Whales show ocean noise stress
© New England Aquarium
Researchers from the New England Aquarium in Boston, Massachusetts have found that whales become stressed in noisy oceans caused by the presence of dense shipping. The study simultaneously confirmed that the population of North Atlantic right whales (Eubalaena glacialis) has recovered after excessive hunting by the Basque people in previous centuries nearly caused their extinction. The study's findings were reported in the Royal Society Journal of Proceedings B.
Ocean noise has risen significantly in recent decades due to the growth in global shipping, and one study demonstrated that the North-Eastern Pacific is 10-12 decibels louder than now it was in the 1960s. When traffic in the Bay of Fundy off the Canadian coast dropped off after the September 11th attacks, researchers registered an instantaneous fall of 6 decibels with particularly pronounced changes in frequencies below 150Hz. The researchers from the New England Aquarium stumbled across this information by accident while reading through the notes of another study and repurposed samples collected by the original study to test their own hypothesis. Measuring stress hormones in whale faeces over an extended period confirmed that stress dropped when the oceans were quieter and that stress rose when there was more noise.
"This is the first time that anyone's documented any physiological effect - these are after all 50 tonne animals so they don't make terribly easy things to study," said Dr Rosalind Rolland, who led the study. "Past studies have shown they alter their vocalisation pattern in a noisy environment just like we would in a cocktail party, but this is the first time the stress has been documented physiologically."
The team now hope to study the relationship between stress hormones and ocean noise in a greater range of locations. It is possible that this might explain the difference in speeds of population recovery between the Northern Atlantic Right Whales and the Southern Right Whales of the South Atlantic, whose numbers have increased at a faster pace since the end of industrial hunting.
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