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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Fish Ecology I
INFLUENCE OF STREAMSIDE VEGETATION ON TERRESTRIAL INVERTEBRATE SUBSIDIES TO SALMONID FOOD WEBS.
J.D. Allan1 and M.S. Wipfli2. 1School of Natural Resources & Environment, University of Michigan, Ann Arbor MI 48109-1115, 2Pacific Northwest Research Station, USDA Forest Service, 1133 N. Western Ave, Wenatchee, WA 98801
Salmonid food webs receive important energy subsidies via terrestrial infall, up- and downstream transport and spawning migrations. We examined the contribution of terrestrially-derived invertebrates (TI) to juvenile coho (Oncorhynchus kisutch) in streams of Southeast Alaska by diet analysis and sampling of TI inputs in 12 streams of contrasting riparian vegetation. Juvenile coho ingested 12.1 mg fish-1 of invertebrate mass averaged across all sites; no significant differences associated with location (plant or forest type) were detected, possibly because prey are well mixed by wind and water dispersal. Terrestrial and aquatic prey comprised approximately equal fractions of prey ingested. Surface inputs were estimated at ~80 mg m-2 day-1, primarily TI. Direct sampling of invertebrates from the stems of six plant species demonstrated differences in invertebrate taxa occupying different plant species, and much lower TI biomass per stem for conifers compared with over- and understory deciduous trees. Traps placed within dense stands of alder vs. conifers consistently captured higher biomass of TI under alders. Management of riparian vegetation is likely to influence the food supply of juvenile coho and the productivity of stream food webs.
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