Passive acoustic methods applied to fin whale population density estimation

TLDR

Cetacean population size in the open ocean has traditionally been estimated by visual surveys, but acoustic monitoring offers a complementary approach that can be calibrated with visual techniques and applied across the 30+ fixed hydrophone sites worldwide. The study aims to estimate fin whale population statistics using near‑continuous recordings from a single hydrophone. Range to calling animals is estimated by transmission loss and multipath methods, and the analysis uses recordings from a hydrophone north of Oahu, Hawaii, to derive a minimum population density estimate. The study found an average calling whale density of 0.027 animals per 1000 km², with a seasonal peak about three times higher at 0.081 animals per 1000 km².

Abstract

Assessing the size of cetacean populations in the open ocean has traditionally relied on visual surveys alone. The addition of acoustic monitoring can complement these surveys if reliable protocols can be formulated and calibrated with visual techniques. A study is presented to estimate fin whale population statistics based on near-continuous recording from a single hydrophone. Range to calling animals is estimated by transmission loss and multipath methods to provide a minimum population density estimate. Results are derived from recordings at a hydrophone site north of Oahu, Hawaii that have been the focus of earlier studies. The average calling whale density is 0.027 animals/1000 km2, while the seasonal maximum calling whale density is about three times the average, or 0.081 animals/1000 km2. Over 30 fixed hydrophone sites are available around the Worlds Oceans from which such statistics could be generated.