Initial Effects of the August 2008 Volcanic Eruption on Breeding Birds and Marine Mammals at Kasatochi Island, Alaska

Kasatochi Island, home to a rich community of largely marine-dependent fauna, erupted with little warning on 7-8 August 2008 and buried the island under up to 30 m of tephra. We visited the island during the summer of 2009 to examine the effects of the eruption on local wildlife. The abundance of sea lions and many seabird species in 2009 was comparable to pre-eruption estimates, suggesting that adult mortality was low for these species. In contrast, shorebirds and passerines formerly breeding on the island were not observed in 2009 and probably perished in the eruption. The largest direct effect of the eruption to individual animals was probably mortality of chicks, with an estimated total 20,000-40,000 young birds lost. Indirect effects on wildlife consisted of loss of foraging habitat for species that relied on former terrestrial, intertidal, or nearshore-subtidal habitat and the near-total destruction of all former nesting habitats for most species. Although several species attempted to breed in 2009, all except Steller's sea lions failed due to lack of suitable breeding sites. The recovery of wildlife at Kasatochi will depend on erosion of the tephra layer blanketing the island to re-expose former breeding habitat.