Theodore C. Bjornn

Behavioral Thermoregulation and Slowed Migration by Adult Fall Chinook Salmon in Response to High Columbia River Water Temperatures

Abstract The relationships between lower Columbia River water temperatures and migration rates, temporary tributary use, and run timing of adult fall Chinook salmon Oncorhynchus tshawytscha were studied using historical counts at dams and recently collected radiotelemetry data. The results from more than 2,100 upriver bright fall Chinook salmon radio-tagged over 6 years (1998, 2000–2004) showed that mean and median migration rates through the lower Columbia River slowed significantly when water temperatures were above about 20°C. Slowed migration was strongly associated with temporary use of tributaries, which averaged 2–7°C cooler than the main stem. The proportion of radio-tagged salmon using tributaries increased exponentially as Columbia River temperatures rose within the year, and use was highest in the warmest years. The historical passage data showed significant shifts in fall Chinook salmon run timing distributions concomitant with Columbia River warming and consistent with increasing use of therm...

Hydrosystem, Dam, and Reservoir Passage Rates of Adult Chinook Salmon and Steelhead in the Columbia and Snake Rivers

Abstract We assessed upstream migration rates of more than 12,000 radio-tagged adult Chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss past a series of dams and reservoirs on the Columbia and Snake rivers. Most fish passed each dam in less than 2 d. Migration behavior in reservoirs and through multiple dam–reservoir reaches varied within and between years and between species. Within years, spring–summer Chinook salmon migrated more rapidly as water temperature and date of migration increased; between years, spring–summer Chinook salmon migrated fastest in low-discharge years. Steelhead migrations slowed dramatically when summer water temperatures peaked within each year, then increased as rivers cooled in fall. Mean summer temperatures explained more between-year variation in steelhead passage rates than did differences in discharge. Fall Chinook salmon migration rates also slowed during periods of warm water. Protracted passage times within the hydrosystem were most likely for fish from all...

Passage Efficiency of Adult Pacific Lampreys at Hydropower Dams on the Lower Columbia River, USA

Abstract Hydropower dams in the lower Columbia River may contribute to declines in the populations of anadromous Pacific lamprey Lampetra tridentata by limiting access to historical spawning locations. To identify obstacles to migration, we documented the movements of radio-tagged adult Pacific lampreys in specific areas of fishways (entrances, collection channels, transition areas, ladders, and counting stations) at the first three dams they encounter as they move upstream (Bonneville, The Dalles, and John Day). From 1997 to 2000, 147-299 radio-tagged lampreys were released downstream from Bonneville Dam. In 1997 and 2000, we also moved 50 radio-tagged lampreys each year to positions upstream from Bonneville Dam to assess the passage success of fish that had not passed through an entire fishway (i.e., “naive fish”). The passage efficiency of lampreys at Bonneville Dam was 38-47%, and the median time required to pass over the dam ranged from 4.4 to 5.7 d. In contrast, 50-82% of the lampreys passed over Th...

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...

Influence of Flow and Temperature on Survival of Wild Subyearling Fall Chinook Salmon in the Snake River

Abstract Summer flow augmentation to increase the survival of wild subyearling fall chinook salmon Oncorhynchus tshawytscha is implemented annually to mitigate for the development of the hydropower system in the Snake River basin, but the efficacy of this practice has been disputed. We studied some of the factors affecting survival of wild subyearling fall chinook salmon from capture, tagging, and release in the free-flowing Snake River to the tailrace of the first dam encountered by smolts en route to the sea. We then assessed the effects of summer flow augmentation on survival to the tailrace of this dam. We tagged and released 5,030 wild juvenile fall chinook salmon in the free-flowing Snake River from 1998 to 2000. We separated these tagged fish into four sequential within-year release groups termed cohorts (N = 12). Survival probability estimates (mean ± SE) to the tailrace of the dam for the 12 cohorts when summer flow augmentation was implemented ranged from 36% ± 4% to 88% ± 5%. We fit an ordinary...

Juvenile Life History of Wild Fall Chinook Salmon in the Snake and Clearwater Rivers

Abstract Dam construction in the 1950s and 1960s blocked passage to the historical spawning area of Snake River fall chinook salmon Oncorhynchus tshawytscha. We obtained water temperature data and collected juvenile fall chinook salmon in three present-day spawning areas from 1992 to 2000 to investigate the relation between water temperature and juvenile life history events. We used historical water temperatures and the literature to depict juvenile life history in the historical spawning area. Water temperatures in the three present-day spawning areas differed significantly from winter to spring, when eggs were incubating (P ≤ 0.0001), as well as during spring, when juveniles were rearing and starting seaward migration (P ≤ 0.0001). When water temperatures were warmer, the timing of most life stages was generally earlier. The life stages included fry emergence (r 2 = 0.85, N = 14, P < 0.0001), growth to parr size (r 2 = 0.94, N = 15, P < 0.0001), and smolt emigration (r 2 = 0.93, N = 14, P < 0.0001). The...

Regurgitation Rates of Intragastric Radio Transmitters by Adult Chinook Salmon and Steelhead during Upstream Migration in the Columbia and Snake Rivers

Abstract Regurgitation rates for radio tags gastrically implanted into adult salmon Oncorhynchus spp. and steelhead O. mykiss are difficult to estimate in the wild because most fish are never recaptured to allow inspection of secondary tags. During 1996–2000, 9,006 Chinook salmon O. tshawytscha and steelhead with both radio tags and secondary tags were released near Bonneville Dam on the Columbia River (Washington–Oregon), and 1,764 fish were recaptured in mid-migration 460 km upstream on the lower Snake River. Minimum annual regurgitation rates ranged from 0.4% to 10.9% for spring–summer Chinook salmon (pooled rate = 3.0%; n = 838), from 3.5% to 4.3% for steelhead (pooled rate = 4.0%; n = 881), and from 0% to 5.6% for fall Chinook salmon (pooled rate = 2.2%; n = 45). Fish that lost transmitters retained them a median of 7 d (average = 14.1 d) before regurgitation, and a majority of losses occurred in the lower Columbia River. Transmitter retention was improved by placing rubber bands or a ring of surgica...

Stock-Specific Migration Timing of Adult Spring–Summer Chinook Salmon in the Columbia River Basin

Abstract An understanding of the migration timing patterns of Pacific salmon Oncorhynchus spp. and steelhead O. mykiss is important for managing complex mixed-stock fisheries and preserving genetic and life history diversity. We examined adult return timing for 3,317 radio-tagged fish from 38 stocks of Columbia River basin spring–summer Chinook salmon O. tshawytscha over 5 years. Stock composition varied widely within and between years depending on the strength of influential populations. Most individual stocks migrated at similar times each year relative to overall runs, supporting the hypotheses that run timing is predictable, is at least partially due to genetic adaptation, and can be used to differentiate between some conspecific populations. Arrival timing of both aggregated radio-tagged stocks and annual runs was strongly correlated with river discharge; stocks arrived earlier at Bonneville Dam and at upstream dams in years with low discharge. Migration timing analyses identified many between-stock ...

Migration depths of adult spring and summer Chinook salmon in the lower Columbia and Snake Rivers in relation to dissolved gas supersaturation

Abstract High spill volume at dams can create supersaturated dissolved gas conditions that may have negative effects on fish. Water spilling over Columbia and Snake River dams during the spring and summer creates plumes with high dissolved gas that extend downstream of dam spillways and throughout reservoirs and creates gas-supersaturated conditions throughout the water column. During the spring and summer of 2000, 228 adult Chinook salmon Oncorhynchus tshawytscha were tagged at Bonneville Dam with archival radio data storage transmitters (RDSTs) that recorded depth and water temperature as the fish migrated through dams and reservoirs of the lower Columbia and Snake rivers. Swimming depths from 131 of the 228 adult spring and summer Chinook salmon tagged with RDSTs were used to estimate the potential for gas bubble formation given in-river dissolved gas concentrations and hydrostatic compensation. We found that adult spring and summer Chinook salmon spent a majority of the time at depths that would have ...

Fallback by Adult Sockeye Salmon at Columbia River Dams

Abstract We implanted radio transmitters into sockeye salmon Oncorhynchus nerka in 1997 to determine the (1) fallback percentage and rate at eight Columbia River dams, (2) effect of fallback on adult counts at each dam, (3) relations between spillway discharge and fallback, (4) relations between injuries and fallback, and (5) relations of fallback and survival to spawning tributaries. The rate of fallback, that is, the total number of fallback events at a dam divided by the number of fish known to have passed the dam, ranged from 1.9% to 13.7% at the eight dams. The rate of fallback was highest at Bonneville Dam, the dam with the most complex fishway. Fallback produced overcounts of 2% to 7% at most dams. Fallback was weakly related to spill volume at Bonneville Dam. Significantly more sockeye salmon with head injuries fell back than fish without head injuries. About 40% of the sockeye salmon had injuries from marine mammals, but these injuries were not associated with the rate of fallback. The rate of su...