Klamath Lake Research Articles

Physiological Development and Vulnerability to Ceratomyxa shasta of Fall‐Run Chinook Salmon in the Upper Klamath River Watershed

AbstractWe evaluated a stock for restoring runs of fall Chinook salmon Oncorhynchus tshawytscha in the Upper Klamath River basin by monitoring its development in Iron Gate Hatchery and in net‐pens in the Williamson River and Upper Klamath Lake in Oregon. We transferred age‐1 hatchery fall Chinook salmon to net‐pens in October 2005 and age‐0 fall Chinook salmon in May 2006. Indices of smolt development were assessed in the hatchery and after 3 and 14 d in net‐pens. Based on gill Na+, K+‐ATPase activity and plasma thyroxine (T4) concentration, age‐1 Chinook salmon were not developing smolt characteristics in the hatchery during October. Fish transferred to the river or lake had increased plasma cortisol in response to stress and increased T4 accompanying the change in water, but they did not have altered development. Variables in the age‐0 Chinook salmon indicated that the fish in the hatchery were smolting. The fish in the river net‐pens lost mass and had gill ATPase activity similar to that of the fish in the hatchery, whereas the fish transferred to the lake gained mass and length, had reduced condition factor, and had higher gill ATPase than the fish in the river. These results, along with environmental variables, suggest that the conditions in the lake were more conducive to smoltification than those in the river and thus accelerated the development of Chinook salmon. No Chinook salmon in the hatchery or either net‐pen became infected with the myxosporean parasite Ceratomyxa shasta (the presence of which in the river and lake was confirmed) during either trial or when held for 90 d after a 10‐d exposure in net‐pens (2006 group). We concluded that that there is little evidence of physiological impairment or significant upriver vulnerability to C. shasta among this stock of fall Chinook salmon that would preclude them from being reintroduced into the Upper Klamath River basin.

Threatened fishes of the world: Deltistes luxatus (Cope 1879) (Catostomidae)

Common name: Lost River sucker, mullet, c’waam. Conservation status: Endangered: (USFWS 1988; Gimenez Dixon 1996). Identification: D 10–12, LL 82–113, gill rakers 23–37 in adults >200 mm, 44–48 post-Weberian vertebrae. Elongate body with long, narrow head, long snout, small eyes. Upper lip thin (two to five rows of large papillae). Lower lip (one to three rows of papillae) deeply notched. Adults up to 1 m TL and 4.5 kg. Maximum recorded age: 43 years. Illustration by Joe Tomelleri. Distribution: Historically widely distributed in upper Klamath and Lost River basins (Oregon/California). Limited to the following lakes/rivers and their tributaries: Upper Klamath Lake, Clear Lake, Lost River, Tule Lake, and Klamath River to Copco Reservoir. Abundance: Historically very abundant; sufficiently abundant to support a fishery. Long-term abundance data limited, but dramatic decline evident (NRC 2004). Current population size estimated in the tens of thousands (USFWS 2007). Low recruitment and low adult survival may indicate future declines (USFWS 2007). Habitat and ecology: Lakes: shallow depths, cool water (16–24°C), moderate alkalinity (pH 7.2– 9.2), DO levels of 6–10 mg/L (Moyle 2002). Feeds benthically on detritus and invertebrates. Reproduction: Spawns at shoreline lake springs and in tributaries from February–May in shallow riffle/run habitat with gravel substrate and moderate current. Matures between 5– 9 years (Scoppettone and Vinyard 1991); most mature by age 9. Iteroparous. Threats: Current threats include hyper-eutrophication of Upper Klamath Lake and mass mortality of adults; loss of aquatic marsh habitat from drainage of wetlands for agriculture; conflicting water management goals; and predation of larvae by nonnative species. Some measures addressing limited access to spawning areas by dams and entrainment by water control structures are underway. Conservation action: ESA listing prompted wetland/riparian restoration, dam removal, and fish screening/passage programs. Remarks: Recovery is complicated by the long life span, episodic recruitment, and multiple demands on water management of the upper Klamath Basin. Environ Biol Fish (2009) 86:401–402 DOI 10.1007/s10641-009-9530-3

Evolutionary Ecology of Redband Trout

AbstractWe examined genetic differences at 29 enzyme encoding loci among 10,541 rainbow trout Oncorhynchus mykiss from 240 collections throughout the species' range, including redband trout (i.e., several rainbow trout subspecies) in pluvial lake basins of the northern Great Basin that have had largely internal drainage with no connection to the Pacific Ocean. Differences among groups accounted for 29.2% of the genetic variation. Although we observed major genetic differences between coastal and inland groups (10.7%), which are currently considered to represent the major phylogenetic division in the species, we found that the greatest evolutionary divergence (19.7%) was related to persistence of three major river systems: The upper Sacramento, Klamath, and Columbia rivers. Genetic traits of redband trout from the northern Great Basin, where we found distinct subspecies or races, indicated that over millennia these pluvial habitats were sources of evolutionary diversity associated with large river systems rather than completely isolated refugia. However, redband trout did not constitute a distinct monophyletic group. Based on our data, redband trout of the Goose Lake, Warner Valley, and Chewaucan basins were distinct genetic races that were part of the diverse complex of Sacramento redband trout O. mykiss stonei. Harney Basin redband trout were a unique genetic race most closely associated with Columbia River redband trout O. mykiss gairdneri. White River and Fort Rock redband trout were associated with the Columbia River but showed allelic divergence comparable with that among other subspecies. Upper Klamath Lake rainbow trout included a previously unrecognized group associated with populations in the headwaters of the basin and a different subspecies from type locations for Upper Klamath Lake redband trout O. mykiss newberrii (i.e., Upper Klamath Lake and the upper Klamath River). The relationship of redband trout from the Catlow Valley to any of these other groups remained unresolved.

Use of satellite data to assess the impacts of irrigation withdrawals on Upper Klamath Lake, Oregon

Abstract. Competition for scarce water resources in the Upper Klamath River Basin, Oregon has generated conflict among its stakeholders, as demonstrated by recent regulations on withdrawals from Upper Klamath Lake. Information on agricultural water usage can help assess the hydrologic impacts of irrigation and support operational decisions. This paper presents an experimental satellite-based evapotranspiration estimation system that is combined with the Variable Inflitration Capacity (VIC) hydrological model to estimate irrigation consumption, which is then used to assess the effects of irrigated agriculture on lake storage volumes and water levels. The hydrological model is calibrated with streamflow observations and used to estimate unmeasured lake inflows and guide water budget calculations. When combined with the VIC model, the satellite-based evapotranspiration estimation system shows that irrigation caused a decline of 0.3 m in average annual water levels and 0.5 m in mean October water levels, and an increase of 0.5 m in annual water level ranges at the lake from 2001 to 2005. The results demonstrate the potential of satellite data for agricultural water resource management at the regional scale.

Phosphorus Fractionation in Sediment Cores Collected In 2005 Before and After Onset of an Aphanizomenon flos-aquae Bloom in Upper Klamath Lake, OR, USA

We tested the hypothesis that there would be measurable losses of phosphorus (P) from surficial sediments of Upper Klamath Lake (UKL), Oregon, if sediments were a source of P during an algal bloom. We compared concentrations of total and forms of P at various depths in cores collected before and after the onset of a large Aphanizomenon flos-aquae bloom. Concentrations of inorganic P were determined in extraction solutions of MgCl2 (1 M, pH 8), citrate-dithionite-bicarbonate, and 1 M HCl. Sediments below 2 cm were dominated by residual P which is defined as total P minus inorganic P. During the study period, data from the top 2-cm of sediment indicated (a) significant decrease in total P concentration, primarily associated with iron oxyhydroxides at one site, and (b) significant increase in total P concentration associated with residual P at a second site. Data from two other sites indicated no net changes in concentrations of total P.

Larval Fish Transport and Retention and the Importance of Location for Juvenile Fish Recruitment in Upper Klamath Lake, Oregon

AbstractIn the Upper Klamath Lake basin of Oregon, we applied the member‐vagrant hypothesis to larval lake fishes, documented marsh and hydrographic retention for larval shortnose suckers Chasmistes brevirostris and Lost River suckers Deltistes luxatus, and examined the effect of larval retention on the shoreline abundance of the juveniles of five species of fish in August. Emigration of larval suckers was highest from natal rivers, and immigration was highest in nonnatal areas downstream of the lake. Lake retention was facilitated by a wind‐generated gyre and advection by an eastern boundary current. Marshes and other shoreline irregularities acted as traps that slowed river and eastern boundary current advection and retained larvae, especially for shortnose suckers, for up to 3 weeks. The interaction of behavior, seasonal spawning, and seasonal system dynamics appears to drive retention patterns. For both species of suckers and three minnow species (fathead minnow Pimephales promelas, blue chub Gila coerulea, and tui chub G. bicolor), the abundance of juveniles along the shoreline increased with distance from the lake outlet and was weakly related to lake elevation, a surrogate for available habitat. For these five species, 45.5% of the variation in August juvenile abundance was determined by distance from the lake outlet. This work suggests that the nonbehavioral component of freshwater retention is complex and depends on hydrographic features, the boundary conditions of hydrographic features, and shoreline habitat.

Benthic nutrient sources to hypereutrophic Upper Klamath Lake, Oregon, USA

Three collecting trips were coordinated in April, May, and August 2006 to sample the water column and benthos of hypereutrophic Upper Klamath Lake (OR, USA) through the annual cyanophyte bloom of Aphanizomenon flos-aquae. A pore-water profiler was designed and fabricated to obtain the first high-resolution (centimeter-scale) estimates of the vertical concentration gradients of macro- and micronutrients for diffusive-flux determinations. A consistently positive benthic flux for soluble reactive phosphorus (SRP) was observed with solute release from the sediment, ranging between 0.4 and 6.1 mg/m(2)/d. The mass flux over an approximate 200-km(2) lake area was comparable in magnitude to riverine inputs. An additional concern related to fish toxicity was identified when dissolved ammonium also displayed consistently positive benthic fluxes of 4 to 134 mg/m(2)/d, again comparable to riverine inputs. Although phosphorus was a logical initial choice by water quality managers for the limiting nutrient when nitrogen-fixing cyanophytes dominate, initial trace-element results from the lake and major inflowing tributaries suggested that the role of iron limitation on primary productivity should be investigated. Dissolved iron became depleted in the lake water column during the course of the algal bloom, while dissolved ammonium and SRP increased. Elevated macroinvertebrate densities, at least of the order of 10(4) individuals/m(2), suggested that the diffusive-flux estimates may be significantly enhanced by bioturbation. In addition, heat-flux modeling indicated that groundwater advection of nutrients could also significantly contribute to internal nutrient loading. Accurate environmental assessments of lentic systems and reasonable expectations for point-source management require quantitative consideration of internal solute sources.

The association between climate teleconnection indices and Upper Klamath seasonal streamflow: Trans‐Niño Index

AbstractThis research investigates large‐scale climate features affecting inter‐annual hydrologic variability of streams flowing into Upper Klamath Lake (UKL), Oregon, USA. UKL is an arid, mountainous basin located in the rain shadow east of the crest of the Cascade Mountains in the northwestern United States. Developing accurate statistical models for predicting spring and summer seasonal streamflow volumes for UKL is difficult because the basin has complex hydrology and a high degree of topographic and climatologic variability. In an effort to reduce streamflow forecast uncertainty, six large‐scale climate indices—the Pacific North American Pattern, Southern Oscillation Index, Pacific Decadal Oscillation (PDO), Multivariate El Niño‐Southern Oscillation Index, Niño 3·4, and a revised Trans‐Niño Index (TNI)—were evaluated for their ability to explain inter‐annual variation of the major hydrologic inputs into UKL.The TNI is the only index to show significant correlations during the current warm phase of the PDO. During the warm PDO phase (1978–present), the averaged October through December TNI is strongly correlated with the subsequent April through September streamflow (r = 0·7) and 1 April snow water equivalent (r = 0·6). Regional analysis shows that this climate signal is not limited to UKL but is found throughout the northwestern United States.Incorporating the TNI variable into statistical streamflow prediction models results in standard errors of forecasts issued on the first of February and earlier that are 7–10% smaller than those for the models without the TNI. This, coupled with other enhancements to the statistical models, offers a significant increment of improvement in forecasts used by water managers. Copyright © 2009 John Wiley & Sons, Ltd.

Distribution and Habitat Associations of Radio‐Tagged Adult Lost River Suckers and Shortnose Suckers in Upper Klamath Lake, Oregon

AbstractRadiotelemetry was used to investigate the summer distribution and diel habitat associations of endangered adult Lost River suckers Deltistes luxatus and shortnose suckers Chasmistes brevirostris in northern Upper Klamath Lake, Oregon. From 2002 to 2004, Lost River and shortnose suckers were tracked by boat, and water depth and water quality were measured at each fish location. A series of water quality monitors were deployed in northern Upper Klamath Lake to provide temporal information on ambient temperature, pH, and dissolved oxygen, and water samples were collected to assess chlorophyll a concentration. Suckers moved into northern Upper Klamath Lake during June and began to leave in late September each year. Kernel density estimates revealed differences in the distribution in the northern portion of Upper Klamath Lake in 2002 and 2004. In 2003, however, both Lost River and shortnose suckers were commonly located within and offshore from Pelican Bay, a shallow (1.0‐2.0 m), groundwater‐influenced area of Upper Klamath Lake. This was especially obvious beginning in late July of 2003, concurrent with reduced dissolved oxygen levels (<4.0 mg/L) in the northern portion of Upper Klamath Lake that resulted from a die‐off of the cyanobacterium Aphanizomenon flos‐aquae. Both Lost River and shortnose suckers were generally associated with water depths greater than the mean depth (2.8 m) of northern Upper Klamath Lake. Evidence ratios did not suggest diel differences in depth, temperature, dissolved oxygen, or pH at sucker locations. Both Lost River and shortnose suckers generally occupied depths greater than 2.0 m, except when suckers sought refuge in Pelican Bay during periods of poor water quality. Despite the potential for increased avian predation, suckers appeared to benefit from moving into Pelican Bay rather than staying in areas where dissolved oxygen was low. Pelican Bay appears to be an important refugium and thus may be important for sucker conservation.

Phosphorus and nitrogen legacy in a restoration wetland, Upper Klamath Lake, Oregon

Abstract The effects of sediment, ground-water, and surface-water processes on the timing, quantity, and mechanisms of N and P fluxes were investigated in the Wood River Wetland 5–7 years after agricultural practices ceased and seasonal and permanent wetland hydrologies were restored. Nutrient concentrations in standing water largely reflected ground water in winter, the largest annual water source in the closed-basin wetland. High concentrations of total P (22 mg L−1) and total N (30 mg L−1) accumulated in summer when water temperature, air temperature, and evapotranspiration were highest. High positive benthic fluxes of soluble reactive P and ammonium (NH4+-N) were measured in two sections of the study area in June and August, averaging 46 and 24 mg m−2 d−1, respectively. Nonetheless, a wetland mass balance simultaneously indicated a net loss of P and N by assimilation, denitrification (1.1–10.1 mg N m−2 h−1), or solute repartitioning. High nutrient concentrations pose a risk for water quality managemen...

Demographic Analysis of Lost River Sucker and Shortnose Sucker Populations in Upper Klamath Lake, Oregon

AbstractWe used 13 years (1995‐2007) of capture‐mark‐recapture data to assess population dynamics of endangered Lost River suckers Deltistes luxatus and shortnose suckers Chasmistes brevirostris in Upper Klamath Lake, Oregon. The Cormack‐Jolly‐Seber method was used to estimate survival, and information theoretic modeling was used to assess variation due to time, gender, species, and spawning subpopulations. Length data were used to detect multiple year‐class failures and events of high recruitment into adult spawning populations. Average annual survival probability was 0.88 for Lost River suckers and 0.76 for shortnose suckers. Mean life span estimates based on these survival rates indicated that Lost River suckers survived long enough on average to attempt reproduction eight times, whereas shortnose suckers only survived to spawn three to four times. Shortnose sucker survival was not only poor in years of fish kills (1995‐1997) but also was low in years without fish kills (i.e., 2002 and 2004). This suggests that high mortality occurs in some years but is not necessarily associated with fish kills. Annual survival probabilities were not only different between the two species but also differed between two spawning subpopulations of Lost River suckers. Length composition data indicated that recruitment into spawning populations only occurred intermittently. Populations of both species transitioned from primarily old individuals with little size diversity and consistently poor recruitment in the late 1980s and early 1990s to mostly small, recruit‐sized fish by the late 1990s. A better understanding of the factors influencing adult survival and recruitment into spawning populations is needed. Monitoring these vital parameters will provide a quantitative means to evaluate population status and assess the effectiveness of conservation and recovery efforts.

Age‐0 Lost River Sucker and Shortnose Sucker Nearshore Habitat Use in Upper Klamath Lake, Oregon: A Patch Occupancy Approach

AbstractWe examined habitat use by age‐0 Lost River suckers Deltistes luxatus and shortnose suckers Chasmistes brevirostris over six substrate classes and in vegetated and nonvegetated areas of Upper Klamath Lake, Oregon. We used a patch occupancy approach to model the effect of physical habitat and water quality conditions on habitat use. Our models accounted for potential inconsistencies in detection probability among sites and sampling occasions as a result of differences in fishing gear types and techniques, habitat characteristics, and age‐0 fish size and abundance. Detection probability was greatest during mid‐ to late summer, when water temperatures were highest and age‐0 suckers were the largest. The proportion of sites used by age‐0 suckers was inversely related to depth (range = 0.4‐3.0 m), particularly during late summer. Age‐0 suckers were more likely to use habitats containing small substrate (<64 mm) than those containing large substrate (>64 mm) and habitats with vegetation than those without vegetation. Relatively narrow ranges in dissolved oxygen, temperature, and pH prevented us from detecting effects of these water quality features on age‐0 sucker nearshore habitat use.

Soil phosphorus release from a restoration wetland, Upper Klamath Lake, Oregon

Many wetland restoration projects are initiated with phosphorus (P) retention as a primary objective. While undisturbed wetlands often are net sinks for P and other nutrients, there is evidence that newly flooded restoration wetlands on former agricultural land initially release P to surface waters. The objectives of this study were to: 1) measure P release from soils to overlying surface waters that would occur when re-flooding agricultural fields to restore a lake fringe wetland connected to Upper Klamath Lake, Oregon; and 2) identify management strategies to abate nutrient release from soils during restoration to minimize P loading to Upper Klamath Lake. We simulated the process of re-flooding soils using mesocosms in a laboratory experiment. The soils were flooded with lake water, and the water was replenished on a weekly basis. The net P flux from soils to surface water was estimated by measuring differences in P concentrations between water that had been in the mesocosms and the lake water used for replenishment. After the flooding experiment, we measured the concentrations of four forms of soil P using a modification of the Hedley procedure, to examine relationships between soil P chemistry and P release. The majority of P was released in the first two days of the experiment, and all detectable P was released by the end of the second month. We estimated that 1-9 g P/m 2 were released from the soils to the water column over the course of the experiment, which amounted to 1%-16% of total soil P. Scaling up to the entire wetland, this totals approximately 64 tons P released over 3,000 ha. We did not find any statistically significant relationships between any of the four forms of soil P and the amount of P released in the flooding experiment. Even though we demonstrate here that P is released while undertaking wetland restoration projects on former agricultural land, it is likely to be a temporary process, and once the wetland begins to resume more natural hydrological and biogeochemical functions and vegetation structure, it will re-start the process of soil accretion and P sequestration.

Mass culture of <i> Aphanizomenon flos-aquae</i> Ralfs ex born. and Flah. var.<i> flos-aquae</i> (cyanobacteria) from Klamath Falls, Oregon, USA, in closed chamber bioreactors

Aphanizomenon flos-aquae Ralfs ex Born. and Flah. var. flos- aquae (Cyanobacteria) was sampled from Upper Klamath lake and subjected to batch culture of 15-litre bioreactors. Growth characteristics viz. doubling time (Dt), specific growth rate (µ), temperature requirement, biomass and chlorophyll-a concentrations were studied during exponential growth phase at a fixed light intensity of 40-45 micromole in a CT medium. CT growth medium when supported by CO2 from a chemical byproduct in a connected chemical reactor resulted in better growth characteristic than either ASM or ASM-1 in literature. A relationship of dry weight (dw) and absorbance of the culture in CT medium was developed for calculations without the absolute need of the time-consuming dry weight measurements. Maximum measured dry weight obtained at this growth condition after 120 hours is 151 g/m 3 . The best growth temperature studied in this work is 20 o C with a supply of CO2. Results are compared with previous findings in the literature and recommendations are made for mass cultivation.

Effects of Habitat Volume and Fathead Minnow Introduction on Larval Survival of Two Endangered Sucker Species in Upper Klamath Lake, Oregon

AbstractWe used laboratory and field studies to evaluate the degree to which the abundance of introduced fathead minnow Pimephales promelas and volume of nursery habitat were limiting factors for survival of larval shortnose suckers Chasmistes brevirostris and Lost River suckers Deltistes luxatus in Upper Klamath Lake. In 20‐h experiments in which we manipulated water depth and vegetation, fathead minnow fed on sucker larvae, but deeper water and the presence of vegetation reduced predation, suggesting that predator and prey densities and cover influenced predation. Older larvae had higher survival than younger larvae in shallow water, and vegetation increased survival for all larvae in shallow water. We also used larval production estimates from 11 years of field surveys to calculate annual larval sucker survival. Average annual larval sucker survival from 10 to 15 mm total length was about 18% (range, 4.4‐48.0%). The shoreline abundance of adult fathead minnow had a negative relationship with—and appeared to set an upper limit on—annual larval sucker survival, which was consistent with the density relationship found in laboratory studies. In addition, the average shoreline abundance of fathead minnow was about three times that of any other species and had negative relationships with the abundance of all other species and lake elevation. Recent management of Upper Klamath Lake has kept June lake elevations near the 1981‐2004 mean, but it is unclear whether fluctuations in the lake's fishes are due to lake management, to larger‐scale processes such as climate, to biotic interactions resulting from environmental changes, or to a combination of those factors. This study illustrates the need to better understand the biological trade‐offs with management‐manipulated variables such as lake elevation. In addition, to manage the competing demands on Upper Klamath Lake, it will be important to recognize that high survival of larval suckers will be less frequent than in the period preceding fathead minnow presence.

Spectral Reflectance Measurements of a Microcystis Bloom in Upper Klamath Lake, Oregon

The objective of this study was to measure the in situ spectral reflectance of lake water that contains a bloom of Microcystis, a species of cyanobacteria. Reflectance spectra (350–2,500 nm) of lake water near a boat dock in Upper Klamath Lake, Oregon, were collected with a portable spectroradiometer on a cloud-free day with sunlight as a source of illumination between 0845 to 0915 hours, Pacific Daylight Time (PDT) on 17 August 2004, at a near-normal angle of observation. The averaged spectrum of the lake water containing the Microcystis bloom exhibits reflectance maxima from 550-590 nm and near 710 nm wavelengths and reflectance minima near 630 nm and 675 nm wavelengths. The reflectance gradually decreases from 810–1,000 nm and has very low reflectance in the 1,000–2,500 nm wavelength region. Our results show that the spectral reflectance of Microcystis at this stage of its bloom remains low for wavelengths longer than 1,000 nm in the near-infrared region of the spectrum. These spectral results have implications in selecting the spectral ratios and refining the algorithms that will be used to estimate phycocyanin content using satellite models. Microcystis is the predominant species of cyanobacteria blooms in Lake Erie, which makes these spectral data as important to the Great Lakes as it is to Upper Klamath Lake. Satellite algorithms have been published that have mapped phycocyanin, a pigment more uniquely associated with cyanobacteria than is chlorophyll a, in Lake Erie with data from LANDSAT TM bands 1, 3, 4, 5, and 7, and the reflectance spectra reported here are the first that cover the entire spectral range of all those LANDSAT TM spectral bands for a Microcystis bloom.

DISTRIBUTION AND HABITAT CHARACTERISTICS OF MANAYUNKIA SPECIOSA AND INFECTION PREVALENCE WITH THE PARASITE CERATOMYXA SHASTA IN THE KLAMATH RIVER, OREGON–CALIFORNIA

A survey for Manayunkia speciosa, the freshwater polychaete host for the myxozoan parasite Ceratomyxa shasta, was conducted from 2003 to 2005 as part of an integrated study of the epizootiology of ceratomyxosis in Klamath River salmonids. Substrata samples (n = 257) were collected in a variety of habitats from Klamath Lake to the mouth of the Klamath River to document occurrence and relative abundance of the polychaete by habitat type and to estimate the prevalence of C. shasta within selected polychaete populations. Populations of M. specios a were identified throughout the Klamath River within pools (51.6%), eddy-pools (47.0%), and runs (40.0%). Large populations of M. speciosa were consistently found at the inflow to the main-stem reservoirs where densities were correlated with distance from the inflow into the reservoir. Using polymerase chain reaction assay and composite samples, 12 of 71 populations identified were tested for C. shasta, revealing a mean infection prevalence of 0.27%. An area of elevated infection prevalence (4.9 and 8.3%) was identified with 2 populations below a barrier to salmonid migration, which explains the high infectious spore densities demonstrated in concurrent studies and observations of C. shasta-induced mortality in Klamath River fall Chinook salmon (Oncorhynchus tshawytscha).

Merging Precaution with Sound Science under the Endangered Species Act

ABSTRACT Hypothesis tests, which aim to minimize type I errors (false positive results), are standard procedures in scientific research, but they are often inappropriate in Endangered Species Act (ESA) reviews, where the primary objective is to prevent type II errors (false negative results). Recognizing this disparity is particularly important when the best data available are sparse and therefore lack statistical power, because hypothesis tests that use data sets with low statistical power are likely to commit type II errors, thereby denying necessary protection to threatened and endangered species. Equivalence tests can alleviate this problem, and ensure that imperiled species receive the benefit of the doubt, by switching the null and alternative hypotheses. These points are illustrated by critiquing a recent review of ESA requirements for endangered fishes in Upper Klamath Lake (southern Oregon).

ONTOGENETIC AND HABITAT-RELATED CHANGES IN DIET OF LATE LARVAL AND JUVENILE SUCKERS (CATOSTOMIDAE) IN UPPER KLAMATH LAKE, OREGON

We describe ontogenetic patterns in the diets of shortnose and Lost River suckers (15.8–92.8 mm standard length) from Upper Klamath Lake in summer 1999. Both species made a transition from surface and planktonic prey to benthic prey at about 20–30 mm standard length, corresponding to the approximate size of the juvenile morphological transition. Surface prey was dominated by adult chironomids and undigestable pollen, while benthic prey was dominated by larval chironomids, chydorids, and ostracods. In the 15–20-mm size class, pollen made up >75% of food particles in 68% of specimens, and only 2 specimens in this size class lacked any pollen grains. A better understanding of the prey selection process in larval suckers is needed to determine the importance of this potential source of starvation. The planktonic prey eaten during the surface-to-benthic feeding transition were widely distributed in the lake, suggesting that larvae use emergent vegetation primarily as a refuge from predators. On a numerical basis, crustaceans and larval chironomids contributed most to the diets of larger juveniles. In specimens >40 mm, shortnose suckers ate more Tanytarsini and Lost River suckers ate more chironomid pupae and chydorids. In specimens >40 mm there was a strong habitat-related difference in diet: specimens collected in offshore samples ate more chironomid larvae and pupae, harpacticoid copepods, and chydorids, whereas onshore specimens ate more cyclopoid copepods and invertebrate eggs. The transition from onshore to offshore habitat appears to occur over a broad size range of about 40–90 mm.

Spatial and Temporal Occurrence of the Salmonid Parasite Ceratomyxa shasta in the Oregon–California Klamath River Basin

AbstractThe parasite Ceratomyxa shasta has been implicated as a significant source of salmonid mortality in the lower Klamath River, California (i.e., below Iron Gate dam). A study of the prevalence of C. shasta and its geographic and temporal distribution throughout the Klamath River basin was conducted to determine when and where juvenile salmonids encounter lethal parasite doses. Susceptible rainbow trout Oncorhynchus mykiss were exposed to C. shasta 3–4 d at seven locations in the Klamath River between Beaver Creek and Keno Reservoir in April, June, July, September, and November 2003. Individuals from a Klamath River strain of fall Chinook salmon O. tshawytscha were held in three locations in the upper Klamath River in April, June, and July. In June 2004, rainbow trout were exposed to the parasite for 4 d at 18 locations from Klamath Lake to the mouth of the Klamath River, including several major spawning tributaries; one exposure occurred in the lower Klamath River. Rainbow trout mortality due to infection for groups exposed in the upper Klamath River was lower (<8.0%) and delayed (mean time to death, 40–110 d) in comparison with that in groups exposed in the lower Klamath River (>98%; mean time to death, 33–36 d). Experimental fall Chinook salmon did not become infected in the upper Klamath River, but infection was detected in Chinook salmon exposed in the lower Klamath River, nearly 50% of these succumbing to infection. These dramatic differences in mortality between the upper and lower Klamath River could not be explained by differences in water temperatures during exposure and are probably a result of differences in infectious dose. Lack of infection in groups exposed in tributaries supports the hypothesis that the parasite life cycle and the invertebrate host are largely confined to the main‐stem Klamath River.