Body density of humpback whales ( Megaptera novaengliae ) in feeding aggregations estimated from hydrodynamic gliding performance
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 glid...
Published in: | PLOS ONE |
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Main Authors: | , , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
2018
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Subjects: | |
Online Access: | https://risweb.st-andrews.ac.uk/portal/en/researchoutput/body-density-of-humpback-whales-megaptera-novaengliae-in-feeding-aggregations-estimated-from-hydrodynamic-gliding-performance(4a7b9ebc-7566-48ba-b61f-5a3fa19e02e8).html https://doi.org/10.1371/journal.pone.0200287 https://research-repository.st-andrews.ac.uk/bitstream/10023/15354/1/Narazaki_2018_PLoSONE_Bodydensity_CC.pdf |
Summary: | 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 (C D Am -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 gliding model, although cross-validation with other techniques is an essential next step. This method for estimating body condition is likely to be broadly applicable across a range of aquatic animals and environments. |
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