From the experts' point of view, whales are the "early warning systems" of the oceans. If they are not doing well, that is a warning sign for the entire marine ecosystem, says whale researcher Els Vermeulen from the South African University of Pretoria in the run-up to a UN high-seas conference. The two-week meeting begins in New York and is expected to adopt an ocean protection agreement.

Vermeulen oversees a project that has been recording the reproductive behavior of southern right whales (Eubalaena australis) for more than 40 years. In addition to counting off the South African coast where southern right whales come each year to give birth, her team attached satellite transmitters to 15 females. The researchers follow the migration of the whales over thousands of kilometers in order to understand how changes in the climate and environment affect their migration routes, their feeding behavior and their reproduction. The latest results showed "drastic changes" in the three areas, says Vermeulen.

Hugely fluctuating numbers

During the most recent whale season in October, the research team counted 304 calving females and 50 adult whales without a calf. Although the number of calving females is slightly higher than the 249 counted in 2015, it is "far below what we would expect under 'normal conditions'," explains Vermeulen. In addition, the registered number of adult southern right whales without calves remains "extremely low", as in the past decade, according to Vermeulen. This indicates that the animals are not coming to the South African coast on the same scale as they were a few decades ago.

"Normal" would be a sighting rate increasing by about 6.5 percent per year, as has been observed in southern right whales off South Africa since the global ban on commercial whaling came into force in 1986. "However, we see enormously fluctuating numbers," says Vermeulen.

Females calved at longer and irregular intervals. "They only give birth (off the South African coast) every four to five years instead of every three years," explains Vermeulen. The reason for this is probably the average body size of the females, which is reduced by a quarter. "We assume that this is due to the reduced occurrence of food in the Southern Ocean due to climate change, especially plankton," says the researcher. The krill fishery could possibly play a factor as well.

Eat less krill or travel more distances

Female right whales rely on fat reserves, which they eat up in the Southern Ocean during the summer months. These are needed during the winter months when they swim off the coast of South Africa to calve. A lower birth rate and poorer body condition mean that the whales in the Southern Ocean have either eaten less krill or had to travel further to get as much krill as before, Vermeulen says. A smaller body size is therefore directly related to the birth rate.

Not only whales but also numerous other marine animals feed on plankton, which consists of microorganisms, including krill. These include seals, crabs, mussels and many fish. Researchers refer to plankton, which makes up almost 98 percent of the world's ocean biomass - as the "base of marine life". "With fewer plankton, the ecosystem could collapse," warns Vermeulen.

A study published in the journal Global Change Biology shows that humpback whale (Megaptera novaeangliae) pregnancies off the West Antarctic Peninsula are directly dependent on krill availability. For example, in 2017, a year after krill became plentiful, 86 percent of female humpback whales there were pregnant. In contrast, in 2020, following a year with fewer krill, it was just 29 percent. The amount of krill varies from year to year. Its availability the year before a whale becomes pregnant is crucial, the researchers say, as females need to fatten up for their upcoming gestation.

It is now known that krill - contrary to what was previously widely believed - is not an unlimited food source for whales, explains the report's lead author, Logan Pallin of the University of California at Santa Cruz. "Continued warming and increased fishing along the West Antarctic Peninsula, which further reduces krill stocks, are likely to impact this humpback whale population and other krill feeders in the region," Pallin said.

Overlapping stressors

Whales are particularly good indicators of the health of many ecosystems because they travel so far, providing data for many parts of the high seas. A humpback whale observed by WWF swam around 19,000 kilometers through the Southern Ocean, through coastal waters of 28 countries and the high seas.

Six of the 13 large whale species are now classified as endangered or even critically endangered, even after decades of protection, says Chris Johnson, director of WWF's Global Whale Conservation Initiative. There are many reasons for this: global shipping, fisheries and plastic pollution, but also the effects of climate change, which have now reached almost every area of ​​the oceans. These overlapping stressors impacted the recovery of some whale populations and severely reduced the numbers of others, Johnson says. For example, the North Atlantic right whale is at its lowest level in about 20 years, with just 336 animals remaining.

A big part of the problem is that only 1 percent of the high seas are protected, Johnson said. According to the WWF, the high seas are "one of the least managed places on earth". The whale experts hope that the forthcoming negotiations in New York will create strict guidelines for a high-seas agreement. After more than a decade of discussions, this year's meeting is set to conclude with the creation of a landmark global framework - a legally binding instrument to protect marine life and their habitats outside national jurisdictions.