Baleen whale distribution and seasonal occurrence revealed by an ocean bottom seismometer network in the Western Indian Ocean

Abstract

From the acoustic data acquired by the RHUM-RUM (Réunion Hotspot and Upper Mantle Réunions Unterer Mantel) Ocean Bottom Seismometer (OBS) network between October 2012 and November 2013, this study revealed baleen whale occurrence in the western Indian Ocean (IO). Low-frequency songs from three species (Antarctic Blue Whales, Pygmy Blue Whales and Fin Whales) as well as P-calls (or Spot-calls) from an unknown species were recorded on the dataset. The wide arrangement of the OBS network (2000 km × 2000 km) provided valuable information to draw seasonal patterns of occurrence and distribution all over the area. These species occurred sympatrically in the western IO, at least during austral autumn months emphasizing the importance of this region for these populations. This data set helped to refine the knowledge on their spatio-temporal distribution and complete the picture built by previous studies. A tighter sub-network of 8 OBSs deployed on the South West Indian Ridge provided ideal inter-sensor spacing for whale tracking. We demonstrated the capability of such array of detecting and tracking the three different whale species up to 50 km and for several hours. As a result and to understand the effect of acoustic wave propagation, songs from the tracking were described at a close and remote distance of the sensor. This work could also help to understand the local behavior of these species during austral autumn months in this area of the western Indian Ocean.

Multiple pygmy blue whale acoustic populations in the Indian Ocean: whale song identifies a possible new population

“…These Chagos whales show thus the wide-ranging distribution of other blue whale populations. To date, the Chagos songs have not been detected in the western Indian Ocean, either in the southwest, around Reunion Island 78 and in the Mozambique Channel, or in the northwest, off Oman (S. Cerchio, pers. comm.…”

Oceanic high-frequency global seismic wave propagation with realistic bathymetry

“…Other potential uses of hydroacoustic phases include early-warning systems for tsunamis (Sasorova et al (2005), ), acoustic thermometry for remote monitoring of long-term changes in ocean temperature (Dushaw et al 1999), detection of glacial and ice-calving events (Chapp et al 2005), as well as monitoring of cetacean populations (e.g. McDonald et al (1995), Dréo et al (2019)) and for illicit nuclear tests in violation of the Comprehensive Nuclear Test Ban Treaty (Mitchell (2002), Okal (2008)).…”

An open access dataset for developing automated detectors of Antarctic baleen whale sounds and performance evaluation of two commonly used detectors

“…Through IWC-SORP, the Acoustic Trends Project working group has built upon the pioneering work done in the first decade of the twenty-first century, and has fostered an increasing number of passive acoustic studies focusing on the calls of Antarctic blue whales and to a lesser extent fin whales across broad time and spatial scales, as well as acoustic data processing and analysis methodology. The data from these studies have been collected both from ships during Antarctic voyages and from long-term moored recording devices 4, [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] . The project working group presently (as of March 2020) has access to more than 300,000 h of passive acoustic data that have been collected throughout the Southern Ocean over the past 20 years.…”