Ground counts during 1959–1968 compared with counts using high resolution (0.6 m2) satellite imagery during 2008–2012 indicated many fewer Weddell seals (Leptonychotes weddellii) at two major molting areas in the western Ross Sea: Edisto Inlet-Moubray Bay, northern Victoria Land, and McMurdo Sound, southern Victoria Land. Breeding seals have largely disappeared from Edisto-Moubray, though the breeding population in McMurdo Sound appears to have recovered from harvest in the 1960s. The timing of decline, or perhaps spreading (lower numbers of seals in more places), is unknown but appears unrelated to changes in sea ice conditions. We analyzed both historic and satellite-derived ice data confirming a large expansion of pack ice mostly offshore of the Ross Sea, and not over the continental shelf (main Weddell seal habitat), and a thinning of fast ice along Victoria Land (conceivably beneficial to seals). Timing of fast ice presence and extent in coves and bays along Victoria Land, remains the same. The reduction in numbers is consistent with an altered food web, the reasons for which are complex. In the context of a recent industrial fishery targeting a seal prey species, a large-scale seal monitoring program is required to increase understanding of seal population changes.