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The Problem
The Columbia and Snake rivers support several species of Pacific salmon that are listed under the Endangered Species Act. Adults migrate upriver from the ocean to spawn, and juveniles migrate downriver to the ocean. The series of hydroelectric facilities (dams) in the Columbia River Basin are obstacles to salmon as they make these migrations. The National Marine Fisheries Service is the federal agency responsible for setting guidelines for salmon recovery. Many of the guidelines that have been set address salmon passage issues at dams operated by the U.S. Army Corps of Engineers (COE). To meet these guidelines, the COE has undertaken a series of studies to improve downstream passage conditions for juvenile salmon. These studies are often designed to evaluate how effective certain dam operational conditions are at passing salmon over the dam, and how quickly they leave the area immediately below the dam (the tailrace). Large volumes of water are being spilled at lower Snake and Columbia river dams to divert juvenile salmon from passage through turbines and to reduce delays in their out migration to the ocean. The conditions in the tailrace are influenced by the dam operating conditions (e.g., how much water is being spilled) and can influence juvenile salmon survival. Impoundment of the river provides habitat and food sources for predators of juvenile salmon, like northern pikeminnow, smallmouth bass, and walleye. Juvenile salmon passing the dam can become disoriented or injured, and therefore be vulnerable to predation in the dam tailrace. This study is being conducted to evaluate how different patterns of spillway operation at John Day Dam affect juvenile salmon passage behavior and dispersal through the turbulent and complex tailrace environment. Objectives Our study objectives are to describe the behavior and distribution of radio-tagged juvenile salmon passed via different routes and different spill regimes into the tailrace of John Day Dam. The study will determine: 1) movement patterns of juvenile salmon in the immediate dam tailrace area 2) residence time/rate of travel from point of release until exit from the tailrace, and 3) relationships between route of travel and travel time. Methodology
This study uses radio telemetry to monitor the movements of juvenile salmon. Small (< 2 g) radio transmitters are implanted into the fish by inserting them into the gastric cavity. The transmitter has a 30-cm antenna, which is bent near the mouth of the fish so that it trails behind the fish as it swims. Radio-tagged fish are held in river water for 24 h following tag implantation, and are then released into specific study locations (e.g., into the spillway, juvenile bypass system or tailrace). Radio-tagged fish are monitored by both boat tracking and by fixed antenna arrays. The fixed arrays line
Highlights and Key Findings It is generally assumed that a greater proportion of spill will create tailrace conditions that aid tailrace egress, allowing the fish to exit the immediate dam area more readily. Our evaluation of egress in 2002 compared two spill conditions: 60% spill (60% of the total river flow went over the spillway, the remainder went through the turbines), and 30% spill (30% of the total river flow as spill). Radio-tagged fish were released through the juvenile bypass system and monitored in the tailrace. The findings were interesting in that fish released through the juvenile bypass system during the lower spill (30%) exited the tailrace more rapidly than those released during higher spill (60%). Concerns were raised that the large volume of water released over the spillway created an area of slack water near the juvenile bypass system outfall. It was hypothesized that fish released through the juvenile bypass system could become entrained in the slack water and delay their exit from the tailrace. Our findings were supported by a USGS evaluation of egress at JDA in 2000 that reported similar trends (more rapid egress under lower spill conditions). Where Are We Headed In 2003 This work will likely be repeated in 2003 under slightly different dam operating conditions. During the 2002 study, a concurrent USGS evaluation showed that the survival of juvenile salmon released under the high spill condition (60%) was much lower than that of fish released during the low spill (30%) condition. Combined, these findings suggested to the COE managers that tailrace egress conditions needed to be addressed. New spill regimes are currently under development, and some of them will be tested during 2003 through ongoing tailrace egress and survival evaluations. Project Contact Theresa Liedtke Email: theresa_liedtke@usgs.gov Publications |
