How 9/11 shed light on stressed whales
FINDINGS MADE POSSIBLE by the attacks on New York’s Twin Towers on September 11, 2001 show for the first time that busy commercial shipping lanes not only alter whale behaviour, but can cause chronic stress.
Only weeks before the 9/11 attack, scientists led by Dr Rosalind Rolland of the New England Aquarium in Boston had undertaken a study of North Atlantic right whales that congregate in late summer in Canada’s Bay of Fundy to feed and nurse their calves.
When shipping traffic on Canada’s east coast dwindled dramatically and researchers noticed the drop in underwater noise levels, they realised it would be an opportunity to investigate whether sound pollution was a cause of stress for right whales.
Stressed, hormonal whales
From July 2001-2005, the researchers used trained dogs to find whale faecal matter floating on the surface of the water. The whale poop contained hormone-related chemicals, called glucocorticoids, mirroring stress levels that could change from one day to the next, or even within hours.
Glucocorticoids are secreted in a crisis: aggression by a predator or competitor, starvation, or drought. In the short run, this rush of hormones helps animals cope by summoning reserves of energy. But over the long haul, constant elevations of the hormone due to stressful situations becomes a detriment, leading to stunted growth, a weakened immune system and a compromised ability to reproduce.
They found that changes in the concentration of the hormone matched perfectly the sudden drop and gradual renewal of maritime traffic in the area after the attack. Over the last 50 years noise caused by cargo and military vessels, along with high-decibel sonars used for oil exploration, has gradually increased in intensity and scope.
Baleen whales, of which right whales are a sub-species, communicate at the same low-frequency wavelengths emitted by some ships, in the range of 20 to 200 hertz (Hz), and some species have adapted by emitting louder and more frequent acoustic signals.
Significant effects on whale numbers
In Australia, it has long been speculated that the slower recovery of the humpback whales on the east coast might have something to do with busier shipping traffic. Since protections were put in place in the 1960s says Dr Curt Jenner, director the WA-based Centre for Whale Research, humpback whales on the west coast have bounced back to about 35,000. Inexplicably, the eastern population has only reached between 15,000-17,000.
“Whales use sound as one of their primary tools, and noise is definitely a factor both good and bad,” Curt says. “Anecdotally, for example, we’ve seen what we think are humpbacks hiding from the echolacation of killer whales in noisy areas.”
“To our knowledge, there were no other factors affecting the population that could explain [increased stress], besides the decrease in ship traffic,” states the new study, published in the journal, Proceedings of the Royal Society B.
Because they live, feed and breed so close to shore, critically endangered North Atlantic whales are already threatened by ship collisions and fishing gear entanglements, two leading causes of death among large cetaceans.
“Acoustic pollution from anthropogenic sources presents a less visible, but pervasive disturbance to these coastal-dwelling whales that may have negative consequences for population viability,” the study concludes.
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