Biology of Endangered Species Fishes, Turtle and
Deepti Manjari Patel#
Kishor K. T. #, Karankumar
and Kapil Sukhdhane*
College of Fisheries, Manglore, Karnataka, India
Institute of Fisheries Education, Seven Bunglows, Versova, Andheri
The Whale Shark
The Whale Shark is the world's largest fish, and one of only three
filter-feeding shark species, along with the Basking Shark
(Cetorhinusmaximus), and the Megamouth Shark
(Megachasmapelagios). The Whale Shark is easily recognizable
due to its broad, flattened head, its large mouth, and its pattern of
light spots and stripes on a dark background. The ventral surface is
typically whitish (Norman, 2002).
The only member of the family Rhincodontidae, the largest Whale Shark
found to date measured 20 metres and weighed 34 tonnes (Chen et
al. 1997, in Chen & Phipps, 2002). Despite its immense size,
the Whale Shark is harmless to humans. It has few defences, although
its ability to reach a very large size combined with a tough (thick)
skin present on the dorsal surface can be used for protection
(Norman, 1999). It is generally encountered singly, though
occasionally in aggregations of up to hundreds of sharks (Compagno,
1984; Norman, 1999). The Whale Shark has typical "K"
selected life history characteristics, including slow growth, late
maturation and extended longevity (Colman, 1997a).
Data on the lifespan of the Whale Shark is limited. Taylor (1994)
indicates that based on the late age of sexual maturity in Whale
Sharks (estimated at around 30 years of age), the Whale Shark may be
one of the longest living animals in the world, with an estimated
lifespan of over 100 years.
There have been two reviews of Whale
Shark growth rates ;ie Wintner (2000) and Uchida (2000). In both data
has come from studies of captive individuals held in aquaria, as well
as from the vertebrae of stranded Whale Sharks from South Africa.
Wintner (2000) studied the growth rate of two animals held in aquaria
and found that growth rates of Whale Sharks kept in captivity were
1.1 -1.3 times higher than would be expected from an animal in the
wild, possibly due to the reliable availability of food in an
aquarium. Uchida (2000) notes life span in aquaria range from three
to 2056 days, with mean growth rate in the latter specimen at 29.5cm
per year. Norman (2004) reports on another juvenile Whale Shark with
a growth rate of 46cm per year over the 630 days while held in
It is likely that due to their very small size at birth (~ 0.5m)
(Joung et al., 1996) and hence lack of defense to
predation in the early stages of life, Whale Sharks grow very fast
initially and then the rate of growth would decline (Norman, 1999).
Some evidence of this rapid growth has been collected from a newborn
Whale Shark that grew 143cm over 143 days while in captivity in
a Taiwanese aquarium (Chang et al., 1997).
The Whale Shark is primarily a suction filter feeder (Compagno,
1984). It feeds on a wide variety of planktonic and nektonic prey,
including small crustaceans, small schooling fishes such as sardines,
anchovies and mackerel, and occasionally on small tuna and squid
(Compagno, 1984; Last and Stevens, 1994). Whale Sharks at Ningaloo
Reef have been observed actively feeding on swarms of the tropical
krill Pseudeuphausialatifrons (Taylor, 1994; Norman,
1999). On a separate occasion, a Whale Shark was seen sucking the
surface slick of coral spawn into its mouth while orientated at 450
to the surface (Norman, 1999). At Christmas Island, Indian Ocean the
Whale Sharks have been observed feeding on localized concentrations
of mysids (Anisomysisspinata) and crab magalopa (G.
natalis) (Norman, 1999).
Three faecal samples analysed by Norman (1999) revealed exoskeletal
remains of calanoid and harpacticoidcopepds, larval decapods and the
scales of small fishes. A further two Whale Shark faecal samples from
Ningaloo Reef contained eyes, legs, and fragments of exoskeleton from
crustacean prey, namely P. latifrons, suggesting that
Whale Sharks aggregating seasonally off Ningaloo Reef feed
predominantly on this tropical krill (Wilson &Newbound, 2001).
Whale Sharks have been observed feeding passively by swimming forward
with mouth agape, and feeding actively by opening their mouths and
sucking in prey. Whale Sharks are also reported as hanging vertically
in the water while feeding (Colman, 1997a).
The Whale Shark is a livebearer with an ovoviviparous mode of
development (Joung et al., 1996). It may be the most
fecund of all live bearing sharks. The only pregnant female found to
date measured 10.6m, weighed 16t, and contained 307 embryos. The
embryos measured between 42 and 63 cm in length (Joung et
There is scant information on the age at which Whale Sharks become
reproductive, although Norman (1999) presents evidence (collected
during an intensive study of this species at NMP between 1995-97)
that the length at maturity of male Whale Sharks is approximately
8.6m TL. Alternatively, examination of two female Whale Sharks (TL =
7.9 and 8.6m) by researchers in India revealed immature ovaries in
each specimen (Pai et al., 1983; SatyanarayanaRao, 1986
in Colman, 1997). Taylor (1994) indicates that the Whale Shark may
not reach sexual maturity until 30 years of age. There is currently
limited evidence with which to accurately determine age at maturity
or the maximum age for this species (Wintner, 2000).
Information on the frequency at which Whale Sharks are able to
reproduce is not available. Likewise, it is not known where Whale
Shark mating takes place, although it is considered likely in the
waters surrounding Taiwan, Philippines and India where sightings of
juvenile Whale Sharks have been recorded (Norman, 2004).
The Green Sea Turtle:
The Green sea turtle (Cheloniamydas)
or green turtle is a large sea
turtle of the familyCheloniidae.
It is the only species in
the genus Chelonia. Its
range extends throughout tropical and subtropical seas
around the world, with two distinct populations in
the Atlantic andPacific
Oceans. Their common name derives from the
usually green fat found
beneath their carapace (upper
The green sea turtle is a sea
turtle, possessing a dorsoventrally flattened
body covered by a large, teardrop-shaped carapace and
a pair of large, paddle-like flippers.
It is usually lightly colored, although parts of the carapace can
be almost black in the Eastern Pacific. Unlike other members of its
family such as the hawksbill
sea turtle and loggerhead
sea turtle, Cheloniamydas is
The adults commonly inhabit shallow lagoons,
feeding mostly on various species of seagrass.
Cheloniamydas is listed as endangered by
the IUCN and CITES and
is protected from exploitation in most countries. It is illegal to
collect, harm or kill them. In addition, many countries have laws and
ordinances to protect nesting areas. However, turtles are still in
danger because of several human practices. In some countries, turtles
and their eggs are hunted for
food. Pollution indirectly
harms turtles at both population and individual scales. Many turtles
die, caught in
fishing nets. Also, real estate development often
loss by eliminating nesting beaches.
As one of the first sea turtle species studied, much of what is known
of sea turtle ecology comes from studies of green turtles. The
ecology of Cheloniamydas changes drastically with
each stage of its life history. Newly emerged hatchlings
are carnivorous, pelagic organisms
part of the open ocean mini-nekton.
In contrast, immature juveniles and adults are commonly found in
seagrass meadows closer inshore as herbivorous grazers.
Green sea turtles move across three habitat types
depending on their life
stage. They lay eggs on beaches. Mature turtles
spend most of their time in shallow, coastal waters with lush
seagrass beds. Adults frequent inshore bays, lagoons and shoals with
lush seagrass meadows. Entire generations often migrate between one
pair of feeding and nesting areas.
Turtles spend most of their first five years in convergence zones
within the open ocean.These young turtles are rarely seen as they
swim in deep, pelagic waters.
Only human beings and the larger sharks feed
on C. mydas adults. Specifically, tiger
hunt adults in Hawaiianwaters. Juveniles
and new hatchlings have significantly more predators,
mammals and shorebirds. In
Turkey, their eggs are vulnerable to predation by red
foxes and golden
C. mydas hatchling
Green sea turtles migrate long distances between feeding sites and
nesting sites. Some C. mydasswim more than
2,600 kilometres (1,616 mi) to reach their spawning
grounds. Mature turtles often return to the exact beach from which
they hatched. Females usually mate every two to four years. Males on
the other hand, visit the breeding areas every year, attempting to
mate. Mating seasons vary between populations. For
most Cheloniamydas in the Caribbean,
mating season is from June to September. The French
Guiana nesting subpopulation nests from March
to June. In the tropics, green turtles nest throughout the year,
although some subpopulations prefer particular times of the year.
In Pakistan, Indian
Ocean C. mydas nest year-round but prefer
the months of July to December.
Green sea turtles mating is similar to other marine turtles. Female
turtles control the process. A few populations practice polyandry,
although this does not seem to benefit hatchlings. After mating
in the water, the female moves above the beach's high tide line where
she digs a hole with her hind flippers and deposits her eggs. Litter
size depends on the age of the female and species, but C.
mydas clutches range between 100 to 200. She then covers the
nest with sand and returns to the sea.
At around 45 to 75 days, the eggs hatch during the night and the
hatchlings instinctively head
directly into the water. This is the most dangerous time in a
turtle's life. As they walk, predators such as gulls and crabs grab
them. A significant percentage never make it to the ocean. Little is
known of the initial life history of newly hatched sea
turtles. Juveniles spend three to five years in the open ocean
before they settle as still-immature juveniles into their permanent
shallow-water lifestyle.It is speculated that they take twenty to
fifty years to reach sexual
maturity. Individuals live up to eighty years in
Each year on Ascension
Island in the South
Atlantic, C. mydas create 6-15,000
nests. They are among the largest green turtles in the world, many
more than a meter in length and weighing up to 300 kilograms
Sea turtles spend almost all their lives submerged but must breathe
air for the oxygen needed to meet the demands of vigorous activity.
With a single explosive exhalation and rapid inhalation, sea turtles
can quickly replace the air in their lungs. The lungs permit a rapid
exchange of oxygen and prevent gases from being trapped during deep
dives. Sea turtle blood can deliver oxygen efficiently to body
tissues even at the pressures encountered during diving. During
routine activity green and loggerhead turtles dive for about 4 to 5
minutes and surface to breathe for 1 to 3 seconds.
Turtles can rest or sleep underwater for several hours at a time but
submergence time is much shorter while diving for food or to escape
predators. Breath-holding ability is affected by activity and stress,
which is why turtles quickly drown in shrimp trawlers
and other fishing gear.
The giant clam, Tridacnagigas (known
as pā'ua in Cook
Islands Māori), is the largest
livingbivalve mollusc. T.
gigas is one of the most endangered clam species. It was
mentioned as early as 1825 in scientific reports. One of a
number of large clam species
native to the shallow coral reefs of
the South Pacific and Indian
oceans, they can weigh more than 200 kilograms
(441 lb) measure as much as 120 centimeters (47.2 in)
across, and have an average lifespan in the wild of 100 years or
more. They are also found
off the shores of the Philippines, where they are
called taklobo. T. gigas lives in
flat coral sand or
broken coral and can be found at depth of as much as 20 m
(66 ft). Its
range covers the Indo-Pacific,
but populations are diminishing quickly and the giant clam has become
extinct in many areas where it was once common. T. maxima has
the largest geographical distribution among giant clam species; it
can be found in high- or low-islands, lagoons,
reefs. Its rapid growth rate is likely due to
its ability to cultivate plants in its body tissue.
Although larval clams
they become sessile in
adulthood. The creature's mantletissues act
as a habitat for
the symbiotic single-celled dinoflagellate algae (zooxanthellae)
from which it gets nutrition. By day, the clam opens its shell and
extends its mantle tissue so that the algae receive the sunlight they
need to photosynthesize.
Young T. gigas are difficult to distinguish from
other species of Tridacnidae.
Adult T. gigas are the only giant clams unable to
close their shells completely. Even when closed, part of the mantle
is visible, unlike the very similar T. derasa. However,
this can only be recognized with increasing age and growth. Small
gaps always remain between shells through which retracted
brownish-yellow mantle can be seen.
T. gigas has four or five vertical folds in its shell;
this is the main characteristic that separates it from the very
similar shell of T. derasa, which has six or seven
vertical folds. As with massive deposition of coral matrices
composed of calcium
the bivalves containing zooxanthellae have
a tendency to grow massive calcium
carbonate shells. The mantle's edges are
packed with symbiotic zooxanthellae
that presumably utilize carbon
and nitrates supplied
by the clam.
Algae provide giant clams with a supplementary source of
plants consist of unicellular algae,
whose metabolic products
add to the clam's filter food. As
a result, they are able to grow as large as100 cm length even in
nutrient-poor coral-reef waters. The
clams cultivate algae in a special circulatory
system which enables them to keep a
substantially higher number of symbionts per unit of volume.
In small clams — 10 milligrams (0.010 g) dry tissue
weight—filter feeding provides about 65% of total carbon needed
for respiration and
growth; large clams (10 g) acquire only 34% of carbon from this
source. A single species of zooxenthellae may be symbionts of
both giant clams and nearby reef—building (hermatypic)
T. gigas reproduce sexually, and
are hermaphrodites (producing
both eggs and sperm).
Self-fertilization is not possible but, this characteristic does
allow them to reproduce with any other member of the species. This
reduces the burden of finding a compatible mate, while simultaneously
doubling the number of offspring produced by the process. As with all
other forms of sexual reproduction, hermaphroditism ensures that new
gene combinations are passed to further generations.
Since giant clams cannot move themselves, they adopt broadcast
spawning. They release sperm and eggs into the water. A transmitter
substance called Spawning Induced Substance (SIS) helps synchronize
the release of sperm and eggs to ensure fertilization. The substance
is released through a syphonal
outlet. Other clams can detect SIS immediately.
Incoming water passes chemoreceptors situated
close to the inccurent syphon, which transmit the information
directly to the cerebral ganglia,
a simple form of brain.
Detection of SIS stimulates the giant clam to swell its mantle in the
central region and to contract its adductor
muscle. Each clam then fills its water chambers and
closes the incurrent syphon. The shell contracts vigorously with the
adductor's help, so the excurrent chamber's contents flows through
the excurrent syphon. After a few contractions containing only water,
eggs and sperm appear in the excurrent chamber and then pass through
the excurrent syphon into the water. Female eggs have a diameter of
100 micrometres (0.0039 in). Egg release initiates the
reproductive process. An adult T. gigas can release
more than 500 million eggs at a time.
Spawning contractions occurred every 2—3 minutes, with intense
spawning ranging from thirty minutes to two and a half hours. Braley
also hypothesized that clams that do not respond to the spawning of
neighbor clams may be reproductively inactive.
The fertilized egg floats in the sea for about 12 hours until
eventually a larva (trocophore)
hatches. It then starts to produce a chalk shell.
Two days after fertilization it measures 160 micrometers (0.0063
in). Soon it develops a "foot", which is used to move on the
ground; it can also swim to search for appropriate habitat.
At roughly one week of age, the clam settles on the ground, although
it changes location frequently within the first few weeks. The larva
does not yet have symbiotic algae, so it depends completely
Free floating zooxanthellae are also captured while filtering food.
Eventually the front adductor
muscle disappears and the rear muscle moves
into the clam's center. Many small clams die at this stage. The clam
is considered a juvenile when
it reaches a length of 20 cm . It is difficult to observe
the growth rate of T. gigas in the wild, but
laboratory-reared giant clams have been observed to grow 12|cm a
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