By Molly Bentley
in 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.
Human-produced noise is shrinking their world
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.
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.
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.
Whale song "illuminates the entire ocean", says Clark
"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.
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.
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."
Tiny creatures devour the fallen whale carcasses
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.
Whale fall events are now very rare
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."