Effect Of Primary And Secondary Productivity On Fish Populations Of The Lower Clark Fork River Drainage Sanders County, Montana

Abstract

This report focuses on the primary and secondary productivity of the tributary systems of the lower Clark Fork River (LCFR) drainage and their influence on resident fish populations. For primary productivity assessment, periphyton accumulation was evaluated. Periphyton was collected on artificial substrates in each of the streams. Photosynthetic pigments were then extracted and the chlorophyll a_ content of each sample was determined using a spectrophotometer. To determine the Autotrophic Index (biomass divided by chlorophyll a_ content) of each sample, the ash-free weight of organic matter was determined. Secondary productivity was determined through evaluation of the compostion, abundance, and distribution of benthic macroinvertebrate populations within the stream. In each reach of every stream, three samples were taken, using a Surber sampler, along a transect. In the lab, macroinvertebrate taxa were enumerated and identified to the lowest feasible taxonomic unit. Both primary and secondary productivity data were correlated with fish, canopy cover, and nutrient data. Because of the small sample size, the resulting data trends were recognizable but weak. The data suggest that the Autotrophic Index is not a good indicator of stream conditions for this study. The data also show that primary and secondary productivity do not significantly influence fish abundance in streams of the LCFR drainage.