Survival of the southern elephant seal, mirounga leonina, population of Marion Island

Abstract

Demographic parameters from a 14-year mark-recapture program on southern elephant seals at Marion Island were investigated. Using the computer package MARK, first year survival was estimated at 0.58 and 0.62, and equated over the first three years of life, 0.69 and 0.74 for males and females respectively. From years four to nine the average survival rate was 0.66 and 0. 75 for males and females respectively. Considerable reductions in fourth- and fifth-year male survival, and fourth year female survival were observed over the study. period. Poor adult survival is implied as the proximate cause, and food limitation as deduced from the _decline in survival of seals with high energetic demands, as the ultimate cause behind the population decline. Fecundity was 0.25 for three-year-olds, 0.42 for four-year-olds, and 0.44 for five-year-olds, with a significant increase in these rates being evident over the course of the study. A conversion factor of3.15 was estimated and applied to annual pup production in order to assess population size. The present population size was estimated at 1263 individuals, and the population declined exponentially at an annual rate of 4.3% from 1986 to 1997, which slowed to 2.5% per annum over the last six years.