UACE: A study of changes in vocalization frequency of Antarctic blue whales and fin whales recorded at CTBTO hydroacoustic stations

• Day: June 16, Monday
    Location / Time: A. TERPSIHORI at 15:30-15:50
• Last minutes changes: -
• Session: 04. Comprehensive Nuclear-Test-Ban Treaty Monitoring, and its Civil and Scientific Applications
  Organiser(s): Georgios Haralabus, Mario Zampolli, Tiago Oliveira, Mark Prior
  Chairperson(s): Georgios Haralabus, Tiago Oliveira
• Lecture: A study of changes in vocalization frequency of Antarctic blue whales and fin whales recorded at CTBTO hydroacoustic stations [Invited]
  Paper ID: 2291
  Author(s): Stephen Robinson, Peter Harris, Michael Ainslie, Peter Tyack, Michele Halvorsen, Alex MacGillivray, Lian Wang, Valerie Livina
  Presenter: Stephen Robinson
  Abstract: A steady decrease in baleen whale call frequency (‘red shift’ adaptation) has been observed since the 1960s. To investigate the effect, we use ambient sound pressure measured by the hydroacoustic stations in the International Monitoring System (IMS) operated by the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO). \nWe focus first on a narrow-band sound around 27 Hz produced as the upper tonal part of the so-called “Z-wave” vocalizations of many distant Antarctic blue whales. These have been shown to undergo a seasonal intensity variation from early February to late October in the ocean off Australia’s southwest coast, as recorded by the CTBTO station at Cape Leeuwin. We analyze the spectral characteristics of long-term patterns in this band over the period from 2003 to 2023, with the frequency of the spectral peak of the tonal call shown to have decreased over the 20 years of observation with a gradient of (-0.1361 ± 0.0016) Hz/a (for a 95 % level of confidence), consistent with the value of (-0.135 ± 0.003) Hz/a originally obtained by Gavrilov et al. (2012) from 2002 to 2010. A partial recovery of the frequency is observed off-season, as are gradual increases in spectral amplitude within the “whale band” relative to the background. Results are also shown for several other CTBTO stations in the southern hemisphere where the calls of Antarctic blue whales are prominent.\nWe also examine a part of the frequency spectrum that is mostly associated with fin whales. Here we focus on the evidence for frequency changes in the 14–18 Hz frequency band at the southern CTBTO station at Wake Island. The component below 18 Hz due to fin whales, most visible in the months of December and January of each year, is a frequency down-sweep which when averaged over longer times looks much less tonal in nature, making the inter-annual changes in the vocalization frequency of fin whales more difficult to distinguish. Over the nine years from 2008 to 2016, a regression analysis applied to the median spectral peak frequencies shows a gradient of (0.006 ± 0.005) Hz/a (for a 95 % level of confidence). Although a positive increase in the spectral peak frequency is detectable, it is very small.\nFinally, some thoughts are presented on the significance of the findings.\n
• Corresponding author: Mr Stephen Robinson
  Affiliation: National Physical Laboratory
  Country: United Kingdom