During dedicated surveys for the Critically Endangered eastern stock of North Pacific right whales Eubalaena japonica (NPRW) in the Bering Sea, focal follows (FFs) were combined with passive acoustic monitoring to correlate vocal activity with dive behavior. During FFs, impulsive gunshot calls (hereafter 'gunshots'), similar to those produced by other right whale populations, were localized to male and female NPRWs. The timing of gunshots correlated strongly with diving behavior observed during the FFs. Log survivorship analysis of inter-blow intervals showed a bout criterion interval of 40 s, separating the data into shorter surfacings and longer dives. For both, gunshots were skewed closer to the end of the sequence (modal gunshot to blow times: 5 s for dives, 7 s for surfacings) than the beginning (modal blow to gunshot times: 22 s for dives, 13 s for surfacings). Gunshots were more commonly produced during dives than surfacings. Mean gunshot calling rate during FFs was 133.0 calls h −1 (range: 38.9−425.0). Other NPRW calls, including upcalls, the predominant call used to identify right whales acoustically, were not detected during the FFs. To determine comparative call detection rates, an additional 180 h of non-FF recordings were analyzed. Gunshots were detected ~50 times more frequently than upcalls (mean: 228. . This is the first study to definitively attribute gunshots to NPRW, and demonstrates the importance of including gunshots in passive acoustic studies, which will greatly increase NPRW detectability while supporting more accurate determinations of their spatio-temporal distribution.

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Killer whales (Orcinus orca) are thought to learn their vocal dialect. Dispersal in the species is rare, but effects of shifts in social association on the dialect can be studied under controlled conditions. Individual call repertoires and social association were measured in three adult female killer whales and three males (two juveniles and an adult) during two periods, 2001-2003 and 2005-2006. Three distinct dialect repertoires were represented among the subjects. An adventitious experiment in social change resulted from the birth of a calf and the transfer of two non-focal subjects in 2004. Across the two periods, 1691 calls were collected, categorized and attributed to individuals. Repertoire overlap for each subject dyad was compared with an index of association. During 2005-2006, the two juvenile males increased association with the unrelated adult male. By the end of the period, both had begun producing novel calls and call features characteristic of his repertoire. However, there was little or no reciprocal change and the adult females did not acquire his calls. Repertoire overlap and association were significantly correlated in the first period. In the second, median association time and repertoire similarity increased, but the relationship was only marginally significant. The results provided evidence that juvenile male killer whales are capable of learning new call types, possibly stimulated by a change in social association. The pattern of learning was consistent with a selective convergence of male repertoires.

2013. Subarctic cetaceans in the southern Chukchi Sea: Evidence of recovery or response to a changing ecosystem. Oceanography 26(4):136-149, http://dx.