Assessment of Habitat and Biota in the West Branch of the Knife River, MN

Abstract

The Lake Superior Steelhead Association (LSSA) received funding from the Lessard-Sams Outdoor Heritage Council in 2012 to fund multiple project phases on the West Branch of the Knife River. The West Knife has received attention by LSSA due to historic reports of this tributary being important for anadromous rainbow trout (steelhead) reproduction, and because most of this watershed lies within public property. In past decades, this watershed has experienced logging, beaver activity, and barriers to migratory fish passage. In 2013 LSSA worked with the Minnesota Department of Natural Resources to improve fish passage conditions over the second falls of the Knife River. Mixed tree species were also planted in one beaver impacted meadow, and there are plans to expand the tree planting activities to other areas within the watershed in 2014. Pre-restoration surveys are important for demonstrating the effect of restoration activities. Good documentation of stream condition, and the organisms that live there, allow post-restoration comparisons, assessment of the most cost-effective restoration activities, and the ability to track trends over time. Natural Resources Research Institute staff were hired by LSSA to complete pre-restoration surveys of seven reaches on the West Branch Knife River; five on the main stem and two on tributaries. Fish and stream habitat were surveyed in all reaches, and aquatic macroinvertebrates were sampled in two reaches (reaches 2 and 3), with a cursory survey on a third reach (reach 1). The pre-restoration survey revealed that rainbow trout (steelhead) were present in all sampled reaches except the farthest upstream reach, which was apparently inaccessible to migratory fish due to beaver activity downstream. Brook trout were the dominant salmonid in all sampled reaches, and were at the greatest densities in the two small tributaries. One of these tributaries (reach 7) had indications of strong groundwater inputs based on water temperature and specific conductivity. This tributary appears to be an important area for brook trout reproduction and as a nursery for juveniles, but had few pools to hold larger fish. Stream bottom substrates in this tributary had large proportions of sand and silt, which are suboptimal habitat conditions for the aquatic macroinvertebrates that provide food for trout and other fish. Most pool habitats were found in downstream sections of the West Knife main stem that were influenced by beaver (reaches 1 and 2). However, these beaver meadow areas contained more nontrout species, which indicates these reaches may periodically have summer water temperatures above the thermal optimum for trout. The stream bottom in reaches 1 and 2 contained rocks that were surrounded and buried in sands, silts, and clays, reducing the amount of living space (habitat) for fish fry and aquatic macroinvertebrates. Thus, aquatic macroinvertebrate assemblages in these two reaches were in poorer condition (rated moderate-low) when compared to other North Shore streams NRRI researchers have sampled. Biotic habitat was best in reach 3, followed by reach 5 (both on the main stem, upstream of reaches 1 and 2). Reach 3 had the most young rainbow trout, as well as a nice population of brook trout, but the macroinvertebrate community was not in as good a condition as expected based on the very good habitat conditions. We speculate that the gravels in this reach are easily moved during high flow (flood) events; this lack of stream bottom stability leaves macroinvertebrates (and often fish fry) with few refugia from high flows, causing many of them to be dislodged and washed downstream. We speculate that this issue may be the reason why macroinvertebrate assemblages do not compare as favorably with those of other north shore streams as we expected. Reach 5 was located within a beaver meadow, but our stream measures indicate that the only measureable negative impact was a loss of riparian tree canopy to shade the stream.