By Shark Info
Once a year scientists from around the world meet to discuss the newest
results from shark and ray research. This year's Symposium of the American Elasmobranch
Society (AES) took place from June 14 to 18 in La Paz, Baja California Sur,
Mexico. Our Shark Info team was there.
The Symposium focused on shark and ray fishing in Baja California and
on whale sharks, but also touched upon other research areas, including the migration
of the white shark (Carcharodon carcharias) in Australia and opinions on how shark
accidents should be assessed and investigated. The following report concentrates
primarily on whale shark activities. Shark Info will cover
the other subjects in future issues.
Once again the Symposium showed that even though whale sharks (Rhincodon typus)
are the largest and most well-known species of ocean sharks, many aspects regarding these
animals still remain a mystery. Astonishingly, they belong to those species who can be
kept in aquariums despite their size. The aquarium in Okinawa has kept whale sharks
for about 20 years, three of their animals having lived longer than five years.
Despite this enormous effort, many biological details are still unsolved. Accordingly,
one of the central questions posed at the Symposium was whether or not they migrated.
Individual observations stemming from the Sea of Cortez appear to show that the
animals are very migratory by nature and that they swim thousands of kilometers each
year. It is important to investigate such indications, especially since whale shark
populations in Asia have recently suffered drastic losses due to the large demand for
"tofu sharks" (whale sharks) in Taiwan. One of the major catch areas has been the
region around the Philippines. Various nature protection organizations and local
universities have now joined forces to find out via satellite trackings more about
where these animals stay and their migration routes. Similar tracking attempts have
previously been undertaken in South Africa and the Honduras. Such projects should help
us improve the monitoring of whale sharks and in turn work out respective protective
measures. In single regions in the Philippines, e.g. Donsol (southern Luzon), whale
sharks have been protected since March 1998 and efforts are under way to replace
illegal fishing with ecological touristic activities. Initial results of such actions
have shown that local communities registered a clear economic upswing. In addition,
application of this successful concept has not been limited to the Philippines.
Another much debated and very interesting question
was: How large are whale shark populations? Do the animals migrate primarily as
single individuals or in groups? Based on information received from local fishermen,
scientists researched regions in Belize (Central America), among other areas.
Observations revealed that whale sharks apparently journeyed there in greater numbers
at certain times of the year. Research showed that up to 25 whale sharks gather there
at the same time when two species of bony fish deposit their eggs and sperm. Whale
sharks live mainly off plankton (microscopic organisms), but in this instance proof
was brought for the first time that they also seek out other food sources such as eggs
layed by bony fish. Various whale sharks were marked during this event and then
tracked during their subsequent migrations. Most of the animals returned to deeper
waters where they appeared to associate with various bony fish species.
part of the Symposium on whale sharks was a documentary video which for the first time
showed how an orca (Orcinus orca) hunted a whale shark. The film was impressive and
certainly unique, abut the observers failed to film the underwater chase so that,
unfortunately, we must continue to speculate on how the whale managed to approach the
whale shark and bite him. Apart from humans and orcas, whale sharks have practically
no enemies, accordingly, the development of their protective mechanisms are more
limited. In the example seen, the whale shark always turned his back to the whale, but
in the end unsuccessfully.
May be published only by indicating the source: Shark Info / Shark Info