Fin whale density and distribution estimation using acoustic bearings derived from sparse arrays

TitleFin whale density and distribution estimation using acoustic bearings derived from sparse arrays
Publication TypeJournal Article
Year of Publication2018
AuthorsHarris, Danielle V., Miksis-Olds Jennifer L., Vernon Julia A., and Thomas Len
JournalThe Journal of the Acoustical Society of America
Volume143
Pagination2980-2993
ISBN Number0001-4966
EndNote Rec Number12176
Abstract

Passive acoustic monitoring of marine mammals is common, and it is now possible to estimate absolute animal density from acoustic recordings. The most appropriate density estimation method depends on how much detail about animals' locations can be derived from the recordings. Here, a method for estimating cetacean density using acoustic data is presented, where only horizontal bearings to calling animals are estimable. This method also requires knowledge of call signal-to-noise ratios, as well as auxiliary information about call source levels, sound propagation, and call production rates. Results are presented from simulations, and from a pilot study using recordings of fin whale (Balaenoptera physalus) calls from Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) hydrophones at Wake Island in the Pacific Ocean. Simulations replicating different animal distributions showed median biases in estimated call density of less than 2%. The estimated average call density during the pilot study period (December 2007?February 2008) was 0.02 calls hr?1 km2 (coefficient of variation, CV: 15%). Using a tentative call production rate, estimated average animal density was 0.54 animals/1000?km2 (CV: 52%). Calling animals showed a varied spatial distribution around the northern hydrophone array, with most detections occurring at bearings between 90 and 180 degrees.