A Comparison of Reproductive Parameters Among Three Populations of Weddell Seals (Leptonychotes weddellii)

Abstract

SUMMARY (1) Tagged populations of Weddell seals at three sites in Antarctica were compared to resolve earlier differences in estimated reproductive parameters and to examine interannual patterns in adult reproduction. (2) The estimated reproductive rate from McMurdo Sound (0-68) was lower than that reported from the Vestfold Hills (0-80). The estimate from Signy Island was found to be biased upward and not comparable to the other two sites. (3) Average age at first sighting with pup was 6 years at McMurdo Sound, 7 years at Signy Island and 8 years at the Vestfold Hills. (4) Sampling at Signy Island and the Vestfold Hills was earlier in the breeding season and less intensive than at McMurdo Sound. Subsets of data from McMurdo were used to simulate the sampling regime at the other two sites. The results were higher estimates of both reproductive parameters (0.80 pups female- and 7 years) such that there were no significant differences between sites. A similar sampling bias probably occurs at Signy and the Vestfold Hills and would account for the differences between sites. (5) Probability of sighting an adult female with a pup was found to correlate well with adult reproductive rate at McMurdo Sound and was used as an index to adult reproduction at all three sites. This reproductive index appears to have fluctuated in approximate synchrony at Signy Island and McMurdo Sound, sites separated by over 145? of longitude, but not at the Vestfold Hills.