Geology topics

Alta C. Harris

Publications and source records attributed to Alta C. Harris.

At least 19 recordsLinked to original sources

USGS2025

Effect of oxygenation and location on survival and growth of endangered Lost River Suckers in net pens

Acclimation of captively reared fishes to their release environment through soft releases and cage culture can improve survival. Recovery strategies for imperiled Lost River Suckers Deltistes luxatus includes soft releases of captive reared juveniles in net pens in Upper Klamath Lake, Oregon. However, intermittent and sometimes extreme hypoxia in the lake can reduce juvenile fish survival in net pets. To ensure juvenile fish receive adequate oxygen for growth and survival, net pens can be placed in areas of higher oxygen concentration or oxygen can be supplemented. We experimented with a low-cost oxygenation system in Upper Klamath Lake net pens and its effects on survival and growth of juvenile Lost River Suckers. Pairs of net pens, one with supplemental oxygen and one without, were located at a deep offshore site with historically higher oxygen concentration called Mid North and a shallow near shore site with historically lower oxygen concentration called Fish Banks. Survival of passive integrated transponder tagged juvenile Lost River Suckers was monitored and evaluated with Kaplan-Meier survival analyses. We measured two full water column hypoxia events at Fish Banks during the study period, but none at the Mid North site. Oxygenation decreased the number of hours oxygen concentration was less than and pH was greater than known lethal and sublethal thresholds for juvenile Lost River Suckers. For juvenile Lost River Suckers that survived the entire July to September study period, growth was faster at Mid North than Fish Banks. Additionally, there was faster growth at the oxygenated than non-oxygenated Fish Bank’s site, whereas growth was faster at the non-oxygenated than oxygenated Mid North site. Survival did not differ between Mid North net pens, and the Fish Banks oxygenated net pen had greater survival compared to the non-oxygenated Fish Banks net pen during our study. Lost River Sucker growth and survival are dependent on net pen site selection and a low-cost oxygenation system can prevent mass mortality because of summertime hypoxia in shallow freshwater ecosystems.

Oregon↗

USGS2024

Growth, survival, and cohort formation of juvenile Lost River (Deltistes luxatus) and shortnose suckers (Chasmistes brevirostris) in Upper Klamath Lake, Oregon, and Clear Lake Reservoir, California—2021–22 monitoring report

Executive Summary The work reported in this publication provides updated data and interpretation for sampling years 2015 and 2022 of the juvenile monitoring project. The study objectives, background, study area, species description, and methods remained the same or similar throughout the years, while the executive summary, results, and discussion were updated each year. Therefore much of this paper was originally presented in previous reports (Bart and others 2020a, b; Bart and others, 2021; Burdick and others, 2016; Burdick and others, 2018; Martin and others, 2022) and is repeated here for the reader’s convenience. Populations of federally endangered Lost River ( Deltistes luxatus ) and shortnose suckers ( Chasmistes brevirostris ) in Upper Klamath Lake, Oregon, and Clear Lake Reservoir (hereinafter, Clear Lake), California, are experiencing long-term decreases in abundance. Upper Klamath Lake populations are decreasing not only because of adult mortality, which is relatively low, but also because they are not being balanced by recruitment of young adult suckers into adult spawning aggregations. Long-term monitoring of juvenile sucker populations is conducted to (1) determine if there are annual and species-specific differences in production, survival, and growth; (2) better understand when juvenile sucker mortality is greatest; and (3) identify potential causes of high juvenile sucker mortality particularly in Upper Klamath Lake. The U.S. Geological Survey (USGS) monitoring program, begun in 2015, tracks cohorts through summer months and among years in Upper Klamath and Clear Lakes. Data on juvenile suckers captured in trap nets are used to provide information on annual variability in age-0 sucker production, juvenile sucker apparent survival, growth, species composition, and health. Upper Klamath Lake indices of year-class strength suggest that the 2022 age-0 cohort is the lowest since standardized monitoring began. The 2021 cohort, like most cohorts, had moderately low catch rates their first year of life, with a steep drop off during the second year. Although the 2020 cohort persisted through the September 2022 sampling, this cohort was sparsely represented after the first year with no representatives from this cohort captured from July 2021 through July 2022. Despite apparently low fall through spring apparent survival, the relatively large 2019 cohort persisted in our 2020–21 samples, but has not been detected since June 2021. Klamath largescale ( Catostomus snyderi ) and shortnose suckers were only differentiated from each other starting in 2020. Shortnose suckers dominated the age-1 catch in 2020 and 2022, whereas age-1 Klamath largescale suckers were slightly more prevalent in 2021. Although there were occasionally age-2 and older suckers captured, none of these fish were Lost River suckers. Except for 2015, 2017, and 2021, there were more age-0 Lost River suckers than presumed shortnose suckers in Upper Klamath Lake. However, in all years sampled, there were more age-1 presumed shortnose suckers than Lost River suckers. Age distribution of suckers captured in Clear Lake indicates greater juvenile survival than in Upper Klamath Lake. Most juvenile suckers captured throughout the years were from the 2016 and 2017 cohorts; however, by 2022 most of these fish were no longer susceptible to standard trap nets and were not as prevalent in 2022 juvenile catches, and these suckers presumedly recruited to the adult population. As the 2016 and 2017 cohorts catches declined, so did the catch in overall numbers of suckers. Excluding age-0 catches, the 2016 cohort catches peaked at age-3 and the 2017 catches peaked at age-2. In 2022, the majority of the catch was composed of age-3 to age-5 suckers. The majority of suckers captured in Clear Lake during this multiyear project were classified as the combination of Klamath largescale suckers and shortnose suckers from the Lost River Basin, from the 2016 and 2017 cohorts. The few suckers identified as Lost River or definitive shortnose suckers were from the 2016 and 2017 cohorts. A lack of age-0 suckers captured in Clear Lake during years with low spawning tributary inflow or lake levels suggested that low water prevented spawning and year class formation. However, recent data indicate that some cohorts with Klamath largescale and shortnose sucker genetics that were not captured as age-0 suckers were detected in later years at age-1 or age-2. This finding indicates that juvenile suckers in Clear Lake may spend one or more years in the tributaries and that these cohorts may primarily be represented by Klamath largescale suckers. The first 7 years of this monitoring program indicated different patterns in recruitment and survival of juvenile suckers between Upper Klamath and Clear Lakes. Since the monitoring program began in 2015, age-0 sucker catch rates, interpreted as indices of year-class strength, were greatest in Upper Klamath Lake in 2016 and 2019. In those years, Lost River suckers made up the majority of age-0 sucker catches. However, in 2017 and 2020, the age-1 sucker catches from these cohorts were mainly composed of shortnose suckers or suckers with genetic markers of both Klamath largescale and shortnose suckers, indicating a low first year survival for Lost River suckers even when age-0 catches were high. Age-0 suckers do not fully recruit to our sampling gear in Upper Klamath Lake until August, experience high mortality by September, and are almost undetectable in subsequent years. In Clear Lake, suckers are often not captured until age-1 or age-2 and juvenile annual survival appears much greater; however, there does appear to be a drop-off in catch rates as the suckers age and become less susceptible to the fishing gear.

California, Oregon↗

USGS2023

Does release size into net-pens affect survival of captively reared juvenile endangered suckers in Upper Klamath Lake?

Objective High juvenile mortality prevents recruitment into the adult populations of endangered Shortnose Sucker Chasmistes brevirostris and Lost River Sucker Deltistes luxatus in Upper Klamath Lake, Oregon. To address the lack of recruitment, the U.S. Fish and Wildlife Service implemented the Sucker Assisted Rearing Program (SARP). Managers developing the rearing program lack information about how length at release relates to survival. To determine how initial length affects survival of captively reared juvenile suckers, we introduced juvenile suckers from the SARP into three net-pens in Upper Klamath Lake. Methods The juvenile suckers ranged from 102 to 284 mm standard length, and each fish was tagged with a passive integrated transponder (PIT) tag. Fish were monitored continuously by PIT antennas and mortality was inferred when movements ceased. Result Estimated survival over 57 days was high in all net-pens (0.79–1.00) and remained high at two net-pens for 76 and 86 days. Adjusted survival curves resulting from a stratified Cox model with standard length as a covariate, indicated that length positively influenced predicted survival by as much as 41% at one site. During the study, pH and dissolved oxygen regularly exceeded no-effect thresholds at two sites and briefly reached lethal thresholds at the same two sites but did not coincide with the observed mortalities. Slower growth and the lowest survival were observed at the third site, where water quality never exceeded thresholds. Conclusion A larger release size and the location of the net-pen can improve the survivability of juvenile suckers in net-pens in Upper Klamath Lake.

Oregon↗

USGS2023

Water and endangered fish in the Klamath River Basin: Do Upper Klamath Lake surface elevation and water quality affect adult Lost River and Shortnose Sucker survival?

In the western United States, water allocation decisions often incorporate the needs of endangered fish. In the Klamath River basin, an understanding of temporal variation in annual survival rates of Shortnose Suckers Chasmistes brevirostris and Lost River Suckers Deltistes luxatus and their relation to environmental drivers is critical to water management and sucker recovery. Extinction risk is high for these fish because most individuals in the populations are approaching their maximum life span and recruitment of new fish into the adult populations has never exceeded mortality losses in the past 22 years. We used a time series of mark–recapture data from the years 1999–2021 to analyze the relationship between lake level, water quality covariates, and survival of adult Shortnose Suckers and two spawning populations of Lost River Suckers in Upper Klamath Lake, Oregon. We compared competing model hypotheses in a maximum likelihood framework using Akaike's information criterion and then ran the top environmental covariates in a Bayesian framework to estimate how much of the variation in survival was explained by these covariates as compared to random variation. The complementary analyses found almost unequivocal support for our base model without environmental covariates. Estimated adult sucker survival was high across the time series and consistent with sucker life history (mean annual survival = 0.82–0.91). This suggests that adult suckers were generally robust to interannual variation in lake levels as well as consistently poor water quality within the years of our data set. Recovery time is limited, as a declining survival trend for adult suckers in recent years may be due to the onset of senescence. The successful recovery of suckers in Upper Klamath Lake may rely on shifting research from the causes of adult mortality and its relationship with lake surface elevation to the causes of poor recruitment into adult populations.

California, Oregon↗

USGS2022

Distribution of bull trout (Salvelinus confluentus) in conjunction with habitat and trout assemblages in creeks within the Klamath Basin, Oregon 2010–16

Bull trout ( Salvelinus confluentus ) in the Klamath Basin are on the southernmost border of the range of the species, where threats are most severe and where bull trout are most imperiled. In their recovery plan the U.S. Fish and Wildlife Service (2015, https://ecos.fws.gov/ecp/report/species-with-recovery-plans ) suggested that Klamath Basin bull trout are at increased risk of extirpation due to habitat fragmentation, degradation of habitat complexity, and introduction of non-native trout species that often outcompete bull trout. The goals of this study were to determine if there was a lack of connectivity between habitat areas impeding migration, habitat differences, or interference by non-native species affecting bull trout distribution in the Klamath Basin. This study examined three populations of bull trout in conjunction with a concurrent native species (redband trout [ Oncorhynchus mykiss gairdnerii ]), and a concurrent non-native species (brown trout [ Salmo trutta ]) in tributaries of the upper Sprague River within the Klamath Basin. Culverts present at the beginning of the study may have impeded migration of bull trout, but culvert upgrades made during the study appeared to eliminate the impediments to migration. The presence of non-native brown trout appeared to cause bull trout to use a smaller portion of Leonard Creek, whereas the low numbers of brown trout in the studied portion of Brownsworth Creek did not appear to interfere with the local distribution of bull trout. Downstream migration of bull trout may have been impeded if there were increased numbers of brown trout or increased temperatures in the lower portions of the creeks outside of the study area. Although habitat complexity was not examined in detail during this study, there was an attempt to enhance the habitat for bull trout by introducing large woody debris into treatment sections of the creeks. We compared bull trout numbers between the treatment sections and nearby control sections prior to and after introduction of the large woody debris. The introduction of large woody debris did not appear to enhance the use of those areas by bull trout, but the large woody debris may not have been of suitable size to enhance the habitat for bull trout.

Oregon↗

USGS2021

Spatial and temporal distribution of radio-tagged Lost River (Deltistes luxatus) and shortnose (Chasmistes brevirostris) suckers in Clear Lake Reservoir and associated spawning tributaries, Northern California, 2015–17

Executive Summary Data from a multi-year radio telemetry study were used to assess seasonal distribution patterns for two long-lived, federally endangered catostomids across substantially different water conditions in Clear Lake Reservoir, northern California. Lost River ( Deltistes luxatus ) and shortnose ( Chasmistes brevirostris ) suckers, two species endemic to the Klamath Basin, were implanted with radio transmitters in each of 3 years in an effort to expand our understanding of seasonal sucker movements within the reservoir and their migrations in spawning tributaries. Clear Lake Reservoir and its tributaries are part of a critical management unit within the Lost River Basin Recovery Unit for populations of Lost River and shortnose suckers. We documented residency and migratory behaviors and how behaviors were affected by lake surface elevations and water management practices. Adult suckers were captured during autumn trammel net sampling in the west lobe of the reservoir and implanted with internal radio transmitters. A total of 163 suckers were radio-tagged (75 in 2014, 64 in 2015, and 24 in 2016); 27 more shortnose suckers were tagged than Lost River suckers to reflect the larger population of shortnose suckers in the reservoir. Sex ratios were approximately equal for each species. Aerial telemetry surveys were used to monitor radio-tagged fish from January 20 to December 2 each year and to document the upstream extent of spawning migrations in the tributaries. Surveys were scheduled more frequently during the spawning season (February–June) when suckers are known to move out of the reservoir and into spawning tributaries.

California↗

USGS2021

Dynamics of endangered sucker populations in Clear Lake Reservoir, California

Executive Summary In collaboration with the Bureau of Reclamation, the U.S. Geological Survey began a consistent monitoring program for endangered Lost River suckers ( Deltistes luxatus ) and shortnose suckers ( Chasmistes brevirostris ) in Clear Lake Reservoir, California, in fall 2004. The program was intended to improve understanding of the Clear Lake Reservoir populations because they are important to recovery efforts for these species. We report results from the ongoing program and include sampling efforts through fall 2019. We summarize catches and passive integrated transponder (PIT) tagging efforts from trammel net sampling in the fall seasons (September–October each year) and detections of PIT-tagged suckers on remote antennas in the spring in each year from 2006 to 2019. We also combine the data from physical captures and remote detections in capture-recapture models to provide estimates of annual survival for suckers in the reservoir. A lack of genetic distinctiveness between shortnose suckers and Klamath largescale suckers ( Catostomus snyderi ) in the Lost River subbasin, including Clear Lake Reservoir, is a likely cause of past difficulty in identification of these species. Field identification can be subjective for many captured individuals, and very few individuals were identified as Klamath largescale suckers in the most recent years of our monitoring program. For this report, we combine individuals that were identified as either shortnose sucker (SNS) or Klamath largescale sucker (KLS) into a single “SNS-KLS” group for most analyses. Identification of Lost River suckers (LRS) is based on external morphological characteristics.

California↗

USGS2019

Examination of movements and survival of Pahranagat roundtail chub (Gila robusta jordani) in the Pahranagat River and adjacent waters, Nevada, 2014–18

Executive Summary The Pahranagat roundtail chub ( Gila robusta jordani ; hereinafter “chub”) was federally listed as endangered in 1970 (U.S. Fish and Wildlife Service, 1970). In the decades following the listing, the chub has declined to extremely low numbers (Tuttle and others, 1990; Guadalupe, 2014). Loss of available habitat appears to be one of the main reasons for the decline of this species. Historically, the chub are assumed to have had approximately 30 kilometers (km) of habitat available to them, whereas currently they appear to primarily occupy 3.5 km of the Pahranagat River, up to 2.5 km of the Pahranagat Ditch, and a small portion of the Pahranagat Drain. Each year in mid-March, a gate at the top of the fish passage structure is closed to divert water down the Pahranagat Ditch, almost completely eliminating any flow into the Pahranagat Drain. The gate is usually removed in mid-October, allowing for flow to reoccur in the Pahranagat Drain. Due to the intermittent nature of the Pahranagat Drain, it is considered a sink for the species, and yearly salvage operations are conducted to remove chub from the Pahranagat Drain. The lower portion of the Pahranagat Ditch is also thought to be a sink for the species, due to high flows and limited structure potentially pushing the chub out of the system. Movements of passive-integrated-transponder (PIT) tagged chub indicate that adults and larger juveniles are not likely to be swept downstream to the point of exiting the system; however, the smaller juveniles and larvae are likely to be entrained in the Pahranagat Drain and possibly the lower portion of the Pahranagat Ditch. Only 2 of 64 PIT-tagged chub (3 percent) were observed to exit the system through the Pahranagat Ditch as they were last recorded on the Lower Ditch antenna. No PIT-tagged chub was observed exiting the system through the Pahranagat Drain. Although capture location was a good predictor of where PIT tagged fish were primarily detected, fish were observed to meander throughout the available habitat. Chub captured and released in the Pahranagat River were detected more often in the upper portion of the Pahranagat River, whereas chub captured and released in the Pahranagat Ditch were more often detected in and near the Pahranagat Ditch. This suggests some degree of site fidelity. However, the two chub that were captured in the Pahranagat Drain and relocated into the middle portion of the Pahranagat River near the Between Bridges antenna were not able to get back to the closed off Pahranagat Drain (closed to fish passage from mid-March through mid-October), but were primarily detected in and near the Pahranagat Ditch. Movements from one end of the system to the other end of the system (3.5 km) could occur within a day and there were no observed seasonal location preferences for the chubs. However, there was more activity in the uppermost sites during fall and winter, presumedly associated with spawning. Furthermore, chub were found to be more active during the daylight hours in fall and winter verses spring and summer. During summer, chubs were the least active, especially during daylight hours. Most of the fish tagged were estimated to be adults based on size; 84 percent of fish tagged in this study were greater than 100 millimeters (mm) total length (TL). One chub monitored during this study (139 mm TL when tagged) was observed for a total of 714 days following capture, indicating that chub can survive at least 3 years. Furthermore, two fish greater than 200 mm TL when tagged were detected for another 7 months after tagging, which supports life history descriptions in the Recovery Plan that states Pahranagat roundtail chub can reach 250 mm TL (U.S. Fish and Wildlife Service, 1998). In addition to natural mortality events, fish may die from extreme temperatures or other environmental stressors. None of the fish tagged in 2014 or 2015 were detected past August 31, 2016, which suggests that there may have been some external influence causing mortality of the few remaining fish from May 1, 2016, to August 31, 2016. Although habitat for chub has been limited for decades to a very small section of the Pahranagat River and the Pahranagat Ditch (U.S. Fish and Wildlife Service, 1998), this study suggests that recent declining numbers of chub are most likely due to mortality events and not due to the fish emigrating from the system through the Pahranagat Ditch or the Pahranagat Drain.

Nevada↗

USGS2019

Assessing causes of mortality for endangered juvenile Lost River suckers (Deltistes luxatus) in mesocosms in Upper Klamath Lake, south-central Oregon, 2016

Executive Summary The recovery of endangered Lost River suckers ( Deltistes luxatus ) in Upper Klamath Lake, south-central Oregon, has been impeded because juveniles are not recruiting into adult spawning populations. Adult sucker populations spawn each spring but mortality of age-0 suckers during their first summer is excessively high, and recruitment of juveniles into adult populations does not occur in most years. The last significant year class to join spawning aggregations was hatched in 1991. Capture rates for age-0 Lost River suckers decrease so substantially each summer that it is thought that mortality is nearly 100 percent within the first year of life each year. Causes of mortality are not understood but poor water quality, parasites, disease, predation, and non-native species are suspected to contribute to mortality. Upper Klamath Lake is hypereutrophic and summer water-quality conditions have large diurnal and seasonal fluctuations. Photosynthesis of Aphanizomenon flos-aquae , the most abundant cyanobacterium in Upper Klamath Lake, is responsible for large fluctuations in dissolved-oxygen (DO) concentrations and pH. We introduced hatchery-raised, passive integrated transponder-tagged juvenile Lost River suckers into large mesocosms located at Fish Banks, Mid North, and Rattlesnake Point in Upper Klamath Lake, Oregon, to assess sucker mortality relative to water-quality conditions. We identified the date of death for each sucker by assessing movement patterns among vertically stratified antennas. We modeled daily mortality using known fate models relative to water-quality conditions measured by sondes. Histopathology was used to understand causes of eminent mortality for moribund suckers. Fish mortality, growth, health, and movement patterns varied among locations, but it was unclear whether this variation was due to water-quality or other factors. Seasonal mortality was 58.8 percent at Fish Banks, 27.4 percent at Mid North, and 11.5 percent at Rattlesnake Point. Growth over the 109-day study period was lowest at Fish Banks (34.5 ±10.0 millimeters [mm] standard length (SL); 18.6 ±7.7 grams [g]), intermediate at Mid North (57.5 ±13.6 mm SL; 40.1 ±15.4 g), and greatest at Rattlesnake Point (78.4 ±13.0 mm SL; 72.5 ±18.7 g). Our ability to assess causes of juvenile sucker mortality in mesocosms using our modelling approach was limited by low daily mortality. Zero to 3 mortalities occurred per day, except on July 30 at Fish Banks when 7 mortalities occurred. Relative to any other measured and tested water-quality condition, mortality was more likely to occur on days with large fluctuations in oxygen percent saturation. When we assessed the fit of the most parsimonious model, performance was poor, which suggested that other factors were contributing to mortality. Our ability to assess the relationship between seasonal patterns in water quality and fish mortality were limited by the absence of substantial differences in water quality among sites, inconsistency in the depth at which measurements were collected, and no clear pattern in conditions leading up to and during mortality events. Except for DO at Rattlesnake Point and diel temperature variations at Fish Banks, seasonally summarized water-quality factors were similar among sites. The locations of water-quality monitors within the water column likely explain the differences in DO at Rattlesnake Point and temperature variation at Fish Banks. Furthermore, DO concentrations and other water-quality factors occurring during and prior to mortality events were inconsistent. Microscopic assessments indicated severe gill hyperplasia, fusion of the secondary lamellae, and severe Ichthyobodo sp. infestations on the gills of most moribund suckers. Liver glycogen was usually depleted in suckers with severe Ichthyobodo sp. infestations. Ichthyobodo sp. infestations probably were the immediate cause of death and probably originated from the Klamath Tribes Fish Research Facility, although this parasite also is present in Upper Klamath Lake and severe water-quality conditions may have contributed to morbidity. As suckers in the mesocosms died, they were replaced with suckers from the Fish Research Facility that likely were heavily parasitized with Ichthyobodo sp. Therefore, it is possible that the gradient in mortality rate among sites was owing to site-varying differences in inadvertent increases in introduced parasite loads.

Oregon↗

USGS2018

Status and trends of adult Lost River (Deltistes luxatus) and shortnose (Chasmistes brevirostris) sucker populations in Upper Klamath Lake, Oregon, 2017

Executive Summary Data from a long-term capture-recapture program were used to assess the status and dynamics of populations of two long-lived, federally endangered catostomids in Upper Klamath Lake, Oregon. Lost River suckers (LRS; Deltistes luxatus ) and shortnose suckers (SNS; Chasmistes brevirostris ) have been captured and tagged with passive integrated transponder (PIT) tags during their spawning migrations in each year since 1995. In addition, beginning in 2005, individuals that had been previously PIT-tagged were re-encountered on remote underwater antennas deployed throughout sucker spawning areas. Captures and remote encounters during the spawning season in spring 2016 were incorporated into capture-recapture analyses of population dynamics. Cormack-Jolly-Seber (CJS) open population capture-recapture models were used to estimate annual survival probabilities, and a reverse-time analog of the CJS model was used to estimate recruitment of new individuals into the spawning populations. In addition, data on the size composition of captured fish were examined to provide corroborating evidence of recruitment. Model estimates of survival and recruitment were used to derive estimates of changes in population size over time and to determine the status of the populations through 2015. Separate analyses were done for each species and also for each subpopulation of LRS. Shortnose suckers and one subpopulation of LRS migrate into tributary rivers to spawn, whereas the other LRS subpopulation spawns at groundwater upwelling areas along the eastern shoreline of the lake. Capture-recapture analyses indicated that with a few exceptions, the survival of males and females in both Lost River sucker subpopulations was high (greater than 0.88) from 1999 to 2015. Survival was notably lower for males from the river in 2000, 2006, and 2012, and for the shoreline areas in 2002. From 2001 to 2015, the abundance of males in the lakeshore spawning subpopulation decreased by at least 64 percent and the abundance of females decreased by at least 56 percent. Capture-recapture models suggested that the abundance of both sexes in the river spawning subpopulation of LRS had increased substantially since 2006; increases were mostly due to large estimated recruitment events in 2006 and 2008. We know that the estimates in 2006 are substantially biased in favor of recruitment because of a sampling issue. We are skeptical of the magnitude of recruitment indicated by the 2008 estimates as well because (1) few small individuals that would indicate the presence of new recruits were captured in that year, and (2) recapture probabilities in recruitment models based on just physical recaptures of fish were lower than desired for robust inferences from capture-recapture models. If we assume instead that little or no recruitment occurred for this subpopulation, the abundance of both sexes in the river spawning subpopulation likely has decreased at rates similar to the rates for the lakeshore spawning subpopulation from 2002 to 2015. Shortnose suckers experienced lower and more variable annual survival than either LRS subpopulation. Annual survival of both sexes was relatively low in 2003, 2004, 2010, and 2012. In addition, female survival was low in 1999 and 2000 while male survival was low in 2002. Survival estimate precision in early years of the study; however, are poor. Capture-recapture models and size composition data indicate that recruitment of new individuals into the SNS spawning population was trivial from 2001 to 2005. Models indicate that more than 10 percent of the population was new recruits in a number of more recent years. As a result, capture-recapture modeling suggests that the abundance of adult spawning SNS was relatively stable from 2006 to 2010. We are skeptical of the estimated recruitment in 2006 because of the known sampling issue. We also are skeptical of the estimated recruitment in other recent years because few small individuals that would indicate the presence of new recruits were captured in any of those years, and recapture probabilities in recruitment models were low. The best-case scenario for SNS, based on capture-recapture recruitment modeling, indicates that the abundance of males in the spawning population decreased by 78 percent and the abundance of females decreased by 77 percent from 2001 to 2015. Decreases in abundance for both sexes are likely greater than these estimates indicate. Despite relatively high survival in most years, we conclude that both species have experienced substantial decreases in the abundance of spawning adults because losses from mortality have not been balanced by recruitment of new individuals. Although capture-recapture data indicate substantial recruitment of new individuals into the spawning populations for SNS and river spawning LRS in some years, size data do not corroborate these estimates. As a result, the status of the endangered sucker populations in Upper Klamath Lake remains distressed, especially for SNS. Our monitoring program provides a robust platform for estimating vital population parameters, evaluating the status of the populations, and assessing the effectiveness of conservation and recovery efforts.

Oregon↗

USGS2017

Status and trends of adult Lost River ( Deltistes luxatus ) and shortnose ( Chasmistes brevirostris ) sucker populations in Upper Klamath Lake, Oregon, 2015

Oregon↗

USGS2017

Brackish groundwater in the United States

For some parts of the Nation, large-scale development of groundwater has caused decreases in the amount of groundwater that is present in aquifer storage and that discharges to surface-water bodies. Water supply in some areas, particularly in arid and semiarid regions, is not adequate to meet demand, and severe drought is affecting large parts of the United States. Future water demand is projected to heighten the current stress on groundwater resources. This combination of factors has led to concerns about the availability of freshwater to meet domestic, agricultural, industrial, mining, and environmental needs. To ensure the water security of the Nation, currently [2016] untapped water sources may need to be developed. Brackish groundwater is an unconventional water source that may offer a partial solution to current and future water demands. In support of the national census of water resources, the U.S. Geological Survey completed the national brackish groundwater assessment to better understand the occurrence and characteristics of brackish groundwater in the United States as a potential water resource. Analyses completed as part of this assessment relied on previously collected data from multiple sources; no new data were collected. Compiled data included readily available information about groundwater chemistry, horizontal and vertical extents and hydrogeologic characteristics of principal aquifers (regionally extensive aquifers or aquifer systems that have the potential to be used as a source of potable water), and groundwater use. Although these data were obtained from a wide variety of sources, the compiled data are biased toward shallow and fresh groundwater resources; data representing groundwater that is at great depths and is saline were not as readily available. One of the most important contributions of this assessment is the creation of a database containing chemical characteristics and aquifer information for the known areas with brackish groundwater in the United States. Previously published digital data relating to brackish groundwater resources were limited to a small number of State- and regional-level studies. Data sources for this assessment ranged from single publications to large datasets and from local studies to national assessments. Geochemical data included concentrations of dissolved solids, major ions, trace elements, nutrients, and radionuclides as well as physical properties of the water (pH, temperature, and specific conductance). Additionally, the database provides selected well information (location, yield, depth, and contributing aquifer) necessary for evaluating the water resource. The assessment was divided into national-, regional-, and aquifer-scale analyses. National-scale analyses included evaluation of the three-dimensional distribution of observed dissolved-solids concentrations in groundwater, the three-dimensional probability of brackish groundwater occurrence, and the geochemical characteristics of saline (greater than or equal to 1,000 mg/L of dissolved solids) groundwater resources. Regional-scale analyses included a summary of the percentage of observed grid cell volume in the region that was occupied by brackish groundwater within the mixture of air, water, and rock for multiple depth intervals. Aquifer-scale analyses focused primarily on four regions that contained the largest amounts of observed brackish groundwater and included a generalized description of hydrogeologic characteristics from previously published work; the distribution of dissolved-solids concentrations; considerations for developing brackish groundwater resources, including a summary of other chemical characteristics that may limit the use of brackish groundwater and the ability of sampled wells producing brackish groundwater to yield useful amounts of water; and the amount of saline groundwater being used in 2010.

Professional Paper↗

USGS2016

Survival, movement, and health of hatchery-raised juvenile Lost River suckers within a mesocosm in Upper Klamath Lake, Oregon

The recovery of endangered Lost River suckers ( Deltistes luxatus ) in Upper Klamath Lake is limited by poor juvenile survival and failure to recruit into the adult population. Poor water quality, degradation of rearing habitat, and toxic levels of microcystin are hypothesized to contribute to low juvenile survival. Studies of wild juvenile suckers are limited in that capture rates are low and compromised individuals are rarely captured in passive nets. The goal of this study was to assess the use of a mesocosm for learning about juvenile survival, movement, and health. Hatchery-raised juvenile Lost River suckers were PIT (passive integrated transponder) tagged and monitored by three vertically stratified antennas. Fish locations within the mesocosm were recorded at least every 30 minutes and were assessed in relation to vertically stratified water-quality conditions. Vertical movement patterns were analyzed to identify the timing of mortality for each fish. Most mortality occurred from July 28 to August 16, 2014. Juvenile suckers spent daylight hours near the benthos and moved throughout the entire water column during dark hours. Diel movements were not in response to dissolved-oxygen concentrations, temperature, or pH. Furthermore, low dissolved-oxygen concentrations, high temperatures, high pH, high un-ionized ammonia, or high microcystin levels did not directly cause mortality, although indirect effects may have occurred. However, water-quality conditions known to be lethal to juvenile Lost River suckers did not occur during the study period. Histological assessment revealed severe gill hyperplasia and Ichthyobodo sp. infestations in most moribund fish. For these fish, Ichthyobodo sp. was likely the cause of mortality, although it is unclear if this parasite originated in the rearing facility because fish were not screened for this parasite prior to introduction. This study has demonstrated that we can effectively use a mesocosm equipped with antennas to learn about the timing of mortality, movement, and health of PIT-tagged hatchery-raised juvenile Lost River suckers.

Oregon↗

USGS2015

Status and trends of adult Lost River ( Deltistes luxatus ) and shortnose ( Chasmistes brevirostris ) sucker populations in Upper Klamath Lake, Oregon, 2014

Executive Summary Data from a long-term capture-recapture program were used to assess the status and dynamics of populations of two long-lived, federally endangered catostomids in Upper Klamath Lake, Oregon. Lost River suckers ( Deltistes luxatus ) and shortnose suckers ( Chasmistes brevirostris ) have been captured and tagged with passive integrated transponder (PIT) tags during their spawning migrations in each year since 1995. In addition, beginning in 2005, individuals that had been previously PIT-tagged were re-encountered on remote underwater antennas deployed throughout sucker spawning areas. Captures and remote encounters during the spawning season in spring 2014 were incorporated into capture-recapture analyses of population dynamics. Cormack-Jolly-Seber (CJS) open population capture-recapture models were used to estimate annual survival probabilities, and a reverse-time analog of the CJS model was used to estimate recruitment of new individuals into the spawning populations. In addition, data on the size composition of captured fish were examined to provide corroborating evidence of recruitment. Model estimates of survival and recruitment were used to derive estimates of changes in population size over time and to determine the status of the populations through 2013. Separate analyses were conducted for each species and also for each subpopulation of Lost River suckers (LRS). Shortnose suckers (SNS) and one subpopulation of LRS migrate into tributary rivers to spawn, whereas the other LRS subpopulation spawns at groundwater upwelling areas along the eastern shoreline of the lake. In 2014, we captured, tagged, and released 496 LRS at four lakeshore spawning areas and recaptured an additional 970 individuals that had been tagged in previous years. Across all four areas, the remote antennas detected 6,370 individual LRS during the spawning season. Spawning activity peaked in April and most individuals were encountered at Cinder Flats and Sucker Springs. In the Williamson River, we captured, tagged, and released 3,038 LRS and 267 SNS, and recaptured 762 LRS and 156 SNS that had been tagged in previous years. Remote PIT tag antennas in the traps at the weir on the Williamson River and remote antenna systems that spanned the river at three different locations on the Williamson and Sprague Rivers detected a total of 23,446 LRS and 6,259 SNS. Most LRS passed upstream in the first and second weeks of April when water temperatures were increasing and greater than 10 °C. In contrast, upstream passage for SNS occurred in two pulses, one in early April and one in late April to early May, when water temperatures were increasing and near or greater than 12 °C. Finally, an additional 375 LRS and 884 SNS were captured in trammel net sampling at pre-spawn staging areas in the northeastern part of the lake. Of these, 111 of the LRS and 390 of the SNS had been PIT-tagged in previous years. For LRS captured at the staging areas that had encounter histories that were informative about their spawning location, 79 percent of the fish were members of the subpopulation that spawns in the rivers. Capture-recapture analyses for the LRS subpopulation that spawns at the shoreline areas included encounter histories for more than 13,200 individuals, and analyses for the subpopulation that spawns in the rivers included more than 36,400 encounter histories. With a few exceptions, the survival of males and females in both subpopulations was high (greater than 0.88) between 1999 and 2012. Notably lower survival occurred for both sexes from the rivers in 2000, for males from the shoreline areas in 2002, and for males from the rivers in 2006 and 2012. Between 2001 and 2013, the abundance of males in the lakeshore spawning subpopulation decreased by at least 55 percent and the abundance of females decreased by at least 42 percent. Capture-recapture models suggested that the abundance of both sexes in the river spawning subpopulation of LRS had increased substantially since 2006; increases were mostly due to large estimated recruitment events in 2006 and 2008. We know that the estimates in 2006 are substantially biased in favor of recruitment because of a sampling issue. We are skeptical of the magnitude of recruitment indicated by the 2008 estimates as well because (1) few small individuals that would indicate the presence of new recruits were captured in that year, and (2) recapture probabilities in recruitment models based on just physical recaptures of fish were lower than desired for robust inferences from capture-recapture models. If we assume instead that little or no recruitment occurred for this subpopulation, the abundance of both sexes in the river spawning subpopulation likely has decreased at rates similar to the rates for the lakeshore spawning subpopulation between 2002 and 2013. Capture-recapture analyses for SNS included encounter histories for more than 19,200 individuals. Most annual survival estimates between 2001 and 2012 were high (greater than 0.80), but SNS experienced more years of low survival than either LRS subpopulation. Annual survival of both sexes was relatively low in 2004, 2010, and 2012. In addition, male survival was low in 2002. Capture-recapture models and size composition data indicate that recruitment of new individuals into the SNS spawning population was trivial between 2001 and 2005. Models indicate that more than 10 percent of the population was new recruits in a number of more recent years. As a result, capture-recapture modeling suggests that the abundance of adult spawning SNS was relatively stable between 2006 and 2010. We are skeptical of the estimated recruitment in 2006 because of the known sampling issue. We also are skeptical of the estimated recruitment in other recent years because few small individuals that would indicate the presence of new recruits were captured in any of those years, and recapture probabilities in recruitment models were low. The best-case scenario for SNS, based on capture-recapture recruitment modeling, indicates that the abundance of males in the spawning population decreased by 77 percent and the abundance of females decreased by 73 percent between 2001 and 2013. Decreases in abundance for both sexes likely are greater than these estimates indicate. Despite relatively high survival in most years, we conclude that both species have experienced substantial decreases in the abundance of spawning adults because losses from mortality have not been balanced by recruitment of new individuals. Although capture-recapture data indicate substantial recruitment of new individuals into the spawning populations for SNS and river spawning LRS in some years, size data do not corroborate these estimates. As a result, the status of the endangered sucker populations in Upper Klamath Lake remains worrisome, especially for shortnose suckers. Our monitoring program provides a robust platform for estimating vital population parameters, evaluating the status of the populations, and assessing the effectiveness of conservation and recovery efforts.

Oregon↗

USGS2015

Effects of lake surface elevation on shoreline-spawning Lost River Suckers

We analyzed remote detection data from PIT-tagged Lost River Suckers Deltistes luxatus at four shoreline spawning areas in Upper Klamath Lake, Oregon, to determine whether spawning of this endangered species was affected by low water levels. Our investigation was motivated by the observation that the surface elevation of the lake during the 2010 spawning season was the lowest in 38 years. Irrigation withdrawals in 2009 that were not replenished by subsequent winter-spring inflows caused a reduction in available shoreline spawning habitat in 2010. We compared metrics of skipped spawning, movement among spawning areas, and spawning duration across 8 years (2006-2013) that had contrasting spring water levels. Some aspects of sucker spawning were similar in all years, including few individuals straying from the shoreline areas to spawning locations in lake tributaries and consistent effects of increasing water temperatures on the accumulation of fish at the spawning areas. During the extreme low water year of 2010, 14% fewer female and 8% fewer male suckers joined the shoreline spawning aggregation than in the other years. Both males and females visited fewer spawning areas within Upper Klamath Lake in 2010 than in other years, and the median duration at spawning areas in 2010 was at least 36% shorter for females and 20% shorter for males relative to other years. Given the imperiled status of the species and the declining abundance of the population in Upper Klamath Lake, any reduction in spawning success and egg production could negatively impact recovery efforts. Our results indicate that lake surface elevations above 1,262.3-1,262.5 m would be unlikely to limit the number of spawning fish and overall egg production.

Oregon↗

USGS2014

Demographics and run timing of adult Lost River ( Deltistes luxatus ) and short nose ( Chasmistes brevirostris ) suckers in Upper Klamath Lake, Oregon, 2012

Data from a long-term capture-recapture program were used to assess the status and dynamics of populations of two long-lived, federally endangered catostomids in Upper Klamath Lake, Oregon. Lost River suckers ( Deltistes luxatus ) and shortnose suckers ( Chasmistes brevirostris ) have been captured and tagged with passive integrated transponder (PIT) tags during their spawning migrations in each year since 1995. In addition, beginning in 2005, individuals that had been previously PIT-tagged were re-encountered on remote underwater antennas deployed throughout sucker spawning areas. Captures and remote encounters during spring 2012 were used to describe the spawning migrations in that year and also were incorporated into capture-recapture analyses of population dynamics. Cormack-Jolly-Seber (CJS) open population capture-recapture models were used to estimate annual survival probabilities, and a reverse-time analog of the CJS model was used to estimate recruitment of new individuals into the spawning populations. In addition, data on the size composition of captured fish were examined to provide corroborating evidence of recruitment. Model estimates of survival and recruitment were used to derive estimates of changes in population size over time and to determine the status of the populations in 2011. Separate analyses were conducted for each species and also for each subpopulation of Lost River suckers (LRS). Shortnose suckers (SNS) and one subpopulation of LRS migrate into tributary rivers to spawn, whereas the other LRS subpopulation spawns at groundwater upwelling areas along the eastern shoreline of the lake. In 2012, we captured, tagged, and released 749 LRS at four lakeshore spawning areas and recaptured an additional 969 individuals that had been tagged in previous years. Across all four areas, the remote antennas detected 6,578 individual LRS during the spawning season. Spawning activity peaked in April and most individuals were encountered at Cinder Flats and Sucker Springs. In the Williamson River, we captured, tagged, and released 3,376 LRS and 299 SNS, and recaptured 551 LRS and 125 SNS that had been tagged in previous years. Remote PIT tag antennas in the traps at the weir on the Williamson River and remote antenna systems that spanned the river at four different locations on the Williamson and Sprague Rivers detected a total of 19,321 LRS and 6,124 SNS. Most LRS passed upstream between late April and mid-May when water temperatures were increasing and greater than 10 °C. In contrast, most upstream passage for SNS occurred in early and mid-May when water temperatures were increasing and near or greater than 12 °C. Finally, an additional 1,188 LRS and 1,665 SNS were captured in trammel net sampling at pre-spawn staging areas in the northeastern part of the lake. Of these, 291 of the LRS and 653 of the SNS had been PIT-tagged in previous years. For LRS captured at the staging areas that had encounter histories that were informative about their spawning location, over 90 percent of the fish were members of the subpopulation that spawns in the rivers. Capture-recapture analyses for the LRS subpopulation that spawns at the shoreline areas included encounter histories for more than 12,150 individuals, and analyses for the subpopulation that spawns in the rivers included more than 29,500 encounter histories. With a few exceptions, the survival of males and females in both subpopulations was high (greater than 0.9) between 1999 and 2010. Notably lower survival occurred for both sexes from the rivers in 2000, for both sexes from the shoreline areas in 2002, and for males from the rivers in 2006. Between 2001 and 2011, the abundance of males in the lakeshore spawning subpopulation decreased by 53–65 percent and the abundance of females decreased by 36–48 percent. Capture-recapture models suggested that the abundance of both sexes in the river spawning subpopulation of LRS had increased substantially since 2006; increases were due to large estimated recruitment events in 2006 and 2008. We know that the estimates in 2006 are substantially biased in favor of recruitment because of a sampling issue. We are skeptical of the magnitude of recruitment indicated by the 2008 estimates as well because (1) few small individuals that would indicate the presence of new recruits were captured in that year, and (2) recapture probabilities in recruitment models based on just physical recaptures were lower than desired for robust inferences from capture-recapture models. If we assume that little or no recruitment occurred in 2006 or 2008, the abundance of both sexes in the river spawning subpopulation likely has decreased at rates similar to the rates for the lakeshore spawning subpopulation between 2002 and 2011. Capture-recapture analyses for SNS included encounter histories for more than 17,700 individuals. Most annual survival estimates between 2001 and 2010 were high (greater than 0.8), but SNS experienced more years of low survival than either LRS subpopulation. Annual survival of both sexes was particularly low in 2001, 2004, and 2010. In addition, male survival was somewhat low in 2002. Capture-recapture models and size composition data indicate that recruitment of new individuals into the SNS spawning population was trivial between 2001 and 2005. Models indicate substantial recruitment of new individuals into the SNS spawning population in 2006, 2008, and 2009. As a result, capture-recapture modeling suggests that the abundance of adult spawning SNS was relatively stable between 2006 and 2010. We are skeptical of the estimated recruitment in 2006, 2008, and 2009 because few small individuals that would indicate the presence of new recruits were captured in any of those years, and recapture probabilities in recruitment models were low. The best-case scenario for SNS, based on capture-recapture recruitment modeling, indicates that the abundance of males in the spawning population decreased by 71 percent and the abundance of females decreased by 69 percent between 2001 and 2011. The worst-case scenario, which assumes no recruitment and seems more likely, suggests an 86 percent decrease for males and an 81 percent decrease for females. Despite relatively high survival in most years, we conclude that both species have experienced substantial declines in the abundance of spawning fish because losses from mortality have not been balanced by recruitment of new individuals. Although capture-recapture data indicate substantial recruitment of new individuals into the adult spawning populations for SNS and river spawning LRS in some years, size data do not corroborate these estimates. In fact, fork length data indicate that all populations are largely comprised of fish that were present in the late 1990s and early 2000s. As a result, the status of the endangered sucker populations in Upper Klamath Lake remains worrisome, and the situation is especially dire for shortnose suckers. Future investigations should explore the connections between sucker recruitment and survival and various environmental factors, such as water quality and disease. Our monitoring program provides a robust platform for estimating vital population parameters, evaluating the status of the populations, and assessing the effectiveness of conservation and recovery efforts.

Oregon↗

USGS2013

The Cambrian-Ordovician rocks of Sonora, Mexico, and southern Arizona, southwestern margin of North America (Laurentia)

Cambrian and Ordovician shelf, platform, and basin rocks are present in Sonora, Mexico, and southern Arizona and were deposited on the southwestern continental margin of North America (Laurentia). Cambrian and Ordovician rocks in Sonora, Mexico, are mostly exposed in scattered outcrops in the northern half of the state. Their discontinuous nature results from extensive Quaternary and Tertiary surficial cover, from Tertiary and Mesozoic granitic batholiths in western Sonora, and from widespread Tertiary volcanic deposits in the Sierra Madre Occidental in eastern Sonora. Cambrian and Ordovician shelf rocks were deposited as part of the the southern miogeocline on the southwestern continental margin of North America. Lower Cambrian shelf units in Sonora consist mainly of quartzite, siltstone, and silty limestone; limestone increases upward in the sequence. Middle Cambrian shelf rocks consist mostly of limestone, dolostone, and siltstone. Upper Cambrian shelf rocks are sparse in Sonora; where present, they consist chiefly of siltsotne and minor limestone. Cambrian shelf rocks display subtle facies changes from est to east across Sonora. In northwestern Sonora, these rocks attain their maximum thickness and may represent the Early Cambrian shelf margin. At the Sierra Agua Verde section, 110 km (68 mi) east of Hermosillo, these rocks thin, have greater proportions of clastic material, and were probably deposited in an inner-shelf setting. A major unconformity is present near the base of the Cambrian in Sonora and is similar to the Sauk I unconformity in the Wood Canyon Formation in Nevada and California. The top of the Cambrian is transitional with overlaying Ordovician strata. The most complete sections of Ordovician shelf rocks in Sonora are 50 km (31 mi) northwast of Hermosillo. In these sections, the Lower Ordovician is characterized by intraclastic limestone, siltstone, shale, and chert. The Middle Ordovician is mostly silty limestone and quartzite, and the Upper Ordovician is cherty limestone and some argillaceous limestone. A major disconformity separates the Middle Ordovician quartzite from the overlying Upper Ordovician carbonate rocks and is similar to the disconformity between the Middle and Upper Ordovician Eureka Quartzite and Upper Ordovician Ely Springs Dolomite in Nevada and California. In parts of northwestern Sonora, Ordovician rocks are disconformably overlain by Upper Silurain rocks. Northeastward in Sonora and Arizona, toward the craton, Ordovician rocks are progressively truncated by a major onlap unconformity and are overliand by Devonian rocks. Except in local area, Ordovician rocks are generally absent in cratonic platform sequences in northern Sonora and southern Arizona.

Arizona, Sonora↗

USGS2012

Demographics and run timing of adult Lost River ( Deltistes luxatus ) and shortnose ( Chasmistes brevirostris ) suckers in Upper Klamath Lake, Oregon, 2011

Executive Summary Data from a long-term capture-recapture program were used to assess the status and dynamics of populations of two long-lived, federally endangered catostomids in Upper Klamath Lake, Oregon. Lost River suckers ( Deltistes luxatus ) and shortnose suckers ( Chasmistes brevirostris ) have been captured and tagged with passive integrated transponder (PIT) tags during their spawning migrations in each year since 1995. In addition, beginning in 2005, individuals that had been previously PIT-tagged were re-encountered on remote underwater antennas deployed throughout sucker spawning areas. Captures and remote encounters during spring 2011 were used to describe the spawning migrations in that year and also were incorporated into capture-recapture analyses of population dynamics. Cormack-Jolly-Seber (CJS) open population capture-recapture models were used to estimate annual survival probabilities, and a reverse-time analog of the CJS model was used to estimate recruitment of new individuals into the spawning populations. In addition, data on the size composition of captured fish was examined to provide corroborating evidence of recruitment. Survival and recruitment estimates were used to derive estimates of changes in population size over time and to determine the status of the populations in 2010. Separate analyses were conducted for each species and also for each subpopulation of Lost River suckers (LRS). One subpopulation of LRS migrates into tributaries to spawn, similar to shortnose suckers (SNS), whereas the other subpopulation spawns at upwelling areas along the eastern shoreline of the lake. In 2011, we captured, tagged, and released 806 LRS at four lakeshore spawning areas and recaptured an additional 1,006 individuals that had been tagged in previous years. Across all four areas, the remote antennas detected 6,547 individual LRS during the spawning season. Spawning activity peaked in April and most individuals were encountered at Sucker Springs and Cinder Flats. In the Williamson River, we captured, tagged, and released 2,742 LRS and 123 SNS, and recaptured 376 LRS and 58 SNS that had been tagged in previous years. Remote PIT tag antennas in the traps at the weir on the Williamson River and remote antenna systems that spanned the river at four different locations on the Williamson and Sprague Rivers detected a total of 16,494 LRS and 5,450 SNS. Most LRS passed upstream between mid-April and mid-May when water temperatures were rising and near or greater than 10 °C. In contrast, the largest peaks in upstream passage of SNS occurred in early and mid-May when water temperatures were rising and near or greater than 12 °C. Finally, an additional 875 LRS and 1,600 SNS were captured in trammel net sampling at pre-spawn staging areas in the northeastern portion of the lake. Of these, 191of the LRS and 571 of the SNS had been PIT-tagged in previous years. For LRS, encounter histories showed that more than 90 percent of the fish captured at the staging areas were members of the subpopulation that spawns in the tributaries. Capture-recapture analyses for the LRS subpopulation that spawns at the shoreline areas included encounter histories for more than 10,500 individuals, and analyses for the subpopulation that spawns in the tributaries included more than 22,000 encounter histories. With a few exceptions, the survival of males and females in both subpopulations was high (greater than 0.9) between 1999 and 2009. Notably lower survival occurred for both sexes from the tributaries in 2000, for both sexes from the shoreline areas in 2002, and for males from the tributaries in 2006. Between 2001 and 2010, the abundance of males in the lakeshore spawning subpopulation decreased by 50–60 percent and the abundance of females decreased by 29–44 percent. Capture-recapture models suggested that the abundance of the river spawning subpopulation of LRS has increased substantially since 2006. The increase over this period was largely due to large estimated recruitment events in 2003, 2006, and 2008. We know that the estimate in 2006 is substantially biased in favor of recruitment due to a sampling issue. We are skeptical of the magnitude of recruitment indicated by the 2003 and 2008 estimates as well because very few small individuals that would indicate the presence of new recruits were captured in those years. If we assume that little or no recruitment has occurred, the abundance of both sexes in the river spawning subpopulation decreased by more than 40 percent between 2002 and 2010. Capture-recapture analyses for SNS included encounter histories for more than 15,500 individuals. The majority of annual survival estimates between 2001 and 2009 were high (greater than 0.8), but SNS did experience more years of low survival than either LRS subpopulation. The survival of both sexes was particularly low in both 2001 and 2004, and male survival also was somewhat low in 2002 and 2006. Capture-recapture models and size composition data indicated that recruitment of new individuals into the SNS spawning population was trivial in nearly all years between 2001 and 2009. As a result, the abundance of males decreased by 64–82 percent and the abundance of females decreased by 62–76 percent between 2001 and 2010. Despite relatively high survival in most years, both species have experienced substantial declines in the abundance of spawning fish because losses from mortality have not been balanced by recruitment of new individuals. Although capture-recapture data indicate substantial recruitment of new individuals into the adult spawning populations for SNS and river spawning LRS in some years, size data do not corroborate these estimates. In fact, fork length data indicate that all populations are largely comprised of fish that were present in the late 1990s and early 2000s. As a result, the status of the endangered sucker populations in Upper Klamath Lake remains worrisome, and the situation is most dire for shortnose suckers. Future investigations should explore the connections between sucker recruitment and survival and various environmental factors, such as water quality and disease. Our monitoring program provides a robust platform for estimating vital population parameters, evaluating the status of the populations, and assessing the effectiveness of conservation and recovery efforts.

California, Oregon↗