From the brink of extinction to an overpopulation crisis: Rapid rise in humpback whale numbers could overwhelm the Southern Ocean and starve the species
- Humpbacks decreased in numbers in the 1960s to just a few hundred in the wild
- Conservation efforts saw that the numbers had recovered to 25,000 in 2015
- Scientists now warn that these efforts may mean that the numbers will fall again
- They say that the population has become 'too large' for the ecosystem to handle
Rapid growth in humpback whales in the Australian Southern Ocean could lead to a 'population explosion' and an even bigger fall in numbers, according to scientists.
Populations are growing at a rate which could cause a 'significant crash' in numbers 'somewhere between 2021 and 2026'.
The population was brought to the brink of extinction in the 1960s, with just a few hundred surviving in the wild, a result of commercial whaling.
However, conservation efforts and the introduction of the Endangered Species Act saw the humpback population almost totally recover by 2015, to more than 25,000.
While this is positive news for the species, experts are now warning that the population could become too large for the ecosystem to support because of declining food sources in our oceans due to climate change.
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Rapid growth in humpback whales in the Australian Southern Ocean could lead to a 'population explosion' and an even bigger fall in numbers, according to scientists. They warn that they are growing at a rate which could get too high causing a 'significant crash'
Researchers from the University of Queensland have been monitoring whale populations during their annual migration since 2004 from a platform at Point Lookout on North Stradbroke Island off Brisbane on Australia's Gold Coast.
They also looked at data collected for decades before that but the authors of the study note that there is not enough on large mammals that saw their population go up after almost going extinct.
Scientists had expected the growth rate to slow as whale numbers stabilised.
'That hasn't happened,' said Dr Michael Noad, who led the study.
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'Whale numbers are still steaming ahead at a tremendous rate — the population is virtually doubling every seven years.
'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.'
The researchers used the example of the population increase in grey whales in US waters after a steep decline.
About a decade of conservation efforts numbers surged before dead grey whales were sighted floating in the ocean and interfering with shipping.
By 2015, the humpback population had almost totally recovered to more than 25,000 whales because of conservation efforts and the introduction of the Endangered Species Act in 1973. Scientists are now warning that the population could become too large for the ecosystem to support (file photo)
This is believed to be because of the population correction but Dr Noad said there wasn't 'good data' on the grey whales' population spike, slump and levelling off.
Dr Noad said however that the grey whale decline could serve as a warning to the humpback whale population, which could seen an even larger fall in number.
'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.
A sudden population slump in humpbacks could see dead whales at sea, and an increase in beachings, as was the case in grey whales.
HUMPBACK WHALE POPULATIONS AND ITS THREATS
Humpback whales live in oceans around the world. They travel incredible distances every year and have one of the longest migrations of any mammal on the planet.
Some populations swim 5,000 miles from tropical breeding grounds to colder, plentiful feeding grounds - this is why it is difficult to estimate population size, according to the NOAA.
Of the 14 distinct populations, 12 are estimated to number more than 2,000 humpback whales each and two are estimated to number fewer than 2,000.
Humpback whales live in oceans around the world. They travel incredible distances every year and have one of the longest migrations of any mammal on the planet
Some populations (such as those off eastern and western Australia) are believed to number in excess of 20,000 animals—a remarkable recovery given that the same populations were almost eradicated by whaling almost sixty years ago.
By contrast, the smallest known population is one which inhabits the Arabian Sea year-round, and may number as few as 80 individuals.
Threats to humpback whales include decline in food like Krill due to a combination of climate change and industrial-scale fishing.
Humpback whales can become entangled by many different gear types including moorings, traps, pots, or gillnets.
Once entangled, if they are able to move the gear, the whale may drag and swim with attached gear for long distances, ultimately resulting in fatigue, compromised feeding ability, or severe injury.
There is evidence to suggest that most humpback whales experience entanglement over the course of their lives, but are often able to shed the gear on their own.
Inadvertent vessel strikes can injure or kill humpback whales.
Humpback whales are vulnerable to vessel strikes throughout their range, but the risk is much higher in some coastal areas with heavy ship traffic.
Underwater noise threatens whale populations, interrupting their normal behaviour and driving them away from areas important to their survival.
Sound has been shown to increase stress hormones in their system and mask the natural sounds humpback whales require to communicate and locate prey
A population crash could have several consequences for Queensland tourism.
'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.'
'We are very likely to see an increase in the number of strandings as well — possibly sick whales beaching themselves, and also whales that die at sea will represent a shipping hazard.'
Dr Noad said that the best approach would be to monitor humpbacks and put in measures to help them if they started to show the population began to slump.
He stressed that it would be extremely counterproductive to start hunting whales again or to introduce a controlled cull of numbers.
'The last thing they need is more stress on the population, especially if the population does start to decline,' he said.
'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 findings were published in Population Ecology.
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