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Scientists
have been trying to unravel whale shark feeding techniques
in the whale shark aggregation found off Holbox and
Contoya between Mexico and Cuba in the Gulf of Mexico,
states a press release from Jim Tharpe, Atlanta
Journal-Constitution.
The
team was led by Dr. Robert Heuter of the Mote Marine
Laboratory, who has been running a research programme
since 2003, in association with
Mexican Authorities. Dr. Heuter is also in charge of the whale
shark project at the Georgia State Aquarium (see Sagren
vol. 4.2). Other team members included Philip
Motta, a biologist from the University of South Florida ,
and Mike Maslanka, a nutritionist with the Georgia State
Aquarium who is responsible for the diet of Atlanta's four
whale sharks.
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Whale shark
feeding in Okinawa aquarium.
Photo John Turner |
The
team made field observations and carried out specific experiments on the sharks feeding
method and prey, with the hope of being able to
better provide for the captive whale sharks in the Georgia
State Aquarium. Last year the annual aggregation of whale
sharks off Holbox was apparently disrupted by the tail-end
of Hurricane Katrina, when the researchers could find only
four sharks in three days of searches. This year the
sharks were back in force with one survey flight revealing
145 sharks in the area.
Plankton
tows by the team indicated that the sharks were feeding on
much smaller zooplankton than the krill currently being
fed to the captive whale sharks in the Georgia State
Aquarium and might enable a change in their diet in the
longer term. Several field experiments were set up to help
reveal details about the whale sharks feeding mechanisms
but the sharks seemed to have other plans!
The
first involved injecting vegetable dye into the water to
see how this would be passed through the shark’s gill
filtering system. However, as soon as the sharks approached the cloud of dye
they simply closed their mouths and swam underneath it…
A
second experiment used rice soaked in sea-water as a
substitute of the same size of the zooplankton the sharks
normally feed on. This fared slightly better as the sharks did take it
into their mouths, however, a few seconds later, they
simply spat it back out again.
While
the field experiments may not have been very successful, Dr.
Heuter was positive about the outcome
in that so little is known about whale sharks, any success
or failure adds to the information on this species. He
also hopes to be able to use some of the lessons learned
to further research on the captive sharks in the Georgia
State Aquarium. The controlled environment of the aquarium
may provide the conditions needed to evaluate the whale
shark’s sensory mechanisms such as smell, taste or
electro-sensory perception.
Based
on a press release from Jim Tharpe, Atlanta
Journal-Constitution
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