Taming the Jez monster: Estimating fin whale spatial density using acoustic propagation modeling.

Abstract

The spatial density of calling animals may be estimated acoustically using methods presented by Buckland et al. [Advanced Distance Sampling (Oxford University Press; Oxford, 2004)]; information on the call (or other cue) rate, the call detection probability as a function of range, and the probability of a false detection to obtain an estimate of spatial density. Here we use similar methods to estimate the density of calling fin whales (Balaenoptera physalus) from the level of received sound near 20 Hz—the so-called “Jez monster.” Using published source levels and call rates of fin whales, a Monte Carlo method is developed that simulates a given spatial density of whales randomly situated around a hydrophone and uses acoustic propagation modeling (specifically, a parabolic equation model) to estimate the resulting level of received sound. Using this technique at several deep-water sites in the North Atlantic, we derive a function that maps loudness to spatial density, and then use this function to estimate spatial density at these locations.