Body density of humpback whales (Megaptera novaengliae) in feeding aggregations estimated from hydrodynamic gliding performance

• Published in: PLOS ONE
• Main Authors: Narazaki, Tomoko, Isojunno, Saana, Nowacek, Douglas P., Swift, Rene, Friedlaender, Ari S., Ramp, Christian, Smout, Sophie, Aoki, Kagari, Deecke, Volker B., Sato, Katsufumi, Miller, Patrick J. O.
• Other Authors: University of St Andrews. Sea Mammal Research Unit, University of St Andrews. School of Biology, University of St Andrews. Scottish Oceans Institute, University of St Andrews. Centre for Research into Ecological & Environmental Modelling, University of St Andrews. Marine Alliance for Science & Technology Scotland, University of St Andrews. Institute of Behavioural and Neural Sciences, University of St Andrews. Centre for Social Learning & Cognitive Evolution, University of St Andrews. Bioacoustics group
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: QH301 Biology; DAS; SDG 14 - Life Below Water; QH301; Antarctic; Antarc*; baleen whales; Humpback Whale; Megaptera novaeangliae; North Atlantic
• Online Access: http://hdl.handle.net/10023/15354; https://doi.org/10.1371/journal.pone.0200287

This study was funded by Strategic Environmental Research and Development Program (https://www.serdp-estcp.org; grant number RC-2337). In addition, the study was partly supported by Core Research for Evolutional Science and Technology by Japan Science and Technology Agency (http://www.jst.go.jp/kisoken/crest/en/index.html, grant number JPMJCR1685) and Bilateral Open Partnership Joint Research Projects by Japan Society for the Promotion of Science (http://www.jsps.go.jp/english/e-bilat/index.html; no specific grant number). Many baleen whales undertake annual fasting and feeding cycles, resulting in substantial changes in their body condition, an important factor affecting fitness. As a measure of lipid-store body condition, tissue density of a few deep diving marine mammals has been estimated using a hydrodynamic glide model of drag and buoyancy forces. Here, we applied the method to shallow-diving humpback whales (Megaptera novaeangliae) in North Atlantic and Antarctic feeding aggregations. High-resolution 3-axis acceleration, depth and speed data were collected from 24 whales. Measured values of acceleration during 5 s glides were fitted to a hydrodynamic glide model to estimate unknown parameters (tissue density, drag term and diving gas volume) in a Bayesian framework. Estimated species-average tissue density (1031.6 ± 2.1 kg m-3, ±95% credible interval) indicates that humpback whale tissue is typically negatively buoyant although there was a large inter-individual variation ranging from 1025.2 to 1043.1 kg m-3. The precision of the individual estimates was substantially finer than the variation across different individual whales, demonstrating a progressive decrease in tissue density throughout the feeding season and comparably high lipid-store in pregnant females. The drag term (CDAm-1) was estimated to be relatively high, indicating a large effect of lift-related induced drag for humpback whales. Our results show that tissue density of shallow diving baleen whales can be estimated using the hydrodynamic ...