Assessing noise exposure to beaked and sperm whales in the California Current

Abstract

The ocean is becoming noisier with increased shipping and offshore human activity. Beaked (Ziphiidae) and sperm whales (Physeteroidea) may be impacted by increasing ocean noise. They rely on acoustic signaling for basic life functions like communication and foraging, but the extent of harm from anthropogenic activity is unclear. Passive acoustic monitoring (PAM) is a non-invasive tool that can provide insight to these species where visual data collection methods fall short. Here, we characterized the extent of spatiotemporal noise exposure in relation to acoustic detections of beaked and sperm whales in the California Current Ecosystem. We built random forest models to identify the most important explanatory variables and assessed whether generalized additive models (GAMs) built from environmental predictors improved with the addition of acoustic covariates. Acoustic data were collected from 13 drifts in 2018 and used to detect whale echolocation and characterize the soundscape. We used Automatic Information System (AIS) data to track vessel movement in the vicinity of the drifts and paired these tracks with sound levels. Sperm whale presence was associated with slightly higher sound pressure levels than when absent. Conversely, Cuvier's beaked whales were more present with slightly lower sound pressure levels than when absent. Hourly probabilities of whale detections before and after loud sound events dropped by 7% for Cuvier's beaked whales and 15% for sperm whales. The highest sound levels did not necessarily align with vessel presence in the 125 Hz third-octave level. For both species, final explained deviances for GAMs were low and improved only slightly with acoustic variables. Our findings highlight the continued need to describe the distributions of noise-sensitive species and assess their disturbance risk in a changing anthropogenic soundscape.