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As detection methods improve, new research has found that blue whales, the largest animals to have ever lived, spend much more time in the waters off the Azores than researchers have initially thought.

Words and photographs by João Rodrigues

“Now,” shouts Mónica Silva, a researcher from the Cetacean Ecology Group of the Okeanos Institute at the University of the Azores. Standing at the bow, she grips a pressure gun tightly and with eyes fixed on the gigantic animal, Rui Prieto, another researcher, presses the trigger. In milliseconds, the rocket launched by the gun hits the whale, attaching a satellite transmitter to its blue back. The happy faces of the researchers aboard the rigid inflatable boat off the coast of Pico Island confirm the success of the operation. 

For centuries, these waters witnessed a different kind of confrontation with cetaceans. In the latter part of the 19th century, whales were extensively hunted throughout the Azores. Whale meat was popular, and the animals offered many other by-products. Today, they still shoot whales off the autonomous archipelago – but in a very different way. Now shooting them doesn’t harm the animals and helps amplify research and conservation. 

Through the subcutaneous implantation of tracking devices capable of satellite communication that can provide the coordinates of the animal whenever it surfaces, scientists aim to better understand the migration patterns and behaviours of blue whales that visit the Azores archipelago in Portugal. The collected information is crucial for the conservation efforts of this threatened species and local researchers are trying to decipher one of the largest questions associated with offshore research: Where do blue whales go throughout the year? By tracking movements and migratory routes since 2009, Mónica Silva’s team has identified critical reproduction, feeding, and resting areas of blue whales and other whale species, thereby contributing invaluable data to help protect them. 

The research team surrounding Silva focusses on studying the migration patterns of blue whales off the coast of the Azores and the Central Northeast Atlantic. In 2013, the team published a groundbreaking article that revealed a new finding: tagged blue whales and fin whales appeared to suspend their spring migration at mid-latitude regions of the Atlantic. Here, it is now believed, they stockpile energy reserves for the rest of their journey. Since then, Silva and Prieto, along with other researchers, have been avidly accumulating information. In just over a decade, they have published articles on movements, timing, destinations, and behaviours before and during these great oceanic voyages, employing various monitoring methodologies. For many years, photo identification had been the main research method the team relied on. This method enables researchers to compare distinctive elements of each individual by using photographs taken by tourists, fishermen, or researchers, thereby learning more about the movement of each species. This identification method was followed by satellite transmitter monitoring which accurately documents the movements of a whale whenever it surfaces. Additionally, the research team uses a technique called stable isotope analysis. 

For it, small pieces of skin are extracted from whales which, in turn, are able to tell a whale’s gastronomic history. Stable isotopes in an animal’s tissue provide clues about its specific diet and the regions where it consumed food. By comparing the isotopic signatures of the blue whale with those of different food sources, Silva and Prieto are able to determine the origin of their food. If hypothetically a whale’s isotopic signature is similar to that of Antarctic krill, it suggests that it primarily feeds on this type of prey.

With the confidence solidified by a decade of samples, it is now known that the blue whales visiting the Azores come from various regions of the ocean. The long-term study has detected individuals that spend the winter in upwelling zones off the West African coast, as well as animals from open ocean areas of the North Atlantic, with biogeochemical characteristics identical to those of the Azores. After a short stay in the archipelago’s waters, the researchers have found, they travel over 3,000km to conclude their long journey in the Central Northeast Atlantic, between Greenland and Iceland.

Silva’s smile grows as she shares the results. “One of the biggest assets that allowed us to complete this puzzle of mysteries was acoustic monitoring,” she explains. In 2020, the biologist co-authored a pioneering article published in the journal Scientific Reports, along with Miriam Romagosa and five other researchers. There was interesting news to communicate: for the first time, the presence of these animals in the waters of the Azores during late autumn and winter was confirmed. Since the waters are stormier, hindering onboard operations, there was no solid information on the subject. However, the hydrophones installed on the seabed didn’t lie. They recorded dozens of whale vocalisations, or as the team likes to say, “the results were noisy”.

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Issue 34
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This feature appears in ISSUE 34: SCOTTISH SEAS of Oceanographic Magazine

Issue 34
Supported by WEBSITE_sponsorlogos_blancpain
Supported by WEBSITE_sponsorlogos_blancpain

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