Identifying a reliable blubber measurement site to assess body condition in a marine mammal with topographically variable blubber, the Pacific walrus
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Full Publication: https://doi.org/10.1111/mms.12186Product Type: Journal Article
Year: 2015
Authors: Noren, S. R., M. S. Udevitz, L. Triggs, J. Paschke, L. Oland, and C. V. Jay
Suggested Citation:
Noren, S. R., M. S. Udevitz, L. Triggs, J. Paschke, L. Oland, and C. V. Jay. 2015. Identifying a reliable blubber measurement site to assess body condition in a marine mammal with topographically variable blubber, the Pacific walrus. Marine Mammal Science 31(2):658-676. doi:10.1111/mms.12186
Abstract
Pacific walruses may be unable to meet caloric requirements in the changing Arctic ecosystem, which could affect body condition and have population-level consequences. Body condition has historically been monitored by measuring blubber thickness over the xiphoid process (sternum). This may be an unreliable condition index because blubber at other sites along the body may be preferentially targeted to balance energetic demands. Animals in aquaria provided an opportunity for controlled study of how blubber topography is altered by caloric intake. Morphology, body mass, blubber thickness (21 sites), and caloric intake of five mature, nonpregnant, nonlactating female walruses were measured monthly (12 month minimum). Body condition (massx standard length-1) was described by a model that included caloric intake and a seasonal effect, and scaled positively with estimates of total blubber mass. Blubber thicknesses (1.91-10.69 cm) varied topographically and were similar to values reported for free-ranging female walruses. Body condition was most closely related to blubber thickness measured dorsomedially in the region of the anterior insertion of the pectoral flippers (shoulders); sternum blubber thickness was a relatively poor indicator of condition. This study demonstrates the importance of validating condition metrics before using them to monitor free-ranging populations.
Keywords: walrus; Odobenus rosmarus; pinniped; blubber; fat; body condition; caloric intake; marine mammal; Arctic
Keywords: Pacific walrus, climate change, blubber, body condition
Annotation
Pacific walruses may be unable to meet caloric requirements in the changing Arctic ecosystem, which could affect body condition and have population-level consequences. We thereby provide a tool for inferring the body condition of free-ranging walruses. Our approach provides a template that can be used by other investigators to develop a similar tool for other marine mammal species. Blubber located dorsomedially in the region of the anterior insertion of the pectoral flippers (shoulders) provided the best indicator of body condition for mature, nonpregnant female Pacific walruses, although other locations may be preferable for other age, sex, and reproductive categories. Discerning body condition is an important tool for understanding how global climate change may be altering the foraging success of Pacific walruses.