Impact of Chaitén Volcano ashfall on native and exotic fish recovery, recolonization, and abundance

The effects of volcanic disturbance on aquatic communities and their recovery are poorly studied. To fill this gap, we explored the effects on fish communities in rivers in Argentina of the 2008 eruption of Chaitén Volcano in southern Chile (42.8° lat. S). The eruption produced volcanic plumes of ash that persisted in the atmosphere for several months. Borne on westerly winds, deposits of tephra crossed the Andes Mountains, reaching the Atlantic coast (Argentina). We compared the pre- and post-eruption abundances of a native catfish Hatcheria macraei, and two introduced trout from rivers covered by the volcanic plumes (Argentina) using Before-After-Control-Impact analysis to explore fish recovery. Total suspended solids from volcanic ashfall, macroinvertebrate abundance and richness, and species ecological attributes influenced the spatial arrangement of fish in rivers. Twenty-one months after the eruption, Rainbow Trout, Oncorhynchus mykiss, had not returned to pre-eruption abundances in the sampled rivers, and only four rivers had regained pre-eruption species composition, suggesting that disturbance is still ongoing. The abundance of introduced fishes was strongly, negatively correlated with TSS, suggesting that ashfall affected these fish probably by clogging and abrasion of the gills. Fish recolonized previously occupied habitats 4 days to 9 months after the disturbance. Hatcheria macraei was the slowest to recolonize, whereas O. mykiss were the pioneer fish in 4 rivers following the eruption and recolonized all 5 rivers where they were present prior to the eruption. In one river, the catfish and the Brown Trout, Salmo trutta, were still absent 21 months post-eruption, potentially owing to the lack of riparian cover that would have deflected the entry of ash. Rainbow Trout suffered significant declines in abundance, whereas Brown Trout and catfish generally did not, owing to their ecological attributes. Total fish abundance was negatively correlated with ash thickness, but positively related to prey availability.