Beam Reach

First-ever localization of mother/calf calls

First ever mother/calf recording!

An amazing scientific feat was accomplished during the first sea-week of the fall 2007 program. At the end of the first deployment of our hydrophone array, a mother and calf were recorded vocalizing on the west side of San Juan Island. While orca calves rarely leave their mother’s side, this calf seemed adventurous. It left its mother and another female foraging along a tidal front, approached the hydrophone array we were towing, made an underwater turn to parallel our heading, surfaced close off our port bow, and then diverged from our course to rejoin its mother.Luckily, the Beam Reach team was already effectively collecting data when this rare mother/calf separation occurred. Most of us were watching and listening carefully enough to remember the course of events. Todd was helping Sam take bearings on the orca calf with a hand-held compass and Shannon was taking photographs to help identify the whales. I was writing down the bearings and GPS-synchronized times, noting when good calls were heard (listening through the deck speakers). Val’s computer was recording the data from each of the four hydrophones in the array. Mike was doing a good job of being Whale Wise and maintaining a steady heading (to keep the array straight).

When the array data were analyzed with software that allows us to “localize” sounds recorded on all four hydrophones, the locations of the calls corresponded well with the visual bearings Sam took and the general sequence of events we all remember (and wrote down). This is remarkable because we have struggled for two years to get all of the technologies functioning together. Courtney (2005) and Peggy (2006) will certainly appreciate how lucky we were to have the ability to localize the calls that were made during this unusual mother/calf interaction.

The localization results tell us a lot. It is clear that the calf’s calls are interspersed with the calls of the two nearby adults (mother or brother). This is the first documented call/response interaction of southern resident killer whales! While we have long suspected that the residents call and respond to each other, it isn’t clear which animal makes which sound when listening through a single hydrophone. The array enables us to learn that different animals are making the calls. It also allows us to assign particular calls — and even voices — to specific individuals. So, now we know what one calf’s call sounds like, and we have an opportunity to compare its voice with its mothers voice. This is a fledgling, but critical, first step to voice-recognition in the southern residents. A final breakthrough is being able to visualize the trajectory of the calf underwater. By combining such “passive localization” techniques with acoustic fish tags and bleeding-edge 3-D active sonar technologies (at frequencies above killer whale hearing), we will soon be able to observe how the whales navigate within their complex ecosystem and interact with other animals, their prey, plankton, and the rest of the environment.

So, the fall 2007 program has already made a great technological leap. Congratulations all around! Let’s hope the Beam Reach class continues to have such great luck. Clearly, we are poised to learn a lot more about the southern residents this year with the array system.