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The secret lives of whales

UH graduate students lead research effort aboard Schmidt Ocean Institute’s R/V Falkor

Scientists from the University of Hawai‘i at Mānoa (UHM) School of Ocean and Earth Science and Technology (SOEST) have been allocated over 100 days at sea, spread out over the next 6 months, aboard the R/V Falkor, the oceanographic research ship belonging to the Schmidt Ocean Institute (SOI; http://www.schmidtocean.org/).

Numerous questions remain about what determines the feeding behaviors of whales in the deep sea. During the first cruise, the first ever student-led cruise on the R/V Falkor, the team aboard R/V Falkor helped answer some of those questions while gaining invaluable at-sea experience.

R/V Falkor at dock

R/V Falkor at dock. Credit: Mark Schrope, Schmidt Ocean Institute

UHM Ph.D. candidate Adrienne Copeland was the chief scientist for this expedition, which focused on deep-diving toothed species found in Hawaiian waters—beaked, short-finned pilot, and endangered sperm whales. While extensive work has been done throughout most parts of the world to study whale migrations and concentrations, much less work has been done to understand the factors that control these migrations. This cruise included two projects focused on that topic with student team members from UHM, including the Hawai‘i Institute of Marine Biology, and the National Oceanic and Atmospheric Administration (NOAA).

Copeland’s study builds on past work using acoustics to learn more about where whales feed. Toothed whales, known formally as odontocetes, sometimes dive down 1,000 meters or more, complicating the job of studying what attracts them and what holds their foraging attention.

Copeland is using sound to locate diving whales and quantify how much food is available in the areas where they spend their time during dives. Her hypothesis is that whales may be targeting places where prey is particularly abundant within or below what’s known as the deep scattering layer.

The deep scattering layer is a layer at which smaller fish, crustaceans, jellies, and other organisms tend to concentrate. During the day, this happens in deep waters below the reach of sunlight, where these smaller animals retreat to the relative safety of darkness to avoid predators. But many feed on algae in shallower waters, so each night about half of the organisms collectively move to shallower depths under the cover of darkness. This daily movement up and down constitutes the planet’s largest migration.

On the same cruise, complementary research was led by Giacomo Giorli, an oceanography Ph.D. student at UHM, to elucidate more of the story that Copeland is working to tell. Giorli’s work focuses on figuring out more specifically what aspects of the deep scattering layer might be most attractive to foraging whales.

Short-finned pilot whale

A short-finned pilot whale.
Credit: Jessica Chen

The idea is that diving several hundred or even a thousand meters down uses up a huge amount of energy, so the payoff must be comparably huge. To make the effort worthwhile, whales must either get lots of small fish and other animals on a single dive, or an equivalent volume of food from larger animals. Giorli’s hypothesis is that the whales are going after larger squid that aren’t necessarily a component of the DSL but might be attracted to it for their own feeding.

SOI is a private non-profit operating foundation established to advance the understanding of the world’s oceans through innovative technologies, intelligent observation, and open sharing of information.

On the future R/V Falkor cruises, SOEST researchers and partners will be creating detailed maps of the seafloor of the Northwestern Hawaiian Islands (http://www.schmidtocean.org/story/show/2216), investigating microbes around Loihi (the emerging seamount south of the Big Island (http://www.schmidtocean.org/story/show/2225), and more.

Read more about the cruise on these blog posts, which include video and photos, stories about life at sea, what it takes to research whale behavior, and what the students learned along the way here: http://www.schmidtocean.org/story/show/2245.

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