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North Pacific right whale calling behavior and habitat characterization in the southeastern Bering Sea

  • Author(s): Munger, Lisa Marie
  • et al.
Abstract

North Pacific right whales (Eubalaena japonica) are critically endangered due to intensive commercial whaling in the 1800s and illegal whaling in the 1960s. Currently the eastern subpopulation probably numbers in the dozens of animals, and little is known about their behavioral ecology. The majority of sightings within the past 50 years have been in the southeastern Bering Sea (SEBS), in shallow waters (< 200 m) over the continental shelf. Moored, passive acoustic recorders were deployed in the SEBS in 2001, 2002, 2004, and 2005 to monitor the middle shelf for right whale calls and recorded for 2 - 11 months per instrument. Deployments were at or near subsurface moorings that recorded oceanographic data including temperature, salinity, and chlorophyll fluorescence. Techniques were developed for efficiently detecting right whale calls in a large data set, and calling behavior was investigated on daily and seasonal scales. Acoustic properties of right whale calls and their propagation on the SEBS shelf were estimated and temporal patterns in right whale calling were examined in relation to oceanographic variables. Automated call detection was useful at guiding analysts to bouts of right whale calling and additional calls were found by manually searching. Right whales occurred in the SEBS as early as May and as late as December. Calling rates were significantly higher during darkness than during daylight, suggesting a relationship to behavior that may vary diurnally, such as foraging. Right whale call source levels were within ranges reported for other balaenid whale species, and calls propagated for long distances (>100 km) on the SEBS middle shelf. Right whales were detected earlier in years with early ice retreat and a late spring bloom and intermittently throughout summer and fall in all years with recording effort. Peak right whale calling rates and the most days per month with calls were in late summer. We hypothesize that right whale occurrence is linked to environmental variables via bottom-up control on production and distribution of copepods, their primary prey. These results are relevant to conservation and form the basis for future investigations of right whale calling behavior and its relationship to habitat use

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