39 research outputs found
Managed Metapopulations: Do Salmon Hatchery ‘Sources’ Lead to In-River ‘Sinks’ in Conservation?
Maintaining viable populations of salmon in the wild is a primary goal for many conservation and recovery programs. The frequency and extent of connectivity among natal sources defines the demographic and genetic boundaries of a population. Yet, the role that immigration of hatchery-produced adults may play in altering population dynamics and fitness of natural populations remains largely unquantified. Quantifying, whether natural populations are self-sustaining, functions as sources (population growth rate in the absence of dispersal, λ>1), or as sinks (λ<1) can be obscured by an inability to identify immigrants. In this study we use a new isotopic approach to demonstrate that a natural spawning population of Chinook salmon, (Oncorhynchus tshawytscha) considered relatively healthy, represents a sink population when the contribution of hatchery immigrants is taken into consideration. We retrieved sulfur isotopes (34S/32S, referred to as δ34S) in adult Chinook salmon otoliths (ear bones) that were deposited during their early life history as juveniles to determine whether individuals were produced in hatcheries or naturally in rivers. Our results show that only 10.3% (CI = 5.5 to 18.1%) of adults spawning in the river had otolith δ34S values less than 8.5‰, which is characteristic of naturally produced salmon. When considering the total return to the watershed (total fish in river and hatchery), we estimate that 90.7 to 99.3% (CI) of returning adults were produced in a hatchery (best estimate = 95.9%). When population growth rate of the natural population was modeled to account for the contribution of previously unidentified hatchery immigrants, we found that hatchery-produced fish caused the false appearance of positive population growth. These findings highlight the potential dangers in ignoring source-sink dynamics in recovering natural populations, and question the extent to which declines in natural salmon populations are undetected by monitoring programs
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Naturally spawning hatchery steelhead contribute to smolt production but experience low reproductive success
We used genetic mixture analyses to show that hatchery summer-run steelhead Oncorhynchus mykiss, an introduced life history in the Clackamas basin of Oregon, where only winter-run steelhead are native, contributed to the naturally produced smolts out-migrating from the basin. Hatchery-produced summer steelhead smolts were released starting in 197 1, and returning adults were passed above a dam into the upper Clackamas River until 1999. In the 2 years of our study, summer steelhead adults, mostly hatchery fish, made up 60% to 82% of the natural spawners in the river. Genetic results provided evidence that interbreeding between hatchery summer and wild winter steelhead was likely minor. Hatchery summer steelhead reproductive success was relatively poor. We estimated that they produced only about one-third the number of smolts per parent that wild winter steelhead produced. However, the proportions of summer natural smolts were large (36-53% of the total naturally produced smolts in the basin) because hatchery adults predominated on the spawning grounds during our study. Very few natural-origin summer adults were observed, suggesting high mortality of the naturally produced smolts following emigration. Counts at the dam demonstrated that hatchery summer steelhead predominated on natural spawning grounds throughout the 24-year hatchery program. Our data support a conclusion that hatchery summer steelhead adults and their offspring contribute to wild winter steelhead population declines through competition for spawning and rearing habitats. [References: 37
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Evaluations of Adult Fish Passage at Ice Harbor and Lower Monumental Dams, 1982.
Evaluations of adult fish passage at Ice Harbor and Lower Monumental Dams were conducted from 12 April to 16 June 1982. Each fishway entrance was monitored with electronic fish detectors and chinook salmon (Oncorhynchus tshawytscha) were radio tracked in the projects\u27 tailraces and fish collection systems. An additional study with electronic detectors was conducted from 23 August though 10 October 1982 at Lower Monumental Dam. The study was conducted during a year of unusually high spring river flows. High spill levels and reductions in powerhouse discharge were characteristic during the spring study at both projects; therefore, results may not fully describe fish behavior during all conditions of project operation. Spill did not occur during the fall study at Lower Monumental. Radio tagged fish characteristically held in areas several hundred feet downstream of the powerhouse at both projects. The behavior was related to high spill and low powerhouse discharge conditions and may have been a response to tailrace eddies that developed during these conditions. The most frequently used entrance into the Ice Harbor fishway under all conditions except low powerhouse discharge was located at the north end of the powerhouse next to the spillway. The next most frequently used entrance, and the most frequently used entrance during low powerhouse discharge, was on the shore at the south end of the powerhouse. The most commonly used entrance to the Lower Monumental fishway was on the shore at the north end of the powerhouse. The entrances at the south end of the Lower Monumental powerhouse, next to the spillway, had either net fallout or low net entry. The use of submerged orifice entrances along the powerhouse generally decreased with increased distance from the shore at both projects. Radio tagged fish moved both up and down the collection channels and held at the ends of the channels, particularly at the north end of the Ice Harbor fishway and near the base of the Lower Monumental powerhouse fish ladder. Also, tagged fish sometimes backed down the fish ladders, especially at the Ice Harbor powerhouse ladder. Several operational conditions were assessed at both projects. The operation of the ice and trash sluiceway at Ice Harbor was associated with decreased entry at the south end of the powerhouse and increased entry along the submerged orifice entrances. The entrances at the south end of the Lower Monumental powerhouse were opened in several combinations during the spring and fall research seasons to study the net fallout phenomenon at the entrances. Net fallout or very low net entry continued at the two entrances facing downstream into the tailrace during all conditions in the spring and fall. Net entry occurred at the entrance facing the spill basin during all conditions in the fall. Radio tagged fish were delayed a median of 118.6 hours at Ice Harbor and 44.8 hours at Lower Monumental. Probable causes of delay included holding downstream of the dams, fallout at the south end of the Lower Monumental fishway, fish backing down fish ladders and falling back over dams, holding at extensive movement in the collection channels, and recovery from handling and tagging stress
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Evaluation of Adult Fish Passage at Little Goose and Lower Granite Dams, 1981
Migratory movements of adult salmonids were studied from 20 April through 19 June 1981 to evaluate adult fish passage at Little Goose and Lower Granite Dams on the lower Snake River in southeastern Washington. Each fishway entrance was monitored with electronic fish detectors and chinook salmon (Oncorhynchus tshawytscha) were radio tracked in the projects\u27 tailraces and fishways. The most frequently used fishway entrances at Little Goose were the north shore and south shore entrances, which combined accounted for 65.3% of total net entries recorded by electronic detectors. At Lower Granite, the south shore entrance was the most heavily used on days without daytime spill discharges, while the north shore entrance was preferred on most spill days. The percentage of total entries at the north shore entrance increased with increasing spill levels up to 50 to 60 thousand cubic feet per second (kcfs), with use of the entrance tapering off again at higher spills. Radio tagged fish took about 1 to 1.5 days for passage at both projects during nonspill periods while up to 7.5 days were required to cross Lower Granite when spill discharges averaged above approximately 40 kcfs. Excessive delays during heavy spill were caused by fish holding downstream of the project and moving into areas on the north side of the navigation lock away from all fishway entrances. Spill occurred during the hours of data collection on 33 days of the 54 day research season at Lower Granite and on only 4 days at Little Goose, resulting in less information on spill effects on fish passage at Little Goose