Skip to main content

    Apparent decrease of Weddell seal numbers in the western Ross Sea

    Request Meeting Document
    Document Number:
    D.G. Ainley, M.A. Larue (USA), I. Stirling (Canada), S. Stammerjohn and D.B. Siniff (USA)
    Submitted By:
    Mr Doug Cooper (CCAMLR Secretariat)

    Ground counts during 1959-1968 compared with counts using high resolution satellite imagery during 2008-2012 indicated many fewer Weddell seals (Leptonychotes weddellii) at the two major molting haul outs in the western Ross Sea: Edisto Inlet - Moubray Bay, northern Victoria Land, and southeastern McMurdo Sound, southern Victoria Land. Breeding seals have apparently all but disappeared from Edisto-Moubray as well. The timing of decline, or perhaps spreading (low numbers of seals in more places), is unknown but appears unrelated to changes in sea ice conditions, which was our initial hypothesis. We analyzed both historic and satellite-derived ice data but found only an expansion of pack ice in the larger region and a thinning of fast ice along Victoria Land (conceivably beneficial to seals). Timing of freeze and breakup of the fast ice remains the same. The only other major change to the Ross Sea ecosystem that would have negatively affected seals has been the large-scale removal of large Antarctic toothfish (Dissostichus mawsoni), a major prey, by a fishery operating full scale by 2003. Coincident with the fishery, lower numbers and size of toothfish have been reported in McMurdo Sound and data from seals tracked by satellite indicate wider foraging range during winter than 20 years ago. A large-scale seal monitoring program is required to prove that the fishery is not involved.