Whale Shark Conservation
-
Upload
derrick-scott-fuller -
Category
Documents
-
view
228 -
download
0
Transcript of Whale Shark Conservation
-
8/18/2019 Whale Shark Conservation
1/6
The whale shark
By Brad Norman
The whale shark ( Rhincodon typus ) ( Brad Norman)
-
8/18/2019 Whale Shark Conservation
2/6
1
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).
-
8/18/2019 Whale Shark Conservation
3/6
2
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).
-
8/18/2019 Whale Shark Conservation
4/6
3
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).
-
8/18/2019 Whale Shark Conservation
5/6
-
8/18/2019 Whale Shark Conservation
6/6
5
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 ).