Blue whale call intensity varies with ambient noise level

Abstract

Blue whales (Balaenoptera musculus) vary the intensity of their sound production level in response to varying ambient noise levels. Blue whales produce tonal, type B calls with a fundamental frequency of 16 Hz, and a strong third harmonic at 48 Hz. These calls, along with other low-frequency baleen whale vocalizations, ambient sea noise, and shipping noise have been monitored and recorded on continuous seafloor acoustic recorders near Cortez and Tanner Banks, offshore Southern California, since August 2000. By separately comparing the intensity in the 16 and 48 Hz spectral level bands with the intensity of ambient noise at and near those frequencies, we observe a correlation between the sound intensity level of blue whale type B calls and ambient noise levels. This is verified by the inspection of individual call intensity in various noise environments. Preliminary analysis indicates a less than unity proportional increase in the call intensity with increasing ambient noise. A trend of increased call intensity with an increased noise level has implications for the effect of shipping, and other natural and artificial noise sources in the marine environment on the behavior of blue whales.