The Humpbacks of Sitka Sound
Whales and Climate Change
(Photo: Alaska Whale Foundation)
Humpback whales in Southeast Alaska are well-known for their bubble-net feeding behavior. While feeding in this way, whales expel streams of air from their blowholes as they swim in a circular pattern, thereby creating bubble cylinders (i.e., ‘nets’) that appear to corral and concentrate their prey.
In Southeast Alaska, bubble-net feeding whales forage in groups of up to 24 or more and target a variety of prey including herring, krill, and juvenile salmonids. Despite widespread familiarity with this behavior, little is known about how bubble-nets are constructed and used to capture prey, the various roles that individual whales adopt when bubble-net foraging together, or how they interact and coordinate their behaviors.
In 2019, Alaska Whale Foundation launched a collaborative effort with Lars Bejder from the Marine Mammal Research Program (Hawaiian Institute of Marine Biology), Jeremy Goldbogen’s lab at Stanford University, and Ari Friedlaender’s lab at the University of California Santa Cruz that uses Unoccupied Aerial Vehicles (“drones”) and CATSCam suction-cup tri-accelerometer video tags to gain further insight into bubble-netting.
Our initial investigations revealed bubble-nets to be complex tools deployed by whales in a remarkably ingenious manner. By blowing multiple rings, each one smaller and nested within the previous one, whales not only corral but concentrate their prey. As well, the whales can adjust the “mesh size” of their bubble-nets’ and modify their shape and size when targeting different types of prey. The bubble-nets also allow the whales to lunge through the prey patch in a more ‘leisurely’ way. Given the high energetic costs that baleen whales incur while lunge feeding, our drone and tag data suggest humpbacks use bubble-nets as tools to increase their foraging gains while simultaneously reducing their energetic costs.
Having begun to elucidate the mechanics of bubble-net feeding, we are now turning our efforts towards understanding the social structure of the whales that engage in this behavior and the various roles that they adopt when feeding together. To this end, AWF principal investigator Dr. Andy Szabo, together with Dr. Lars Bejder and PhD candidate Fabien Vivier (Hawaiian Institute of Marine Biology), are heading to Sitka Alaska in March to join Bill and Patsy Urschel aboard the research vessel Endeavour.
The team will deploy CATSCam video tags on bubble-net feeding whales that have just returned from their winter breeding grounds in Hawaii. These minimally invasive tags, which are deployed from a small boat and attached to the whales using suction cups, collect high-resolution audio/video data and have onboard sensors that record the tagged animal’s underwater swimming behavior.
Once the video tags are deployed, we will use drones to monitor the whales’ surface behaviors.
After roughly 4 to 12 hours, the tags pop off and float to the surface, at which point they begin transmitting a satellite signal that allows us to relocate them. We can then access the stored data and recreate the whale’s underwater behavior and interactions with other whales. All of these activities are authorized under AWF’s National Marine Fisheries Permit #19703.
Although working at this time of year means contending with Alaska’s winter marine conditions, it also means the water is largely free of phytoplankton that limit visibility and make underwater filming later in the year challenging.
The goal of the expedition is to shed light on how these cooperative whales coordinate their behavior, divvy up the necessary tasks, and work together to drive their prey into their bubble-nets.
Andy Szabo PhD
Alaska Whale Foundation
Andy is Alaska Whale Foundation’s Executive Director. He has been leading research projects in Alaska since 2001. His research interests include whale predator-prey interactions, social behavior, communication, human-whale conflicts, and whale health.
Andy holds a Masters degree from the University of Victoria, BC and a Doctorate degree from Oregon State University's Marine Mammal Institute. He is also a National Geographic Explorer and Affiliate Faculty member at both Oregon State University and University of Alaska Southeast.
For more about the Alaska Whale Foundation and how you can get involved, visit their website at www.alaskawhalefoundation.org.
(Photo: Alaska Whale Foundation)