Abstract

Environmental and ecological impacts must be considered when designing any engineering works. In rivers, streams and other aquatic systems, this, in part, means identifying changes to physical and chemical parameters affecting habitats of the aquatic community. Due to Provincial and Federal legislation, fish habitat is typically isolated as the key indicator of aquatic impacts as a consequence of instream works. Understanding where fish locate themselves, and why, makes evaluating the impacts and restoration of streams more efficient and effective. One way to predict where fish habitat is optimal is to identify locations in the stream where energetic costs are low and energetic benefits (food) are high for a given fish type. This bioenergetic approach to modeling provides a physically-based quantification of the total amount and quality of fish habitat available under different flow conditions and stream configurations.

For drift feeding fishes, such as salmon or trout (important fisheries), inputs to this type of model include stream velocities (from hydraulic models) and the number of invertebrates drifting in the water column within range of the fish location. Previous field investigations have shown that the number of invertebrates drifting is heterogeneous over space and time. In numerical modeling discussed in this chapter, invertebrate start position and behaviour can change the velocities experienced, and thereby substantially alter the invertebrate travel path in the water column. This may have an impact on fish habitat suitability if invertebrate densities on the stream bed are patchy or if invertebrate behaviours vary daily and/or seasonally. With more information on spatial food availability in the form of invertebrate drift dynamics, physically-based bioenergetic approaches could offer great improvements over conventional fish habitat models for streams.

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