Tuesday, May 27, 2008
529

Assessing the ecological integrity of Southeast Alaska streams using the stable isotope composition of juvenile salmon

Alexander J. Reisinger1, Dominic T. Chaloner2, Scott D. Tiegs2, Janine Rüegg2, and Gary A. Lamberti2. (1) Division of Biological Sciences, Kansas State University, Manhattan, KS 66506, (2) Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556

Pacific salmon (Oncorhynchus spp.) deliver marine-derived nutrients to the stream ecosystems in which they spawn and die. While such nutrients are thought to contribute to the ecological integrity of Southeast Alaska streams, their utilization and incorporation may be altered by physical changes in the stream resulting from watershed management, such as timber harvest.  Juvenile salmon consume salmon eggs and tissue, resulting in isotopic enrichment that holds potential as a useful metric of stream ecological integrity.  Prerequisites for using such a tool include assessing natural variability in isotopic enrichment due to species-specific differences in feeding and fish size. The nitrogen and carbon isotopic composition of juvenile coho salmon (O. kisutch) was determined for two years in seven watersheds on Prince of Wales Island, Southeast Alaska, that exhibit varying degrees of timber harvest intensity (5 – 68% of the watershed harvested).  Although fish from streams that received adult salmon clearly showed isotopic enrichment, we found no clear relationship between timber harvest, or fish size, and isotopic enrichment. Results suggest that the isotopic enrichment of juvenile salmon may not necessarily be a straightforward metric for assessing stream ecological integrity, and that other variables (e.g., spawner abundance) should be considered when interpreting such information.


Web Page: Pacific salmon, stable isotopes, ecological integrity