Acoustic Vector Sensing of Blue and Fin Whale Habitat Occupancy off Central California

John P Ryan , Paul Leary, Kevin Smith, Jarrod Santora, Kelly J Benoit-Bird, William K Oestreich , John E Joseph, Tetyana Margolina, John Calambokidis, James Fahlbusch, Andrew DeVogelaere, Brandon Southall, Jeremy Goldbogen

Temporally varying geographic distributions of whale populations are difficult to visually monitor across large marine ecosystems. Acoustic vector sensing (AVS) of the powerful calls produced by baleen whales enables continuous monitoring over large areas with spatial information contained in the bearing estimates to whales. Using three years of AVS data in Monterey Bay National Marine Sanctuary, we examine the habitat occupancy of endangered blue and fin whale populations. The calls of fin whales persistently originated primarily in offshore deep-water (ODW) habitat, shifting into shelf / slope habitat only occasionally. The calls of blue whales originated primarily in shelf / slope habitat. However, detection of blue whales in ODW habitat increased significantly across the study period with stronger wind-driven upwelling that increased krill abundance and expanded foraging habitat. This expansion increased both the spatial overlap of blue and fin whales and the exposure of blue whales to ship strike risk. AVS is an effective method of passive acoustic monitoring for informing marine ecological research and conservation.