Thomas A. Friesen

Management of Northern Pikeminnow and Implications for Juvenile Salmonid Survival in the Lower Columbia and Snake Rivers

Abstract Predation by large northern pikeminnow (formerly northern squawfish) Ptychocheilus oregonensis is a major source of mortality for juvenile salmonids Oncorhynchus spp. in the lower Columbia and Snake rivers. Large-scale, agency-operated fisheries have been implemented in this area since 1990 to harvest northern pikeminnow with a goal of 10–20% exploitation. We used indirect methods to analyze the success of the fisheries, and examined benefits to salmonid populations. From 1991 to 1996, three fisheries (sport-reward, dam-angling, and gill-net) harvested approximately 1.1 million northern pikeminnow that were 250 mm in fork length or longer, with the sport-reward fishery contributing 86.5% of the total catch. Total exploitation averaged 12.0% (range, 8.1–15.5) for 1991–1996 and met program goals in all years except 1993. Gill-net and dam-angling fisheries harvested larger northern pikeminnow (which consume a greater number of juvenile salmonids) than the sport-reward fishery. Modeling results indic...

Genetic Stock Composition of Subyearling Chinook Salmon in Seasonal Floodplain Wetlands of the Lower Willamette River, Oregon

Abstract We used genetic identification methods to examine the stock composition of subyearling Chinook salmon Oncorhynchus tshawytscha in floodplain wetland and main-stem habitats of the lower Willamette River, Oregon. Using a microsatellite DNA baseline of 13 standardized loci and 30 Columbia River basin populations, we analyzed 280 subyearlings collected in winter and spring 2005-2006 from wetland and main-stem river sites. Genetic stock identification analysis indicated that spring Chinook salmon originating from the Willamette River made up a substantial proportion of the samples and contributed 16-71% to sample mixtures representing the wetland habitat sites. Fall Chinook salmon from lower Columbia River sources were also present and contributed 58% of winter samples. Spring Chinook salmon from lower Columbia River populations were present in both wetland (17%) and river (16%) samples in spring 2005, and subyearlings from summer-fall-run populations in the middle and upper Columbia River contributed...

Smallmouth Bass in the Pacific Northwest: A Threat to Native Species; a Benefit for Anglers

As a popular sportfish, smallmouth bass (Micropterus dolomieu) generates considerable angling opportunities with benefits to local economies even outside of their native range. Smallmouth bass was first introduced to the Pacific Northwest region of North America as a sportfish over 80 years ago, and this species is now widely distributed. More recently, smallmouth bass have become a large component of the fish community in many streams, rivers, and lakes. Smallmouth bass thrive in the Pacific Northwest largely due to the habitat created by human modifications of the landscape. While a desired sportfish, smallmouth bass may also negatively affect native fishes. Of greatest concern is predation on threatened and endangered Pacific salmon; however, the current level of knowledge is inadequate to make informed management decisions for smallmouth bass. Management options for smallmouth bass are complicated further because fisheries agencies are simultaneously charged with enhancing fishing opportunities and controlling predators of threatened and endangered salmon. To advance conservation science, there is a need to determine the utility of different management approaches, and testing options in key areas of overlap between smallmouth bass and salmon is suggested.

Outmigration of Juvenile Chinook Salmon in the Lower Willamette River, Oregon

We used direct sampling and radio telemetry to describe the outmigration of juvenile Chinook salmon (Oncorhynchus tshawytscha) in the lower Willamette River downstream of Willamette Falls from 2000 to 2003. Juvenile Chinook salmon were present all year, with peak densities occurring in winter and spring. Small, naturally-produced (and therefore ESA-listed) fish were present in December and January, a period when in-water work (e.g. dredging) is authorized. Small fish were likely spring-run stocks that outmigrated as subyearlings. Juvenile Chinook salmon were significantly larger at downstream sampling sites, suggesting growth occurs, or larger fish entering from the Columbia River use this area as rearing habitat. Radio-tagged fish (>100 mm fork length) migrated at a median rate of 11.3 km/d, and hatchery fish migrated significantly faster than naturally-produced fish (12.4 vs. 8.4 km/d). Fork length and river flow were significant predictors of migration rate. Radio-tagged fish were distributed evenly across the river channel regardless of year, time of day, or origin (hatchery or naturally produced). Except for a possible affinity for pilings, the distribution of radio-tagged fish appeared to closely follow the proportional availability of nearshore habitat types, suggesting they do not select for specific habitats during their outmigration. We recommend that additional work focus on subyearling fish, which may have more specific habitat requirements and are more vulnerable to predation and other limiting factors. Considering the large number of subyearling juvenile Chinook salmon present during winter, restricting in-water work to July–October may help protect and recover these stocks.

Genetic Diversity and Population Structure of Spring Chinook Salmon from the Upper Willamette River, Oregon

AbstractEffective management of Pacific salmon requires an accurate understanding of both population genetic diversity and structure. Spring Chinook Salmon Oncorhynchus tshawytscha from the upper Willamette River (UWR), Oregon, are listed as threatened under the U.S. Endangered Species Act, and although this evolutionarily significant unit is recognized to be distinct from other Columbia River stocks, genetic relationships among its constituent hatchery and wild populations remain obscure. We used genotypic data from 13 microsatellite loci to test whether hatchery populations of UWR spring Chinook Salmon are most similar to wild populations within the same subbasin, or whether hatchery populations from different subbasins are more similar to each other than to local wild populations. We also tested for differences between the genetic diversities of hatchery and wild populations, as measured through heterozygosity and allelic richness. Our results suggest that populations are weakly structured among subbas...

Genetic Population Structure of Willamette River Steelhead and the Influence of Introduced Stocks

AbstractConservation genetics studies are frequently conducted on Pacific salmon Oncorhynchus spp. to delineate their population structure and to quantify their genetic diversity, especially for populations that have experienced declines in abundance and are subject to anthropogenic activities. One such group of salmonids is steelhead O. mykiss (anadromous Rainbow Trout) from the Willamette River, a tributary of the Columbia River. Within the Willamette River there are multiple steelhead life history and run-timing types, some of which originated from nonnative populations. Late winter-run steelhead and Rainbow Trout are native to the Willamette River, whereas early winter-run and summer-run steelhead have been introduced into the system via releases from artificial propagation efforts. We conducted genetic analyses of Willamette River steelhead to determine the effect that nonnative steelhead released into the Willamette River basin have had on the genetic population structure of native steelhead. We fou...

Infection of Juvenile Salmonids by Salmincola californiensis (Copepoda: Lernaeopodidae) in Reservoirs and Streams of the Willamette River Basin, Oregon

AbstractWe assessed infection prevalence and intensity by the ectoparasitic copepod Salmincola californiensis among salmonid species rearing in reservoirs and streams upstream of reservoirs in the Willamette River basin, Oregon, during 2012 and 2013. Infection levels of juvenile Chinook Salmon Oncorhynchus tshawytscha, Rainbow Trout O. mykiss, and Cutthroat Trout O. clarkii were greater in reservoirs than in streams and increased with the age and size of fish. Copepods were more likely to be attached within the brachial cavity of reservoir fish (79%), whereas fins were the most common attachment site on stream fish (71%). Chinook Salmon in reservoirs were more vulnerable to infection than other species. Age-0 Chinook Salmon in reservoirs showed increasing infection prevalence throughout the year, reaching 84% by fall (compared with 11% in streams). Infection intensity was greater for age-0 Chinook Salmon in reservoirs than for those in streams. Infection prevalence for reservoir-rearing Rainbow Trout was ...