Relationship Between Invertebrates and Stream Order: Implications for Fish Distribution

Reagan Sutherland, University of New Brunswick Department of Biology (email: b561a@unb.ca)

According to the River Continuum Concept (RCC), invertebrate community structure changes in a predictable fashion from small headwater tributaries to larger mainstem streams, due to hydrological influences, riparian influences and nutrient flow. In the headwaters, streams are small, and terrestrial inputs from surrounding vegetation are the primary sources of energy (food). Primary production by aquatic plants is minimal due to stream shading by surrounding vegetation. As the size of the stream increases, in-stream primary production also increases and there is less influence from the surrounding vegetation. This change in food sources reflects changes in invertebrate and fish communities. Several studies have tested the predictions of the RCC on community structure, however few have examined secondary production in relation to stream size or have linked invertebrate production to fish distribution. This leads to the question: do fish distribution patterns reflect food (invertebrate) availability? The objective of this study is to quantify the biotic diversity found in streams of different orders in Fundy National Park (FNP), New Brunswick, Canada. Predictions are twofold: 1. invertebrate abundance decreases with increasing stream order (size) and 2. biomass of brook trout (most common fish species) is directly related to invertebrate abundance. Four sites on each of two rivers were chosen, representing 1st(smallest), 2nd, 3rd and 4th(largest) order streams. Aquatic invertebrate abundance and brook trout density were determined at each site over three seasons. Preliminary results show that invertebrate abundance, trout biomass, and trout density were higher in small order streams. These results provide evidence for the inverse relationship between biotic abundance and stream size. The markedly low trout biomass in larger streams in Fundy Park may be due to warm water temperatures (>20 C) and/or biological constraints (e.g. food availability).

Young brook trout

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