Population density of sperm whales in the Bahamas estimated using non-linked sensors

Abstract

Estimates are presented of sperm whale click detection probability and sperm whale population density at the U.S. Navy’s Atlantic Undersea Test and Evaluation Center (AUTEC) in the Bahamas. The estimation of the probability of detecting whale echolocation clicks at multiple non-linked sensors uses estimates of sperm whale source level distribution, beam pattern of click emission, distribution of whale locations and orientations with respect to the sensors while clicking, acoustic transmission loss from source (whale) to receiver (bottom hydrophone), and noise levels at the receiver. These data are combined in a Monte Carlo model that propagates simulated clicks from whales at various random positions to each receiving hydrophone to estimate the signal-to-noise ratio at the receiver and the detection function, the probability of detecting clicks as a function of distance. The estimated detection function for each receiving hydrophone is then combined with information on the detector’s rate of missed calls and false detections as a function of signal-to-noise ratio, average sperm whale click rates, and the actual number of clicks detected in a given period of time in order to estimate population density. Results are compared to multi-sensor cases where detection functions were estimated analytically.