Table 1. Comparison of actual mass, parameter estimations, and percent error across estimation methods given as mean ± standard deviation for 56 animals.
Mass was estimated using three methods: elliptical “cones”, “correction equation”, and “silhouette slice”. Percent error was calculated as 100*the difference between the estimated mass and the actual mass divided by the actual mass. Superscript letters denote a significant difference in parameters across estimation methods. The sedation, equipment, and time requirements for all methods are noted.
| Parameter | Elliptical Cones | Photogrammetry, Correction Equation | Photogrammetry, Silhouette Slice |
|---|---|---|---|
| Actual Mass (kg) | 346 ± 73 | 346 ± 73 | 346 ± 73 |
| Estimated Volume (m3) | 0.323 ± 0.074 a | 0.399 ± 0.082 b | 0.346 ± 0.075 a |
| Estimated Mass (kg) | 343 ± 76 a | 345 ± 71 a | 346 ± 75 a |
| Apparent Density (g cm-3) | 1.08 ± 0.06 ¥ a | 0.87 ± 0.05 b | 1.00 ± 0.05 c |
| Error (kg) | -3 ± 20 a | -1 ± 20 a | 0 ± 19 a |
| Error (%) | 1 ± 5 a | 0 ± 6 a | 0 ± 6 a |
| Sedation Required | Yes | No Ω | No Ω |
| Apparent Density Required | No | Yes | Yes |
| Equipment | Maximum | Moderate | Moderate |
| Field Data Collection Time (Minutes) | 30 | 2–5 θ | 2–5 θ |
| Data Processing Time (Minutes) | 15 | 25–40 | 30–45 |
Ω Animals were sedated during this study to measure mass for validations and apparent density calculations.
¥ To ensure comparability across methods, density for the elliptical cones method was calculated using the estimated volume and actual mass, rather than incorporating the lean and blubber volumes and densities.
θ The time required for field data collection will be slightly more for non-sedated animals (~5 minutes) than it was in this study (~2 minutes).