asia and Indonesia.

T s spec es s w e y str ute n Austra an waters.

A t oug most common at NMP an to a esser extent at

C r stmas Is an an n t e Cora Sea , s g t ngs ave een

conrmed further south than Kalbarri (on the mid-west coast of

Western Australia) and near Eden (New South Wales). Whale

sharks have also been recorded from Australian waters between

Austra a an In ones a.

Biology

T s spec es s c ose y re ate to t e ottom- we ng s ar s

(Orectolobiformes), which include the wobbegong. There

is a pattern of lines and spots on the skin of each shark

that enables them to ‘blend’ into their surroundings. This‘camou age’ ma es t e s ar s ess consp cuous n t e r

ocean c env ronment. T e un que pattern ng oes not appear to

change over time and can be used to identify individuals (see

photoid.whaleshark.org).


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One o on y t ree ter- ee ng s ar s t e ot er two e nghe basking and megamouth sharks), the whale shark feeds

on minute organisms (gure 3) including krill, crab larvae,

jellysh, etc, and has been known to feed on larger prey

e.g. sar nes, anc ov es, mac ere s, sma tunas an squ .

t oug t ey ave approx mate y 3000 t ny teet eac ess

an 6 mm n engt , t ese teet are not use w e ee ng.

Instead, the whale shark can sieve prey items as small as 1 mm

hrough the ne mesh of the gill-rakers. They are able to open

heir mouth to a great width (greater than 1 metres) to optimise

ee ng an are occas ona y s g te ang ng vert ca y n t e

ater a ow ng a t s an ot er concentrate oo tems to e

sucked’ in.

Reproduction

a e s ar s ave nterna ert sat on an pro uce ve young

(the eggs hatch in the uterus prior to birth [ovoviviparity]).

hey have more young than any shark, producing litters of

around 300 pups—although these are very small at an average

engt o aroun 55 cm. T e engt o gestat on, ow o ten

ey ree , an w ere t ey ree rema ns un nown. T e on y

pregnant female whale shark ever recorded was found off the

coast of Taiwan. There have been very few juvenile whale

sharks seen at any location throughout their range.

Stu es o t e w a e s ar s at NMP ave esta s e t at

a e w a e s ar s o not usua y mature e ore t ey reac a

ength of around 8–9 metres. Males can be distinguished by

he presence of two claspers (absent in females) near the pelvic

n. The size at maturity of female whale sharks cannot beeterm ne t roug externa o servat on.

Habitat and ecology

Although whale sharks are most often observed swimming

at the surface during ‘seasonal’ aggregations, evidence from

trac ng stu es n cate t at w a e s ar s can ve to great

ept s ~700 metres . T ey can a so rema n eneat t e sur ace

for long periods.

They regularly appear at locations where seasonal food

‘pu ses’ are nown to occur. T e pre cta e annua w a e

s ar aggregat on at NMP s c ose y n e w t an ncrease

n pro uct v ty o t e reg on assoc ate w t a mass cora

spawning that occurs around March–April each year. It is likely

that this represents a critical habitat in the life cycle of this

spec es.

Acoust c-trac ng stu es at NMP revea t at n v ua w a e

sharks sometimes stay close to Ningaloo Reef over day–night

periods. In addition, using the ECOCEAN Whale Shark Photo-

identication Library it has been possible to record many

s ar s return ng to N nga oo n erent years an rema n ng

t ere over ong per o s ur ng t e w a e s ar ‘season’. As

an example, one individual (A-012) was resighted at NMP on

14 separate days over a 28-day period within a very restricted

area. In addition, some sharks appear to show a level of‘s te-attac ment’ w en return ng to t e Austra an nort west

coast ne.

Migration

W a e s ar s are regar e as g y m gratory—a t oug

t e r ‘m grat on patterns’ are poor y un erstoo . Researc at

NMP suggests t e s ar s may un erta e a nort er y m grat on

when leaving the area. Their seasonal appearance at Christmas

Island and sightings near Ashmore Reef provide support for

this theory (gure 4). It is when the sharks leave Australian

waters t at t ey are potent a y at r s o ‘unsusta na e unt ng pressure’.

Satellite tracking of whale sharks in waters off the United

States of America and also in the South China Sea reveals

t at t ese an ma s can trave great stances t ousan s o

ometres . T ese m grat ons may ta e years to comp ete. A

ar greater un erstan ng o w a e s ar movements w e

possible with the continuation of tagging and tracking studies

throughout the world and through expansion of the ECOCEAN

Whale Shark Photo-identication Library. Using ‘natural

tagg ng’ v a p oto- ent cat on, t s poss e or snor e ers

an SCUBA vers rom aroun t e wor to e p w tresearch on this species, by sending basic sighting information

(e.g. date and location) with a photograph of the unique natural

patterning on the skin of each shark to the online Library.

igure 3. Copepods and juvenile

cra s are eaten y w a e s ar s

Brad Norman).


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Threats

Targeted or bycatch sheries

• he most signicant threat to the species appears to be

umans. In one s ery a one In a , as many as 1000 w a e

s ar s were e eve e n 1999 an 2000. T e r a t o

sw mm ng at t e sur ace ma es t em part cu ar y suscept e

to shing. In previous times, the ns of whale sharks were

sold for high prices on the Asian market, although demand has

declined. There is still a market for whale shark meat in several

countr es nc u ng Ta wan an C na.

• In Ta wan, t ere s a quota o 120 w a e s ar s or capture

per year, a t oug t s s eare to e unsusta na e. O great

concern is the reduction on the size of individuals caught in

the Taiwanese shery today compared with those of the early

1980s.

Natural predators

• ere are very ew nown pre ators o t e w a e s ar . In

nature, t e most angerous per o n t e r e cyc e appears to

be before reaching a substantial size (i.e., when the sharks are

still very young). Pups are a fraction of their adult size—only

approximately 55 cm in length at birth. The skin of an adult

w a e s ar prov es t e r ma n protect on. On average, t e

t c ness o t e s n on t e orsa sur ace s 12–15 cm, greater

than that of any other living animal. In young whale sharks,

however, this ‘protection’ his not fully developed.

gure . ate te-tagge w a e s ar s n

http://www.marine.csiro.au/research/pelagic/tagging/hopetraveller/

n ex. tm .

gure . a) - p otograp e n w t orsa n ntact;

ttp: www.s ep er pro ect.org s ar s. sp s ar = - );

b) A-076 photographed in 2003 with dorsal n damaged from attack

http://www.shepherdproject.org/sharks.jsp?shark=A-076).


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For further information

ECOCEAN Whale Shark Conservation:

http://www.ecocean.org/whalesharks01.html

Nat ona P an o Act on or t e Conservat on an Management

of Sharks (Shark-plan):

http://www.daff.gov.au/sharkplan

c now e gements

The following organisations/individuals are acknowledged for their

contr ut ons: un ng: atura er tage rust an t e s er es

esources esearc un ustra an overnment epartment

of Agriculture, Fisheries and Forestry). oor nat on o pro ect:

ar ne n ustr es nv ronment ranc an t e ureau o ura

c ences ustra an overnment epartment o gr cu ture,

isheries and Forestry). rtwor : Brett Cullen and Trish Hart.

ev ewers: aro yn tewar son an ert aton.

© Brad Norman ([email protected]).

This information sheet may be copied for educational purposes.

For any other purpose please contact the author.

gure . n ustry management gu e nes to m n m se

mpacts on sharks from ecotourism activities

ttp: www.ca m.wa.gov.au tour sm w a es ar s_

sw mm ng. tm ).

whale shark conservation

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