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

Area of Science:

• Marine Biology
• Bioacoustics
• Acoustic Oceanography

Background:

• Passive acoustic monitoring (PAM) is increasingly used for marine mammal research.
• Estimating absolute animal density from acoustic data is challenging but achievable.
• The accuracy of density estimation depends on the precision of animal location data.

Purpose of the Study:

• To present a novel method for estimating cetacean density using acoustic data when only horizontal bearings are available.
• To assess the method's performance through simulations and a pilot study on fin whales.

Main Methods:

• Developed a density estimation method utilizing horizontal bearings, signal-to-noise ratios, and auxiliary data (source levels, sound propagation, call rates).
• Validated the method with simulations under various animal distribution scenarios.
• Applied the method to passive acoustic monitoring data from fin whale calls recorded by CTBTO hydrophones.

Main Results:

• Simulations demonstrated median biases in call density estimation below 2%.
• Pilot study yielded an average call density of 0.02 calls hr^-1 km² (CV: 15%).
• Estimated average fin whale density was 0.54 animals/1000 km² (CV: 52%), with spatial distribution analysis.

Conclusions:

• The developed acoustic method effectively estimates cetacean density with limited location information.
• The findings support the utility of PAM for quantitative marine mammal density assessments.
• Further refinement of call production rates can improve density estimation accuracy.