Sound Reveals Giant Blue Whales Are Dancing With The Wind To Find Food

A study by MBARI researchers and their collaborators published today in Ecology Letters sheds new light on the movements of mysterious endangered blue whales. The research team used a directional hydrophone on MBARI’s underwater observatory, integrated with other state-of-the-art technology, to listen to blue whales’ booming vocalizations. They used these sounds to track the movements of blue whales and learned that these giants of the oceans react to changes in the wind.

Along the central California coast, spring and summer bring coastal upwelling. From March to July, seasonal winds push the upper water layer out to sea, allowing cold water below to rise to the surface. The cooler, nutrient-rich water fuels blooms of tiny phytoplankton, kickstarting Monterey Bay’s food web, from tiny shrimp-like krill to giant whales. When winds create an upwelling event, blue whales seek out cooler water plumes, where krill are most abundant. When the upwelling stops, the whales move offshore into habitat crossed by shipping lanes.

“This research and its underlying technologies open new windows into the complex and beautiful ecology of these endangered whales,” said John Ryan, biological oceanographer at MBARI and lead author of the study. “These results demonstrate a new resource for managers looking for ways to better protect blue whales and other species.”

The directional hydrophone is a specialized underwater microphone that records sounds and identifies the direction they are coming from. To use this technology to study the movements of blue whales, researchers needed to confirm that the hydrophone was tracking the whales reliably. This meant matching acoustic bearings to a calling whale that was tracked by GPS. With confidence in established acoustic methods, the research team reviewed two years of acoustic monitoring of the regional population of blue whales.

This study builds on previous research by MBARI Senior Scientist Kelly Benoit-Bird, which found that swarms of forage species – anchovies and krill – responded to coastal upwelling. This time, the researchers combined satellite and mooring data of upwelling conditions and echosounder data on krill aggregations with the acoustic tracks of foraging blue whales recorded by the directional hydrophone.

“Previous work by the MBARI team revealed that when the coastal upwelling was strongest, anchovies and krill formed dense swarms in the upwelling plumes. Now we have learned that blue whales follow these plumes dynamic, where abundant food resources are available,” explained Ryan.

Blue whales recognize when the wind changes their habitat and identify places where upwellings gather their essential food, krill. For a massive animal weighing up to 150 tons (165 tons), finding these dense aggregations is a matter of survival.

While scientists have long recognized that blue whales seasonally occupy Monterey Bay during upwelling season, this research has revealed that whales closely follow the upwelling process on a very fine spatial scale ( kilometers) and time (days to weeks).

“Tracking many individual wild animals simultaneously is a challenge in any ecosystem. It’s especially difficult in the open ocean, which is often opaque to us as human observers,” said William Oestreich, a former graduate student at Stanford University’s Hopkins Marine Station and now an MBARI postdoctoral fellow. “The integration of technologies to measure the sounds of these whales has enabled this important discovery of how groups of predators find food in a dynamic ocean. We are excited about the future discoveries we can make by listening to blue whales and other noisy sea animals.

Background

Blue whales (Balaenoptera musculus) are the largest animals on the planet, but despite their large size, scientists still have many unanswered questions about their biology and ecology. These gentle giants seasonally congregate in the Monterey Bay area to feed on small shrimp-like crustaceans called krill.

Blue whales are elusive animals. They can travel great distances underwater very quickly, making them difficult to track. MBARI researchers and collaborators used a new technique to track blue whales: sound.

MBARI’s MARS (Monterey Accelerated Research System) observatory provides a platform to study the ocean in new ways. Funded by the National Science Foundation, the wired observatory provides continuous power and data connectivity to support a variety of instruments for science experiments.

In 2015, MBARI researchers installed a hydrophone, or underwater microphone, on the observatory. The hydrophone’s wealth of acoustic data has provided important insights into the soundscape of the ocean, from the migratory and feeding behaviors of blue whales to the noise impact of human activities.

In 2019, MBARI and the Ecole Supérieure Navale installed a second hydrophone on the observatory. The directional hydrophone gives the direction a sound is coming from. This information can reveal spatial patterns for sounds underwater, identifying where the sounds are coming from. By tracking the blue whale’s B call — the loudest and most widespread vocalization among the regional population of blue whales — the researchers were able to track the movements of individual whales as they foraged in the area.

The researchers compared the directional hydrophone recordings to data recorded by beacons that Stanford University scientists had previously deployed on blue whales. The validation of this new acoustic tracking method opens new opportunities to simultaneously record the movements of several whales. It can also enable the search for animal-borne tags by helping researchers find whales to tag. “The integrated suite of technologies presented in this article represents a transformative toolkit for interdisciplinary research and mesoscale ecosystem monitoring that can be deployed at scale in protected marine habitats. It’s a game-changer and takes both cetacean biology and biological oceanography to the next level,” said Jeremy Goldbogen, associate professor at Stanford University’s Hopkins Marine Station and co-author of the study. .

This new methodology has implications not only for understanding how whales interact with their environment and with each other, but also for advancing management and conservation.

Despite the protections, blue whales remain in danger, mainly because of the risk of collision with ships. This study showed that blue whales in the Monterey Bay National Marine Sanctuary regularly occupy habitat crossed by shipping lanes. Acoustic tracking of whales can provide real-time information to resource managers to mitigate risk, for example, through vessel speed reduction or re-routing during critical times. “These kinds of integrated tools could allow us to spatially and temporally monitor, and possibly even predict, short-lived biological hotspots. This promises to be a breakthrough in adaptive risk management for protected and endangered species,” said Brandon Southall, President and Chief Scientist of Southall Environmental Associates Inc. and co-author of the research study.

Support for this research was provided by the David and Lucile Packard Foundation. The National Science Foundation funded the installation and maintenance of the MARS wired observatory through awards 0739828 and 1114794. The directional acoustic treatment work was supported by the Office of Naval Research, Code 32. The work were funded in part by the National Science Foundation (IOS-1656676), the Office of Naval Research (N000141612477), and a Terman Fellowship from Stanford University.

About MBARI

MBARI (Monterey Bay Aquarium Research Institute) is a private, non-profit oceanographic research center founded by David Packard in 1987. MBARI’s mission is to advance marine science and technology to understand a changing ocean. Learn more at mbari.org.

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