| The
largest fish in the sea has been in the news lately, in
both good news and not-so-good.
The
whale shark (Rhincodon typus) is different enough
from other fishes that it gets its own family (Rhicodontidae),
and is actually most closely related to the slow, bottom-dwelling
nurse and leopard sharks. But instead of munching crabs
and such, the whale shark is a filter feeder that slowly
cruises the ocean surface, growing to as large as 30,000
pounds.
The
Convention of International Trade in Endangered Species
(CITES) listed it as vulnerable to extinction in 2002: “Catches
have declined and populations apparently have been depleted
by harpoon fisheries in several countries targeting localized
concentrations of this huge, slow-moving and behaviorally-vulnerable
species, and there is incidental capture in other fisheries.”
In
the proposal to list the whale shark as vulnerable, Philippine
representatives pointed out that whale shark populations
have declined drastically between 1994 and 2000 –
particularly where they have been hunted. During this period,
populations declined by 60 to 70 percent in the Philippines,
by 48 percent in India and by as much as 99 percent in South
Africa.
The
“tofu shark” is highly valued as food in some
cultures. Whale shark meat is said to be very soft, mild
and white – which, like tofu, must be an acquired
taste. Though listing by CITES includes no enforcement sanctions,
most countries have now have banned the harvest of whale
sharks. Some areas where whale sharks are readily seen –
such as the Philippines and Mexico – are finding the
animals are worth much more as tourist attractors than they
ever were as food.
Whale
sharks have also been a feature attraction at the Georgia
Aquarium in Atlanta. The aquarium was in the news after
losing two of their whale shark specimens to what may have
been an ill-advised parasite treatment. The Humane Society
has protested that there is no good reason to hold these
special animals, but the aquarists insist that valuable
knowledge about the species is being acquired, and the public
is learning more about the protection of this species.
Reports
of whale shark sightings in the Gulf of Mexico are not uncommon.
As more fishing activity is carried further offshore, more
and more photos of these animals are brought back. Between
1989 and 1998, aerial surveys were conducted in the open
Gulf to count cetaceans – whales and porpoises. Data
on sea turtles and whale sharks was also collected, and
119 whale sharks were spotted in 59,530 flight miles.
More
whale sharks were seen during the summer season, and the
highest concentrations were seen in the area 87 miles southwest
of the Mississippi River mouth. Nutrient loading from the
Mississippi and Atchafalaya probably supports the high surface
productivity sought by these huge filter feeders. Groups
of whale sharks (up to 23 individuals) were most common
at Ewing Bank, Bright Bank and 28 Fathom Bank.
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