The recovery of the humpback whale population in the Southern Ocean is one of the great conservation success stories but researchers are warning the whales could wind up being their own worst enemies.
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Researchers from the University of Queensland have been monitoring whale populations during their annual migration up and down the east coast of Australia since 2004, and have access to data collected for decades before that.
They have found that after being hunted to the brink of extinction in the 1960s, with just a few hundred humpbacks surviving in the wild, the humpback population had almost totally recovered to more than 25,000 whales in 2015.
Associate Professor Michael Noad from UQ’s School of Veterinary Science said that was great news, but the problem would be if the population became too large for the ecosystem to handle.
“The problem was the whales had got back to where they should be but they were still increasing at a rapid rate,” Dr Noad said.
“They’re either going to go up to a fairly high number and level off, about 40,000 or 50,000, or they could peak and then crash.”
“If that peak is going to happen it’s not far away. We reckon anywhere between 2021 and 2026 and there could be a significant crash in the whale numbers after that.”
Dr Noad said one of the problems with extrapolating the humpback numbers was there was not any other good data gathered on large mammals which had almost gone extinct but then saw their numbers go back up.
A warning sign was the case of the repopulation of grey whales in US waters, which like humpbacks had dwindled in population, before conservation efforts saw their numbers surge.
About a decade ago the grey whale population surged, which the researchers believe was a population correction that saw dead whales floating in the ocean disrupting shipping as well as an increase in the number of beachings.
Dr Noad said there wasn’t good data on grey whales’ population spike, slump and levelling off, but it served as a warning for the humpback population in Australian waters.
“So there is a precedent for this in whales, and the rate of increase in east Australian whales is higher than the grey whale, so we fear if there is a correction it will be significantly larger,” he said.
As in the case of the grey whales, a sudden population slump in humpbacks could see dead whales at sea, and an increase in beachings, not to mention the impact to Queensland’s $100 million whale watching industry.
“The whale watching industry would take a hit not only because there’d be fewer whales at sea, but the whales that were there would be thin, stressed, mums would be struggling to feed the calves,” Dr Noad said.
“And that then raises the question of whether whale watching vessels should be approaching these animals. They might simply be too sick to put up with the added stress of vessels near them.”
Dr Noad stressed it would be extremely counterproductive to start hunting whales again or to introduce a controlled cull of numbers.
Because of the lack of data, Dr Noad said the best approach was to keep monitoring the humpback populations, and if whales started showing signs of population collapse put in place measures to help them.
“The last thing they need is more stress on the population, especially if the population does start to decline,” he said.
“The story is a positive one - these whales are resilient and they’ve recovered from exploitation.
“It’s about what happens next. We shouldn’t just drop the ball and stop worrying about them and assume everything will be fantastic from here on in.”
The research finding have been published in the journal Population Ecology.
