The stranding of humpback whales on the Brazilian coast reached an atypical number in 2021. According to a survey by the Humpback Whale Project, until December 22, there were 216 episodes, a record in the historical series started in 2002.
The distant second place went to 2017, with 122 strandings.
The growth in the number of strandings still does not have a precise explanation. But, according to Milton Marcondes, research coordinator for the Humpback Whale Project, the main hypothesis is the decrease in krill.
Krill (tiny crustaceans) are one of the main foods for humpbacks, which also eat small fish. Whales suck water from the sea and “filter” their prey.
In addition to the record in 2021, there was another atypical factor in the records. Nearly 95% of stranded animals were juveniles — animals from 1 to 5 years of age, when they reach sexual maturity.
“We’ve never had such a large percentage of a category,” says the expert.
The stranding of thin juveniles is another clue, according to Marcondes, that the lack of krill may be responsible for the situation. That’s because, in case of food shortages, more experience (i.e. more years of life at sea) can help in catching food. As a result, younger people would find it more difficult in this scenario and would reach the Brazilian coast without having had adequate food.
Adult animals also have a greater capacity to store fat, another advantage over juveniles.
The humpbacks (Megaptera novaeangliae) that swim along the Brazilian coast, in general, feed in the Antarctic waters of Georgia do Sul and come to Brazil to breed and have little whales. By the way, the Abrolhos National Marine Park is known as an important nursery for these whales in the South Atlantic Ocean, which provides cetacean watching tourism in the area.
Another sign of the lack of krill is the whales approaching the shore in search of fish. São Paulo and Santa Catarina, states with large shoals, are the leaders in strandings. There were records, says Marcondes, of animals entering fishing pens at sea looking for food and getting caught in nets.
Another record for the year was the —underestimated— number of animals caught in fishing nets: 58 (but not all the animals died). With fishermen and whales going after the same resource, accidents like this end up becoming more likely.
Finally, another sign of the lack of krill came from afar from Brazil. Namibian researchers contacted the Humpback Whale Project researcher and stated that they also had above normal records of strandings and young individuals.
And the interesting thing is that the animals that pass along the coast of Namibia belong to another population that, in general, feeds in a different region (Bouvet Island and close to the Cape of Good Hope) from the feeding area of Brazilian whales.
The lack of krill can possibly be explained by the effect of the climate crisis on these crustaceans, which have a complex life cycle and an important role in the food chain.
Research published in the journal Nature Climate Change pointed out that climate change can move the areas where krill develops further south and also trigger a mismatch between its life cycle and ocean conditions during the year.
There are records of associations, for example, from low availability of krill to the decline in the reproductive success of fur seals, penguins and albatrosses and species that prey on these crustaceans.
“Each year, humpback whales migrate from the tropics to the poles to feed on the huge amount of summer krill. If the krill peak occurs earlier, the whales must adapt by arriving earlier or they will end up hungry,” wrote the researchers. authors of the survey on The Conversation website.
Species status
Despite the high numbers of strandings and accidents with fishing nets, humpbacks are not on the latest ICMBio (Chico Mendes Institute for Biodiversity Conservation) list of threatened species.
According to the institute, the hunting ban and conservation initiatives are essential for the species to remain out of risk.
Commercial whaling has had a strong impact on humpback populations around the world. A whaling moratorium, instituted by the International Whaling Commission and in effect since 1985/1986, has helped in the recovery of humpbacks, according to NOAA (National Oceanic and Atmospheric Administration, US agency).
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