Aerial photogrammetry and tag-derived tissue density reveal patterns of lipid-store body condition of humpback whales on their feeding grounds
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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jan 27, 2021
- Source ID
- 10.1098/rspb.2020.2307
Entities
People
- Ailsa J. Hall
- Charlotte Bellot
- Christian Ramp
- Joanna L Kershaw
- Kagari Aoki
- Katsufumi Sato
- Lucía M. Martín López
- Martin Biuw
- Patrick J O Miller
- Patrick Pomeroy
- Paul J. Wensveen
- René Swift
- Saana Isojunno
- Takashi Iwata
- Tomoko Narazaki
- Yu Akiyama
Organizations
- Norwegian Institute of Marine Research
- Office of Naval Research
- Strategic Environmental Research and Development Program
- University of Neuchâtel
- University of St Andrews
- University of Tokyo