Evaluation of the hydraulic and biological performance of the portable floating fish collector at Cougar Reservoir and Dam, Oregon, 2014

The biological and hydraulic performance of a new portable floating fish collector (PFFC) located in a cul-de-sac within the forebay of Cougar Dam, Oregon, was evaluated during 2014. The purpose of the PFFC was to explore surface collection as a means to capture juvenile salmonids at one or more sites using a small, cost-effective, pilot-scale device. The PFFC used internal pumps to draw attraction flow over an inclined plane about 3 meters (m) deep, through a flume at a design velocity of as much as 6 feet per second (ft/s), and to empty a small amount of water and any entrained fish into a collection box. Performance of the PFFC was evaluated at 64 cubic feet per second (ft³/s) (Low) and 109 ft³/s (High) inflow rates alternated using a randomized-block schedule from May 27 to December 16, 2014. The evaluation of the biological performance was based on trap catch; behaviors, locations, and collection of juvenile Chinook salmon (Oncorhynchus tshawytscha) tagged with acoustic transmitters plus passive integrated transponder (PIT) tags; collection of juvenile Chinook salmon implanted with only PIT tags; and untagged fish monitored near and within the PFFC using acoustic cameras. The evaluation of hydraulic performance was based on measurements of water velocity and direction of flow in the PFFC.

The PFFC collected 156 juvenile Chinook salmon and 280 individuals of other species, primarily dace (Cyprinidae) and largemouth bass (Micropterus salmoides). The collection included one of the 212 acoustic+PIT-tagged fish detected near the PFFC and two of the 1,505 PIT-tagged fish released near the head of the reservoir. No juvenile salmonids were collected between early July and early September when water temperatures near the water surface were greater than about 16 degrees Celsius (°C). Depths of acoustic+PIT-tagged fish indicated a preferential selection of water temperature of 13–15 °C, which was often deeper than the entrance to the PFFC, and those fish rarely were at depths with water temperatures greater than 16 °C. Dam passage of acoustic+PIT-tagged fish was similar to previous years, but much of the passage occurred prior to the date the PFFC began operation. Discovery Efficiency, the proportion of acoustic+PIT-tagged fish detected in the cul-de-sac that were within 10 m of the PFFC entrance and 0–6 m deep (the Discovery Zone), was 0.736 during the Low treatment and 0.639 during the High treatment. Entrance Efficiency, the proportion of fish in the Discovery Zone that were collected by the PFFC, was 0.007 during the Low treatment and 0.000 during the High treatment. Fish Collection Efficiency, the proportion of acoustic+PIT-tagged fish collected of those detected in the cul-de-sac, was 0.005 and 0.000 during the Low and High treatments, respectively. The areas of highest use by acoustic+PIT-tagged fish were between the stern of the PFFC and the outlet of the reservoir (a water temperature control tower), with the greatest use being near the tower.

Results from untagged fish detected with acoustic cameras indicated that most fish near and within the PFFC were in the 90–250-millimeter length bin and few were less than 60 millimeters long; most fish were present during crepuscular periods; trajectories of fish outside the PFFC were rarely directed toward the entrance; and many fish entering the PFFC swam back out before they could be collected.

The hydraulic performance of the PFFC did not achieve the design goals of smooth acceleration of inflow culminating in a peak water velocity of 6 ft/s and, as a result, the hydraulic performance likely contributed to the low biological performance. The greatest water velocity measured in the PFFC (1.87 ft/s) was lower than designed due at least in part to the PFFC being lower in the water column than expected. Additionally, difficulties during anchor deployment prevented placement of the PFFC as near to the reservoir outlet as planned, resulting in a PFFC position outside the prevailing flow field and known areas of high fish densities. Overall, the results indicate that location, hydraulic conditions, water temperature, and shallow depth of the entrance were among the factors contributing to the low biological performance of the PFFC in 2014.