(ORDO NEWS) — The number of southern fin whales, which were almost exterminated by whalers in the 20th century, has begun to recover. This conclusion was reached by zoologists after analyzing the results of expeditions to the Antarctic Peninsula in 2018-2019.
Researchers estimate that about 8,000 fin whales gather in local waters to feed on krill, and for the first time in more than two hundred years, they have begun to form groups of more than 15 individuals.
As noted in an article for Scientific Reports, some of these aggregations consist of about 150 individuals, which is unusually large for baleen whales.
Fin whales (Balaenoptera physalus) are the second largest whales in the world after blue whales (B. musculus). Like other species of whales, they have suffered greatly from whalers.
For example, if at the beginning of the twentieth century the number of the southern subspecies of fin whales (B. p. quoyi) reached approximately 325,000 individuals, then by the mid-1970s, as a result of intensive fishing, it had decreased to one or two percent of the original.
Southern fin whales were especially actively hunted near the northern tip of the Antarctic Peninsula, where they were found in places of their mass feeding. According to previous studies, these whales did not return here even decades after the end of fishing.
For example, members of the expeditions organized by the International Whaling Commission in 1978-2004 very rarely met them in the vicinity of the Antarctic Peninsula. According to some estimates, in 2000 there were only about 4,500 fin whales in the waters around the peninsula and along the South Antilles range.
However, in the 21st century, fin whales began to be observed off the coast of Antarctica much more often. For example, an aerial survey conducted off the South Shetland Islands in 2013 revealed aggregations of up to 70 of these whales.
A team of zoologists led by Helena Herr set out to find out if the number of southern fin whales has really begun to recover. During an expedition on the German icebreaker Polarstern in the spring of 2018, researchers used a helicopter to conduct a whale count off the northern tip of the Antarctic Peninsula.
In total, they made 22 sorties. In 2019, scientists returned here on the Pelagic Australis yacht to capture fin whale concentrations on video.
During helicopter counts, Herr and her colleagues encountered fin whales a hundred times. Sometimes they were single whales, and sometimes they were groups of two to four individuals.
During the flight to the area of the survey route, the authors also recorded a cluster of fifteen fin whales that were feeding with Kerguelen fur seals (Arctocephalus gazella) and chinstrap penguins (Pygoscelis antarcticus).
In addition, two groups of these whales were observed from the vessel, numbering about 50 and about 70 individuals. Finally, during the 2019 expedition, the team members found five concentrations of fin whales near Mordvinov Island, two of which numbered about 150 individuals.
In most cases, fin whales in aggregations were busy feeding. They lunged with their mouths open, turned sharply and dived. Although the authors did not collect samples from the whales’ aggregations, they hypothesize that they were eating Antarctic krill (Euphausia superba).
The authors believe that fin whales congregate where krill density reaches a certain threshold. Most likely, these are relatively rare and spontaneous events, since no group of more than four individuals was noted during helicopter counts.
Evidence of concentrations of more than 15 fin whales is not mentioned in the literature after the beginning of the 19th century, when intensive whaling started. Moreover, baleen whales generally rarely gather in such large groups as have been recorded off the coast of the Antarctic Peninsula.
Only the so-called supergroups of humpbacks (Megaptera novaeangliae) off the coast of South Africa and Eastern Australia reach a similar size. It is possible that fin whales have again begun to form huge concentrations due to the fact that their numbers have partially recovered after the ban on whaling and they have returned to their traditional feeding grounds.
Calculations by Herr and her co-authors indicate that there are three high concentrations of fin whales along the western shelf of the Antarctic Peninsula.
There are especially many of them around Mordvinov Island, Even according to minimal estimates, about 3,600 individuals feed here. In total, about 8,000 fin whales can come to the study area for feeding.
The return of fin whales to the shores of the Antarctic Peninsula after a long absence is good news for the entire local ecosystem. These whales eat iron-rich krill, and then their droppings fertilize the surface layers of the water with iron and promote the growth of phytoplankton.
As a result, the abundance of krill, which feed on phytoplankton, is also increasing. Moreover, the increase in primary production due to the vital activity of fin whales contributes to a more active absorption of carbon from the atmosphere and slows down global warming.
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