Snake-Columbia River Research Articles

Determining Optimum Size at Release for Hatchery‐Origin Tucannon River Spring Chinook Salmon Using PIT Tags

AbstractThe Tucannon River spring Chinook Salmon Oncorhynchus tshawytscha hatchery program has consistently failed to reach the program target adult (age 4 and older) smolt‐to‐adult return (SAR) rate of 0.87%. This has resulted in the hatchery program falling short of meeting its hatchery adult return goal of 1,152 fish. To determine whether hatchery fish released at a larger size would increase the number of returning adults, we released 95,256 PIT‐tagged, hatchery‐origin spring Chinook Salmon with known FLs (range = 73–212 mm) categorized into five length‐classes (<120, 120–139, 140–159, 160–179, and ≥180 mm FL) over eight brood years (2006–2013) to examine how size at release affected the smolt‐to‐adult survival (SAS) rate to the Columbia–Snake River system and the SAR rate to the Tucannon River. We used this information to determine an optimum size range at release to maximize adult returns to the Tucannon River and determine whether the program target SAR of 0.87% was achieved by any of the length‐classes. Return of hatchery adults (age 4 and older) for both SAS and SAR peaked for the 140–159‐mm length‐class. Smaller size at release resulted in lower survival, whereas fish larger than this size range matured prematurely either as minijacks or jacks and the majority never made it back to the Tucannon River. Based on this study, to maximize adult returns, hatchery smolts from the Tucannon River spring Chinook Salmon hatchery program should be released in the 140–159‐mm range. None of the length‐classes came close to reaching the adult SAR target of 0.87% (SAR for fish that were 140–159 mm at release was 0.15%). The expectation that changes to smolt size will lead to reaching the 0.87% SAR target is unrealistic for this population under current hatchery rearing and environmental conditions.

Water Availability for Biorefineries in the Contiguous United States and the Implications for Bioenergy Production Distribution.

Renewable biofuel production depends on many factors, including feedstock availability, refinery and shipment infrastructure, and in particular, water availability. This study assesses water requirement and availability for mainstream biorefinery technologies in the contiguous United States (CONUS). The assessment is conducted in newly defined spatial units, namely, biorefinery planning boundaries, considering feedstock availability, transportation cost, and refinery capacity requirement for cost-effectiveness. The results suggest that the total biorefinery water use in the CONUS by 2030 will be low compared to the total water availability. However, biorefinery water requirements can aggravate the water stress situation in many regions, including the Great Plains, California Central Valley, and the upper Columbia-Snake River basin in Washington. Bioenergy productions in these regions can be largely constrained by water. It is projected that biofuel production will concentrate in Northern Plains, Lake States, and Corn Belt regions, which contribute 94.4% of the conventional, 86.1% of biodiesel, and 54.8% of cellulosic biofuel production mandated by the renewable fuel standard. If biorefineries are constrained to use less than 10% of the locally available water, up to 7% of planned cellulosic biofuel production will be affected. Findings from this study can aid the sustainable planning of national bioenergy production.

Technical fishway passage structures provide high passage efficiency and effective passage for adult Pacific salmonids at eight large dams

Fishways have been widely used for upstream passage around human-built structures, but ‘success’ has varied dramatically. Evaluation of fishway success has typically been conducted at local scales using metrics such as fish passage efficiency and passage time, but evaluations are increasingly used in broader assessments of whether passage facilities meet population-specific conservation and management objectives. Over 15 years, we monitored passage effectiveness at eight dams on the Columbia and Snake rivers for 26,886 radio-tagged spring-summer and fall Chinook Salmon O. tshwaytscha, Sockeye Salmon O. nerka, and summer steelhead O. mykiss during their migrations to spawning sites. Almost all fish that entered dam tailraces eventually approached and entered fishways. Tailrace-to-forebay passage efficiency estimates at individual dams were consistently high, averaging 0.966 (SD = 0.035) across 245 run×year×dam combinations. These estimates are among the highest recorded for any migratory species, which we attribute to the scale of evaluation, salmonid life history traits (e.g., philopatry), and a sustained adaptive management approach to fishway design, maintenance, and improvement. Full-dam fish passage times were considerably more variable, with run×year×dam medians ranging from 5–65 h. Evaluation at larger scales provided evidence that fishways were biologically effective, e.g., we observed rapid migration rates (medians = 28–40 km/d) through river reaches with multiple dams and estimated fisheries-adjusted upstream migration survival of 67–69%. However, there were substantive uncertainties regarding effectiveness. Uncertainty about natal origins confounded estimation of population-specific survival and interpretation of apparent dam passage ‘failure’, while lack of post-migration reproductive data precluded analyses of delayed or cumulative effects of passing the impounded system on fish fitness. Although the technical fishways are effective for salmonids in the Columbia-Snake River system, other co-migrating species have lower passage rates, highlighting the need for species-specific design and evaluation wherever passage facilities impact fish management and conservation goals.

In Search of a Cost‐Effective Approach for Estimating Dam Passage Survival

AbstractPassage of downstream‐migrating fishes through hydropower dams poses a management issue in rivers throughout the world. As such, regulations have been enacted at many locales to understand and limit fish losses by requiring dam passage survival estimation. However, limiting estimates of survival to the dam and immediate tailrace presents a challenge to researchers. In this study, two alternative release–recapture methods were used to estimate dam passage survival of juvenile salmonids through Lower Granite Dam on the Snake River, Washington, in 2018. One approach, the virtual/paired‐release (ViPRe) model, was extensively used in the Columbia–Snake River basin at federally operated hydroelectric dams during 2010–2014. This existing approach uses three releases of tagged smolts to isolate dam passage survival, defined as survival from the upstream dam face to the tailrace mixing zone 1–2 km downstream of the dam. An alternative approach, the virtual release/dead‐fish correction (ViRDCt) model, uses one live‐release group paired with a release of dead tagged fish at the dam to estimate the same survival parameter. The alternative estimation approaches were tested on two spring out‐migrating stocks, yearling Chinook Salmon Oncorhynchus tshawytscha and steelhead Oncorhynchus mykiss, and on a summer out‐migrating stock of subyearling Chinook Salmon. The alternative estimates for these stocks were all within 1 SE. However, the ViRDCt model produced survival estimates with SEs that were 59% smaller than those of the existing ViPRe model and did so using 42% fewer tagged fish and one less downstream acoustic detection array. Because of the reduced sample size, nearly US$540,000 less in tag costs and 4,000 fewer labor‐hours were required to implement the ViRDCt model compared to the ViPRe model. As such, the ViRDCt model represents a cost‐effective and precise approach to characterizing dam passage survival.

Steelhead Overshoot and Fallback Rates in the Columbia–Snake River Basin and the Influence of Hatchery and Hydrosystem Operations

AbstractTributary overshoot occurs when adult salmonids homing to natal sites continue upstream past the mouth of their natal stream. Although overshooting is a common behavior by steelhead Oncorhynchus mykiss in the Columbia River basin, it has not been adequately quantified or explained. Using multistate release–recapture models, we examined the prevalence of overshooting and fallback to natal tributaries by 37,806 PIT‐tagged steelhead from 14 tributaries of the Columbia River basin during 2005–2015. Eight populations had overshooting rates exceeding 50% in at least 1 year. Source of hatchery stock, rearing location, and release practices were found to have appreciable effects on overshoot rates. Overshooting was elevated in hatchery stocks reared upstream of release sites, but this effect may be lessened by utilizing endemic broodstocks and acclimating juveniles within the release basin. For one population of hatchery steelhead, acclimation within the release basin was found to decrease overshooting from 81% to 40%. Across both hatchery and wild populations, successful homing was found to decline 4 percentage points for every 5‐percentage‐point increase in overshoot rate. Average annual fallback probabilities ranged from 0.18 for Walla Walla River hatchery steelhead to 0.75 for Umatilla River wild steelhead. Fish stocks with the greatest fallback probabilities also had the greatest interannual variability in fallback rates. For John Day River wild steelhead and Tucannon River hatchery steelhead, the interannual range in fallback probabilities exceeded 0.50. We found evidence that spill at dams during March may enhance the fallback of overshooting steelhead and contribute to increased homing to natal tributaries. Therefore, additional attention should be paid to facilitating downstream dam passage of adult salmon.

Veligers of the invasive Asian clam Corbicula fluminea in the Columbia River Basin: Broadscale distribution, abundance, and ecological associations

ABSTRACTHassett W, Bollens SM, Counihan TD, Rollwagen-Bollens G, Zimmerman J, Katz S, Emerson J. 2017. Veligers of the invasive Asian clam Corbicula fluminea in the Columbia River Basin: broadscale distribution, abundance, and ecological associations. Lake Reserv Manage. 00:00–00.The invasive Asian clam Corbicula fluminea was introduced to North America in the 1930s and now inhabits most regions of the conterminous United States; however, the distribution and ecology of C. fluminea in the Columbia River Basin is poorly understood. During 2013 and 2014, 5 Columbia-Snake River reservoirs were sampled monthly from May through September, along with 23 additional lakes and reservoirs sampled once each summer. Associations among C. fluminea veligers, other components of the plankton, and environmental variables were analyzed using non-metric multidimensional scaling and canonical correspondence analysis. Corbicula fluminea veligers were found in high abundances in all mainstem Columbia-Snake River reservoirs, with an annual mean abundance of 71.2 individuals per cubic meter (inds./m3). Only 3 of 23 lakes and (non-mainstem) reservoirs contained C. fluminea, with abundances considerably lower (maximum = 21.2 inds./m3) than in the mainstem reservoirs. A diatom-dominated community preceded the spawning of C. fluminea in early summer at all sites. Corbicula fluminea veligers characterized the plankton community in late summer and were associated with cyanobacteria and high water temperatures. A third community, characterized by cyanobacteria, was apparent in non-mainstem sites in July and August. Our analyses describe the relationship of C. fluminea to the plankton community and environment, which contributes to our understanding of the possible effects of C. fluminea infestations and which waterbodies in the Columbia River Basin are at risk for infestation. Understanding the effects and environmental determinants of invasive mollusks will be increasingly important in the future with the possible arrival of zebra (Dreissena polymorpha) or quagga (D. bugensis) mussels to the region.

Continental Glacier meltwater contributions to late summer stream flow and water quality in the northern Wind River Range, Wyoming, USA

The Wind River Range in Wyoming contains more than 60 glaciers that are part of the headwaters for the Wind-Missouri, Green-Colorado and Snake-Columbia River systems. Continental Glacier lies on the crest of the northern Wind River Range and covers approximately 2.5 km2 with meltwater flowing into West Torrey Creek and the Wind River. Discharge measurements of upper Continental Glacier meltwater were made in August 2012 and 2014. Water samples were collected in 2014 for the analysis of stable isotopes, field parameters and 23 trace elements. This study demonstrated that Continental Glacier meltwater accounted for a mean of 32.91 ± 8.4 % of Torrey Creek flow, and 4.11 ± 18.38 % of Wind River flow as measured above Red Creek for August 2012 and 2014. Scaling of these results to all perennial snow and ice in the upper Torrey Creek basin yielded an estimate of 82.70 % contribution to Torrey Creek flow, and 10.32 % of Wind River flow above Red Creek, during August. Glacier meltwater contributions versus snow melt to Torrey Creek based on δ18O ratios ranged from 81.05 to 82.70 % of flow, with a mean of 81.88 ± 1.17 % for August 2014. Continental Glacier meltwater accounted for 89.99 % of nitrate-nitrite and 34.83 % of total phosphorus loading to Torrey Creek in August 2014. The pH of the snow and glacier meltwater was less than 6.0, likely the result of nitrate-nitrite and other atmospheric deposition. Finally, analysis of trace elements showed distinct differences between water sources.

Collaborations with Tribal Elders for Sustainability Education

Environmental sustainability studies are enhanced through local and regional partnerships between academicians and curriculum developers with members of area First Nation communities who have lived sustainably since time immemorial. Recent collaborative efforts between Seattle Pacific University’s School of Education and Snake River-Palouse tribal elder Carrie Jim Schuster have led to the development of a one semester, secondary level integrated history, geography, literature, and science curriculum investigating the indigenous peoples and environment of the Pacific Northwest’s Columbia-Snake River system. Seven core principles of cultural and environmental sustainability are discussed that were formulated through this collaboration involving Northwest tribal elders.

Public Perceptions of the Legitimacy of Water Governance Organizations in Nebraska and Washington

Environmental scholars propose increasing organizational legitimacy to improve the effectiveness of natural resource governance. This study applies Suchman's (1995) organizational legitimacy types to understand how Washington and Nebraska residents legitimize organizations involved in the governance of the Ogallala Aquifer and the Columbia–Snake River system. Using a representative survey, I explore the views of members of the public on which water governance organization they believe should be most responsible for resolving conflicts over their respective water system, and how they legitimize their selection. Results indicate almost half of Nebraska and Washington residents view state government as most responsible, followed by either local or federal government organizations. Findings also show similarities in the ways residents legitimize their selections, though multivariate analyses demonstrate certain legitimacy types are more predictive of a person's selection of one governance organization over another. This study shows the importance of balancing multiple legitimizing factors to effectively govern water resources.

Seasonal dynamics of zooplankton in Columbia–Snake River reservoirs, with special emphasis on the invasive copepod Pseudodiaptomus forbesi

The Asian copepod Pseudodiaptomus forbesi has recently become established in the Columbia River. However, little is known about its ecology and effects on invaded ecosystems. We undertook a 2-year (July 2009 to June 2011) field study of the mesozooplankton in four reservoirs in the Columbia and Snake Rivers, with emphasis on the relation of the seasonal variation in distribution and abundance of P. forbesi to environmental variables. Pseudodiaptomus forbesi was abundant in three reservoirs; the zooplankton community of the fourth reservoir contained no known non-indigenous taxa. The composition and seasonal succession of zooplankton were similar in the three invaded reservoirs: a bloom of rotifers occurred in spring, native cyclopoid and cladoceran species peaked in abundance in summer, and P. forbesi was most abundant in late summer and autumn. In the uninvaded reservoir, total zooplankton abundance was very low year-round. Multivariate ordination indicated that temperature and dissolved oxygen were strongly associated with zooplankton community structure, with P. forbesi appearing to exhibit a single generation per year. The broad distribution and high abundance of P. forbesi in the Columbia– Snake River System could result in ecosystem level effects in areas intensively managed to improve conditions for salmon and other commercially and culturally important fish species.

Fatty‐acid profiles of white muscle and liver in stream‐maturing steelhead trout Oncorhynchus mykiss from early migration to kelt emigration

The profiles of specific fatty acids (FA) in white muscle and liver of fasting steelhead trout Oncorhynchus mykiss were evaluated at three periods during their prespawning migration and at kelt emigration in the Snake-Columbia River of Washington, Oregon and Idaho, to improve the understanding of energy change. Twenty-seven FAs were identified; depletion of 10 of these was positively correlated in liver and white muscle of prespawning O. mykiss. To observe relative changes in FA content more accurately over sampling intervals, the lipid fraction of tissues was used to normalize the quantity of individual FA to an equivalent tissue wet mass. Saturated and monounsaturated FAs were depleted between upstream migration in September and kelt emigration in June, whereas polyunsaturated FAs were more conserved. Liver was depleted of FAs more rapidly than muscle. Three FAs were detected across all sampling intervals: 16:0, 18:1 and 22:6n3, which are probably structurally important to membranes. When structurally important FAs of O. mykiss are depleted to provide energy, physiological performance and survival may be affected.

Patterns of Population Structure Vary Across the Range of the White Sturgeon

AbstractCritical unknowns surrounding the basic biology of White Sturgeon Acipenser transmontanus have hindered management and conservation efforts. Population genetic data may be used to address some of these uncertainties, but previous examinations of population structure in White Sturgeon have been limited by the highly duplicated nature of the species’ genome. We report results from an analysis of White Sturgeon population structure within and among drainages using 13 polysomic microsatellite loci. Genetic diversity levels varied widely among regions, and the lowest levels were observed in the endangered Kootenai River Distinct Population Segment and the highest levels were detected in regions with access to estuarine and marine habitat. Patterns of within‐drainage population structure varied, and no structure was detected in the Sacramento–San Joaquin drainage and a complex pattern of isolation by distance was revealed in the Columbia–Snake River drainage. These results contrast a previously published evaluation of a White Sturgeon population structure in the Fraser River, which revealed several genetically distinct populations within a single drainage. Examination of population structure among drainages, including from samples collected across the species range, revealed six populations. Populations in the Sacramento–San Joaquin, Kootenai, lower Fraser, and upper Fraser River drainages were distinct. The complex isolation‐by‐distance pattern discovered in the within‐drainage analysis of the Columbia–Snake River drainage was supported by the among‐drainage population structure analysis. Our results provide little support for the practice of managing each impounded reach of the Columbia–Snake River system as a genetically distinct population as adjacent reaches show little to no genetic divergence in these analyses. Variation in patterns of population structure across the species range indicates that the scale of spawning site fidelity for White Sturgeon varies regionally, which has implications for recruitment failure mitigation.

Real-Time Assessment of the Columbia–Snake River Extended Lock Outage

Waterborne movements, one of the more economical methods of all modes of transportation, are a key component of the multimodal transportation system in the Pacific Northwest of the United States. The Columbia–Snake River system in the Pacific Northwest underwent a sustained lock outage from December 2010 to March 2011. This outage eliminated barge transportation on much of the upper Columbia River and all of the Snake River. Shippers, carriers, and ports on the river projected the impact of the loss of a major mode of transportation to be substantial and the impact on demands of other modes of transportation to be dramatic. A study done in real time took advantage of the disruption of the Columbia–Snake system to determine the dynamics of the overall process and the impacts of such a change induced by an outage. The study reported specifically on the Pacific Northwest wheat industry, 75% of downriver commodity movement. A transportation disruption like that of the extended lock outage on the Columbia–Snake River system had never occurred in the United States. The study authors were able to evaluate the logistic, economic, and environmental impacts of a sustained halt in barge transportation. Overall, Columbia–Snake River stakeholders were well prepared and managed to navigate the disruption in transportation without incurring inordinate costs at a net cost per bushel of 6 cents.

Assessing compliance with fish survival standards: a case study at Rock Island Dam, Washington

Abstract Safe fish passage through hydroprojects is of paramount importance in the Pacific Northwest of the United States where anadromous runs of salmon smolts pass through as many as nine dams on the Columbia River on their way to the ocean. Minimum survival standards through the dams or hydroprojects (i.e., reservoir and dam) have been established by the 2008 Federal Columbia River Power System (FCRPS) Biological Opinion or by Habitat Conservation Plans (HCPs) in order to protect salmon stocks. These federal requirements have prompted the need to conduct scientifically and statistically rigorous and precise smolt survival studies at federally and publicly operated hydroprojects throughout the Snake-Columbia River Basin. Successful studies have been the cooperative results of regulators, hydro managers, fish biologists, engineers, and biometricians working together to conduct these high value investigations. Rock Island Dam, Washington, is used as a case study where a total of 17 release-recapture studies were conducted over a nine-year period on three salmonid species to assess compliance with HCP survival standards.

Rethinking Dams: Pacific Salmon Recovery May Rest on Other Factors

Rethinking Dams: Pacific Salmon Recovery May Rest on Other Factors

Asian copepods on the move: recent invasions in the Columbia–Snake River system, USA

Abstract Cordell, J. R., Bollens, S. M., Draheim, R., and Sytsma, M. 2008. Asian copepods on the move: recent invasions in the Columbia–Snake River system, USA. – ICES Journal of Marine Science, 65: 753–758. Nine Asian copepod species have been introduced into the Northeast Pacific, seven of which are largely confined to the San Francisco estuary. However, several of these copepods recently invaded the Columbia–Snake River system in Washington state, USA. In addition to the calanoid copepod Pseudodiaptomus inopinus, which appeared in the 1980s, the Columbia River now has populations of the calanoids Pseudodiaptomus forbesi and Sinocalanus doerrii, and the cyclopoid copepod Limnoithona tetraspina. Sampling in the Columbia–Snake River system in 2005 and 2006 indicated that (i) newer invaders may have displaced the previously introduced P. inopinus; (ii) P. forbesi had moved upstream into the first five reservoirs in the system; (iii) the other species occurred only in the tidal regions of the lower river; (iv) P. forbesi dominates the late summer holoplankton in the lower river and estuary; and (v) P. forbesi is relatively rare, and the holoplankton is dominated by native species in upstream free-flowing segments of the Columbia River and in reservoirs of the Snake River. Zooplankton samples from ships in Puget Sound suggest that ballast water from California is a major source of the introduced copepods and that the Columbia River itself may be a new source of ballast-introduced copepods.

Overwintering Distribution, Behavior, and Survival of Adult Summer Steelhead: Variability among Columbia River Populations

AbstractUnlike most anadromous salmonids, summer steelhead Oncorhynchus mykiss overwinter in rivers rather than the ocean for 6–10 months prior to spring spawning. Overwintering in rivers may make summer steelhead more vulnerable to harvest and other mortality sources than are other anadromous populations, but there has been little systematic study of this life history strategy. Here, we used a large‐scale radiotelemetry study to examine the overwintering behaviors and distributions of 26 summer steelhead stocks within the regulated lower Columbia–Snake River hydrosystem. Over 6 years, we monitored 5,939 fish, of which 3,399 successfully reached spawning tributaries or the upper Columbia River basin and were assigned to specific populations. An estimated 12.4% of fish that reached spawning areas overwintered at least partially within the hydrosystem (annual estimates = 6.8–19.6%), while the remainder overwintered in tributaries. Across all populations, later‐arriving fish were more likely to overwinter in the hydrosystem; overwintering percentages ranged from less than 1% for fish tagged in June to over 40% for those tagged in October. Proportionately more interior‐basin steelhead (Clearwater, Salmon, and Snake River metapopulations) overwintered in the hydrosystem than did fish from lower‐river populations. Steelhead were distributed in mixed‐stock assemblages throughout the hydrosystem during winter, usually in reservoirs closest to their home rivers but also in nonnatal tributaries. Overwintering fish moved upstream and downstream between reaches in all months; a nadir occurred in early January and peak egress into spawning tributaries was in March. The estimated survival to tributaries was higher for fish that overwintered in the hydrosystem (82%) than for fish that did not (62%); this difference was largely attributable to low winter harvest rates. Our results suggest that large main‐stem habitats, including reservoirs, may be widely used by overwintering summer steelhead. The complex migration behaviors of steelhead indicate both the potential for adaptation and possible susceptibility to future river environment changes.

Understanding Grain Movements for Demand Estimation: The Columbia-Snake River System in Washington State

Grain producers and handlers in Washington State have benefited from a multimodal transportation network of roads, railroads, and the Columbia-Snake River barge system to move large amounts of grain effectively in a timely and economic manner. The competitive environment of the grain industry brings many changes, including the number of firms and houses, mergers, and modal competitiveness. Additionally, marketing strategies are affected because choices of available transportation modes reflect the decision processes of warehouses or firm managers. This aggregate study of grain marketing and transportation in the Pacific Northwest helps lay the groundwork for subsequent estimates of empirical demand. Such subsequent modeling attempts may include revealed and stated preference analysis in discrete choice demand models. A thorough understanding of the industry and market characteristics should improve empirical estimation efforts and produce more defensible policy analysis. Based on a 90% shipment volume response rate, results show that in the Columbia-Snake River grain situation, one destination absorbs more than 90% of shipments. Modal competition is active; barge has a market share of more than 50%, down 12-16% from 10 years ago. Multiple-car shipments have increased, but not drastically. Rates are consistently competitive over the period. Finally, grain demand is seasonal but generally has been stable over time. The revealed preferences from this aggregate analysis suggest that price elasticity may vary across shippers, times of movement, and modal availability.

Understanding Grain Movements for Demand Estimation

Grain producers and handlers in Washington State have benefited from a multimodal transportation network of roads, railroads, and the Columbia–Snake River barge system to move large amounts of grain effectively in a timely and economic manner. The competitive environment of the grain industry brings many changes, including the number of firms and houses, mergers, and modal competitiveness. Additionally, marketing strategies are affected because choices of available transportation modes reflect the decision processes of warehouses or firm managers. This aggregate study of grain marketing and transportation in the Pacific Northwest helps lay the groundwork for subsequent estimates of empirical demand. Such subsequent modeling attempts may include revealed and stated preference analysis in discrete choice demand models. A thorough understanding of the industry and market characteristics should improve empirical estimation efforts and produce more defensible policy analysis. Based on a 90% shipment volume response rate, results show that in the Columbia–Snake River grain situation, one destination absorbs more than 90% of shipments. Modal competition is active; barge has a market share of more than 50%, down 12–16% from 10 years ago. Multiple-car shipments have increased, but not drastically. Rates are consistently competitive over the period. Finally, grain demand is seasonal but generally has been stable over time. The revealed preferences from this aggregate analysis suggest that price elasticity may vary across shippers, times of movement, and modal availability.

A molecular phylogeny of aquatic gastropods provides a new perspective on biogeographic history of the Snake River Region

Mitochondrial DNA sequences of aquatic gastropods of the subgenus Pyrgulopsis (Natricola) were analyzed to test a commonly accepted hypothesis concerning the early history of the Snake River in the northwestern US. Distributions of Natricola and other regional biota were previously used to infer that the Snake River flowed to the Pacific through southeastern Oregon and northern California during the Neogene prior to its capture by the Columbia River in the late Pliocene (2Ma). A molecular phylogeny based on partial sequences of COI and NDI (1149bp) indicates that the Natricola clade is restricted to the modern Snake-Columbia River Basin and the Oregon Lakes region whereas northern California populations previously assigned to this subgenus belong to other lineages. The Natricola clade is not deeply subdivided into Oregon Lakes and Snake River Basin units consistent with late Pliocene fragmentation of the hypothesized paleodrainage, but instead is shallowly structured and contains multiple transitions among these two geographic areas. The strongly supported sister relationship between Natricola and a species from northwest Nevada (P. imperialis) is consistent with a recent proposal that the ancestral Snake River did not flow through southeast Oregon but instead flowed south to the Humboldt River. Within the context of this hypothesis, the multiple transitions between the Snake River Basin and the Oregon Lakes region that occurred within Natricola may be attributed to a late Pleistocene connection between these areas that was unrelated to the early course of the Snake River.