Geographically distinct blue whale song variants in the Northeast Pacific

• Published in: Endangered Species Research
• Main Authors: Carbaugh-Rutland, Alexander, Rasmussen, Jeppe Have, Sterba-Boatwright, Blair, Sirovic, Ana
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: blue whales; song variability; population structure; call frequency shift; passive acoustic monitoring; Gulf of Alaska; Pacific; Balaenoptera musculus; Blue whale; Alaska
• Online Access: https://hdl.handle.net/1969.6/93957; https://doi.org/10.3354/esr01145

The Northeast Pacific (NEP) population of blue whales Balaenoptera musculus musculus is currently managed as a single stock. We investigated the fine-scale frequency characteristics of 1 NEP blue whale song unit, the B call. We analyzed B calls from passive acoustic data collected between 2010 and 2013 at 2 low-latitude sites, Palmyra Atoll and the Hawaiian Islands, and 3 higher-latitude sites, off southern California, off Washington state and in the Gulf of Alaska. Frequency measurements were extracted along the contour of the third harmonic from each call, and data from each region were compared. Calls from the Gulf of Alaska and Hawai‘i presented a downshift in frequency, beginning just past the midway point of the contour, which was not present in calls recorded from southern California or Palmyra Atoll. Calls from Washington displayed intermediate characteristics between those from the other 2 high-latitude sites. Cluster analysis resulted in consistent grouping of call contours from Washington and southern California, in what we termed the NEP B1 variant, while contours from Hawai‘i and the Gulf of Alaska were grouped together, as a NEP B2 variant. Frequency differences were also observed among the variants; the Gulf of Alaska displayed the highest frequency on average, followed by Washington, then south ern California. Consistent with other studies, a yearly decline in the frequency of B calls was also observed. This discovery of at least 2 geographically distinct variants provides the first evidence of vocally distinct subpopulations within the NEP, indicating the possibility of a need for finer scale population segmentation. HARP data collection was supported by the Chief of Naval Operations CNO-N45 (Frank Stone, Ernie Young and Bob Gisiner) and the US Pacific Fleet Environ mental Monitoring Program (Chip Johnson). Data from ACO were provided by James Potemra, Bruce Howe and Fernando Santiago-Mandujano from the University of Hawai‘i. ACO was supported by research and instrumentation grants from the ...