Weight watching: Morphometric indices of ontogenetic and reproductive stages in Weddell seals

• Main Author: Monnin, Mee-ya A.
• Other Authors: Horning, Markus, Oregon State University. Honors College
• Format: Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Weddell Seals
• Online Access: https://ir.library.oregonstate.edu/concern/honors_college_theses/h989r507z

We investigated ontogenetic changes in body morphology of Weddell seals (Leptonychotes weddellii) using three three-dimensional (3D) photogrammetry, to estimate surface areas and body volumes for 42 Weddell seals. We sampled ten weaned pups, twelve juveniles (age one or two years), 11 non-breeding adult females, and 9 adult females who had recently weaned a pup. We developed predictive values for surface-area-to-volume (SA:V) ratios of juvenile seals using a morphological growth projection based on data from pups and adult females, then compared to measured values. Juveniles were longer than pups but groups overlapped at their extremes. Juveniles had significantly smaller SA:V ratios than pups. However, the shortest juveniles had larger SA:V ratios than the longest pups. Within both groups, SA:V ratios declined with increasing body length. Juveniles and post-reproductive female SA:V ratios consistently exceeded values predicted from the pup-to-adult growth projection, suggesting that morphological changes as well as increasing body length influenced SA:V ratios in juveniles. Ultrasonically measured blubber thickness indices were lower in juveniles and post-reproductive females, but mean body densities estimated from mass and volume did not differ. We suggest that surface area, volume, and blubber morphometrics may provide meaningful indicators of body condition not identified with ratios of adipose to lean tissue.