Impacts of Ambient Noise on Minke Whale (Balaenoptera acutorostrata) Habitat Use and Behavior

This study examines the soundscape of minke whale habitat in the Scottish Inner Hebrides around the islands of Mull, Coll and Muck and near the Ardnamurchan Peninsula of the Scottish mainland. To compare the soundscape with minke whale presence and behavior, acoustic recordings were paired with behavior and respiration data. Acoustic recordings were taken using a Soundtrap 300, deployed from a whale watching vessel. Data was taken from June - September 2016. The soundscape was analyzed by comparing power spectral density averaged into octave bands (center frequencies from 16 Hz – 128 kHz). The soundscape of the region is ephemeral, with some locations having very different acoustic patterns depending on transient animal and human activity. Humans contribute to the soundscape through movement of small ships and dredging. Notable biological contributors to the soundscape include dolphins and snapping shrimp. Outside the island of Coll is quieter at mid-frequencies (2-8 kHz octave bands). Inside Coll is quieter at frequencies in the 16-128 kHz octave bands. Ardmore point, in the Sound of Mull, is louder for most frequencies. These differences create a potential way for animals to navigate or orient based on sound. Observed minke whale behaviors were categorized into behavior states to create a behavior budget. Minke whales in this area spend 56% of their daytime feeding, 7% traveling and 39% in other activities. The average inter-breath interval for minke whales in this study was 60.7s. Minke presence and behavior were compared with sound levels in 1/3rd octave bands using generalized linear models. Minke whale presence and behavior both correlate with changes in the Soundscape. Minke whales are less likely to be seen with higher levels of low (31 Hz) and high (25.4 kHz) frequency sound. Higher levels of sound at low (63 Hz) frequencies were associated with lower probability of minke whales feeding. Higher probability of minke whales feeding in higher levels of high (25.4 kHz) frequency sound may indicate that minke whales are optimizing that time which is spent in regions with higher levels of noise at these frequencies.