Field stories: Humpback bubble-nets
In July, the Vancouver Aquarium’s research vessel “Skana” made its inaugural trip to the top of B.C.’s coastline. As part of our new North Coast Initiative sponsored by the BG Group, we dedicated nearly two weeks to surveying the area from Dixon Entrance to Squally Channel. Our aim was to collect data on the occurrence and distribution of cetaceans in this northern-most section of the coast.
The area didn’t disappoint, there was stunning scenery and great whale encounters, but most memorable was our day recording and observing a group of eleven bubble-net feeding humpback whales!
Bubble-netting is a feeding strategy employed by humpback whales to concentrate their food. Humpbacks may use this technique individually, as documented in this earlier field blog from the central coast. However, even more impressive is group coordinated bubble-net feeding. This tactic, which commonly involves 4-20 whales, is most often observed in the northerly waters of B.C. and in Alaska.
Our first indication that group bubble-net feeding was occurring in the area came through the hydrophone, an underwater microphone used to listen for sounds produced by cetaceans. What first sounded like the distant drone of an outboard motor, actually turned out to be the specialized feeding call used by bubble-netting humpbacks. As we got closer, the calls became more distinct and we finally spotted the whales off of the northern tip of Zayas Island, close to the Alaskan border.
From the Skana, we listened to the feeding call of the whales. Seconds after a feeding call would go silent the most dramatic part of bubble-net feeding occured: the whales would erupt out of the water, mouths agape. It was heart-pounding excitement every time! After a few breaths to reposition, the whales would begin again. Have a look at our video to see and hear our experience on the Skana (the feeding call can be heard over our speakers on board):
Bubble-net feeding can be pretty spectacular to observe, but also puzzling. What exactly is happening underwater?
Dr. Fred Sharpe and the Alaska Whale Foundation have studied group bubble-net feeding in Southeast Alaska for over twenty years. Their research has pieced together the complicated and coordinated strategy employed by the whales. While bubble-netting, individual whales have different roles to play, much like different positions on a sports team. One whale is the bubble blower, creating a ring of bubbles that will act as a net to contain the prey. Another whale is the caller, using the feeding call to scare herring towards the ring of bubbles being created. The other whales in the group use their bodies to corral the fish into the net. The white undersides of humpback flippers may actually be used as “flashers” to scare the herring in the right direction. The bubbles, haunting calls, and corralling whales work in tandem to concentrate large balls of herring, which the group then engulfs as they lunge, mouth open, towards the surface. Check out this video, to better visualize bubble-netting.
Watching these whales work in such a coordinated fashion is truly a spectacle to see and was one of the highlights of our inaugural north coast field season.