Estimating body mass and condition of leopard seals by allometrics

Leopard seals (Hydrurga leptonyx) are formidable marine predators and require sedation before scientific examination. Mass-specific drug dosage for leopard seals has usually been determined from generic allometric equations or visual estimates. However, the leopard seal is a slender phocid and generic equations are likely to return inaccurate mass estimates, which may lead to fatal overdoses of drugs. We used published and unpublished morphometric data to construct allometric models for estimating leopard seal body mass. The model using volume (Vol), which combined measures of snout-tail length (STL) and the square of girth (G²), provided our best estimate of mass (r ² = 0.97). The model using STL alone was sample-site specific (each r² ≥ 0.85), highlighting G as an important measure to obtain where possible. The confidence and prediction intervals associated with each model broadened with increased seal size and decreased sample size, suggesting the use of extra caution when estimating drug dosage for larger seals to avoid over- or under-dosing. We also developed a seal body condition index that can assist wildlife management when deciding if rehabilitation of vagrant seals is warranted. Body condition may also affect the induction, duration and recovery times of anaesthetized leopard seals.