Song variability and change in the Australian pygmy blue whale song—Implications for passive acoustic abundance estimation

Abstract

Blue whales were heavily exploited throughout the early 20th century with many populations hunted to near extinction. Today, several known sub populations of blue whale exist, separated by geographic range and the acoustic signals they produce. The eastern Indian Ocean subpopulation of pygmy blue whales is easily identified by the production of a characteristic Australian song type. Long term collection of passive acoustic data from the Perth Canyon, Western Australia and Portland, Victoria, have revealed unprecedented levels of variability in the vocal behaviour of Australian pygmy blue whales. These levels of variability have significant implications for any attempts to assess the abundance of this population with acoustic techniques. Further, these findings may indicate higher levels of cognitive capability than previously expected in blue whales. The mechanisms behind variability in song production are unclear, though there is research to suggest that changes in vocal behaviour may be culturally driven or caused by changes in the ambient noise and environmental conditions. These findings highlight shortfalls in the current methods for measuring acoustic abundance, as well as indicate that higher than expected levels of variability may exist in the vocal behaviour of other pygmy blue whale subpopulations.