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Secrets of the Belize Whale Sharks Revealed

By Richard Black

High-tech electronic tags on the whale shark, the world's largest
fish, have revealed how and where they find food.

Researchers in Belize have tracked the sharks as they dive almost a
kilometre in search of food, and find shoals of spawning fish in order
to eat the eggs.

The sharks grow to 20m in length, and are listed as vulnerable to extinction.

The researchers believe their findings will help to plan tourism
operations around whale sharks in a way which does not harm the
creatures themselves.

These new, unprecedented insights into the whale shark's world come
from the Belize Barrier Reef, the world's second largest barrier reef
system and a site given UN World Heritage status.

"Our study showed that sharks dive much deeper than previously
believed, reaching depths of over 1,000m in search of food," said
Rachel Graham of the US-based Wildlife Conservation Society (WCS).

"Water this deep is only a few degrees above freezing; and this
explains why tropical whale sharks have an insulating fat layer just
below their skins, something which has perplexed scientists for
years."

Day or night

During the night, the sharks generally remain in shallow water,
feeding off plankton, and reserving deep dives for the heat of the
day.

Deep dives often end with a high-speed ascent, perhaps to deliver a
burst of oxygen to their bodies after a period in deeper, less
oxygenated water.

Whale sharks patrol the reef promontory waiting for snappers to spawn
[Photo credit: Rachel T Graham]
Despite its size, the whale shark eats plankton not people

Around the time of the full moon, Cubera snappers come together near
the shore to spawn, forming huge masses of writhing bodies in a soup
of freshly-released eggs.

For the whale sharks, this is a feast, and they swim through the egg
soup time and time again, filling their giant mouths with snapper
caviar.

This habit of surfacing during spawning allowed the scientists to
attach electronic tags to the whale sharks.

The tags make regular recordings of temperature, water pressure and
light level. After a pre-programmed period, they automatically detach
from the shark, float to the surface and beam their data back as an
e-mail via satellite.

Slow and easy

The whale shark (Rhincodon typus) is found globally, both in open
water and near shore.

Despite its huge size, it eats plankton rather than people, and its
slow movements make it easy to catch by harpoon or net.

IUCN, the World Conservation Union, lists the whale shark as
"vulnerable" in its Red List of threatened species.

Owing to a demand for fins, trade in its parts is now regulated under
the Convention on International Trade in Endangered Species (CITES).

However, a different industry is now growing in some parts of the
world, including Belize, using the creatures as a tourist attraction.

"Knowledge of the whale shark's dive behaviour can help us tailor
conservation policies in a way which minimises impact on them," Dr
Graham told the BBC News website.

"We now know that the spawnings, the predictable pulses of food, are
important enough to the shark that they change their regular behaviour
to make use of them.

"So protection of the critical habitat that these feeding sites
represent, and of the sharks when they're visiting, is key to
sustaining the sharks."

The WCS and University of York scientists publish their findings in
the Royal Society's journal Interface.

Can one just imagine how many more groupers, snappers,grunts, porgies,reef tropicals, and so on and so on would exist (hatch to grow)if the Whale Shark didnt exist? That should stir up the environmental kettle!?

Pardon he use of the word "hatch" much too simplex!

They eat snapper eggs (for a limited season) because of the method the snapper use to fertilize their eggs; they eat plankton the rest of the time. If you've ever seen a snapper spawn you'll know that there's plenty of left-overs. I don't know where the rest of the species come in.

The other species spawn similarly in different regions of the world (groupers-Honduras and CR) and Whale sharks are there similarly as near Glovers AT'
Basically a destructive, useless creature! C'mon enviros!!!!)

:p NO bites????

"Basically a destructive, useless creature!"

Um, so is humankind, what's your point.

You've already made it - precisely- destructive, useless creature!

Not that it matters much to this "discussion", but just to add a little more insight, they eat more than plankton and spawn. The also eat whole fish like tuna.

Now before any of you "experts' out there contradict that, my knowledge comes from diving with them and watching them in schools of tuna with their huge mouths wide open as they engulf the tuna.

The "experts" have your back: http://www.boattalk.com/sharks/whaleshark.htm

Thanks for the collaboratin Simon.

And by the way, the whale shark steaks you had waiting for me in my refrigerator when I arrived were excellent.

OK bywarren had to be something stronger than a few Belikins prior to the dive you "saw" a Whale shark engulfing tuna? Something mind alterring by any chance?? As Warner Wolf would say - "gimme me a break"!!!!

Show us a picture of that one and I'll buy the first round of Whale shark steaks for every person on the island!!

Be careful what you offer. Look me up when you are in AC and I will show the pictures and a video. If I am not there when you are, just look up Jose Gonzales (fishing guide) phone number 226-2344. He also has copies.

To quote Walter Brennan, "no brag, just facts."

PS: and it was not "a whale shark." I used the term "them" and "their" i.e. plural. Have been diving with them many years seeing it many times.

bywarren: You're on!

High-Tech Tags Reveal Whale Sharks
By Rossella Lorenzi, Discovery News


AP Photo/Beatrice Larco

Oct. 6, 2005- Whale sharks, the world's largest fish, dive nearly a mile in search of food, according to high-tech electronic tags that have recorded every aspect of the fish's life.

Rachel Graham, of the U.S.-based Wildlife Conservation Society (WCS) and colleagues from the University of York, U.K., attached electronic tags to nine whale sharks swimming at the Gladden Spit reef off Belize, the world's second-largest barrier reef system.

Thousands of snappers gather there under full moons in the spring to spawn, turning the sea a milky color and drawing normally solitary whale sharks, which feast on snapper fish "caviar."

Part of the folklore of the reef's fishermen, the spectacle has proved to be a unique possibility for the researchers to attach satellite-controlled tagging devices to the fish's thick skin.

The tags made regular recordings of temperature, water pressure and light level for 206 days. After this preprogrammed period, they automatically detached from the fish, floating to the surface and sending their data back via satellite.

Downloaded to a computer, the recorded information showed that whale sharks made dives beyond 979.5 meters (3,213 feet) - the tag's maximum depth recording - to temperatures below 7.6° Celsius (46° Fahrenheit).

"A whale shark may be able to withstand low temperatures due to its subcutaneous fat layer," the researchers wrote in the current issue of the Royal Society's journal Interface.

While at night the sharks remained in shallow waters, they made deep dives during the day. These often ended with fast ascents, to re-oxygenate the gills after time spent in less-oxygenated depths.

Growing up to 65 feet (20 meters) long and weighing up to 15 tons, the nonaggressive whale shark (Rhincodon typus) lives in tropical seas and feeds mainly on plankton.

Contrary to its name, the fish is not related to whales, which are mammals.

A highly migratory species capable of transoceanic movements, whale sharks, threatened by overfishing, are one of the species listed as vulnerable to extinction.

"We now know how the world's largest fish behaves night and day and that their behavior is not random; it has patterns that are geared to food availability," Graham told Discovery News.

"This has conservation implications whereby we need to focus more on protection of their key feeding sites where they are most vulnerable to capture," she said.

Indeed, the data from tags revealed that whale sharks' dives are influenced by food sources, with shallower dives made during fish spawning periods. Even the different diving patterns during the night and daytime are related to food.

"They may be linked to migration of zooplankton that usually aggregate near the surface by night and descend to deeper depths during the day," said the researchers.

According to Heidi Dewar, a marine biologist at the TOPP program - Tagging of the Pacific Pelagics - in La Jolla, Calif., the study "provides valuable data on a very poorly understood and endangered species."

"It also takes the analysis to a new level using a novel approach to quantifying patterns, rather than just describe them qualitatively. Rigorous quantitative analysis is critical to developing any models that will predict the distribution of whale sharks for conservation efforts," Dewar told Discovery News.

http://dsc.discovery.com/news/briefs/20051003/whaleshark.html

Hmmm, filets or steaks, grilled -butter,garlic YUM! YUM!

Very cool program, been to their base on the Silk Cayes, twice during tagging, which is as difficult as it sounds. Treat yourself to a whale shark dive with Julie Berry, who worked with Rachel and is now runing the dive shop at Turtle Inn in Placencia.