Lower Granite Research Articles

Ecology of nonnative Siberian prawn (Palaemon modestus) in the lower Snake River, Washington, USA

We assessed the abundance, distribution, and ecology of the nonnative Siberian prawn Palaemon modestus in the lower Snake River, Washington, USA. Analysis of prawn passage abundance at three Snake River dams showed that populations are growing at exponential rates, especially at Little Goose Dam where over 464,000 prawns were collected in 2015. Monthly beam trawling during 2011–2013 provided information on prawn abundance and distribution in Lower Granite and Little Goose Reservoirs. Zero-inflated regression predicted that the probability of prawn presence increased with decreasing water velocity and increasing depth. Negative binomial models predicted higher catch rates of prawns in deeper water and in closer proximity to dams. Temporally, prawn densities decreased slightly in the summer, likely due to the mortality of older individuals, and then increased in autumn and winter with the emergence and recruitment of young of the year. Seasonal length frequencies showed that distinct juvenile and adult size classes exist throughout the year, suggesting prawns live from 1 to 2 years and may be able to reproduce multiple times during their life. Most juvenile prawns become reproductive adults in 1 year, and peak reproduction occurs from late July through October. Mean fecundity (189 eggs) and reproductive output (11.9 %) are similar to that in their native range. The current use of deep habitats by prawns likely makes them unavailable to most predators in the reservoirs. The distribution and role of Siberian prawns in the lower Snake River food web will probably continue to change as the population grows and warrants continued monitoring and investigation.

Acclimation Enhances Postrelease Performance of Hatchery Fall Chinook Salmon Subyearlings While Reducing the Potential for Interaction with Natural Fish

AbstractOne form of prerelease acclimation of hatchery anadromous salmonid Oncorhynchus spp. juveniles is to truck the fish to remote points for extended holding at low densities in rearing vessels (e.g., tanks, raceways, or in‐ground ponds) supplied with river water. We conducted a 3‐year study to determine whether such acclimation enhanced the postrelease performance of hatchery fall Chinook Salmon O. tshawytscha subyearlings and reduced the potential for interaction with natural fall Chinook Salmon subyearlings. In comparison with hatchery subyearlings that were released directly into the lower Snake River just downstream of the acclimation facility, acclimated hatchery subyearlings (1) passed downstream to Lower Monumental Dam (the third dam encountered during seaward migration) faster, (2) passed the dam earlier, and (3) survived from release to the dam tailrace at higher rates. The differences in downstream passage rate and dam passage timing were also much greater between acclimated hatchery subyearlings and natural subyearlings than between directly released hatchery subyearlings and natural subyearlings. Thus, acclimation provided a survival advantage to the hatchery fish while reducing the potential for (1) aggressive and nonaggressive social interactions with natural fish while in transit through the reservoirs associated with Lower Granite, Little Goose, and Lower Monumental dams; and (2) confinement with natural fish at those three dams, where fish collection and raceway holding were followed by transport in tanker trucks. Our findings support acclimation as a method for enhancing postrelease performance of hatchery fall Chinook Salmon subyearlings and reducing their potential interactions with natural conspecifics.Received July 25, 2012; accepted January 9, 2013

Estimation of smolt-to-adult return percentages for Snake River Basin anadromous salmonids, 1990–1997

From numbers of juvenile salmonids (smolts) tagged between 1990 and 1997 with passive-integrated-transponder (PIT) tags and detections at downstream hydropower projects on the lower Snake and Columbia Rivers, we applied and adapted stratified tagrecapture methods to estimate the number of PIT-tagged smolts that experienced each possible detection history through the dams. Using adult detection recordsupon, return after 1–3 years of ocean residence, we estimated smolt-to-adult return (SAR) percentages for fish in detection-history categories that included downstream barge transport, migration in-river following detection, and migration in-river with no detection. We used bootstrap methods to estimate 95% confidence intervals for estimated SARs and ratios of SARs for selected detection-history categories. In general, though small numbers of returning adults and statistical uncertainty at various stages of the estimation procedure led to fairly imprecise SAR estimates, some general trends were evident. Adult return percentages for spring/summer yearling chinook salmon and steelhead were highest for fish transported from Lower Granite and Little Goose Dams but only slightly higher than for nondetected fish. Passage routes of nondetected fish (through spill and turbines) may represent optimal passage conditions. Once a juvenile fish is entrained in a bypass system ata “collectordam,” transporting the fish maximizes the probability of its eventual return as an adult.

Fall Chinook Salmon Spawning in the Tailraces of Lower Snake River Hydroelectric Projects

Abstract We conducted studies from 1993 to 1997 to identify and characterize potential spawning habitat of “endangered” fall chinook salmon Oncorhynchus tshawytscha in areas downstream of four Snake River dams. This information was needed to provide guidelines for future operation of the lower Snake River hydroelectric system, including assessment of reservoir drawdown, and for site-specific construction planning. We used Geographic Information System mapping technology to direct our initial search efforts. Suitable spawning habitat was defined based on physical habitat characteristics of the tailrace areas. Redd surveys were conducted in primary search areas and planned construction sites from mid-November through December with an underwater video system. The survey path and redd locations were mapped by using a Global Positioning System. During the 4-year study, fall chinook salmon redds were found in the tailrace downstream of Lower Granite (LGR), Little Goose (LGO), and Ice Harbor (IH) dams. The redds...

A multiple-reach model describing the migratory behavior of Snake River yearling chinook salmon (Oncorhynchus tshawytscha)

A multiple-reach model was developed to describe the downstream migration of juvenile salmonids in the Columbia River system. Migration rate for cohorts of fish was allowed to vary by reach and time step. A nested sequence of linear and nonlinear models related the variation in migration rates to river flow, date in season, and experience in the river. By comparing predicted with observed travel times at multiple observation sites along the migration route, the relative performance of the migration rate models was assessed. The analysis was applied to cohorts of yearling chinook salmon (Oncorhynchus tshawytscha) captured at the Snake River Trap near Lewiston, Idaho, and fitted with passive integrated transponder (PIT) tags over the 8-year period 1989-1996. The fish were observed at Lower Granite and Little Goose dams on the Snake River and McNary Dam on the Columbia River covering a migration distance of 277 km. The data supported a model containing two behavioral components: a flow term related to season where fish spend more time in regions of higher river velocity later in the season and a flow-independent experience effect where the fish migrate faster the longer they have been in the river.

Focal depth distribution of Swedish earthquakes

Instrumental and macroseismic focal depths of Swedish earthquakes show statistically a high degree of correlation. The majority of the earthquakes is located in the lower granite, probably associated with a low-velocity layer, whereas crustal discontinuities appear to be relatively less seismic.