Effects of Trout Habitat Alteration on Plum Creek, Sayner, Wisconsin
Jackson, Robert R.
University of Wisconsin-Stevens Point, College of Natural Resources
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The effects of habitat alteration on substrate composition, permanent trout cover and stream surface area; the benthic invertebrate community and drift of these invertebrates; rates of colonization, species preference and density of invertebrates inhabiting the wood used for habitat structures and changes in the availability of food organisms for brook and brown trout were assessed in Plum Creek, Wisconsin. Two 37-m study zones in areas not altered by habitat work and a 146-m study zone in an area altered by the 1976 habitat program were sampled during ice-free periods from May, 1976 to October, 1977. Surface area and the percentage of sand bottom decreased by 11 and 13%, respectively, following habitat alteration. Permanent overhanging bank cover increased by 9%, while gravel substrate increased by 10%. Habitat alteration did not decrease the number of benthic invertebrate taxa. There was a drastic initial reduction in mean numbers and biomass, however, 17 months (October, 1977) after habitat alteration gravel and sand substrate invertebrate numbers and weights were higher in the altered zone than the unaltered zone. Trichoptera and Diptera accounted for 86.6% of the total numbers and 75.2% by weight for gravel substrate in the altered zone. Pelecypoda was most abundant in the unaltered zone sand substrate with 66.0% occurrence. Plum Lake appears to have the greatest influence on the invertebrate composition found in both study zones. Habitat alteration did not change the number of taxa found in the drift. The unaltered zone, however, contained significantly higher (P< .05) numbers and biomass of drifting organisms. Seasonal and diel variations occurred in the drift. Mean numbers and biomass of aquatic invertebrates in the drift were significantly higher (P<.05) than terrestrial invertebrates. Differences in correlations existed between monthly particulate organic carbon and invertebrate number densities by habitat zones. Colonization of invertebrates increased with the amount of time the artificial substrates were left in the stream. The number of taxa, however, decreased with time. Chironomidae and Hydropsycidae accounted for 76.9% of the total numbers and 60.3% by weight for combined artificial substrate intervals. Artificial substrate invertebrate numbers and biomass were comparable with gravel and sand substrate totals in both the altered and unaltered areas. Habitat alteration in Plum Creek did not appear to affect the availability of food organisms for brook and brown trout. There was no significant difference for mean number of food items per stomach between the altered and unaltered habitat zones. The contents of the trout stomachs in the altered habitat zone contained the greatest variety of taxa. Major aquatic and terrestrial insect orders and families found in the benthos, drift and artificial substrate samples were utilized by the trout.