The Secret Lives of Whales
Student Cruise One
A short-finned pilot whales, one of the three species that will be the focus of the expedition. Credit: Jessica Chen
Numerous questions remain about what determines the feeding behaviors of whales in the deep sea. During the first of three student cruises, the team aboard RV Falkor will be answering some of those questions while gaining invaluable at-sea experience.
The focus will be 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 will include two projects focused on that topic with student team members from the University of Hawaii at Manoa (UH), the Hawaii Institute of Marine Biology, and the National Oceanic and Atmospheric Administration (NOAA).
Adrienne Copeland, a Ph.D. zoology student at UH, will be chief scientist for the cruise to the waters off the Kona Coast on the west side of the Island of Hawaii. She will be building on past work using sonar 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 will use sonar to track 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 (DSL) 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.
What They Will Do
Studying all of this will take a few components. First off, students will be standing watches on the observation deck during daylight hours looking for whales. This will help the team target areas for research. They’ll also take photos of the whales they spot for use by NOAA researchers in ongoing programs that identify individual whales and track their movements using a photo database of the animals’ unique dorsal fins. To expand on observations the students will also lower hydrophones to confirm that their target whale species are eating in the area based on the whales’ characteristic echolocation clicks.
In areas where the whales are congregating, the team will run surveys using Falkor’s advanced fisheries sonar system. In this case the system will use acoustic signals to map the location and concentration of the deep scattering layer. The students will also run these sonar surveys in areas where they don’t find whales for comparison. And at various locations the team will collect water samples at different depths using the ship’s CTD rosette. Ultimately Copeland will analyze the results to see if in fact DSL concentration can be reliably tied to where the whales are found. If so, it could aid whale conservation efforts by identifying areas that migh require increased protection.
Complementary research during the cruise by Giacomo Giorli, an oceanography Ph.D. student at UH, will 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.
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.
Giorli will be using a tool called a Dual-Frequency Identification Sonar (DIDSON). He’ll work with other students and the crew to lower the instrument over the side to get much higher resolution information than normal sonar systems provide. The DIDSON produces remarkably detailed sonar images that look almost like video and make it possible to identify individual organisms underwater, even from 30 meters away. The system is most frequently used for applications such as tracking fish moving up rivers. For this cruise, Giorli will use it to identify things like squid in or below the DSL, and he’ll also be able to learn specifics about the size, number, and types of other animals found there.
Besides correlating DSL data with the areas where the whales are directly detected or observed, the team will also be able to tie information about DSL structure and inhabitants in various spots with a longer-term record of whale locations. For about a year, the team has had two Ecological Acoustic Recorders (EARs) deployed in the area where they’ll be working. These acoustic listening devices record the whales’ clicks, which enables tracking. They’ll also be comparing all their findings on this cruise against past work to look for any seasonal differences in the whales’ behaviors.
For the students involved, Falkor’s availability, announced in November, was welcome news and an opportunity that should significantly advance not just individual research projects, but also the skills and aspirations of the students aboard. “It’s really hard to get ship time,” says Copeland, “When this popped up it was a great opportunity and my colleagues and I jumped on it.”
--Mark Schrope, for Schmidt Ocean Institute
An estimated 660 students and 17 classes in Hawaii followed The Secret Lives of Whales blog. Additionally, three classroom visits were made by the graduate students to share about their research and experiences, upon returning from the cruise.
All Things Marine radio show March 13, 2014
University of Hawaii News February 14, 2014
Kaunana: The Research Publication of the University of Hawaii Manoa February 14, 2014