Detection probability and density estimation of fin whales by a seaglider

Abstract

The effectiveness of gliders is evaluated for passive acoustic density estimation of fin whales. An estimate of the probability of detection as a function of range (or, equivalently, effective survey area) is required to estimate density from acoustic data collected by a single-hydrophone glider platform. A cabled hydrophone array was used to estimate fin whale localizations and tracks concurrently with a glider survey. Fin whale tracks were used as detection trials and a detection function for snapshots containing fin whale 20 Hz pulses recorded by the glider was modeled using a generalized additive model. Detection probability was strongly dependent on 40 Hz noise levels recorded on the glider. At the median noise level of 97 dB re 1μPa2/Hz, detection probability was near one at zero horizontal distance, and maximum detection range was near 40 km. The estimated effective survey area at this noise level was 870 km2. Using estimates of vocal rates and group size from tagged and tracked fin whales, respectively, the density was estimated as 2.4 fin whales per 1000 km2 (coefficient of variation 0.55). The framework presented here could be applied to other baleen whale species to advance the use of gliders for density estimation of cetaceans.