Aerial photogrammetry and tag-derived tissue density reveal patterns of lipid-store body condition of humpback whales on their feeding grounds

Kagari Aoki*, Saana Isojunno, Charlotte Bellot, Takahashi Iwata, Joanna Louise Kershaw, Yu Akiyama, Lucía Martina Martín López, Christian Ramp, Martin Biuw, Rene James Swift, Paul Wensveen, Patrick Pomeroy, Tomoko Narazaki, Ailsa Jane Hall, Katsufumi Sato, Patrick Miller

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)
4 Downloads (Pure)

Abstract

Monitoring the body condition of free-ranging marine mammals at different life-history stages is essential to understand their ecology as they must accumulate sufficient energy reserves for survival and reproduction. However, assessing body condition in free-ranging marine mammals is challenging. We cross-validated two independent approaches to estimate the body condition of humpback whales (Megaptera novaeangliae) at two feeding grounds in Canada and Norway: animal-borne tags (n = 59) and aerial photogrammetry (n = 55). Whales that had a large length-standardized projected area in overhead images (i.e. whales looked fatter) had lower estimated tissue body density (TBD) (greater lipid stores) from tag data. Linking both measurements in a Bayesian hierarchical model to estimate the true underlying (hidden) tissue body density (uTBD), we found uTBD was lower (−3.5 kg m−3) in pregnant females compared to adult males and resting females, while in lactating females it was higher (+6.0 kg m−3). Whales were more negatively buoyant (+5.0 kg m−3) in Norway than Canada during the early feeding season, possibly owing to a longer migration from breeding areas. While uTBD decreased over the feeding season across life-history traits, whale tissues remained negatively buoyant (1035.3 ± 3.8 kg m−3) in the late feeding season. This study adds confidence to the effectiveness of these independent methods to estimate the body condition of free-ranging whales.
Original languageEnglish
Article number20202307
Number of pages10
JournalProceedings of the Royal Society of London Series B: Biological Sciences
Volume288
Issue number1943
DOIs
Publication statusPublished - 27 Jan 2021

Keywords

  • Tissue body density
  • UAV
  • Feeding season
  • Animal-borne sensor
  • Neutral buoyancy
  • Cetacean

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