The role of acoustics in defining killer whale populations and societies in the Northeastern Pacific Ocean.

Abstract

Stable, culturally inherited repertoires of discrete pulsed calls are characteristic of the acoustic behavior of killer whales. Call repertoires may have important roles in the evolution of social segregation and reproductive isolation of sympatric killer whale populations. Here we present the results of analyzes of recordings collected from killer whale populations in coastal waters of the Northeastern Pacific from the Aleutian Islands to the Gulf of California over the past 30 years. At least three acoustically, genetically, and ecologically distinct lineages of killer whales, known as residents, transients, and offshores, inhabit these waters. Call repertoires within these lineages can further distinguish populations, communities, or smaller social groups, depending on social structure and patterns of dispersal. Salmon-feeding residents live permanently in their natal matrilines and have group-specific dialects that encode maternal genealogy. Mammal-feeding transient groups have less stable societies and tend not to have group-specific dialects, though there are regional call differences among subpopulations. Offshore killer whales, which range widely along the continental shelf and may specialize on sharks, have distinct call repertoires that appear to vary among groups. Killer whale calls can provide important insights into the structure of populations at a scale that cannot be resolved through genetic studies.