Estimated body density for adult, female Weddell seals calculated from actual body mass and estimated volume.

<p>The elliptical “cones” method estimated a higher density than both “correction equation” and “silhouette slice” methods. For reference, vertical lines show the density of seawater (black dotted line, 1.027 g cm^-3 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189865#pone.0189865.ref036" target="_blank">36</a>]), blubber (black dashed line, 0.920 g cm^-3, this paper), and lean tissue (black dashed-dotted line, 1.1 g cm^-3 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189865#pone.0189865.ref035" target="_blank">35</a>]).</p

Calculation of subcutaneous fat for seal WS12-22 using traditional truncated cones with circular cross-sections.

<p>Radius outer cone = Girth/2π;</p><p>Radius difference = base − roof of cone;</p><p>Straight Length = sqrt(Curvilinear Length² − Radius Difference²);</p><p>Radius inner cone = Radius outer cone – (2 × Blubber Depth);</p><p>Outer/Inner Cone Volume = (1/3)π × [(Radius Outer/Inner₁)² + (Radius Outer/Inner₁ × Radius Outer/Inner₂) + (Radius Outer/Inner₂)²];</p><p>Blubber Volume =  Outer Cone Volume − Inner Cone Volume;</p><p>Mass Conversions: Core Mass =  Core Volume × 1.1; Blubber Mass =  Blubber Volume × 0.94; Total Body Mass =  Core Mass + Blubber Mass.</p

Calculation of subcutaneous fat for seal WS12-22 using truncated cones with modified, elliptical cross-sections.

<p>Minor radius outer cone = Body Height/2;</p><p>Minor radius difference = base − roof of cone minor radius;</p><p>Straight Length = sqrt(Curvilinear Length² – Minor Radius Difference²);</p><p>Diameter inner cone major/minor axis =  Body Height/Width – (2 × Blubber Depth);</p><p>Outer/Inner Cone Volume =  [(Straight length × π)/12] × [D₁D₂ + D₃D₄ + sqrt(D₁D₂D₃D₄)];</p><p>Blubber Volume =  Outer Cone Volume − Inner Cone Volume;</p><p>Mass Conversions: Core Mass =  Core Volume × 1.1; Blubber Mass =  Blubber Volume × 0.94; Total Body Mass =  Core Mass + Blubber Mass.</p

Differences in additional physiological parameters determined by circular vs. elliptical truncated cones.

<p>Mean ± SE total body volume, surface area, surface area-to-volume ratios, buoyant force, and calculated density in Weddell seals (<i>N</i> = 11). Surface area remains the same between circular and elliptical cones. Buoyancy was calculated following Webb et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0091233#pone.0091233-Webb1" target="_blank">[9]</a>, and density was calculated using measured M_T. <i>Asterisk</i> indicates a significant difference in estimated parameter using circular versus elliptical models (paired t-tests; all <i>P</i><0.001).</p

HTO equilibration curve for five Weddell seals showing plateau by 90 min.

<p>HTO equilibration curve for five Weddell seals showing plateau by 90 min.</p

For the “silhouette slice” method, the portion of the seal below the ground plane is identified in PhotoModeler (top panel) and is removed to reduce error (bottom panel).

<p>For the “silhouette slice” method, the portion of the seal below the ground plane is identified in PhotoModeler (top panel) and is removed to reduce error (bottom panel).</p

Morphometric measurements taken for each study animal.

<p>(<b>A</b>) <i>SL</i> = Standard length, <i>CL</i> = Curve length, Girths =  white lines, Blubber depths =  white dots, Cone section length calculations =  grey triangle and “L”. Site of blubber biopsy is marked with “X”. (<b>B</b>) Reconstruction of truncated cones with segment length “<i>L</i>” and blubber depth “<i>b</i>” (<i>At left</i>). Circular and elliptical cross-sections shown (<i>At right</i>). Because an ellipse has a major and minor radius “r,” the model can account for different dorsal and lateral blubber depths (x and y) and more accurately reflect true animal shape.</p

Weddell seal body cross-sections are elliptical.

<p>Mean ± SE width-to-height ratios along the body of adult female Weddell seals (<i>N</i> = 11), with a circle having a ratio = 1. <i>Asterisk</i> indicates that the width-to-height ratio of the inner core cone is significantly greater than the outer, total body cone.</p

Morphometric measurements to estimate body mass and composition.

<p>Stepwise forward multiple regressions using morphometric measurements to estimate total body mass (M_T) and lipid mass (TBL_HTO; absolute kg and as %M_T). Factors that were included in each model are shown under the estimated parameter. Each step is shown to elucidate which measurements should be taken preferentially, if animal handling time is limited (all <i>P</i><0.001). * =  Note that the additional parameter in this model had slightly increased the variance inflation factor, and the variance in the coefficients. All lengths, girths, and blubber depths were measured in cm, and when season is a significant parameter, the coefficient should be multiplied by “0” for January and “1” for October study animals. Root-square-mean-error (RMSE) of models is presented as absolute (kg) and as a percentage of the study’s mean M_T or TBL_HTO.</p

The photogrammetry procedure requires the photographer to slowly circle the seal, taking 8–12 photographs from all possible perspectives (i.e. kneeling, standing, portrait photographs, and landscape photographs).

<p>Photos are imported into PhotoModeler and a 3D shape is created by referencing scaled photographs to one another.</p