Trophic relationships of anadromous salmonids in the Atlantic Patagonian Continental Shelf

JAVIER CIANCIO; MIGUEL PASCUAL

Santa Cruz

Simposio; 12th Salmon Ocean Ecology Meeting; 2010

National Marine Fisheries Service NOAA and UCSC

For centuries, humans have been spreading salmonids in rivers around the World. Southern Patagonia is the region where anadromous species have most successfully established: both Pacific and Atlantic rivers have self-sustaining anadromous chinook salmon, rainbow and brown trout populations. Salmonids are top predators that may produce changes on receiving communities. We studied the marine distribution, trophic relationships, and potential effects of anadromous salmonids in Patagonia. We applied a combination of methods, including the analysis of fish caught at sea, a bibliographic review of critical life cycle and behavior traits from other regions of the world, and stable isotope analysis (SIA). The southern portion of the Patagonian Continental Shelf was identified as the area with optimal temperature ranges for salmonids of the genus Oncorhynchus and brown trout. The potential distribution areas were validated by comparison with catch records in fisheries. Using a geographic information system, we built trophic scenarios for the temporal and spatial overlap among salmonids, potential prey, and competitors. Because of their similar trophic behavior, two penguin species were chosen as models to compare with salmonids. SIA identified different functional assemblages within this ecosystem. Chinook salmon and brown trout, showed a piscivorous behavior, having the same trophic level as the piscivorous Magellanic Penguin (Spheniscus magellanicus). Anadromous rainbow trout showed a distinctly different trophic position as compared to their native range. They feed mainly on zooplankton and fish larvae, having the same trophic level as the zooplanktophagous Rockhopper Penguin (Eudyptes chrysocome). Both species were clustered together with species that feed on large-bodied zooplankton crustacean, fish larvae, and small cephalopods.