Visual and acoustic surveys of whales: A Monte Carlo model

Abstract

There has been much interest lately in decreasing the high variability of cetacean abundance estimates by coupling passive acoustics with visual surveys. To estimate the advantages and disadvantages of a dual-mode survey, a Monte Carlo model was created. The model can reflect the species and the methodology of a particular survey. The whale population is defined by the parameters of group size and encounter rate, swimming speed and direction, surfacing rate and pattern, and source level and rate of vocalization. The survey process is constrained by the additional parameters of vessel speed, sighting probability, hydrophone array characteristics, and sound propagation. With results from the model, researchers can compare the abundance estimates and variability from a visual survey only, a passive acoustic survey only, or a dual-mode survey. They can also determine which parameters are important for a species, region, and methodology, and design their surveys accordingly. Sample results from a hypothetical minke whale population demonstrate that adding passive acoustics significantly increased the number of groups detected and decreased the time the groups were in the survey area before being detected.