An Analysis of the Dynamics of a Weddell Seal Population
1977
Siniff, D. B. | DeMaster, D. P. | Hofman, R. J. | Eberhardt, L. L.
A breeding population of the Weddell seal (Leptonychotes weddelli) was studied annually during the 2 1/2—mo pupping and breeding season in McMurdo Sound, Antarctica, from 1969 through 1974. Components of the population were estimated by direct counts of adult ♂ ♂ with pups, by capture—recapture studies of nonparous ♀ ♀ and adult ♂ ♂, and by aerial counting. Total population size was estimated as being on the order of 2,500—3,000 seals. The Seber—Jolly method was adapted to circumstances of the present study. Reproductive rates (measured in terms of successful pupping) were ~ 0.5 pups/♀ for the entire breeding colony, and ~ 0.7 pups/♀ for a subset of tagged ♀ ♀ observed for 4 yr in sequence. Age—specific reproductive data were also obtained, and it appears that full reproductive activity of ♀ ♀ is achieved at ~ age 7. The annual survival rate for adult ♀ ♀ is in the range of 0.80 to 0.85, as determined (by several methods) from tagging data. Survival rates for adult ♂ ♂ are lower (perhaps 0.50), but are not as well established. Little information was obtained on the subadult class (1 to 3 yr of age). Underwater territories of adult °° on one breeding colony were studied by acoustic tagging and found to be steadily patrolled by dominant ♂ ♂.Two experimental colonies having different densities ties of ♂ ♂ with pups demonstrated increased interactions at higher densities, but lower weight losses on the part of the °° (presumably due to isolated location of the colonies). We infer from the available data that the McMurdo Sound population is somehow regulated by a physiological or social connection between the number of adult ♀ ♀ at the pupping colonies and subsequent years' pup population.
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