Effects of Canopy Removal on Invertebrates and Diet of Juvenile Coho Salmon in a Small Stream in Southeast Alaska

The effect of riparian condition on invertebrate drift in mountain streams

“…For example, when Nakano et al (1999a) excluded terrestrial insect inputs into streams, fish relied more heavily on aquatic invertebrates, which led to an increase in stocks of stream periphyton due to the subsequent reduction of grazers. In our case, the relatively higher density and flux of terrestrial drift in streams with 10 m riparian reserves may benefit higher trophic levels (e.g., Wilzbach et al, 1986) directly as terrestrial invertebrates may contribute as much as 80 % of the annual energy budget to predatory fish such as Dolly Varden (Salvilinus malma), Rainbow trout (Oncorhynchus mykiss), and juvenile Coho salmon (Oncorhynchus kisutch) (Cloe and Garman, 1996;Hetrick et al, 1998;Nakano et al, 1999b;Kawaguchi and Nakano, 2001). Such differences can be substantial for young Coho salmon (i.e., age-0) where terrestrial invertebrates contributed 28 % of stomach contents in a closed-canopy reach versus 68 % in an open-canopy reach of the same stream .…”

“…Consequently, regulatory agencies use "riparian reserve strips" adjacent to streams in an attempt to mitigate the impacts of forest harvesting on stream channel dynamics and water quality, and to ensure the maintenance of natural stream processes (e.g., British Columbia Ministry of Forests, 1995;review in Pusey and Arthington, 2003). Despite the long history of forest harvesting, the effects of forestry on many stream processes including invertebrate drift are not well known (Carlson et al, 1990;Naiman and DØcamps, 1997), are equivocal in terms of the relative contribution of terrestrial and aquatic invertebrates to the drift (Wilzbach et al, 1986;Edwards and Huryn, 1996;Hetrick et al, 1998;Keith et al, 1998;Kawaguchi and Nakano, 2001), and have centered on coastal rather than interior headwater streams in British Columbia. Regardless, changes in the composition of the drift could ultimately influence higher trophic levels (e.g., Wilzbach et al, 1986;Davies and Nelson, 1994;Hartman et al, 1996;Baxter et al, 2005).…”

Present Effects of Past Wildfires on the Diets of Stream Fish

“…For example, clearing of forested and riparian areas can directly affect fish assemblages by increasing stream temperatures and discharge (Hetrick et al 1998b). Indirectly, reduction of terrestrial vegetation may alter in-stream cover by reducing inputs of large woody debris, and by potentially altering the prey base (Hetrick et al 1998a, Keith et al 1998.…”

Effects of clearcut logging on organic matter and invertebrate drift exported from headwater streams in the interior of British Columbia.

“…Logging can increase the trophic resources for drift-feeding fish such as salmonids if they are food limited (Bilby and Bisson 1992;Hetrick et al 1998). There are several ways that invertebrate responses to logging adjacent to headwater streams may achieve this.…”

“…If logging affects the density or composition o f invertebrates in the drift of headwater reaches, the response can carry through to affect fish production (Bilby and Bisson 1992;Hetrick et al 1998). Since drift is a subset of the benthic community, effects of clearcut logging on benthic invertebrates are useful as comparisons to the effects on drift; however, the mechanism of the effect and characteristics o f drift require consideration.…”