A review of the biology and ecology of the whale shark

Abstract

The information available on the biology and ecology of the whale shark is reviewed, and is updated from material published since 1986. Research work carried out on the seasonal aggregation of whale sharks at the Ningaloo Reef in Western Australia is summarized. Future research studies on whale sharks in the Ningaloo Marine Park are discussed in the context of management of sustainable whale shark interaction tourism.

Full text

Journal of Fish Biology (1997) 51, 1219–1234
A review of the biology and ecology of the whale shark
J. G. C
Marine Conservation Branch, Department of Conservation and Land Management,
47 Henry Street, Fremantle, Western Australia 6160, Australia
(Received 11 January 1997, Accepted 4 July 1997)
The information available on the biology and ecology of the whale shark is reviewed, and is
updated from material published since 1986. Research work carried out on the seasonal
aggregation of whale sharks at the Ningaloo Reef in Western Australia is summarized. Future
research studies on whale sharks in the Ningaloo Marine Park are discussed in the context of
management of sustainable whale shark interaction tourism.
?1997 The Fisheries Society of the British Isles?1997 The Fisheries Society of the British Isles
Key words: whale shark; Rhiniodon typus; Ningaloo Reef.
INTRODUCTION
The whale shark, Rhiniodon typus Smith 1828, has a very widespread distri-
bution and occurs throughout the world’s tropical and warm temperate seas, and
yet knowledge of its biology and ecology is very limited. Like many other shark
species, the species has innate biological characteristics, such as large size, slow
growth, late maturation and extended longevity, that probably limit recruitment
and make it particularly susceptible to exploitation. These characteristics may
also mean that populations are slow to recover from any overexploitation (Jones
& Kaly, 1995).
With the worldwide growth of marine nature-based tourism, recreational
snorkelling and scuba diving, there has been a steady increase in the number of
encounters with whale sharks. In a few locations, such as the Ningaloo Reef in
Western Australia, the Galapagos Islands, the islands of the Andaman Sea off
the west coast of Thailand, and the Sea of Cortez and Baja California in the
eastern Pacific, where occurrences of whale sharks appear to be predictable, they
are being targeted increasingly by commercial tourist operations. These opera-
tions provide a rare opportunity for close encounters between humans and large
marine fauna, but may result in unknown effects on the shark’s behaviour and
ecology. International conservation status of the species is unclear—it is listed as
having an ‘ indeterminate ’ status on the World Conservation Union’s Red List
of Threatened Animals (IUCN, 1994). This category applies to animals known to
be ‘ endangered ’, ‘ vulnerable ’ or ‘ rare ’, but there is not enough information
available to say which of these three categories is appropriate. Casey et al. (1992)
considered the whale shark to be at potential risk from pelagic fisheries. There
are indications that even small traditional fisheries may be unsustainable, with
catches from a seasonal fishery in the Philippines declining over recent years, but
the reason for this downward trend is unknown (Trono, 1996). Globally,
commercial fisheries for whale sharks are limited at present, but may expand
from an increased demand for food products.
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0022–1112/97/061219+ 16 $25.00/0/jb970526 ?1997 The Fisheries Society of the British Isles

A seasonal aggregation of whale sharks occurs in the waters of the Ningaloo
Marine Park in Western Australia (Fig. 1) from March to May each year. Over
the last 4 years, this predictable occurrence has led to the development of a small
but expanding tourist industry, focusing on human–whale shark interactions.
From 1993 onwards, commercial whale shark tourism has been managed by the
F. 1. Ningaloo Marine Park. ., Cape Range National Park; , Ningaloo Marine Park (Common-
wealth jurisdiction); , Ningaloo Marine Park (State jurisdiction); /, Sanctuary zones.
1220 ..

Western Australian Department of Conservation and Land Management
(CALM) through a system of controls, including the licensing of a limited
number of operators for whale shark interaction tours within the Marine Park.
Presently, it is unclear whether increased tourism pressure is generating any
short- or long-term detrimental impacts on individuals sharks or the group as a
whole. The natural variability in whale shark abundance and distribution, the
reasons for the aggregation at the Ningaloo Reef and the carrying capacity of the
industry are all unknown. Consequently, evidence of any impacts is difficult
to obtain and interpret. With the limited information currently available a
precautionary approach to management has been adopted.
To improve the management of the interaction, and in the long-term, to
provide the scientific basis to determine if current management strategies need to
be modified to minimize any impacts, CALM has developed a management
programme for whale shark interaction tourism. This has included an extensive
and up-to-date review of the biology and ecology of the species, in the context of
the seasonal aggregations at the Ningaloo Reef. Once more information is
available and appropriate monitoring programmes are implemented it will be
possible to ensure that the whale shark population in the Ningaloo Marine Park
is not being subjected to an unacceptable level of disturbance, and that
development of whale shark tourism is sustainable and equitable.
The published literature on whale sharks is extensive and consists mainly of
sightings records, anecdotal reports, speculative reviews of distribution and
movement patterns, and limited observations of general biology, feeding and
behaviour. Much of the material is derivative, superficial in content, and of
limited scientific use. The definitive bibliography (Wolfson & Notarbartolo di
Sciara, 1981) collated all available literature to 1980, listed and annotated 345
references, and categorized these under 19 broad headings. This review was
updated later by a consolidation of reported sightings (Wolfson, 1986). Silas
(1986) updated records from Indian waters and carried out a comprehensive
review of the information available on the whale shark’s biology and ecology.
The aim of this overview is to examine these and other key papers published
before 1986, plus any further material published since 1986, and to review
research carried out at Ningaloo Reef in the last 10 years, in order to update the
existing knowledge of the biology and ecology of R. typus. A comprehensive
reference database and reprint collection have been established at CALM’s
Marine Conservation Branch. Currently, the database lists 541 references and
contains 130 articles which were either not listed in previous reviews, or have
been published since 1986. The relational database and reprint collection are
being made available to researchers carrying out studies on whale sharks.
DESCRIPTION OF SPECIES
The species was first described and named by Dr Andrew Smith from a
specimen harpooned in Table Bay, South Africa in 1828 (Smith, 1828,1829,
1849). Historically, there has been considerable synonymy at family, generic
and specific level, and in 1984 the International Commission on Zoological
Nomenclature suppressed previous generic variations in favour of genus
Rhincodon, family Rhincodontidae (Melville, 1984). Alternate generic names
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most commonly used are Rhiniodon and Rhineodon. Systematically, Rhinco-
dontidae (with the single type species Rhiniodon typus) is placed in the order
Orectolobiformes, which also includes nurse sharks (Ginglymostomatidae),
leopard sharks (Stegostomatidae), and wobbegongs (Orectolobidae). The inter-
relationships between these families are based upon a number of anatomical and
morphological similarities, including skeletal anatomy, tooth and dermal
denticle morphology, fin placement and barbel morphology (Compagno, 1973;
Dingerkus, 1985).
The whale shark is the world’s largest living fish. It is characterized externally
by a broad, flattened head, a very large and nearly terminal mouth, very large gill
slits, three prominent longitudinal ridges on its upper flanks, a large first dorsal
fin, a semi-lunate caudal fin and a unique ‘ checkerboard ’ pattern of light spots
and stripes on a dark background (Compagno, 1984;Last & Stevens, 1994). The
function of this distinctive pattern of body marking is unknown. Many
bottom-dwelling sharks have bold and disruptive body markings that act as
camouflage through disruptive coloration (Bass, 1978). The whale shark’s
markings could be a result of its phyletic relationship with bottom-dwelling
orectolobiform carpet sharks. Sharks have a high degree of visual development
(Gruber, 1977) and distinctive markings in a pelagic species could be linked to
social activities such as postural displays and recognition processes (Myrberg,
1991). Another possibility is that these pigment patterns could be an adaptation
for radiation shielding, important in a species that may spend a significant
proportion of time in surface waters possibly exposed to high levels of ultraviolet
radiation.
The whale shark is one of three species of very large filter-feeding sharks that
occur in Western Australian waters, the other two being the basking shark
Cetorhinus maximus (Gunnerus), and the megamouth shark Megachasma
pelagios (Taylor, Compagno & Struhsaker).
BIOLOGY AND ECOLOGY
DISTRIBUTION AND HABITAT
R. typus is thought to be cosmopolitan in distribution, occurring in all tropical
and warm temperate seas apart from the Mediterranean. It is found in a band
around the equator between about 30)N and 35)S, in both coastal and oceanic
waters (Compagno, 1984). It occurs throughout the Indian Ocean and has been
reported from the Maldives, Seychelles and Comores Islands, and along the
coastlines of Madagascar, South Africa, Mozambique, Kenya, Pakistan, India,
Sri Lanka, Thailand, Malaysia and Indonesia. In Australia, whale sharks occur
mainly offnorthern Western Australia at the Ningaloo Reef, the Northern
Territory and Queensland, with isolated reports from New South Wales and
Victoria (Wolfson, 1986).
In contrast to the majority of orectolobiform sharks, which are benthic species,
the whale shark has a pelagic habitat. Iwasaki (1970) collated and analysed
environmental data from skipjack tuna fishing vessels that encountered whale
sharks in the western Pacific Ocean from 1955 to 1967. Analysis of air
temperatures, seawater temperature and salinity profiles, and wind and current
patterns revealed changes in the seasonal frequency and distribution of whale
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sharks that appeared to be linked to a number of environmental variables,
including the warm Kuroshio current and warm SSW–WSW winds. Offthe east
coast of Japan their range encompassed areas with surface water temperatures
from 18 to 30)C, but they appeared to prefer locations with surface water
temperatures between 21–25)C, where cool nutrient-rich upwellings mingle with
warm surface waters of salinities between 34–34.5‰ (Iwasaki, 1970). These
conditions may well be optimal for the production of the planktonic and
nektonic prey upon which the sharks feed.
Sightings of whale sharks, made during aerial surveys along the south coast of
Texas, occurred in waters with surface temperatures of 29)C(Hoffman et al.,
1981). Arnbom & Papastavrou (1988) reported several sightings of whale sharks
in the Galapagos Islands, in an area of very deep water (2000–3000 m) close to
the edge of the continental shelf, known for its upwellings and high primary
productivity. Surface seawater temperatures recorded during these encounters
were between 23·5 and 26·5)C.
FEEDING
The whale shark is a filter-feeder that appears to feed on a wide variety
of planktonic and nektonic prey, including small crustaceans such as krill,
crab larvae and copepods, small schooling fishes such as sardines, anchovies,
mackerel, and occasionally larger prey such as small tuna, albacore and squid
(Compagno, 1984;Last & Stevens, 1994). Also, phytoplankton and macroalgae
may form a component of the diet (McCann, 1954;Kaikini et al., 1959;
Satyanarayana Rao, 1986;Karbhari & Josekutty, 1986). An analysis of the
stomach contents of a specimen caught offthe coast of India in 1961 revealed a
variety of material, ‘ including large quantities of zooplankton, partly digested
remains of fish, crustaceans, molluscs, and small quantities of seaweed and algae,
undoubtedly suggesting an omnivorous diet ’ (Silas & Rajagopalan, 1963).
However, it is possible that algal matter found in the gut contents of these
specimens could have been swallowed accidentally, either during the course of
normal feeding activities or whilst being captured.
The animal is not dependent on forward motion to operate its filtration
mechanism, but rather relies on a versatile suction filter-feeding method, which
enables it to draw water into the mouth at higher velocities than dynamic
filter-feeders, such as the basking shark (Compagno, 1984). This enables it to
capture larger, more active nektonic prey as well as zooplankton aggregations,
but probably means it can filter a far smaller volume of water making it less
efficient in concentrating diffuse planktonic food. Therefore, the whale shark
may be more dependent on dense aggregations of prey organisms. Taylor et al.
(1983) reviewed the feeding biology and filter apparatus of R. typus in relation to
M. pelagios and C. maximus and concluded that the dense filter screens of the
former act as more efficient filters for short suction intakes, in contrast to the
flow through systems of the latter two species.
Individuals have been observed feeding passively (cruising with mouth agape)
and also sometimes hanging vertically in the water and feeding actively by
opening their mouths and sucking in prey-rich water. They have been seen
feeding in this manner on aggregations of small crustaceans (including
euphausids), squid, anchovy and sardines (Silas, 1986). They have also been
       1223

observed coughing, which is thought to be a mechanism employed to clear or
flush the gill rakers of accumulated food particles. Groups of individuals have
been observed feeding actively at dusk or after dark by ploughing through the
surface waters with mouth agape and jaw distended, sometimes also moving
their heads from side to side vacuuming in sea water rich in prey, or aggressively
cutting swathes through schools of prey (Clark, 1992;Taylor, 1994). At the
Ningaloo Reef in Western Australia, individuals and groups of whale sharks
have been observed feeding actively on swarms of the tropical krill
Pseudeuphausia latifrons (G. O. Sars) (Taylor, 1994).
REPRODUCTION AND DEVELOPMENT
Information about the reproduction and development of the whale shark is
very limited. Historically, there has been much debate about their mode of
development, and it was unclear whether the whale shark is oviparous (egg cases
expelled from the female’s body and hatching on the sea floor) or ovo-viviparous
(egg cases hatching in utero, with the female giving birth to live young).
Southwell (1912/1913) reported that a specimen taken offthe coast of Sri Lanka
was found to contain a ‘ very large ovary, oviduct full of eggs, 16 cases counted,
same form as in dogfish ’. This observation suggested oviparity. Until recently,
the only known whale shark embryo was a near-term 36-cm specimen retrieved
alive from a large egg case trawled from the sea floor in the Gulf of Mexico in
1953 (Baughman, 1955;Reid, 1957;Garrick, 1964). Whilst this appeared to
suggest an oviparous mode of development, Wolfson (1983) believed it was more
likely that the egg case had been aborted, and that the whale shark is actually
ovo-viviparous. This conclusion was based on the absence of other occurrences
of ‘ free-living ’ egg cases and the fact that the Gulf of Mexico egg case was
extremely thin and lacked tendrils (which anchor the egg case to the sea floor).
The embryo also had large reserves of yolk and only partially developed gill
sieves, which combined with the discovery of umbilical scars on a free-living
juvenile of 55 cm length (Wolfson, 1983), provide further support for the theory
that whale sharks have an ovo-viviparous mode of development.
In July 1995, a female whale shark, measuring approximately 11 m in length,
was harpooned offthe eastern coast of Taiwan (Joung et al., 1996). The twin
uteri of this specimen were found to contain 300 embryos, from 42 to 63 cm in
length. Fifteen of the embryos were alive and one, measuring 58 cm in length,
was reared for 143 days in an aquarium in Japan where it developed from fetal
through to juvenile stage (Leu et al., unpublished). This discovery finally
confirms that the species is a live-bearer, with an ovo-viviparous mode of
development.
LIFE HISTORY
A total of only nine juveniles, ranging from 55 to 93 cm in length, has been
recorded in the literature (Wolfson, 1983;Anon., 1989;Kukuyev, 1996). One of
the juveniles recorded by Kukuyev (1996) was found in the stomach of a blue
shark Prionace glauca (L.), caught in central tropical Atlantic waters. A further
specimen, measuring 61 cm in length, was found in the gut contents of a blue
marlin Makaira mazara (Jordan & Snyder) caught offthe northern coast of
Mauritius in 1993 (D. Goorah, pers. comm.). The juvenile was alive when
1224 ..

recovered from the marlin’s stomach, as it had just been ingested prior to the
intake of a bonito Sarda orientalis (Temminck & Schlegel).
There are no confirmed records of whale sharks between 93 cm and 3 m.
Animals over 3 m in length are encountered worldwide. Most specimens
reported in the literature are between 4 and 10 m, but maximum total length is
uncertain. The largest accurately measured specimen was 12 m in length
(Karbhari & Josekutty, 1986), but there is a report of a specimen from the
Seychelles that measured nearly 14 m in length (Wright, 1870), and a specimen
measuring just over 14 m was landed in India in 1975 (Devadoss et al., 1990).
Whale sharks may reach possibly as much as 18 m in length, although the very
large specimen reported from the Gulf of Siam (Smith, 1925) was not measured
accurately and therefore total length may have been overestimated.
Information about size at sexual maturity and longevity is sparse. Taylor
(1994) speculated that whale sharks do not reach sexual maturity until they are
over 30 years of age, and that they may have a life span of over 100 years. Also,
he observed that the only sexually mature male seen at the Ningaloo Reef was
probably over 9 m in length. Two large female sharks captured offthe Indian
coastline (Pai et al., 1983;Satyanarayana Rao, 1986), which measured 8–9 m in
length, were both found to have immature ovaries. The evidence suggests that
sexual maturity in both sexes may not occur until the sharks are over 9 m in
length. Data on sex ratio is also very limited. Of 31 specimens reported from
India, 17 were male and 14 were female (Silas, 1986). Taylor (1994) observed
that the majority of whale sharks encountered at Ningaloo are immature males.
On the basis of current information it is not possible to say whether sexual
segregation, of either a behavioural or geographical nature, occurs.
GROWTH AND AGEING
Virtually nothing is known about growth rates or ageing in whale sharks. As
accurate measurements of size parameters are difficult to obtain from whale
sharks in the water, morphometric studies of this species have made little
progress. Generally, growth curves for sharks have been derived from age
estimates based upon growth zones (bands or rings) in calcified structures such as
vertebral centra. The growth of whale sharks has been studied opportunistically
from animals held in captivity in the Okinawa Expo Aquarium in Japan (Uchida
et al., 1990). One of these animals was fed food laced with tetracycline, on
several occasions over a period of more than a year (Cailliet et al., 1986).
Preliminary results indicated that one pair of growth zones was deposited per
year in captivity. How this relates to growth in the wild can be determined only
by examination of growth zones in vertebral centra samples collected from dead
specimens.
Studies of this nature are hampered by sample size, as very few dead animals
are available for collection of hard tissues. There are no records of whale shark
strandings along the Western Australian coastline, although there is an uncon-
firmed report of a small (2 m length) whale shark being found on the beach at
Sandy Bay, North West Cape (Fig. 1) in 1982 (N. Nannup, pers. comm.). For
the last 3 years, researchers in South Africa have been retaining vertebrae
samples from specimens that strand occasionally along the KwaZulu/Natal coast
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(G. Cliff, pers. comm.). Some information on ageing of whale sharks may be
available from subsequent examination of these samples.
MOVEMENT PATTERNS
In general, occurrences of whale sharks appear to be sporadic and unpredict-
able, which is partly a reflection of the lack of knowledge about the animal’s
habitat and ecology. Generally, whale sharks are encountered singly but
aggregations of over 100 animals have been seen (Anon., 1961), which suggests
that schooling activity does occur. They are usually observed on or near the
surface and at times have been seen apparently basking.
Whale sharks are thought to be highly migratory but currently there is no
direct evidence to support this. Their movements are related probably to
increases in local productivity such as plankton blooms and invertebrate
spawning events, with associated increases in zooplankton and bait fish shoals,
and also to changes in water temperature, currents, winds and other environ-
mental parameters (Compagno, 1984). It has been suggested that whale sharks,
with their suction filter-feeding strategy, are probably more dependent on
localized productivity events (J. Stevens, pers. comm.). Different locations
appear to be preferred at various times of the year and they may undertake either
fairly localized migrations or alternatively large-scale transoceanic movements,
governed by the timing and location of production pulses and possibly by
breeding behaviour. Seasonal migrations have been postulated for various areas
but more information is needed to confirm these patterns (Wolfson, 1986).
Taylor (1994) postulated that the appearance of whale sharks at the Ningaloo
Reef during the austral autumn period is linked to the high levels of productivity
associated with mass synchronous coral spawning events after the March and
April full moons (Simpson, 1991). Currently, it is unknown whether the whale
sharks present at Ningaloo in March to May are resident in the eastern Indian
Ocean throughout the rest of the year. These animals could move offshore to
deeper waters and may be seen only when they come inshore and into surface
waters to exploit periodic increases in plankton productivity, such as those
around the time of mass coral spawning. Inshore sightings of significant
numbers of whale sharks have been made in December and January along the
Western Australian coastline between Kalbarri and Shark Bay (P. Wieland, pers.
comm.). Unconfirmed reports suggest the occurrence of numbers of whale
sharks around the Montebello Islands on the North West Shelf of Western
Australia at the same time of year. Whether either of these separate aggregations
consist of the same individuals as those aggregating at the Ningaloo Reef during
the autumn months is not known at present.
Episodic aggregations of whale sharks also occur in two other locations in
Australian waters. During December and January significant numbers of whale
sharks have been reported from Christmas Island in the Indian Ocean
(J. Stevens, pers. comm.) and this aggregation occurs at the same time that the
red crab Gecarcoidea natalis (Pocock) spawns en masse. In the Coral Sea regular
sightings of whale sharks occur in October and November in association with
aggregations of tuna Thunnus spp. (Gunn et al., 1992). It is believed that these
aggregations may be associated with large concentrations of spawning lantern
fish Diaphus spp., rather than with synchronous coral spawning along the Great
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Barrier Reef that occurs during the same period (J. Stevens, pers. comm.). In the
Maldives, whale sharks show distinct seasonal movements, in phase with the
changing monsoons and associated current movements, as well as up-welling
events and plankton blooms (Anderson & Ahmed, 1993).
There are several reports in the literature of seasonal aggregations of whale
sharks in Indian coastal waters from December to April (Silas, 1986), in the
Seychelles during August and November (R. Salm, pers. comm.), and offthe
west coast of Mexico from Cabo San Lucas to Acapulco from March to August
(Wolfson, 1986,1987). Significant numbers of whale sharks have been reported
from inshore waters offsouthern Mozambique and the northern coast of South
Africa, from October through to March (A. Gifford, pers. comm.). Since 1993,
researchers from the Shark Research Institute in South Africa have been
carrying out whale shark aerial surveys and a tagging programme along the
KwaZulu/Natal coastline (A. Gifford, pers. comm.). An aerial survey in
January 1994 recorded a total of 95 whale sharks along 110 km of coastline.
During the 1994 and 1995 seasons, a total of 72 sharks were tagged. The
researchers are hoping to expand their tagging effort along the east African
coast, using tags of identical design but with different colour coding according to
the tagging location. Returns could assist in the determination of large-scale
migratory patterns throughout the Indian Ocean region. The Kenya Wildlife
Service recorded 60 whale sharks, with a conservative population estimate of
219, whilst carrying out an aerial survey of marine mammals and turtles in
November 1994 (N. Muthiga, pers. comm.). The sharks were distributed
all along the Kenyan coastline but with a higher frequency of sightings in
northern waters.
FAUNAL ASSOCIATIONS
Whale sharks are often associated with schools of pelagic fish that are
probably feeding on the same prey organisms. There are numerous references in
the literature to sightings of whale sharks in association with several tuna and
trevally species, and with bonito, mackerel and schools of small bait fish such as
sardines and anchovies. These associations could have foraging advantages for
the whale sharks. Wolfson (1987) reported the sighting of a whale shark
swimming amongst a school of more than 500 hammerhead sharks Sphyrna
lewini (Griffith & Smith) offBaja California, and Arnbom & Papastavrou
(1988) observed tiger sharks Galeocerdo cuvieri (Peron & Lesueur) swimming
close to whale sharks in the Galapagos Islands. Groups of whale sharks
have been observed swimming with manta rays Manta birostris (Walbaum) off
Baja California (Wolfson, 1987) and offthe Zuytdorp Cliffs, north of Kalbarri
in Western Australia (P. Weiland, pers. comm.). Other common associates
include several species of remora Remora spp., and the pilot fish Naucrates
ductor (L.). At Ningaloo Reef, Taylor (1994) reported that whale sharks are
often seen accompanied by juvenile golden trevally Gnathanodon speciosus
(Forsska˚l).
HUMAN INTERACTION
In the past, the whale shark has been of little interest to man, as it poses no
threat nor is it widely exploited for human consumption or for other products.
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Consequently, there has been virtually no sustained scientific research on this
species and it has been the target of only limited commercial fisheries in the past.
The flesh is soft and bland and has a very high water content, with levels of 68%
(Satyanarayana Rao, 1986) and 75% (A. Gifford, pers. comm.) being reported.
Whale shark meat is sought after in Taiwan (Joung et al., 1996), where it is
described as being like tofu and fetches a high price, and currently two
Taiwanese whale shark fisheries are believed to take approximately 100 sharks
annually (Uchida, 1984; J. Stevens, pers. comm.).
Sudhakara Rao (1986), recorded the landing of 40 whale sharks over a
4-day period in 1982, from a harpoon fishery offthe Veraval coast in
India. After removal of the liver the carcasses were discarded as there was no
local demand for the flesh. In the past, harpoon fisheries have been reported
from India (Sudhakara Rao, 1986), Pakistan (Anon., 1955;Silas, 1986),
Indonesia (Muller, 1995) and Iraq (Mahdi, 1971). A seasonal (April to May)
fishery exists in the Philippines, where 90 sharks were taken during the
1996 season (Trono, 1996). The anti-tumorogenic properties of whale shark
liver oil have been investigated in China (Zhang et al., 1988). There may
be a developing market for whale shark fins, with reports that some may
recently have been sold in Hong Kong (Smith, 1996). In the Maldives, the
limited fishery for liver oil (Anderson & Ahmed, 1993) has ceased in recent
years, and in 1995 the Ministry of Fisheries and Agriculture introduced
legislation banning all fishing for whale sharks (C. Anderson, pers. comm.).
This protection was introduced because of the low monetary value of the
fishery, the possible serious impact that the fishery may have been having on
whale shark stocks, and the likely benefits to the tuna fishery and tourist
industry.
Occasionally whale sharks are taken accidentally in gill and purse seine net
fisheries offthe coast of India (Silas, 1986;Devadoss et al., 1990;Seshagiri Rao,
1992). Usually these specimens are discarded, as neither the flesh nor other
products are in high demand. Occasionally some of the flesh is eaten either fresh
or salted and dried, and the liver oil is utilized for water-proofing wooden fishing
boats and other appliances, for the manufacture of shoe polish (Satyanarayana
Rao, 1986) and as a treatment for some skin diseases (Karbhari & Josekutty,
1986). The processing of whale shark fins and fin rays has been reported in India
(Ramachandran & Sankar, 1990).
Often the species is used as a fish ‘ aggregator ’ or indicator of waters rich in
plankton and plankton-feeding fish that will, in turn, attract more valuable
species such as tuna. In the Gulf of Guinea and elsewhere tuna purse seiners seek
out whale sharks on the surface and set nets on them to catch associated fish
species (Stretta & Slepoukha, 1983). However, potential damage to fishing gear
from entangled whale sharks causes them to be avoided in other areas. Several
whale sharks have been kept in captivity in aquaria in Japan (Roth, 1986;
Uchida et al., 1990), but few details are available. There have been a few cases
reported of whale sharks inadvertently ramming boats (Smith, 1967), but
generally the sharks are more at risk from being struck accidentally by vessels
whilst basking or feeding on the surface. There are numerous reports, from the
first half of this century, of collisions between steam ships and whale sharks
(Anon., 1962;Gudger, 1938a,b,1940).
1228 ..

RESEARCH AT THE NINGALOO REEF
Since 1982, whale shark enthusiast G. Taylor has been studying and photo-
graphing whale sharks at the Ningaloo Reef (Fig. 1). He was the first person to
document the seasonal aggregation of whale sharks in the area, initially through
the collection of informal sightings records from boats. Taylor conducted
preliminary population surveys, and investigated the relationships between mass
coral spawning, the Leeuwin Current, and whale shark occurrences and move-
ment patterns. With funding from the Australian National Parks and Wildlife
Service (ANPWS) he carried out aerial surveys between 1989 and 1992, which
suggested that whale sharks congregate along the reef front during the autumn
months, shortly after synchronous mass coral spawning episodes (Taylor, 1996).
Further work involved limited plankton sampling to try and identify prey
species, observations of feeding behaviour, and initial satellite tracking studies
(Taylor, 1994).
In order to gather more information about population size and sex ratio and
to investigate whether the same animals revisit Ningaloo on a seasonal basis,
Taylor conducted a limited tagging study using conventional game fish tags.
This study, with individuals being re-identified by the location of the tag rather
than its number, was initiated in 1992 and a total of 25 individuals have been
tagged (Taylor, 1994). His estimates of local population size, based upon the
frequency of re-sightings and an estimated tag shedding percentage of 40–50%,
are between 200 and 300 individuals (G. Taylor, pers. comm.). Taylor also
recorded the sex of whale sharks encountered on the reef and investigated the
feasibility of identifying individuals through scars, deformities and the pattern of
spots and stripes behind the gill slits. He has used gross scarring to verify the
long-term stability of the lateral markings and has suggested that these distinc-
tive patterns can be used as a repeatable method of identifying individuals
(Taylor, 1994). He has compiled a photo-identification library, which contains
photographic records for 162 individuals, and it is apparent from these data
that some individual sharks are re-sighted at Ningaloo in successive seasons
(G. Taylor, pers. comm.).
In addition, Taylor has undertaken a long-term study to measure the dorsal
fins of whale sharks at Ningaloo. Repeated re-measurement of the height of the
first dorsal fin of individual sharks, over a period of 10 years or more, may
provide an indication of the growth rate of the fin. If there is a relationship
between this parameter and overall size of the shark, Taylor believes it may be
possible to estimate age of the sharks and to determine when they reach sexual
maturity.
In 1994, researchers from the Commonwealth Scientific and Industrial
Research Organisation (CSIRO) Division of Fisheries tracked two tagged whale
sharks successfully (one for a period of 26 h) using acoustic telemetry, and
attached archival tags to six individuals, one of which was recovered after 24 h.
The archival or ‘ smart ’ tags can collect data on the date, time, the shark’s
position and swimming depth, and the water temperature for up to 5 years,
giving a record of the shark’s long-term movements once the tag is retrieved
(J. Stevens, pers. comm.). Detailed information on the short-term movements of
the sharks was obtained from the acoustic telemetry tracking and from the single
       1229

archival tag retrieved (Stevens, 1994). Swimming speed ranged from approxi-
mately 0·1 to 1·5 m s
"1
, with the fastest speeds being recorded during the night.
Data from both the acoustic telemetry and the archival tag revealed that the
tagged sharks made numerous dives throughout the 24-h period, to maximum
depths of 90 m, often to within a few metres of the bottom. Diving behaviour of
these individuals did not appear to be linked to the location of the thermocline,
with the acoustically tracked sharks spending the majority of the time above the
thermocline, and the shark tagged with an archival tag spending the day above
the thermocline and most of the night either within or below it. Some of the
tracks revealed that the sharks were circling on the surface offa reef passage,
during ebb tides when water was flowing out of the lagoon, possibly to take
advantage of aggregations of prey associated with mats of algae (J. Stevens, pers.
comm.).
DISCUSSION
The accessibility of the seasonal aggregation of whale sharks at the Ningaloo
Reef provides an excellent opportunity for researchers to undertake studies of
this rarely encountered and poorly understood shark. Initial research efforts
lacked clearly defined objectives and were often hampered by limited scientific
knowledge and resources. Dedicated and sustained research of whale sharks
in the Ningaloo Marine Park should not only seek to improve the knowledge of
the whale shark’s biology and ecology, but also to provide information to
managers in order to minimize possible detrimental impacts of tourism pressure.
As suggested by Wolfson (1986), researchers studying whale sharks should
‘ move beyond the purely descriptive natural history approach and design and
implement sustained programmes of investigation, using the most advanced
equipment and techniques that are amenable to statistical treatment ’.
In developing a scientifically objective research and monitoring programme,
there are a number of factors to be considered, including ethical, technical and
logistical issues. The large size, free-swimming epipelagic nature, and sporadic
appearance of whale sharks makes study of these animals intrinsically difficult
and creates numerous technical and methodological problems. As has been seen
with cetacean research, the time required and complexity of programmes
examining any large marine animal have to be considered at the design stage.
There are problems in initiating further research in an area where a whale shark
watching industry is already in place. Attempts to investigate the population size
and structure may suffer from sample size and range problems. Population
studies require large sample sizes and this is a major problem when working with
rarely encountered species, especially if individuals cannot be captured or
restrained. Accurate morphometric data and samples for age and growth rate
determination (such as vertebral centra) can usually be obtained only from
restrained or dead animals.
A key factor in sustainable management of whale shark–human interactions is
a clear understanding of the population dynamics of the animal. Until both
seasonal and interannual variability in abundance and distribution are known, it
will be difficult to identify any long-term impacts. Therefore, monitoring studies
have to establish an independent and repeatable series of population counts.
1230 ..

Reliable estimates of whale shark population size at Ningaloo are difficult to
obtain. In the past there has been no standardized collection of data. If
segregation by age occurs, which appears to be the case from anecdotal evidence,
sightings in the area are not a random sample of the population. Habituation to
boats may occur, which also negates random sampling. A sufficient sample size
is required also. At present it is impossible to fix the spatial boundaries of the
population, as there is no indication where the sharks may migrate. A long-term
aerial survey programme to monitor interannual variability in the whale shark
population is a high priority for future management of human–whale shark
interaction in the Ningaloo Marine Park.
My thanks to C. Simpson, J. Burt and J. Stevens for reviewing the manuscript, to R.
Laurie for supplying the map of the Ningaloo Marine Park and to all those who provided
information for this review, including C. Anderson, G. Cliff,A.Gifford, D. Goorah,
S. Menzies, N. Muthiga, N. Nannup, R. Salm, G. Taylor and P. Wieland.
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