July 25, 2008 -- Humans have over-exploited the whale shark
-- the world's largest living fish -- to such a degree that the ocean
giants are actually shrinking in size, according to new research.
The whale shark population has also fallen by approximately 40
percent over the past decade in Western Australian waters, the new
study has found, suggesting that this once prevalent shark, which can
reach lengths up to 42 feet, is undergoing a severe decline in certain
"We are all very alarmed at our findings, which really did defy our
expectations," co-author Ben Fitzpatrick, a University of Western
Australia biologist, told Discovery News.
The researchers analyzed the largest-ever database of sightings and
size information on whale sharks. The database represents a long-term,
continuous record of sightings -- 4,436 in total -- as well as photo ID
information concerning age and size, all pertaining to whale sharks at
Ningaloo Reef, Western Australia.
Because the sharks gather seasonally at the picturesque reef from
March to June, a profitable industry has been built around "dive with
sharks" activities. Usually by air sightings, tour operators regularly
gather information on the sharks, compiled in the extensive database.
Fitzpatrick and his colleagues not only detected the population drop at
the reef, but they also discovered the sharks have shrunk in body
length by an average of over 6.5 feet. The overall reduction appears to
be due to the disappearance of older, larger females, along with some
males, within whale shark groups.
"I think it is mostly because the larger animals are being hunted
for food and other products, such as for soup fins," explained Barry
Brook, another co-author of the study and director of the Research
Institute for Climate Change and Sustainability at The University of
"The larger the fin, the more valuable it is," Brook added.
The findings are published in the latest issue of Biological Conservation.
The scientists believe a selection effect may also be at work,
whereby pressures are forcing smaller, younger whale sharks to breed
earlier, but they believe this is just "a minor piece of the puzzle."
Brook said that while the whale sharks enjoy protection in Ningaloo
Reef waters, the sharks migrate over large distances, often traveling
thousands of miles.
"Artisanal fisheries via harpoons for meat, for example, off the
coasts of India and Indonesia, but mostly by Taiwanese and Chinese
commercial fisheries" are likely responsible for the declines, he said,
adding that whale shark meat is referred to as "tofu fish" due to its
texture, which is also prized in shark fin soup and Chinese medicine.
Ship strikes also tend to kill larger adults, he said, though
evidence for the strikes is hard to compile since resulting deaths
would usually remain unknown.
These latest findings counter a study
late last year by Brad Norman and Jason Holmberg of ECOCEAN, a research
education and conservation organization. That report, based on multiple
underwater images of the sharks, concluded that Ningaloo Reef whale
sharks are thriving. Norman did, however, admit to Discovery News that
the species is "rare" and "vulnerable to extinction."
Brook and his colleagues have authored a written response to Norman's paper, which is still under consideration by the journal, Ecological Applications.
They say that while whale sharks receive some trade protection from the
Convention on International Trade in Endangered Species, "it is
difficult to police non-international trade or local hunting by
The migratory habits of whale sharks, Brook said, "mean it is
impossible to protect the Ningaloo population once the sharks leave
Australian waters for Indonesia and the Philippines."
The researchers urge officials to establish well-enforced
international protection for the sharks. They also hope that
collaborative tagging studies in the future will help to better
identify and monitor whale shark migration routes.
Copyright: Discovery Channel