Having narrowly escaped extinction, there are now signs that the population of the second largest animal in the world is recovering: researchers have observed up to 150 fin whales eating together in the Antarctic. As they point out, the comeback of sea giants is doubly gratifying. Because they play an important role in nutrient recycling in the Southern Ocean, other species in the ecosystem also benefit from the recovery.
Hardly missed out: fin whales are the largest animals on earth after the blue whales – and like their relatives, commercial whaling was almost their undoing: only a tiny part of the original population of fin whales still existed until the catch quota was finally set to zero in 1976 . But the stocks of the approximately 22 meter long and 70 ton animals recovered only slowly. After more animals were sighted again during individual expeditions in the 2000s, the research team led by Bettina Meyer from the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research in Bremerhaven is now reporting clear indications of a recovery in the stocks.
“Eating aggregations” observed
The expedition with the research vessel Polarstern was primarily intended to investigate the effects of climate change on Antarctic krill. These shrimps, which are up to six centimeters long, form the basis of the food web in the Southern Ocean: they serve as food for fish, penguins, seals and baleen whales. During their explorations, the scientists finally encountered southern fin whales (Balaenoptera physalus quoyi) in addition to the schools of these small crustaceans. To count them, they sent the Polarstern helicopter on reconnaissance flights. In 22 missions, the scientists initially counted 100 fin whale groups consisting of one to four animals. However, they then encountered surprisingly large groups around Elephant Island in the Weddell Sea near the Antarctic Peninsula: around 50 to 70 animals were cavorting in the water together. As the researchers explain, it was a matter of so-called feeding aggregations.
“I rushed straight to our monitor, on which we can use acoustic measurement methods to see whether and to what extent there are swarms of krill in the water,” reports Bettina Meyer. “In fact, we were able to use the data to identify schools of krill and even see the whales chasing the krill. I’ve never seen so many whales in one place and was mesmerized by watching these huge groups feeding,” says Meyer. In the year after the Polarstern expedition, the scientists and a team from the British broadcaster BBC returned to Elephant Island on a specially chartered ship to continue the observations. In the end, they even documented groups of up to 150 animals.
Stand recovery with additional benefits
“This high animal density and the recurrence of so-called feeding aggregations, which have not been observed since whaling began, indicate a population recovery,” explains senior author Helena Herr from the University of Hamburg. From the researchers’ point of view, the ban on whaling shows success. “Even though we don’t know the total number of fin whales in Antarctica due to a lack of synchronous observations, it could be a good sign that the fin whale population in Antarctica is recovering almost 50 years after commercial whaling was banned,” says Meyer.
As the researchers point out, the comeback of sea giants is not only gratifying from a whale conservation perspective: the entire ecosystem can benefit. Because the excretions of the fin whales provide more nutrients in the upper water layers, especially iron, which in turn benefits the growth of algae and thus other living beings. The effect, known as the “whale pump”, could also be relevant in the fight against climate change: “The microorganisms that benefit from the richer supply of nutrients absorb a lot of CO2 and thus make an important contribution to reducing carbon in the atmosphere ‘ said Mr. The scientists say that the CO2 sequestration of one of the world’s most important marine areas could be increased by the larger whale populations.
Source: University of Hamburg, Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research. Specialist article: Scientific Reports, doi: 10.1038/s41598-022-13798-7