June 10, 2013
by Andrew Darby
In the first count since the hunt off Western Australia was banned, researchers found fewer than half of the whalers’ favoured target, bull sperm whales, compared to during the whaling era.
The finding contrasts sharply with the booming Australian humpback whale population.
But it accords with other research that failed to find any evidence of recovery in the sperm whale population, hunted since the days of author Herman Melville’s 19th century white monster.
”It’s time to put sperm whales back on the agenda,” said Macquarie University researcher Gemma Carroll.
”Because they have been so widespread, there is often an assumption that they are not in trouble,” she said.
”In fact we just don’t know what’s out there.”
The world’s largest toothed animal, the deep-diving sperm whale, uses echo-location to find prey in the black ocean depths.
”They are amazing predators,” Ms Carroll said. ”It’s almost as if they exist in another realm.”
Sperm whales off Albany hunt mainly squid in offshore canyons in the continental shelf slope. They were last hunted themselves in 1978, before the Fraser government outlawed whaling in 1980.
For 10 years previously, Cheynes Beach Whaling Company used spotter aircraft to find the whales. They took both male and female, but preferred to concentrate on the larger bulls that yielded more fine oils and stock feed.
Records showed these whaling spotters saw an average of 6.3 sperm bulls on each flight.
According to a paper before the International Whaling Commission’s scientific committee, when researchers replicated these flights 49 times over, they sighted an average of only three bulls.
Other whales, such as humpbacks, can calve every two years. This aids a population boom like that under way off the Australian east coast, where numbers revived from a few hundred in the 1960s to more than 15,000 now.
Ms Carroll said sperm bulls did not reach sexual maturity until the age of 20. ”They also have very few offspring,” she said. ”Perhaps one every five years.”
There were signs of trouble for the Albany population during the whaling era, with sharply declining pregnancy rates among females coinciding with the reduction in bulls.
Leading sperm whale scientist Hal Whitehead confirmed to Fairfax that there was little hard evidence of a re-growth in the animal’s populations globally.
”In my own studies in the eastern tropical Pacific it seemed that the harmful effects of whaling persisted long after the end of the whaling, and the new Australian study also points this way,” said Professor Whitehead, of Dalhousie University in Canada.
”Sperm whales are highly social animals, so the whalers may have debilitated sperm whale society by their indiscriminate killing, and affected the ability of the population to rebound.”
Ms Carroll said with sperm whales in Australian waters listed as ”data deficient”, there was a need for more survey work to obtain a better understanding of the population.
”The apparent decline in the number … off Albany despite full protection is concerning, with implications for the management of sperm whales globally.”