Scientists use acoustic data to track blue and fin whale occurrences in the Arctic

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The long-term analysis of blue whale and fin whale vocalizations in the eastern Fram Strait offers valuable insights into seasonal and annual patterns regarding these species' occurrence in the region. For example, blue whales can primarily be heard in the summer and autumn, whereas the acoustic data on fin whales indicates that their occurrence is much longer and more variable.

The unprecedented long-term dataset also confirms the sporadic occurrence of blue whales—the largest fauna on the planet—during the winter months. The team of researchers, led by the Alfred Wegner Institute, has just published these findings in the journal PLOS ONE.

The eastern Fram Strait is hard-hit by the impacts of climate change, which also affect the species living there. For example, rising water temperatures are leading to a significant decline in sea ice and to shifts in the food web.

For baleen whale species, which undertake seasonal migrations, the eastern part of Fram Strait between Svalbard and Greenland is an important region, as an ocean current transports comparatively warm water to the Arctic there, which in turn sparks high biological productivity.

The Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI), has operated the ocean-monitoring system FRAM (Frontiers in Arctic Marine Monitoring), designed to assess long-term changes, in the region since 2014. Among others, FRAM gathers long-term observations with the aid of moored hydrophones (underwater microphones) that record local sounds, such as whale vocalizations.

This data provides the basis for analyzing species occurrence, particularly with regard to the potential effects of climate change. Some of the devices were installed before the FRAM observatory was created; in addition, NOAA's Pacific Marine Environmental Laboratory maintains two datasets.

"Progressing changes in the habitat, such as the loss of sea ice, will likely have substantial impacts on the occurrence of marine mammals," reports Marlene Meister, a doctoral candidate at the Alfred Wegener Institute and first author of the study.

Accordingly, the experts predict that blue whales and fin whales, which chiefly migrate to Fram Strait to feed in summer and autumn, will expand both the duration and spatial extent of their time there, or might even stay there year-round. Accordingly, in the current publication, they investigate seasonal patterns in the acoustic occurrence of blue and fin whales in the period 2012 to 2021.

"Fin whales' migratory behavior is known to be relatively flexible, and the animals could be heard throughout the year. However, we were surprised to find that in three of the ten years, there were blue whale vocalizations on individual days in January and February," says Marlene Meister—which is unusual in her view, since the general assumption is that the animals are in waters farther south at that time of year.

"Their sporadic acoustic occurrence in winter indicates that individual specimens extend their seasonal stay in Fram Strait or return there from waters farther south at this time of year. The migratory behavior of blue whales in the North Atlantic is considered to be highly stable, which is why I only expected to hear them in summer and autumn," the AWI biologist adds.

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However, since there are no long-term acoustic recordings from the eastern Fram Strait predating 2012, it cannot be said with certainty whether the (acoustic) occurrence of blue whales there in winter constitutes a new, climate-change-related phenomenon. Generally speaking, the research team was able to confirm that ocean temperatures and zooplankton abundance have a significant influence on the acoustic occurrence of blue whales.

The team has made an important contribution to investigating species occurrence, and to documenting potential climate-change-related shifts. Moreover, the publication underscores Fram Strait's relevance as a valuable habitat for baleen whales (most likely as feeding grounds) and contributes to a better understanding of various species' migratory behavior.

The method applied—passive acoustic monitoring (PAM)—is particularly important for monitoring the (acoustic) occurrence of species year-round and also under adverse conditions; accordingly, the AWI will continue to apply PAM as part of FRAM's long-term observations. After all, especially in winter, sea-ice cover and darkness make visual observations virtually impossible.

A better understanding of species occurrence, habitat use, and migratory behavior can pave the way for more targeted protective measures, which are now particularly important: The declining sea ice is making the Arctic Ocean increasingly accessible for human activities. Rising ship traffic in the Arctic, e.g., in the Northwest and Northeast Passage, is producing increased anthropogenic stress for marine mammals. Underwater noise, especially from ships' motors and seismic surveying, is already hampering communication between baleen whales.

Other potential hazards include more collisions between ships, habitat destruction, and oil spills. As such, in the age of climate change, effective measures for reducing anthropogenic stress are more important than ever.

More information: Marlene Meister et al, A multi-year analysis of acoustic occurrence and habitat use of blue and fin whales in eastern and central Fram Strait, PLOS ONE (2024). DOI: 10.1371/journal.pone.0314369

Journal information: PLoS ONE

Provided by Helmholtz Association of German Research Centres