REPRODUCTIVE EFFORT OF MALE HOODED SEALS (CYSTOPHORA-CRISTATA) - ESTIMATES FROM MASS-LOSS

This study investigated mass loss, body composition, and behaviour pat terns of male hooded seals during the reproductive season. During the 6 years of study (between 1989 and 1995), 139 records of male mass wer e 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 s eason. 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 estimate s of 51.6 +/- 1.6% water, 29.3 +/- 2.4% fat, 16.9 +/- 0.7% protein, an d 1.9 +/- 0.2% ash. Time-depth recorders attached to three males indic ated that they spent 84.7 +/- 15.4% of their time hauled out on the su rface of the ice during the breeding season. Each of these males was o n the ice for a few days; they then spent a few hours at sea before re turning to the ice surface. Mean dive depth was only 14.1 +/- 3.2 m (m aximum 66 m) and mean dive duration was only 1.7 +/- 0.3 min (maximum 28 min). Extrapolating mean daily rates of body massless to encompass a 2.5-week breeding season, males would lose an average of 44 kg, whic h represents 14% of their mean body mass. Compared with values for mal es of other phocid species this value is conservative. It appears that the short breeding season among hooded seals is energetically advanta geous for both sexes.