Density and Abundance of Cuvier’s and Blainville’s Beaked Whales in the Mariana Archipelago Estimated Using Drifting Acoustic Recorders

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NOAA Fisheries Science Centers have recently incorporated drifting acoustic spar buoy recorders (DASBRs) into their standard large-scale survey designs. Drifting autonomous instruments have many advantages, especially for species that are difficult to see at the surface, are vocal at depth, and whose sounds have been well characterized such that they can be readily identifiable from autonomous recordings. Pacific Islands Fisheries Science Center deployed DASBRs throughout the survey region with the goal of collecting data on the occurrence of beaked whales and other cryptic deepdivers. Traditional line-transect assessments for those species are often challenged by very low encounter rates, resulting in density and abundance estimates with high uncertainty, or in some cases, no estimates if groups were not seen during the ‘on-effort’ portions of the survey. Previous experience in the Marianas suggested that encounter rates for beaked whales on the DASBRs would be orders of magnitude higher within the DASBR data than in the visual survey or towed array datasets, likely enabling examination of density for some beaked whale species using the newly developed methods of Barlow et al. (2021a). Here, we detail our methodology to estimate density and abundance using 2021 survey dataset and how 2018 survey data were used to inform the detection parameters. This analysis has resulted in the first preliminary acoustic density and abundance estimates for Cuvier’s and Blainville’s beaked whales in the Mariana Islands region.