Evaluation of Chinook salmon (Oncorhynchus tshawytscha) fry survival at Lookout Point Reservoir, western Oregon, 2017

Abstract

A field study was conducted to estimate survival of fry-sized juvenile Chinook salmon (Oncorhynchus tshawytscha) in Lookout Point Reservoir, western Oregon, during 2017. The field study consisted of releasing three groups of genetically marked fish in the reservoir and monthly fish sampling. Fish were released during April 18-19 (43,950 fish), May 30-June 2 (44,145 fish), and on June 28, 2017 (3,920 fish). Reservoir sampling began in May and occurred monthly through October, consisting of 5-day events where juvenile Chinook salmon were collected using various gear types (electrofishing, shoreline traps, gill nets). Data were analyzed using two models: (1) a staggered release-recovery model (SRRM), and (2) a parentage-based tagging (PBT) N-mixture model. The SRRM provided survival estimates from two periods: (1) mid-April to late May (SSRRM1), and (2) late May to late June (SSRRM2). Multiple estimates of survival were possible for each period using different combinations of recovery data from the three groups of fish that were released. Survival estimates for SSRRM1 ranged from 0.470 to 0.520. Estimates for SSRRM2 ranged from 0.968 to 0.969; cumulative survival from mid-April to late June (SSRRM2) was estimated at 0.870. We suspect that issues with the third release group led to biased survival results using the SRRM. The PBT N-mixture model provided survival estimates from six periods: (1) mid-April to mid-May (SNMIX1), (2) mid-May to mid-June (SNMIX2), (3) mid-June to mid-July (SNMIX3), (4) mid-July to mid-August (SNMIX4), (5) mid-August to mid-September (SNMIX5), and (6) mid-September to mid-October (SNMIX6). Survival estimates from the PBT N-mixture model were lowest for SNMIX1 (0.461) and increased monthly to a high of 0.970 for SNMIX6. Cumulative survival from mid-April to mid-July was 0.233 and overall survival from mid-April to mid-October was 0.188. This suggests that most mortality occurred early in the study when juvenile Chinook salmon were small. This could be because these fish were most vulnerable to predation in the reservoir at that time. We determined that mortality of juvenile Chinook salmon was high in the reservoir during this study and similar estimates of parr-to-1 U.S. Geological Survey 2 Oregon State University 2 smolt survival have been observed in other systems. Additional analyses are required, including results from the second year of study (2018), and potentially similar evaluations will need to be made at other locations to determine if reservoir mortality is a limiting survival factor for Chinook salmon in the Middle Fork Willamette River.

Review of trap-and-haul for managing Pacific salmonids (Oncorhynchus spp.) in impounded river systems

“…The intent of the adult releases includes restoring biological contributions of salmon to the ecosystem, providing forage for native bull trout that were recently reintroduced, and supporting research on Chinook salmon prespawn mortality (Sharpe et al 2016;Myers 2017). Middle Fork Willamette River reservoirs have high growth opportunity for juvenile salmonids but contain large populations of predatory fishes and consequently juvenile mortality rates can be high (Brandt et al 2016;Kock et al 2019b). Juvenile Chinook salmon primarily pass dams during fall and winter months in the Middle Fork Willamette River when reservoir elevations are relatively low and deepwater passage routes are available at the dams, though passage mortality through these routes can be quite high (Keefer et al 2012(Keefer et al , 2013.…”

“…Head-of-reservoir collection ( Fig. 1) is currently being considered at several sites where in-reservoir conditions are thought to limit the number of juvenile outmigrants that survive, move downstream, and enter a dam forebay for potential collection (Liedtke et al 2010;Clancey et al 2017;Kock et al 2019b). Headof-reservoir systems may be effective in reservoirs that are very large, have complex bathymetry or hydrology, or lack velocity cues needed for juvenile salmonids to successfully orient and move downstream (e.g., Shasta Reservoir on the Sacramento River, California; Clancey et al 2017).…”

“…Headof-reservoir systems may be effective in reservoirs that are very large, have complex bathymetry or hydrology, or lack velocity cues needed for juvenile salmonids to successfully orient and move downstream (e.g., Shasta Reservoir on the Sacramento River, California; Clancey et al 2017). Such systems may also be appropriate in reservoirs with large populations of piscivorous fishes that can substantially reduce survival of downstream migrants, as in Lookout Point Reservoir on the Middle Fork Willamette River (Kock et al 2019b) and in Fall Creek Reservoir (Murphy et al 2019). Development and testing of head-of-reservoir collection systems is an emerging research topic in trap-and-haul science (Liedtke et al 2010;Clancey et al 2017).…”

“…Survival to spawning of trap-and-hauled adult salmonids can be highly variable among watersheds and among years (Keefer et al 2010;DeWeber et al 2017;Bowerman et al 2018;Kock et al 2019b). Variation in prespawn mortality may be in part explained by seasonal, annual, and watershed-scale variation in environmental conditions affecting infection and/or disease resistance rates, as prespawn mortality has frequently been associated with pathogens (Benda et al 2015;Bowerman et al 2016).…”

Prey Supply and Predation as Potential Limitations to Feasibility of Anadromous Salmonid Introductions in a Reservoir

“…Kock et al [10] reported considerable variation in the effectiveness of the programs reviewed, but also noted that success is context-dependent and defined by different management objectives of stakeholders. Limitations to success of reintroduction into reservoirs are varied [10] and can include migration delays and handling stress leading to high mortality rates for adults, differences in stock-specific production rates of the donor populations [11], the differential fitness of hatchery fish and impacts of interbreeding [12,13], high juvenile mortality rates associated with predation in reservoirs [14], and other challenges for downstream migrating juveniles (e.g., mismatch between water operations and migration timing, collection efficiency of smolt traps, handling stress during collection) [15,16].…”