Chief Joseph Kokanee Enhancement Project; Strobe Light Deterrent Efficacy Test and Fish Behavior Determination at Grand Coulee Dam Third Powerplant Forebay, 2005-2006 Annual Report.
- Pacific Northwest National Laboratory
The construction of Grand Coulee and Chief Joseph dams on the Columbia River resulted in the complete extirpation of the anadromous fishery upstream of these structures. Today, this area is totally dependent upon resident fish resources to support local fisheries. The resident fishing is enhanced by an extensive stocking program for target species in the existing fishery, including kokanee (Oncorhynchus nerka kennerlyi) and rainbow trout (O. mykiss). The kokanee fishery in Lake Roosevelt has not been meeting the return goals set by fisheries managers despite the stocking program. Investigations of physical and biological factors that could affect the kokanee population found predation and entrainment had a significant impact on the fish population. In 1999 and 2000, walleye (Sander vitreum) consumed between 15% and 9%, respectively, of the hatchery kokanee within 41 days of their release, while results from a study in the late 1990s estimated that entrainment at Grand Coulee Dam could account for up to 30% of the total mortality of the stocked fish. To address the entrainment loss, the Bonneville Power Administration commissioned a study to determine if fish would avoid areas illuminated by strobe lights in the forebay of the third powerplant. This work was conducted by Pacific Northwest National Laboratory (PNNL) in conjunction with the Confederated Tribes of the Colville Reservation (Colville Confederated Tribes). From 2002 through 2004, six strobe lights were suspended in the center of the opening to the third powerplant forebay during summer months. Results from those studies indicated that fish appeared to be attracted to the illuminated area but only at night and when flow conditions within the third powerplant forebay were minimal. However, small but consistent results from these studies indicated that under high flow conditions, fish might be avoiding the lights. The 2005 study was designed to examine whether, under high flow conditions near the penstock openings, fish would avoid the lighted regions. Four omnidirectional strobe lights were deployed on the one trash rack directly in front of one turbine penstock. Seven splitbeam transducers were deployed to monitor fish approaching three penstock openings either from in front of the trash racks or moving down the dam behind the trash racks. Four key results emerged from the 2005 study. The results provide insight into the current level of entrainment and how fish respond to strobe lights under high flow conditions. First, very few fish were detected inside the trash racks. Of the more than 3,200 targets identified by the data processing, less than 100 were detected inside the trash racks. Only 23 fish were found inside the trash racks behind the strobe lights. Of those 21 fish, 13 were detected when the lights were on. Most of the fish detected behind the trash racks were above the turbine penstock but were headed downward. No fish were detected at night when minimal flows occurred between midnight and 4:00 a.m. Second, significantly more fish (P < 0.001) were detected in front of the trash racks when the lights were on at night. On a count-per-hour basis, the difference between lights off and lights on was apparent in the early morning hours at depths between 25 m and 50 m from the transducers. The lights were approximately 34 m below the splitbeam transducers, and fish detected at night with lights on were found at a median depth of approximately 35 m, compared to a median depth of from 20.6 to 23.5 m when the lights were off. The differences in depth between lights on and off at night were also significant (P < 0.001). Additionally, the increase in fish occurred only in front of the trash rack where the strobe lights were mounted; there was no increase in the number of detections by the transducers aimed away from the lights. Third, fish clearly manifested a behavioral response to the strobe lights during the day. When the lights were on, fish detected by three of the four transducers generally were swimming north, parallel to the face of the dam. However, the distribution of swimming directions for fish detected by the transducer immediately to the north of the lights was bimodal, with some fish swimming south toward the lighted region. This behavior was similar to that seen at night when the lights were on. Fourth, kokanee, rainbow trout, and walleye were detected near the strobe lights. Data were obtained from three sources: fish size from the hydroacoustic sensors and fish species from gill netting and video recording. Fish ranging in length from 30 to 600 mm (averaging 125 mm) were detected by the splitbeam transducers. There was little difference in target strength for fish detected above 25 m depth with respect to time of day or light treatment. Below 25 m and closer to the strobe lights, larger fish were present when the lights were on during the night, and smaller fish were present during the day.
- Research Organization:
- Bonneville Power Administration (BPA), Portland, OR (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- 652 REL 15
- OSTI ID:
- 962004
- Report Number(s):
- DOE/BP-00000652-33; R&D Project: 1995-011-00; TRN: US200915%%381
- Country of Publication:
- United States
- Language:
- English
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