University of São Paulo: Never seen so many humpback whales off the coast of São Paulo as in 2021

Seeing a humpback whale sailing through the waters of the north coast of São Paulo was very rare until a few years ago. No more. The number of humpback sightings in the region hit a record in 2021: there were 130 records in the year, more than double that of 2020, according to Projeto Baleia à Vista ( Probav ), a citizen science project that monitors the presence of these large cetaceans in the region. region. “Something different happened this year, which still needs to be explained”, the founder and coordinator of the project, Julio Cardoso , told Jornal da USP .

Each record corresponds to one or more whales seen together in the wild. Photographic records are used to differentiate the animals and make an estimate of individuals, as each humpback has unique morphological characteristics, especially in the tail, which serve as a “fingerprint” of the animal. The data are still under review for publication, but point to a 90% growth in the number of animals sighted between 2019 and 2021, according to Probav. “The numbers of sightings and individuals have grown at the same rate,” says biologist Aline Athayde, who has been collaborating with the project since 2018 and will begin, this year, at USP, a master’s research on whales.

The São Paulo record was accompanied by another historic milestone: a record of humpback strandings in national territory. According to the Humpback Whale Project, which has been monitoring the species in the country for over 30 years, 230 humpback strandings were recorded in Brazil in 2021, compared to 76 in 2020. The previous record was 131 strandings in 2017. (Each ” aground” means a fatality: a whale that has already arrived dead or died stranded on dry land.)



It is likely that the two phenomena are connected – an increase in the number of strandings and whales close to the coast – but it is still too early to make a scientific diagnosis of the causes and consequences. One hypothesis raised by the researchers is that a combination of population growth (due to the hunting ban and conservation efforts of the species in the last 50 years) with reduced food supply in Antarctica (due to seasonal variations, potentially exacerbated by climate change) is causing more humpbacks to arrive in Brazil still “hungry” and, consequently, approach the coast in search of food.

Humpbacks are migratory animals that traditionally spend their summers feeding in the polar regions and winters breeding in the calm, warm waters of tropical latitudes. In the case of populations that travel along the Brazilian coast, this itinerary translates into Antarctica (including the South Georgia and South Sandwich Islands), in summer, and the Bahian coast, in winter (mainly in the region of Banco dos Abrolhos, in the south of Bahia and northern Espírito Santo).

“We are trying to understand the dynamics of what happened this year (2021) — if it is really related to the issue of food availability — and what could happen from now on”, says the research coordinator of the Humpback Whale Project (PBJ), Milton Marcondes. As of this year (2022), the project, based in Bahia, will include the north coast of São Paulo in its monitoring area, whose southern limit, until now, was Espírito Santo.

“Are they just passing through here on their way to Abrolhos, or are they here to stay? Would it be a reoccupation of territories that they already occupied in the past? Are they eating around here too?” — are some of the questions that remain adrift to be answered, evaluates Aline.

The main food for these large mammals in Antarctica is krill, a small, shrimp-like swimming crustacean that breeds in the millions in that region. Krill, in turn, feed on microscopic algae (phytoplankton), whose abundance depends on the seasonal ebb and flow of the Antarctic sea ice cover. Any anomaly that interferes with this food chain can negatively impact the lives of humpbacks. If there is a sharp decrease in the amount of krill, due to climate change and other human interference (as several studies indicate is happening), at the same time that the number of whales is increasing due to a conservation effort, the result could be be worrying.

An important change that was observed in relation to previous years, both in São Paulo and in the rest of the country, was the large number of young whales sighted in 2021, many of them skinny – which suggests that they did not eat enough in Antarctica. “With less food, young animals that are not of breeding age may have stayed on the coast of Santa Catarina and São Paulo in search of food, because the waters are more productive than in Bahia and Espírito Santo”, ponders Marcondes. More than 90% of the whales that beached last year were juveniles, he said. “This is unprecedented. I have never seen a year with so many juveniles dying.” And most strandings occurred precisely in these two states: Santa Catarina (65) and São Paulo (58).

In addition to krill, humpbacks eat other crustaceans and fish that are easier to snap up in coastal (shallower) than oceanic waters. Fishing nets also seem to attract these younger whales, either out of hunger or out of sheer curiosity — which can result in harm to fishermen and potentially death or injury to whales that tangle with them.

Humpbacks, like other species of whales, were heavily hunted in the past for meat and oil. The tide only began to turn for the better in the late 1960s, when the International Whaling Commission (IWC), recognizing that the species was at risk of extinction, ordered a suspension of humpback hunting — reinforced in the 1980s by a global moratorium on whales. hunting of any species of whale, which remains in force to this day. In Brazil, more specifically, commercial whaling was prohibited by decree in January 1986 and by law in December 1987.

Researchers estimate that there were between 25,000 and 30,000 humpback whales in Brazilian waters in the early 19th century. This population was almost wiped out by hunting, reduced to around 500 whales in the early 1950s. and effective conservation programs (led in Brazil by the Baleia Jubarte Project ) that the species began to recover. In 2014 it was officially removed from the national list of endangered species; and today it is estimated that there are somewhere around 20,000 humpbacks circling this Brazil-Antarctic migratory route — almost the same number as in the pre-hunt period.

caveats
For biologist Marcos César de Oliveira Santos, professor at the Oceanographic Institute (IO) and coordinator of the Laboratory of Biology for the Conservation of Aquatic Mammals (LABCMA) at USP, there is no doubt that the humpback population is growing and, therefore, it is the number of sightings and strandings is expected to increase. But it’s important to take some factors into account when interpreting the numbers, he says. At the same time that the number of whales in the sea has increased, the number of people in the water with the capacity to see them has increased and the monitoring of strandings on beaches has intensified. This can lead to “observation bias” — that is, making present-day statistical variations appear larger than they actually are.

The number of vessels (such as speedboats and sailboats) circulating along the coast of São Paulo and Rio de Janeiro has tripled since 2000, according to Santos. “There are many more people today navigating this region, with cell phones in hand to photograph and post on social networks.” The monitoring of strandings only started to be done in a systematic way from 2015, when Petrobras was forced to finance a beach monitoring program ( PMP ), as a condition for the exploration of oil and gas in the Santos Basin. “Before that, the carcasses went to the dump and the scientists didn’t even know about it”, recalls Santos. “We need more robust indices to make these comparisons”, completes the researcher, who earlier this year published a digital book free information about the presence of cetaceans (whales and dolphins) on the coast of São Paulo.

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The increase in the number of vessels makes it easier to spot whales, but also creates problems for them. Whales communicate through sound, and the noise pollution generated underwater by boat engines can scare them away or even disorient them, increasing the risk of strandings and collisions. Which leads Santos to raise another hypothesis about what may have happened in 2021: “Could it be that the humpbacks did not take advantage of a moment of peace in the pandemic to get closer to the coast, since there were fewer boats in the water?”, he asks. the researcher. “We have to ask them.”

The relationship with a possible decrease in the supply of krill in Antarctica is a “plausible hypothesis”, says Santos, but one that still needs to be scientifically tested. Although there are no conclusive visual records of humpbacks feeding in São Paulo waters, chemical analyzes conducted on skin samples from some of these younger animals indicate that they are indeed feeding on fish typical of the Southeast region of Brazil, according to Santos. “They are feeding here, in these subtropical areas”, says the researcher.

tourist attraction
Whatever the reason for the humpbacks to approach the north coast of São Paulo, the fact is that they have already become a winter tourist attraction in the region, mainly in Ilhabela and São Sebastião. City halls already run publicity campaigns, warning that “the whales have arrived”, and organize training courses for boat pilots and tourism operators interested in working with cetacean observation.

So far there have been no reports of accidents, but you have to be careful — not only for the safety of the whales, but also of the vessels, since an adult humpback can measure 15 meters and weigh 40 tons. The municipality of Ilhabela prepared a video with guidelines, in partnership with Probav. The Humpback Whale Project, which is sponsored by Petrobras, also has a whale watching guide available online for download .

As long as there is no danger to them or their young, humpbacks are typically docile and calm animals. “They are very curious; you get on the boat and they come close to spy”, says Cardoso, a former executive of large companies who left his corporate life to live by the sea and dedicate himself to the observation of marine fauna, his great passion. He launched Probav in 2016, in partnership with his partner, biologist and nature photographer Arlaine Francisco.

At 73, Cardoso has what every professional cetacean researcher would like to have: time and money to be at sea all the time, with a pair of binoculars and a camera around his neck. Between June and October, the Probav team makes five field trips a week to monitor an area up to 40 kilometers away from the coast between São Sebastião and Ubatuba. Observations are made following scientific methodology and the records are sent to an international repository of whale photoidentification, called Happy Whale . “We know much less than we think we know about cetaceans, and as long as I can help find out more, I will be at sea, even with the cost of fuel at the highest,” jokes the former executive, who pays for all of his own work. pocket.

Aline, 40 years younger, follows a similar trajectory. Passionate about whales since childhood, she became a systems analyst for the sake of opportunity, but never gave up on her dream of working with marine mammals. “As soon as I stabilized myself financially, I went to study biology”, he says. Even before graduating, in 2019, she started working as an intern at Probav. It was enough to see a whale in the wild for the first time to fall in love with the animals once and for all. “At that moment I was sure, I’ve been a biologist since I was born”, she says. Your master’s degree at USP will be with Bryde’s whales, a resident species off the coast of São Paulo. But it is certain that you will find many humpbacks along the way.

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