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Managing intraspecific hybridization is crucial for maintaining a balance between inbreeding and outbreeding depression in winter and summer run steelhead (Oncorhynchus mykiss). While spatial distance is a common factor in maintaining reproductive isolation between these two ecotypes, physical barriers may also prevent hybridization, particularly in short river systems. To determine the effect of barriers and their removal on hybridization, we studied winter and summer steelhead populations in the Siletz River of northern coastal Oregon, which were historically separated by a physical barrier that was removed in the 1950s. We observed a large degree of admixture in the summer run population but little in the summer hatchery or wild winter populations, the former of which was established shortly after the removal of the barrier. This suggests that the high level of admixture in the wild summer run may be due to the removal of the barrier. We also found reduced genetic diversity in the wild summer run and in both hatchery populations. This highlights the need to balance inbreeding and outbreeding depression in hybridizing subpopulations.

A fish ladder designed to facilitate fish passage at the outlet end of perched culverts is investigated with a 3D computational fluid dynamics model. The fish ladder consists of a series of alternating arch baffles with geometries providing options for fish passage over varying flow and debris conditions within the ladder. At high flows, the baffle’s protruding center arch increases pool depth, reducing the volumetric bulk turbulence of the pools and improving fish habitat. The arch baffle is compared to a standard baffle design currently in use and demonstrates potential advantages for fish passage. A recirculation zone of low velocity occupies a large volume of the pool believed to provide appropriate hydraulic habitat for resting and staging jump attempts upstream. This numerical study provides an acceptable design for future physical prototype testing in the laboratory or field to verify hydraulics and evaluate fish passage effectiveness.

Following construction of a fish ladder at Landsburg Diversion Dam on the Cedar River, Washington, USA, in fall 2003, we used DNA-based parentage to identify second generation Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon as recruits that were produced above the dam or “strays” dispersing into the new habitat that were produced elsewhere. For both species, strays colonized immediately but decreased as a proportion of the total run over time. Chinook salmon strays were more numerous in years when the species was more abundant below the dam and included a much larger proportion of hatchery origin salmon than did coho salmon. Productivity, calculated as the ratio of female recruits sampled at the dam to female spawners, exceeded replacement in all four coho salmon cohorts but only two of five Chinook salmon cohorts, leading to more rapid population expansion of coho salmon. However, estimates of fishing mortality and recruitment into the Cedar River below the dam substantially increased Chinook salmon productivity estimates. Our results demonstrate that Pacific salmon are capable of rapidly recolonizing habitat made accessible by restoration and emphasize the importance of demographic exchange with preexisting populations during the transition from recolonization to self-sustainability.

Diadromous fish are an important link between marine and freshwater food webs. Pacific salmon ( Oncorhynchus spp.) strongly impact nutrient dynamics in inland waters and anadromous alewife ( Alosa pseudoharengus ) may play a similar ecological role along the Atlantic coast. The annual spawning migration of anadromous alewife contributes, on average, 1050 g of nitrogen and 120 g of phosphorus to Bride Brook, Connecticut, USA, through excretion and mortality each year. Natural abundance stable isotope analyses indicate that this influx of marine-derived nitrogen is rapidly incorporated into the stream food web. An enriched δ15N signal, indicative of a marine origin, is present at all stream trophic levels with the greatest level of enrichment coincident with the timing of the anadromous alewife spawning migration. There was no significant effect of this nutrient influx on water chemistry, leaf decomposition, or periphyton accrual. Dam removal and fish ladder construction will allow anadromous alewife to regain access to historical freshwater spawning habitats, potentially impacting food web dynamics and nutrient cycling in coastal freshwater systems.

This technical note presents a method of analyzing the flow in pool-orifice fishways by dividing it into vertical slot and submerged orifice flow regimes. For a pool-orifice-weir fishway, with flow through the orifice as well as over the weir, a method has been suggested for predicting the total flow rate in the fishway. Experimental observations are presented in support of these methods. Key words: open-channel flow, hydraulics, fishways, turbulent flow.

A series of tests were conducted to investigate the sense of smell in migrating coho (Oncorhynchus kisutch) and spring salmon (O. tshawytscha). By pouring dilute solutions of each of 54 substances into the path of the salmon moving up a fish ladder at Stamp Falls, B.C., positive responses were noted by recording changes in the rate of migration. Representative samples of alcohols, aldehydes, ketones, esters, organic acids and oils, as well as shark repellent and a pulp-mill effluent caused no significant change in the migration. However, dilute water rinses of mammalian skins had distinct repellent action. An acute olfactory sense enabling adult Pacific salmon to detect predators from a downstream position was considered to have survival value. The use of mammalian predator skins to repel salmon from destructive river locations is suggested.

A device that can be used for rapid detection and separation of migrating adult coho salmon marked as juveniles with magnetized wire tags was tested in November and December 1967 at the Minter Creek Hatchery of the Washington Department of Fisheries. About two-thirds of the test fish in the holding pond entered the structure; the device correctly separated 89% of the fish with tags and 99% of the untagged fish. Placement of this equipment in streams, fish ladders at dams, and in hatcheries, would facilitate removal of tagged specimens from the general population of fish.

Columbia River fish ladders were surveyed as a possible ecological niche for Chondrococcus columnaris, the causative agent for columnaris disease of fishes. Water samples from Bonneville, McNary, Priest Rapids, and Rocky Reach fish ladders during periods of warm-water temperature and high population density of fishes showed C. columnaris levels of from 0.06 to 4.1 organisms/ml. Samples taken upstream or downstream from the ladders were consistently negative. Average agglutinating titers and incidence of C. columnaris infection in largescale suckers were higher at the Bonneville ladder than at a site several miles downstream Coho salmon from an upper-river fish ladder (Rocky Reach) showed a higher incidence of infection and greater antibody production than at the downriver Bonneville ladder. It is concluded that fish-ladder facilities on the Columbia River are important sites for repetitive exposure of anadromous salmonids to C. columnaris.

Blood lactic acid concentration of anadromous alewives (Alosa pseudoharengus) sampled during their upstream migration through a pool and weir fishway was not extremely high (46.7 mg/100 ml) and the degree of exercise exhibited during ascent was judged to be moderate. For fish that were subjected experimentally to severe exercise, the concentration (108.7 mg/100 ml) was more than five times that for rested fish (18.9 mg/100 ml). Of the three groups of fish sampled directly from the fishway pools, only one had an average concentration that differed significantly from that for the rested state.