Population Dynamics of the Weddell Seal (Leptonychotes Weddelli) in McMurdo Sound, Antarctica, 1966–1968

  1. William Henry Burt
  1. Ian Stirling

Published Online: 3 APR 2013

DOI: 10.1029/AR018p0141

Antarctic Pinnipedia

Antarctic Pinnipedia

How to Cite

Stirling, I. (1971) Population Dynamics of the Weddell Seal (Leptonychotes Weddelli) in McMurdo Sound, Antarctica, 1966–1968, in Antarctic Pinnipedia (ed W. H. Burt), American Geophysical Union, Washington, D. C.. doi: 10.1029/AR018p0141

Author Information

  1. Zoology Department, Canterbury University, Christchurch, New Zealand

Publication History

  1. Published Online: 3 APR 2013
  2. Published Print: 1 JAN 1971

ISBN Information

Print ISBN: 9780875901183

Online ISBN: 9781118664773

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Keywords:

  • Density-dependent factors;
  • Leptonychotes weddelli;
  • McMurdo Sound;
  • Pup mortality;
  • Subadults;
  • Weddell seal

Summary

This paper presents data on the population parameters of the Weddell seal (Leptony chotes weddelli) in McMurdo Sound from 1966 to 1968, compares them with other pinnipeds, and discusses factors important in the natural regulation of their numbers. For the study 2854 Weddell seals were individually tagged. Subadults were separable on the basis of size alone up to 3 years of age. At least 50 seals were nonselectively shot in February 1966, 1967, and 1968, and data on age structure and pregnancy rates were obtained. The average age of adults was 8 to 9 years; the maximum recorded longevity was 18 years. Of female seals 3 years of age or older, 97% ovulated and 80.5% were pregnant. Only 54.5% of females aged 3 to 5 years were pregnant. Of 1250 Weddell seal pups, 51.2% were males and 48.8% were females. Minimum survival rates of adult males and females through 1 year were 76.1% and 82.8%, respectively. Subadult and pup survival could not be calculated accurately. A time-specific l x life and fecundity table for adult females is presented.

The following points suggest that intrasexual competition is taking place in McMurdo Sound and is affecting the reproductive rate. The factors include (1) exclusion of parts of the population from the pupping colonies, (2) avoidance patterns, (3) pregnancy rates and growth rates below their maximum potential, and (4) spacing on the sea ice.

Availability of exit cracks for Weddell seal pupping colonies is determined by physical factors independent of the density of seals. Density-dependent factors come into play when more seals are competing for the best pupping habitat than there is space available. Under such circumstances, social stress may retard reproduction. The annual production of female pups far exceeds the mortality rate of adult females, which indicates that natural regulation of total numbers is not governed by the breeding population. The mechanism of total population regulation may only be speculated on, because of the extreme difficulties associated with studying the non-breeding part of the population. Dental wear may be an important ultimate cause of adult mortality.