Johannesburg - After being almost hunted to extinction, southern right whales might face another potential threat: climate change.
An annual aerial survey by the University of Pretoria’s whale research unit between Nature’s Valley and Muizenberg has recorded the second-lowest number of southern rights in 24 years - 200.
The steep decline is puzzling scientists like Dr Els Vermeulen, whale unit research manager at the university’s mammal research institute.
Shortages of small crustaceans, linked to climate change, in their feeding grounds in the Southern Ocean could be the culprit, she said.
The unit said sightings in their breeding ground have not been at normal levels since 2010. Last year, a record number were spotted.
“After last year, we regained a bit of hope that things would recover. But then the continuously low number of unaccompanied adults since 2010 does show that the rate at which the population is increasing is decreasing,” Vermeulen said.
In total, 190 females and calves (95 pairs) were counted and photographed, as well as 10 adult whales without calves - so-called “unaccompanied adults” - this year.
“What we saw this year was again an extreme low number of females with calves and of unaccompanied adults,” Vermeulen said. “So, we’ve seen in South Africa, a decrease in the unaccompanied adult component, the males, since 2010, after which the numbers crashed quite dramatically.
“Normal numbers prior to 2010 would be in the 300s and this year we counted 10. For females with calves - their numbers have crashed since 2015. We had a low count in 2015, an extreme low count in 2016 and 2017 and then we had an all-time record of sightings of calves in 2018. This year again, there was an extremely low number - only 95 calves. Last year, we had over 700 calves.”
The unit’s early data strongly suggests the whales might not be finding enough food in their feeding grounds to sustain the energy they need to migrate from Antarctica and to reproduce. “Where they are then, is a big question - we don’t know.”
Similar trends have been observed in the breeding grounds of Argentina and Brazil and Australia. “We’re looking into the aspect of climate playing a role in the availability of food; we’re looking at the whales’ physical body composition and comparing that to the late 1980s, to see if whales are literally skinnier or not than before.
“We’re looking at finding out the exact location of their feeding grounds and then trying to look at those areas in the Southern Ocean and see how climate may be influencing the productivity of those areas. We don’t know if there’s a general decrease in the amount of food or if there’s a relocation of their food due to current changes in ocean conditions.”
If right whales are being affected by changing food availability, they won’t be the only marine species.
“Other whales, seals, marine birds and fish will be affected by the same thing - right whales are just indicating to us that there’s a problem.”
Female right whales are now giving birth on average every four instead of three years, reducing the rate at which the population is increasing.
“Even if we find that why this is happening is related to climate change, it might not be something that’s easily fixed. The change needs to come at the global level. That’s probably the most worrying aspect. We can only hope this is a temporary trend.”
As a species, southern right whales are still recovering from whaling, when they were hunted to near extinction - today, the global population is only at 30% of its original numbers.
Regional (southern African) abundance is estimated at just over 6000 individuals, with a global population size of just under 15000 individuals.
The species is the backbone of the local whale watching industry.
“We’re trying to do a lot of outreach work for people to understand this is a global issue - people think it’s a South African problem related to pollution for example, but the problem is not in South Africa.
“It’s in the Southern Ocean. The low amount of rights does affect the tourism industry, without a doubt.”