Preweaning mortality of Weddell seal pups

Abstract

We examined mortality prior to weaning of Weddell seal pups (Leptonychotes weddellii), using resighting data collected from 1984 to 1993 on the annual ice of McMurdo Sound, Antarctica. Mortality rates were estimated using counts of dead pups found on the surface and mark–recapture techniques. The standard Jolly–Seber model for open populations fit the recapture data best and corresponded well to the known biology of these animals. Yearly mortality rates estimated by mark–recapture techniques ranged from 6 to 22%, with a mean across years of 13%. These values are twice as high as those previously reported for Weddell seals and those calculated from counts of dead pups in this study. This suggests that there is significant unseen mortality due either to undiscovered fatalities on the ice surface or to significant mortality occurring in the water.