Reproductive effort of male hooded seals ( Cystophora cristata ): estimates from mass loss

• Published in: Canadian Journal of Zoology
• Main Authors: Kovacs, Kit M., Lydersen, Christian, Hammill, Mike, Lavigne, David M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1996
• Subjects: Animal Science and Zoology; Ecology, Evolution, Behavior and Systematics; Cystophora cristata
• Online Access: http://dx.doi.org/10.1139/z96-166; http://www.nrcresearchpress.com/doi/pdf/10.1139/z96-166

This study investigated mass loss, body composition, and behaviour patterns of male hooded seals during the reproductive season. During the 6 years of study (between 1989 and 1995), 139 records of male mass were obtained that involved 115 individuals. Body masses of males ranged from 147 to 434 kg. Mean mass at first capture was 312.5 ± 53.0 kg (N = 119). Year, date of sampling, and age all significantly influenced mass. Nineteen males were recaptured at least twice during a single season. Mean rate of mass loss among these individuals was 2.5 ± 1.1 kg/day (range 0.7–4.6 kg/day). Body composition early in the breeding season, measured using tritiated water (N = 6), produced mean estimates of 51.6 ± 1.6% water, 29.3 ± 2.4% fat, 16.9 ± 0.7% protein, and 1.9 ± 0.2% ash. Time–depth recorders attached to three males indicated that they spent 84.7 ± 15.4% of their time hauled out on the surface of the ice during the breeding season. Each of these males was on the ice for a few days; they then spent a few hours at sea before returning to the ice surface. Mean dive depth was only 14.1 ± 3.2 m (maximum 66 m) and mean dive duration was only 1.7 ± 0.3 min (maximum 28 min). Extrapolating mean daily rates of body mass loss to encompass a 2.5-week breeding season, males would lose an average of 44 kg, which represents 14% of their mean body mass. Compared with values for males of other phocid species this value is conservative. It appears that the short breeding season among hooded seals is energetically advantageous for both sexes.