Unweaving The Song Of Whales
By Molly Bentley - BBC News - 2 March 2005
WASHINGTON, DC -- For nearly a decade, Cornell University researcher
Christopher Clark has been eavesdropping on the ocean, hoping to
decipher the enigmatic songs of whales.
Using old US Navy hydrophones once employed to track submarines,
he has collected thousands of acoustical tracks of singing blue,
fin, humpback and minke whales.
His bioacoustics lab is now able to pinpoint the location of individual
singers, and determine the length of their song. As a result, he's
had to redraw the map of whale acoustics.
"The range is enormous," explained Dr Clark. "They
have voices that span an entire ocean."
Drawing on newly declassified acoustic data from the Sound Surveillance
System (SOSUS), and using new tools that can crunch high volumes
of them, Dr Clark has determined that whales' songs travel over
thousands of kilometres and also that increasing noise pollution
in the oceans impedes the animals' ability to communicate.
Booming voices
It is not certain whether whales thousands of kilometres apart communicate
directly with each other, or what their messages contain. But the
results support a 30-year theory that, before the advent of modern
shipping, the animals' booming voices would have resounded from
one ocean basin to another.
With sound that is loud and low, in other words, "beautifully
designed" for long distance travel, the singing of a whale
in the waters off Puerto Rico could carry 2,600km to the shores
of Newfoundland, says Dr Clark.
When scientists create a digital map of the sound as it propagates
in the water, it "illuminates the entire ocean", he adds.
The pan-oceanic range is fitting for massive 30-190-tonne creatures
that rely on reflected sound, rather than light, to navigate.
"You are dealing with animals that are highly acoustically
oriented," said Dr Clark. "Their consciousness and sense
of self is based on sound, not sight."
Dr Clark and other whale researchers spoke at the recent annual
meeting of the American Association for the Advancement of Science
in Washington DC about how new technologies are revealing whale
secrets at the same time that human activity continues to threaten
their well-being.
He is particularly concerned with noise pollution, or "acoustic
smog". Noise from shipping vessels doubled every decade, said
Dr Clark, which means a whale's world decreases by a factor of two.
Over 20 years, its 1,600km acoustic radius shrinks to 400 km, and,
presumably, limits the range over which animals can navigate and
find food or mates.
"We are slowly, inexorably, raising the tide of ambient noise
so that their worlds are shrinking just to the point where they're
dysfunctional," Dr Clark believes.
Military Sonar
He distinguishes between the chronic noise from ships and the acute
bursts of noise from military sonar, which recent evidence suggests
startles the animals and leads to decompression sickness or stranding.
Despite the ban on commercial fishing, other menaces besides noise
pollution, such as commercial fishing nets and ocean contaminants
also continue to threaten the health of whale populations, according
to Roger Payne, president of the conservation group Ocean Alliance.
His team is in the final year of a five-year expedition designed
to establish the first baseline levels of synthetic pollutants in
the ocean. Long-lived industrial pesticides, such as DDT and PCBs,
re-concentrate as they move up the marine food chain. Whales are
at the top of that chain.
"Insect repellents and insecticides which have been spread
on fields on land have now gotten out to whales in mid-ocean,"
said Dr Payne.
His ship, the Odyssey, and its crew have travelled across the Pacific
Ocean taking tissue samples of sperm whales, whose longevity allow
plenty of time for chemicals to accumulate in their fatty tissue.
They have collected 1,100 tissue samples so far, and have run preliminary
analysis on 30 of them.
"We find these substances present in every single one of those
samples," explained Dr Payne, who adds he will test all the
samples once the voyage is complete.
"Toxic dumps"
The study will be the first global measure of pollution in a single
species at the top of aquatic food chain, although high levels of
pollutants in marine animals have been detected in previous studies.
PCB toxicity is defined as 50 parts of contaminant per million parts
of animal, (50 milligrams per kilo) tests have revealed up to 400
ppm in killer whales, 3,200 in beluga whales and 6,800 in bottlenose
dolphins.
It makes the animals "swimming toxic dump sites," according
to Dr Payne.
Contaminants such as PCBs and DDT have been shown to inhibit a mammal's
immune system, its ability to function, and the development of its
young.
"The young receive roughly the contaminant concentration that
their mother has, add to it what they get in their food during their
lifetime, and then pass that double dose to their offspring,"
said Dr Payne.
He is also concerned about the possibility of what he calls "double
stressors," in which seemingly weak threats to an animal are
combined and create a one-two punch that causes serious harm, even
death.
He cited a 2003 University of Pittsburgh study in which bullfrog
tadpoles had little reaction to pesticides and to the smell of predators
when exposed to them in separate experiments. When the stressors
were combined, mortality rose to 80-90%.
Biologists had yet to determine whether such synergistic effects
apply to other vertebrates, such as whales, said Dr Payne, who suggests
that a combination of acute noise, contaminants or predation, could
serve as double stressors.
While some whale populations are recovering since the 1986 moratorium
on commercial whaling, anthropogenic influence may play a decisive
role with populations that are at critical levels and endangered,
such as the Northern right whale.
Specialised ecosystems
When whales are threatened, so are the specialised ecosystems that
depend on them - and on their carcasses.
New research into whale falls - the sinking of whale carcasses to
the ocean bottom - is revealing a weird and diverse assortment of
creatures; some not found anywhere else in the ocean.
A whale fall is such a rare find that scientists like University
of Hawaii oceanographer Craig Smith have made a practice of towing
dead beached whales to sea and sinking them themselves.
"It's really a community service," said Dr Smith. "A
rotting beached whale is a big, stinking mess."
Then they watch to see who shows up. A whale fall provides an organic
smorgasbord - up to two million grams of carbon in its blubber and
oily bones - for a host of creatures, some of which may be so specialised,
they rely on dead whales to complete their lifecycle.
First scavengers such as hagfish appear and eat the soft tissue.
Then bacteria and invertebrates devour the skeleton. Chemoautotrophs
- including bone-eating zombie worms - gather when the bones begin
to emit sulphide. At this stage, whale falls provide parallels to
the sulphide-loving ecosystems at hydrothermal vents.
Scientists speculate that creatures that require sulphide may use
whale falls as sulphide stepping stones - to disperse to new hydrothermal
vent communities - and may even have a spot in the evolutionary
lineage of some of the vent species, according to Dr Smith.
"It's quite possible that the ancestors of the giant tube worms
on vents were actually animals that were living on dead whales,"
he says.
Bone-eating zombie worms
Evidence from DNA sequencing techniques also suggests that, not
only may whale falls host more species than thrive at hydrothermal
vents, some have highly specialised adaptations.
The bone-eating zombie worms, for example, use internal bacteria
to break down the fats in the whalebone and appear to be unique
to whale falls.
"It is increasingly evident that there are major kinds of habitats,
major types of organisms with extreme evolutionary novelty that
remain to be discovered," said Dr Smith.
But as the whales disappear, so do these exotic ecosystems.
By some estimates, large whale populations have been reduced by
75% as a consequence of whaling. Following conservation biology
theory, said Dr Smith, a 75% drop in one population meant that 30-40%
of the species that depend on it would go extinct.
"We are beginning to appreciate what whaling may have done
to these specialised communities," explained Dr Smith. "And
it's very likely that there either have been or - may be on-going
- species extinctions on the deep sea floor connected with whaling."
© BBC MMV
http://news.bbc.co.uk/1/hi/sci/tech/4297531.stm
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