Observation and modeling of an unusual spatiotemporal pattern in underwater bioacoustic chorusing

This talk presents a stochastic numerical model that replicates many aspects of an unusual underwater biological chorus recorded in the Southern California Bight. During one experiment, the directionality of the chorusing region repeatedly evolved upcoast over time, suggestive of “The Wave” performed by fans periodically standing and sitting in sports stadia around the world. The modeling approach is based on the physics of excitable media. Each calling animal (unit), randomly placed in a spatial grid, transitions in order between three states; “excitable,” “active (calling),” and “resting.” The probability of transitioning from excitable to active is partly determined by the received sound level at each animal, creating a non-linear acoustics-based coupling between units. (Transitions from resting to excitable and from active back to resting occur after fixed specified time periods). With appropriate inputs, many determined from measurements of the chorus and individual animal calls, simulations replicate the cycling levels in the night-long chorus, the continuous din of the sunset chorus, and the periodic upcoast evolution of the chorusing region (“The Wave”). The addition of noise from a transiting ship appreciably changes the chorus' spatiotemporal characteristics, in ways corresponding to changes observed during the experiment. [Work supported by ONR]