Year-round acoustic monitoring of Antarctic blue and fin whales in relation to environmental conditions off the west coast of South Africa

• Published in: Marine biology 2022-03, Vol.169 (3), Article 41
• Main Authors: Letsheleha, Ishmail S., Shabangu, Fannie W., Farrell, Dara, Andrew, Rex K., la Grange, Philip L., Findlay, Ken P.
• Format: Article
• Language: English
• Subjects: Acoustic data; Acoustic propagation; Acoustic tracking; Acoustics; Aquatic mammals; Balaenoptera musculus; Behavior; Biomedical and Life Sciences; Blue whale; Breeding; Cetacea; Chlorophyll; Chlorophyll a; Distribution; Environmental aspects; Environmental conditions; Environmental monitoring; Fins; Freshwater & Marine Ecology; Habitats; Life Sciences; Marine & Freshwater Sciences; Marine biology; Marine mammals; Microbiology; Oceanography; Original Paper; Overwintering; Sea surface; Sea surface temperature; Temperature anomalies; Water depth; Whales; Whales & whaling; Wind speed; Zoology
• ISSN: 0025-3162; 1432-1793
• DOI: 10.1007/s00227-022-04026-x

Antarctic blue and fin whales were once abundant in the southeastern Atlantic Ocean, yet their occurrence and ecology in this region is still poorly understood. Seasonal acoustic occurrence and behaviour of Antarctic blue and fin whales off the South African west coast were determined using bio-acoustic data collected through two autonomous acoustic recorders between December 2015 and January 2017. Blue whale Z-calls were detected year-round with a peak in July, while fin whale 20 Hz pulses were detected seasonally with a peak in June by a recorder deployed at 1118 m water depth. Blue and fin whale calls were detected seasonally with a similar peak in May by a recorder deployed at 4481 m water depth. The blue whale 27 Hz chorus, and blue and fin whale 18–28 Hz chorus followed a similar trend as the seasonal acoustic occurrence of individual Z-calls and 20 Hz pulses. A maximum detection range of 800 km estimated by acoustic propagation modelling suggests that detected calls originate from whales within the South African west coast waters. Random forest models classified month of the year, wind speed, log-transformed chlorophyll-a, and sea surface temperature anomaly as the most important predictors of blue and fin whale acoustic occurrence and behaviour. Our study highlights the South African west coast as an important year-round habitat and seasonal breeding or overwintering habitat of these whales. Additionally, the year-round acoustic occurrence in this region supports the notion that blue whale migration patterns are more dynamic than previously perceived.