Charles T. Boggs

Fallback, Reascension, and Adjusted Fishway Escapement Estimates for Adult Chinook Salmon and Steelhead at Columbia and Snake River Dams

Abstract During their upstream spawning migration in the Columbia River basin, some adult salmonids Oncorhynchus spp. ascend and then fall back over main-stem hydroelectric dams. Fallback can result in fish injury or death, migration delays, and biases in fishway counts, the primary index for escapement and the basis for production estimates and harvest quotas. We used radiotelemetry to calculate fallback percentages and rates, reascension percentages, biases in fishway escapement estimates due to fallback, and occurrence of behaviorally motivated fallback (correcting overshoot of natal sites) by spring–summer and fall Chinook salmon O. tshawytscha and steelhead O. mykiss. The study area included eight Columbia River and Snake River dams evaluated from 1996 to 2001. For all years combined, about 22% of spring–summer Chinook salmon, 15% of fall Chinook salmon, and 21% of steelhead fell back at least once at a dam. Fallback percentages for spring–summer Chinook salmon were generally highest at Bonneville an...

Effects of Body Size and River Environment on the Upstream Migration of Adult Pacific Lampreys

Abstract Dams in the Columbia River basin present significant obstacles to declining populations of anadromous Pacific lampreys Lampetra tridentata. Mitigation efforts have focused on fine-scale improvements in passage at individual dams, but there is an increasing need for basinwide estimates of survival and escapement. We developed a half-duplex passive integrated transponder (PIT) tag monitoring array at five Columbia and Snake River dams to evaluate adult lamprey migrations. We tagged 3,598 lampreys over 3 years and calculated the rates of main-stem escapement through 15 river reaches. From these data, we assessed the relative effects of lamprey size, river discharge, water temperature, and migration timing on upstream passage. The results indicated high attrition as lampreys progressed upstream. In each year, about one-half of the fish passed one dam, 28–33% passed two dams, 17–19% passed three dams, 4–5% passed four dams, and about 1% passed the first dam on the Snake River (five dams and >300 km up...

Iteroparity in Columbia River summer-run steelhead (Oncorhynchus mykiss) : implications for conservation

We used ultrasound imaging and passive integrated transponder (PIT)-tagging programs to assess maturation status and iteroparity patterns in summer-run steelhead (anadromous rainbow trout, Oncorhynchus mykiss) of the interior Columbia River Basin (Pacific Northwest, USA). Postspawn kelts examined in downstream fish bypass systems at Columbia River and Snake River dams were disproportionately female (>80%) and majorities were of wild origin, unlike prespawn steelhead at these sites. Annual repeat migration estimates varied from 2.9% to 9.0% for kelts tagged at lower Columbia River dams (n = 2542) and from 0.5% to 1.2% for Snake River kelts (n = 3762). Among-site differences reflected greater outmigration distance and additional dam passage hazards for Snake River kelts. There was also strong evidence for condition-dependent mortality, with returns an order of magnitude higher for good- versus poor-condition kelts. Disproportionately more females and wild fish also returned, providing potentially valuable g...

Variability in migration timing of adult Pacific lamprey (Lampetra tridentata) in the Columbia River, U.S.A.

We examined the effects of river environment on the timing of spawning migrations by anadromous Pacific lamprey, Lampetra tridentata, in the Columbia River (U.S.A.). In a 41-year time series of adult lamprey counts, migration timing was earliest in warm, low-discharge years and latest in cold, high-flow years. Threshold temperatures associated with run timing were similar throughout the dataset despite significant impoundment-related warming, suggesting that temperature-dependent migration cues have been temporally stable. Within each year, migration rates of PIT-tagged lampreys were positively correlated with temperature and negatively correlated with discharge through multiple river reaches, offering additional evidence for environmental control of upstream movement. Both visual count and PIT-tag data indicated that there may be population-based differences in migration timing within the aggregate Columbia River lamprey run. These life history and behavioral results have potentially far-reaching implications for management of lamprey species.

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

Abstract Unlike most anadromous salmonids, summer steelhead Oncorhynchus mykiss overwinter in rivers rather than the ocean for 6–10 months prior to spring spawning. Overwintering in rivers may make summer steelhead more vulnerable to harvest and other mortality sources than are other anadromous populations, but there has been little systematic study of this life history strategy. Here, we used a large-scale radiotelemetry study to examine the overwintering behaviors and distributions of 26 summer steelhead stocks within the regulated lower Columbia–Snake River hydrosystem. Over 6 years, we monitored 5,939 fish, of which 3,399 successfully reached spawning tributaries or the upper Columbia River basin and were assigned to specific populations. An estimated 12.4% of fish that reached spawning areas overwintered at least partially within the hydrosystem (annual estimates = 6.8–19.6%), while the remainder overwintered in tributaries. Across all populations, later-arriving fish were more likely to overwinter i...

Transportation of Steelhead Kelts to Increase Iteroparity in the Columbia and Snake Rivers

Abstract We tested the feasibility of transporting steelhead Oncorhynchus mykiss kelts (postspawned adults) around hydroelectric dams on the Snake and Columbia rivers to increase the returns of repeat spawners. Altogether, 5,878 kelts were collected, tagged with passive integrated transponder tags, and assigned to transported or in-river treatment groups at Lower Granite Dam (n = 5,320 [2002–2004]) on the Snake River and John Day Dam (n = 558 [2002]) on the Columbia River. Returns of repeat spawners differed by site and year: 11.1% (62/558) for the John Day Dam sample and 1.4% (27/1,959), 0.5% (6/1,241), and 0.8% (17/2,120) for the Lower Granite Dam samples in 2002, 2003, and 2004, respectively. Transportation tests indicated that kelts transported from the Snake River were approximately 2.3 times more likely to return than fish allowed to migrate in-river. Transport benefits were greatest for wild-origin female kelts, a demographic with high conservation value. There was no significant benefit for kelts ...

Inter-Observer Bias in Fish Classification and Enumeration Using Dual-frequency Identification Sonar (DIDSON): A Pacific Lamprey Case Study

Abstract Dual-frequency Identification Sonar (DIDSON) is increasingly used as a fish monitoring and enumeration tool, but many studies do not evaluate potential observer biases. In this project, we assessed inter-observer differences in the identification and enumeration of adult Pacific lamprey (Entosphenus tridentatus) imaged with DIDSON passing a large dam fishway. Six trained viewers independently identified lamprey observation ‘events’ in the same ∼ 12 h of DIDSON data collected at several fishway locations using two sonar orientations. Among-viewer variability in lamprey enumeration was high and viewer agreement on individual lamprey was often low. A total of 274 unique potential Pacific lamprey events was identified, but individual viewers scored only 89–173 events each (mean = 131, CV = 24%) or 32–63% of the total. Viewer identification rates (events/h) varied several-fold at some sites which we attributed primarily to event non-detection rather than species misclassification. Identification differences were related to viewer confidence, image duration, total fish density, and sonar orientation. Among-viewer agreement was highest in standard-orientation deployments lateral to the swimming lamprey, where images appeared as though acquired from overhead. Imagery in standard orientation had longer event duration and enhanced detection of anguilliform swimming, the most important characteristic for distinguishing Pacific lamprey from other species. Lamprey events observed in rolled orientation (sonar rotated 90°) tended to be short duration with foreshortened head- or tail-first images that reduced viewer confidence. Our results highlight the importance of quality control assessments in acoustic imaging studies, especially those targeting cryptic species and those conducted in hydraulically challenging, multi-species environments.