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Variation in outer blubber lipid concentration does not reflect morphological body condition in humpback whales

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  • Fredrik Christiansen
  • Kate R. Sprogis, Murdoch University
  • ,
  • Jasmin Gross, Griffith University Queensland
  • ,
  • Juliana Castrillon, Griffith University Queensland
  • ,
  • Hunter A. Warick, Murdoch University
  • ,
  • Eva Leunissen, University of Otago
  • ,
  • Susan Bengtson Nash, Griffith University Queensland

An animal’s body condition provides valuable information for ecophysiological studies, and is an important measure of fitness in population monitoring and conservation. While both the external body shape of an animal and its internal tissues (i.e. fat content) can be used as a measure of body condition, the relationship between the two is not always linear. We compared the morphological body condition (external metric obtained through aerial photogrammetry) of migrating humpback whales (Megaptera novaeangliae) with their outer blubber lipid concentration (internal metric obtained through blubber biopsy sampling) off the coast of south-west Australia early and late in the breeding season (spanning ∼4.5 months). The external body condition index of juvenile and adult humpback whales decreased by 26.9 (from 18.8% to −8.1%) and 12.0 percentage points (from 8.6% to −3.4%), respectively, between the early and late phase. In contrast, we found no intra-seasonal change in blubber lipid concentration, and no difference between reproductive classes (juveniles, adults and lactating females); however, the small sample size prevented us from effectively testing these effects. Importantly, however, in the 33 animals for which paired metrics were obtained, we found no correlation between the morphometric body condition index and the blubber lipid concentration of individual whales. The lack of a linear relationship suggests that changes in outer blubber lipid concentration do not reflect external changes in body shape, thus limiting the utility of outer blubber lipid reserves for individual body condition evaluation. The wider spectrum of change in body morphometry captured with aerial photogrammetry supports the use of body morphometry as a reliable and well-tested method.

Original languageEnglish
Article numberjeb213769
JournalJournal of Experimental Biology
Number of pages9
Publication statusPublished - Apr 2020

    Research areas

  • Baleen whales, Biopsy sampling, Cost of reproduction, Energy reserves, Photogrammetry, Unmanned aerial vehicle

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