Thursday, May 29, 2008 - 2:00 PM
565

(TALK WITHDRAWN BY AUTHOR) interactions of watershed landuse and stream condition on fish trophic structure and invertebrate prey subsidies

Mazeika S. P. Sullivan, Fish and Wildlife Resources, University of Idaho, 6th and Line, Moscow, ID 83844-1136

Streams and their riparian zones are tightly-linked, and reciprocal transfers of energy between terrestrial to aquatic environments are becoming increasingly-recognized.  In particular, terrestrial invertebrates entering streams constitute an important prey subsidy for fish species.  The effects of timber harvest are expected to compromise these links between terrestrial and aquatic systems, and may lead to impaired energy exchanges and shifts in the terrestrial:aquatic invertebrate prey ratio of fish consumers.  To investigate this hypothesis, aquatic and terrestrial invertebrates were collected at 19 stream reaches across three Idaho watersheds.  Resident salmonids and sculpin (Cottus spp.) were also collected.  Stable carbon and nitrogen isotope, and fish stomach content analyses were used to investigate the contribution of terrestrially- versus aquatically-derived food sources.  At each reach, stream geomorphology and habitat, as well as riparian extent and condition were characterized.  Results indicate significant differences in fish community trophic structure and terrestrial:aquatic invertebrate prey ratios, with terrestrial invertebrates ranging from 10-60% of the diet of the salmonid species.  Data suggest that timber harvest practices leading to even small reductions in forest cover and changes in composition interact strongly with local stream and riparian condition to structure dependence on terrestrial subsidies.


Web Page: terresrial invertbrate subsidies, fish trophic structure, energy exchanges

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