Potential Impact of Mid-Frequency Active Sonar on Whales from Passive Acoustic Monitoring Data

The potential for Mid-Frequency Active Sonar (MFAS) to disrupt activities of marine mammals has received high international attention because several mass stranding events have coincided with the use of MFAS. Behavioral response studies of tagged whales have documented an adverse reaction to MFAS. Here we examine the acoustic response of Cuvier’s beaked whales (Ziphius caviostris) and blue whales (Balaenoptera musculus) to sonar operations at three sites of frequent naval activity in Southern California waters from 2009 to 2015. Specially, our goal was to estimate the probability that sonar exposure at a particular decibel level and temporal scale will result in behavioral disturbance. The relationship between MFAS and the acoustic behavior of whales is complex and requires accounting for natural temporal and spatial variability in species presence. Generalized estimating equations (GEEs) were used to model relationships between species acoustic presence and temporal and sonar covariates.

Both species showed considerable inter-annual, seasonal and diel variability in calling. A higher probability of detecting beaked whale clicks was identified after about a week since the cessation of sonar use. We found declining probabilities of click detections with increasing peak-to-peak received levels of sonar and with higher proportions of sonar in 1-minute bins. We present analyses of blue whale response and a comparison of multiple sites with varying degrees of call and sonar detections.

This work represents substantial progress in our understanding of the impact of MFAS on marine mammals which is crucial for ensuring effective context-dependent management of anthropogenic activities.