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When One Ocean Is Not Enough |
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By Marcela Valente*
Argentine
scientists have proved that elephant seals require vast areas of
ocean environment in order to survive. The finding could lead to
improved conservation plans for these sea mammals.
BUENOS AIRES - Thanks to satellite tracking,
a team of Argentine scientists found that southern elephant seals
need much more ocean space to survive than previously thought. They
can dive to a depth of 1,200 meters in search of food in the southwest
Atlantic, and cross the Strait of Magellan to the Pacific.
The mapping of the movements of the Mirounga leonina, which goes
far beyond the Patagonian Sea, is being done in the context of the
Sea and Sky Project, a joint initiative of the Wildlife Conservation
Society and Argentina's National Patagonian Center.
The results "alert us to the fact that to conserve ocean biodiversity
the small protected areas are not enough, that greater dimensions
are needed, in accordance with the space of the species to be protected,"
the project's executive director, Claudio Campagna, told Tierramérica.
"An integrated model allows us to understand the ecosystem as a
whole, incorporating into the management equation the cost of the
impacts, in order to assure ourselves that the natural capital isn't
being compromised," he said.
The Patagonian Sea, which covers two million square kilometers in
the southwest Atlantic, is one of the planet's richest and most
productive temperate marine ecosystems, according to the experts
at the Sea and Sky Project, who promote a management system based
on the precautionary principle.
The waters off the east coast of Patagonia, in southern Argentina,
hold high concentrations of phyto- and zooplankton, the sustenance
of a wide array of squid, crustaceans and mollusks. And feeding
on those species are many types of birds and sea mammals that reproduce
along the shore.
That natural food chain is threatened by overfishing. "The idea
is to find a balance between the necessities of biodiversity and
those of humans. We hope to determine where the sea can be used
without worry, and where its use causes an environmental impact
that should be stopped," Campagna explained.
In this context, the elephant seal is a good indicator of whether
the environment is viable.
Biologist Valeria Falabella receives satellite data about the location
of the animals from when they leave the Valdés Peninsula, on the
coast of Chubut province, home to the National Patagonian Center.
A reproductive colony of the elephant seals is found on the coast.
The data is entered into a computer program that depicts the path
followed by the individual seal wearing a transmitter. The program
shows where the elephant seal spends its time, where it stops to
feed, providing a comprehensive map of the species' movement.
"Determining areas of relevance for the survival of the species
is fundamental for progress in conservation efforts, and these tools
help us understand the biological requirements of the species and
how human activities interfere," Falabella told Tierramérica.
Since the project began in 2003, 23 elephant seals have been studied
using satellite data. Currently, 11 are being tracked.
Elephant seals are born weighing about 40 kilograms and are weaned
at just three weeks, when they weigh 130 kg, gained solely from
mother's milk. Adult females weigh 600 kg on average, while males
are much larger, reaching 3,000 kg. "Adults live to just 14 or 15
years," said Campagna.
Tracking the elephant seals has revealed that the adult males feed
mostly along the continental platform and slope -- a band extending
about 300 kilometers from the coast, where there are important fisheries.
The movements of females, meanwhile, extend up to 1,000 km from
shore.
Two of the females that were tracked from the Valdés Peninsula reached
the Pacific, and one returned 228 days later, through the Strait
of Magellan. In her journey of more than 1,800 km, she gained 179
to 196 kg, indicating a long but successful trip.
Another female reached South Georgia Island, at the southeastern
limit of the Patagonian Sea, and there are data from other seals
that reached the Antarctic Peninsula. In their travels, the elephant
seals dive as deep as 1,200 meters, returning to the surface every
half hour to breathe.
Each time they emerge, the satellite transmitters they wear on their
head emits a locator signal.
Mirtha Lewis, a veterinarian and co-director of the elephant seal
project at the National Patagonian Center, told Tierramérica that
every October about 14,000 pups are born on the Valdés Peninsula,
where the total population is estimated at 42,000.
"But that total is not simultaneously found on the coast," she explained.
"The elephant seals alternate feeding periods at sea with periods
of several weeks on land when they don't eat," said Lewis. The maximum
observed along a 200-km stretch of coastline there is 25,000, she
added.
"In contrast, when the elephant seals are feeding at sea, the area
of distribution is much broader, covering about 4.7 million square
km in the southwest Atlantic, but some cross to the Pacific and
others reach the Georgia Islands," said the expert.
* Marcela Valente is an IPS correspondent. |
