Evaluation of Culvert Influences on Seasonal Movements of Juvenile Salmonids, Slikok Creek, Alaska

This was a two year “before and after” assessment of juvenile fish passage at a road crossing of Slikok Creek in southcentral Alaska. Fish movements at a perceived barrier (old) culvert and its replacement (new) culvert were monitored using paired pass-through antennas located upstream and downstream of the culvert. Approximately 1,200 juvenile salmonids (Chinook, Oncorhyncus tshawytscha; coho, O. kisutch, and  Dolly Varden, Salvelinus malmo) were annually PIT tagged with 77% detected the first year and 99% the second year.

There was a significant improvement in downstream (z = -8.83, p < 0.01) and upstream (z = -2.38, p = 0.01) passage between the old and new culverts. Successful passage downstream was 44% and upstream was less than 1% at the old culvert. These values respectively improved to 79% and 54% with the new culvert. Fish accumulating at the culvert due to impeded passage was determined by the number of round trips fish made between paired antennas. The proportion of fish accumulating at both the upstream and downstream ends of the culvert was significantly greater for the old culvert than the new culvert (z = 3.48, p < 0.01; z = 27.17, p < 0.01; respectively).

Fish moved downstream through the old culvert at a wide range of discharges, including the highest (1.3m³/s). Of the five fish that passed upstream, four passed at discharges less than 0.5m³/s. Downstream and upstream fish passage through the new culvert occurred at most all discharge levels during the assessment, including the highest (1.8 m³/s). A flow duration curve showed the old culvert as a barrier to upstream passage at discharges above the 24% exceedance level while the new culvert allowed upstream fish passage at near 1% exceedance.

Before and after assessments of fish passage restoration projects are important in understanding how culverts and stream discharge effect fish movement and passage, ultimately contributing to improved culvert designs.

Recipient of American Fisheries Society, Fisheries Administration Section, 2009 Federal Aid in Sportfish Restoration Award.