- 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.
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- 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.
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- 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.
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- "The range is enormous," explained Dr Clark.
"They have voices that span an entire ocean."
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- 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.
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- Booming voices
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- 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.
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- 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.
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- When scientists create a digital map of the sound as
it propagates in the water, it "illuminates the entire ocean",
he adds.
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- The pan-oceanic range is fitting for massive 30-190-tonne
creatures that rely on reflected sound, rather than light, to navigate.
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- "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."
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- 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.
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- 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.
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- 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.
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- "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.
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- Military Sonar
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- 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.
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- 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.
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- 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.
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- "Insect repellents and insecticides which have been
spread on fields on land have now gotten out to whales in mid-ocean,"
said Dr Payne.
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- 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.
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- "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.
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- "Toxic dumps"
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- 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.
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- 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.
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- It makes the animals "swimming toxic dump sites,"
according to Dr Payne.
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- 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.
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- "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.
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- 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.
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- 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%.
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- 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.
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- 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.
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- Specialised ecosystems
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- When whales are threatened, so are the specialised ecosystems
that depend on them - and on their carcasses.
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- 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.
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- 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.
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- "It's really a community service," said Dr
Smith. "A rotting beached whale is a big, stinking mess."
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- 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.
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- 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.
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- 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.
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- "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.
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- Bone-eating zombie worms
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- 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.
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- 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.
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- "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.
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- But as the whales disappear, so do these exotic ecosystems.
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- 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.
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- "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."
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- © BBC MMV
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- http://news.bbc.co.uk/1/hi/sci/tech/4297531.stm
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