Effect of anthropogenic low-frequency noise on the foraging ecology of Balaenoptera whales

The human contribution to ambient noise in the ocean has increased over the past 50 years, and is dominated by low-frequency (LF) sound (frequencies < 1000 Hz) from shipping, oil and gas development, defence-related and resea rch activities. Mysticete whales, including six endangered species, mag; be at risk from this noise pollution because all species produce and probably perceive low-frequency sound. We conducted a manipulative field experiment to test the effects of loud, LF noise on foraging fin blue (B. musculus) a nd (Balaenoptera physalus) whales off San Nicolas Island, California. Naive observers used a combination of attached tracking devices, ship-based surv eys, aerial surveys, photo-identification and passive monitoring of vocal b ehaviour to examine the behaviour and distribution of whales when a loud LF source (US Navy SURTASS LFA) was and was not transmitting. During transmis sion, 12-30% of the estimated received levels of LFA of whales in the study area exceeded 140 dB re 1 mua. However, whales continued to be seen foragi ng in the region. Overall, whale encounter rates and diving behaviour appea red to be more strongly linked to changes in prey abundance associated with oceanographic parameters than to LF sound transmissions. In some cases, wh ale vocal behaviour was significantly different between experimental and no n-experimental periods.. However, these differences were nor consistent and did not appear to be related to LF sound transmissions. Rt the spatial and temporal scales examined, we found no obvious responses of whales to a lou d, anthropogenic, LF sound. We suggest that the cumulative effects of anthr opogenic LF noise over larger temporal and spatial scales than examined her e may be a more important consideration for management agencies.