Detection distances of the sounds of large whales recorded on hydrophones in the offshore Gulf of Alaska

Abstract

The current status of most species of endangered baleen whales, including blue, fin, and humpback whales, in the Gulf of Alaska is unknown due to a lack of basic information on distribution and seasonal abundance. Remote passive acoustic monitoring can provide this information for vocal whales. However, to begin to estimate an index of abundance of calling animals, the distance at which they can be detected needs to be determined. In order to estimate transmission loss, a parabolic equation acoustic propagation model was used to provide mean loss estimates along four transects at 0.1a intervals to 5a to the N, E, S, and W from each of four receivers moored in the sound channel for species-specific frequencies and at depths at which the animals are thought to produce sound. For all species and locations, the detection range was largely determined by the choice of ambient noise levels. This suggests that masking due to anthropogenic noise could limit the range over which these animals can be detected by the moored instrument and, more importantly, the range over which they might communicate.