Survival Of Chinook Salmon Research Articles

Effects of rearing system on growth responses and saltwater tolerance in spring Chinook Salmon (Oncorhynchus tshawytscha)

Pacific salmon (Oncorhynchus spp.) produced in United States conservation hatcheries are commonly reared in tanks and raceways supplied with single-pass water. As controlled studies comparing water reuse vs. traditional single-pass aquaculture systems are limited, we conducted a 20-week growth trial followed by a one-week saltwater challenge to compare growth, survival and saltwater tolerance of juvenile spring Chinook salmon (O. tshawytscha, 5.2 g initial weight) reared in single-pass rectangular tanks (hereafter rectangular tanks), single-pass circular tanks (hereafter circular tanks), or in circular tanks of recirculating aquaculture systems (RAS, 3% constant makeup water on a flow basis) or partial recirculating aquaculture systems (PRAS, 20% constant makeup water on a flow basis). Water volume provided to rearing tanks did not differ among systems, but water velocities in the circular tanks and in the RAS and PRAS fish culture tanks were higher than in the rectangular tanks. Dissolved oxygen levels declined throughout the study in all systems and were significantly lower in RAS than in the single-pass systems. By week 16, ammonia levels were significantly reduced while nitrite‑nitrogen (NO2-N) and nitrate‑nitrogen (NO3-N) levels were significantly elevated in RAS compared with single-pass systems.Salmon grown in rectangular tanks exhibited significantly lower weight gain and feed efficiency (FE; g gain/g feed) compared with fish reared in the other systems. Survival of salmon grown in the rectangular tanks (99.1%) also was significantly lower than that of fish reared in circular tanks (100%) or PRAS (100%), but was not different from that of fish reared in RAS (99.8%). Survival during the saltwater challenge was significantly reduced in salmon that were reared during the growth trial in rectangular tanks (70%) compared with that of fish that were reared in the other systems (92–96%). Results of this study suggest lower growth and survival of salmon reared in rectangular tanks may be related to reduced water velocity and that RAS and PRAS may be appropriate for rearing spring Chinook salmon for conservation purposes.

Maximizing salmonid bycatch survival with passively operated commercial fish traps

Commercial fish traps were recently implemented at a limited scale in the lower Columbia River in efforts to selectively harvest hatchery-origin fishes with minimal mortality of wild-origin salmonids listed under the U.S. Endangered Species Act. Prior studies of a modified passive trapping technique demonstrated nearly 100 % survival among adult salmonids released as bycatch. Building upon this research, additional survival studies for adult coho salmon, spring-run Chinook salmon, and summer-run Chinook salmon were conducted between 2019 and 2021 at two separate fish trap sites in the lower Columbia River. Over three years of study, we used mark-recapture and net pen holding methodologies to estimate post-release survival of Chinook salmon and coho salmon, respectively. Evaluating detections of Chinook salmon tagged and released from a passively operated fish trap in 2019, detection at Bonneville Dam over a mean 6.5 d upriver migration (167 km) was 1.000 (95 % CI: S ≥ 0.970) for the sample genetically assigned to populations originating upriver of Bonneville Dam. Through two separate net pen holding studies, post-release survival of coho salmon was estimated at 1.000 (95 % CI: S ≥ 0.975) over 4 d in 2020 and 0.965 (95 % CI: 0.948 ≤ S ≤ 0.969) over 6 d in 2021. Given that these analyses lacked control groups to adjust survival estimates for confounding mortality effects, study results are inherently conservative. Ultimately, the findings of our research support the conclusions of prior studies and further suggest that passively operated fish traps may allow for selective harvesting of targeted fish stocks with little to no mortality of adult salmonid bycatch.

Effects of sediment flushing operations versus natural floods on Chinook salmon survival

Flushing is a common measure to manage and reduce the amount of sediment stored in reservoirs. However, the sudden release of large volumes of sediment abruptly increases the suspended solids concentration and alters the riverbed composition. Similar effects can be produced also by natural flood events. Do flushing operations have more detrimental impacts than natural floods? To answer this question, we investigated the impact of flushing on the survival of the Chinook salmon (Oncorhynchus tshawytscha) in the Sandy River (OR, USA), assuming that sediment is flushed from hypothetical bottom gates of the, now decommissioned, Marmot Dam. The effects of several flushing scenarios are analyzed with a 2D morphodynamic model, together with habitat suitability curves and stress indicators. The results show that attention has to be paid to duration: the shorter the flushing operation, the lesser the stresses on fish survival and spawning habitats. Flushing causes high stress to salmon eggs and larvae, due to unbearable levels of suspended sediment concentrations. It also decreases the areas usable for spawning due to fine-sediment deposition, with up to 95% loss at peak flow. Without the dam, the corresponding natural flood event would produce similar effects, with up to 93% loss. The study shows that well-planned flushing operations could mimic a natural impact, but only partly. In the long-term, larger losses of spawning grounds can be expected, since the removal of fine sediment with the release of clear water from the reservoir is a lengthy process that may be undesirable due to water storage reduction.

Survival of a threatened salmon is linked to spatial variability in river conditions

Extirpation of the Central Valley spring-run Chinook salmon ( Oncorhynchus tshawytscha) evolutionary significant unit (ESU) from the San Joaquin River is emblematic of salmonid declines across the western seaboard of the United States. Habitat restoration and fish reintroduction efforts are ongoing, but recent telemetry studies have revealed low outmigration survival of juveniles to the ocean. Previous investigations have focused on modeling survival relative to river discharge and geographic regions, but have largely overlooked the effects of habitat variability. To evaluate the link between environmental conditions and survival of juvenile spring-run Chinook salmon, we combined high spatial resolution habitat mapping approaches with acoustic telemetry along a 150 km section of the San Joaquin River during the spring of 2019. While overall outmigration survival was low (5%), our habitat-based classification scheme described variation in survival of acoustic-tagged smolts better than other candidate models based on geography or distance. Two regional mortality sinks were evident along the longitudinal profile of the river, revealing poor survival in areas that shared warmer temperatures but that diverged in chlorophyll a, fluorescent dissolved organic matter (fDOM), turbidity, and dissolved oxygen levels. These findings demonstrate the value of integrating river habitat classification frameworks to improve our understanding of survival dynamics of imperiled fish populations.

Quantification of thermal impacts across freshwater life stages to improve temperature management for anadromous salmonids.

Water temperature is the major controlling factor that shapes the physiology, behaviour and, ultimately, survival of aquatic ectotherms. Here we examine temperature effects on the survival of Chinook salmon (Oncorhynchus tshawytscha), a species of high economic and conservation importance. We implement a framework to assess how incremental changes in temperature impact survival across populations that is based on thermal performance models for three freshwater life stages of Chinook salmon. These temperature-dependent models were combined with local spatial distribution and phenology data to translate spatial–temporal stream temperature data into maps of life stage-specific physiological performance in space and time. Specifically, we converted temperature-dependent performance (i.e. energy used by pre-spawned adults, mortality of incubating embryos and juvenile growth rate) into a common currency that measures survival in order to compare thermal effects across life stages. Based on temperature data from two abnormally warm and dry years for three managed rivers in the Central Valley, California, temperature-dependent mortality during pre-spawning holding was higher than embryonic mortality or juvenile mortality prior to smolting. However, we found that local phenology and spatial distribution helped to mitigate negative thermal impacts. In a theoretical application, we showed that high temperatures may inhibit successful reintroduction of threatened Central Valley spring-run Chinook salmon to two rivers where they have been extirpated. To increase Chinook salmon population sizes, especially for the threatened and declining spring-run, our results indicate that adults may need more cold-water holding habitat than currently available in order to reduce pre-spawning mortality stemming from high temperatures. To conclude, our framework is an effective way to calculate thermal impacts on multiple salmonid populations and life stages within a river over time, providing local managers the information to minimize negative thermal impacts on salmonid populations, particularly important during years when cold-water resources are scarce.

Effects of early-life stage and environmental factors on the freshwater and marine survival of Chinook salmon (Oncorhynchus tshawytscha) in rivers of Southeast Alaska

Effects of early-life stage and environmental factors on the freshwater and marine survival of Chinook salmon (Oncorhynchus tshawytscha) in rivers of Southeast Alaska

Phenology and Fraser River sockeye salmon marine survival

Inspired by the pioneering work of Dr. Bill Peterson who demonstrated the utility of ocean indicators at predicting survival of coho and chinook salmon in the Columbia River, we investigated whether the phenology of primary productivity could explain variable marine survival of Fraser River sockeye salmon. Building on a study that had found a strong correlation between satellite-derived spring chlorophyll concentrations in Queen Charlotte Sound (British Columbia) and smolt survival, we hypothesized that smolt migration phenology could help to explain interannual survival differences among years. Applying a new migration model to 18 years of smolt migration data from Chilko Lake demonstrated that interannual differences in smolt migration timing were organized in up to 3 pulses of abundance with a general trend by the largest peak toward earlier peak migration dates over the time series (1998–2016). Analysis of satellite-derived fluorescence line height data within Queen Charlotte Sound identified 4 productivity domains through which most young sockeye salmon would migrate. Each domain had distinct seasonal productivity patterns. With these data, we were unable to demonstrate significant correlations between spring bloom dates in these domains and smolt marine survival, or between smolt migration timing and marine survival. Having separate survival estimates for each pulse and phenological indicators of the sockeye salmon prey base might improve our ability to test the hypothesis that phenology matters to sockeye salmon in the Queen Charlotte Sound region.

Evaluation of Juvenile salmon passage and survival through a fish weir and other routes at Foster Dam, Oregon, USA

AbstractDownstream passage for juvenile Chinook salmon Oncorhynchus tshawytscha (Walbaum) and steelhead Oncorhynchus mykiss (Walbaum) through the fish weir at Foster Dam, Oregon, was evaluated to assess the weir's efficacy as a long‐term passage solution. Radio telemetry was used to estimate survival, passage and effectiveness for the fish weir, spillway and turbines. Survival of Chinook salmon through the fish weir varied by season and reservoir elevation (66%–87%), and passage proportions were low (8%–20%). Fish weir effectiveness was low to moderate (0.39–2.09). Steelhead survival was lower (57%–77%) but passed the fish weir in higher proportions (77%), and weir effectiveness was consistently high (2.96–5.49). The results indicate the existing fish weir will not be a suitable long‐term passage solution for all species. However, because of the high passage proportions and effectiveness observed for steelhead, further development of the surface‐flow concept appears to be promising for safely passing downstream‐migrating fishes.

Understanding the behavior and ecology of Chinook salmon (Oncorhynchus tshawytscha) on an important feeding ground in the Gulf of Alaska

Population declines and demographic changes of Chinook salmon (Oncorhynchus tshawytscha), have been documented throughout this species’ range, though information on natural and anthropogenic mechanisms related to these changes are not fully understood. To provide insights into marine behaviors and survival of Chinook salmon, 40 pop-up satellite archival tags (PSATs), that collected environmental data, were attached to large (69–100 cm FL) Chinook salmon caught in the marine waters of Cook Inlet, Alaska. PSATs provided evidence of predation on tagged Chinook salmon by ectothermic and unconfirmed predators, and provided valuable information about the migratory characteristics and occupied depths and temperatures of this species while occupying Cook Inlet and the Gulf of Alaska. The results from this study suggest that late-marine mortality of Chinook salmon of a variety of stock-origins by apex predators is more common in Cook Inlet than previously thought, and may be used to improve our understanding this species’ population dynamics. Furthermore, results from this study adds to the existing knowledge of marine habitat use by Chinook Salmon and may be useful in assessing the vulnerability and interactions between this species and anthropogenic activities.

Juvenile Chinook Salmon Survival, Travel Time, and Floodplain Use Relative to Riverine Channels in the Sacramento–San Joaquin River Delta

AbstractFloodplains provide multiple benefits to both resident and migratory fish species, including juvenile Chinook Salmon Oncorhynchus tshawytscha, but direct comparisons of survival during migration through a floodplain versus riverine routes are scarce. The Yolo Bypass is a broad floodplain of the Sacramento River that floods in about 30% of years in response to large, uncontrolled runoff events. We analyzed data from an acoustic telemetry study conducted in winter 2016 to estimate the proportion of tagged juvenile Chinook Salmon entrained from the Sacramento River into the Yolo Bypass and their spatial distribution within the Yolo Bypass. In addition, we compared survival and travel time of Chinook Salmon that migrated through the Yolo Bypass to those migrating via alternative non‐floodplain migration routes at varying stages of a flood event that activated the Yolo Bypass. We found that entrainment into the Yolo Bypass ranged from 1% to 80% among different release groups, with the highest entrainment coinciding with the peak of the March 2016 flooding event. Survival for Chinook Salmon migrating through the Yolo Bypass was similar to survival of those migrating through main‐stem migration routes. At the relatively high flows necessary to enable flooding of the Yolo Bypass, survival estimates varied little among release groups and migration routes. Furthermore, mean daily survival rates for Chinook Salmon migrating through the flooded Yolo Bypass were comparable to those of fish migrating through the other non‐floodplain routes. Median travel times remained relatively constant during various stages of flooding in the Yolo Bypass. This research should help managers to better understand the potential costs and benefits to floodplain restoration and routing of migrating Chinook Salmon into off‐channel habitat.

Correspondence between scale growth, feeding conditions, and survival of adult Chinook salmon returning to Puget Sound and coastal Washington: Implications for forecasting

In this study, we used scale analysis of returning adults to examine the relationship between early marine growth and survival for Chinook salmon (Oncorhynchus tshawytscha) returning to the Puget Sound and coastal Washington, USA. In total, we examined scales from 2604 individuals from 5 stocks over 7 outmigration years characterized by a range of survival conditions (range from 0.11 to 9.50%). We observed a positive relationship between growth during the first year at sea and survival for adults returning to Puget Sound and the Washington coast. Scale growth during the first year at sea did not co-vary between coastal Washington and Puget Sound stocks, and in most years coastal Chinook salmon attained a larger size at the end of the first year at sea. Large scale oceanographic variables (PDO, NPGO) were not significantly related to variation in scale growth, but for some Puget Sound populations, scale growth was higher in years of cooler sea surface temperatures and lower Pink salmon (O. gorbuscha) abundance. We developed a biological indicator for forecasting cohort survival of Tumwater Falls hatchery Chinook salmon on the Deschutes River, WA using marine growth estimates of the earliest returning fish (age-21). The marine growth index predicted survival better for 8 brood years compared to a recent 5 year average returns forecasting approach (3.40% vs 35.41% Mean Percent Error). Results from this study suggest that early marine growth is important to the survival of Puget Sound and coastal Washington Chinook salmon and may be a useful biological indicator to improve pre-season forecasting of Chinook salmon populations in Washington State.

Experimental Quantification of Piscivore Density and Habitat Effects on Survival of Juvenile Chinook Salmon in a Tidal Freshwater Estuary

Introduction of non-native piscivores has been implicated in the decline of native Chinook Salmon Oncorhynchus tshawytscha via predation during juvenile life stages. However, isolating effects of predation on Chinook Salmon survival is complicated by changes in physical habitat that are often concomitant with non-native piscivore establishment. We performed two field experiments with enclosures deployed in tidal freshwater habitat to quantify effects of non-native Largemouth Bass Micropterus salmoides density and habitat type on the survival and movement behavior of juvenile Chinook Salmon. In experiment one, bass densities were doubled and quadrupled across treatment levels with a baseline value of field-observed densities. In experiment two, three habitat types (dock, submerged aquatic vegetation (SAV), and open water) were tested while bass density was held at the medium (doubled) value. Juvenile Chinook Salmon implanted with passive integrated transponders were released into the enclosures to assess their survival and movement through the treatments over multiple trials. Mark-recapture models indicated that the survival of juvenile Chinook Salmon was reduced in the medium bass density, but not the high-density treatment, when compared to the lowest density value suggesting relationships may be non-linear. The SAV treatment had a well-supported negative effect on juvenile Chinook Salmon survival relative to a dock or open water. Residence time was positively related to bass density. Relationships with a habitat were not consistently different. These results suggest that restoration strategies targeting non-native SAV control could reduce predation on juvenile Chinook Salmon by Largemouth Bass. However, piscivore density manipulation may only be effective over a narrow range of densities.

Historic drought influences outmigration dynamics of juvenile fall and spring-run Chinook Salmon

Riverine ecosystems around the world have undergone extensive anthropogenic alterations, often to the detriment of native aquatic biodiversity. Migratory fishes are particularly vulnerable to habitat fragmentation and degradation. For example, Chinook Salmon populations in the Sacramento River, CA have been declining for nearly a century. Its Mediterranean climate, position in a landscape dominated by urban and agricultural land use, and the presence of an inland delta that serves as the hub of California’s vast water conveyance system, makes this a particularly perilous region for migrating juvenile salmon. This study used acoustic telemetry to investigate survival and routing of juvenile fall and spring-run Chinook Salmon through their riverine and estuarine migratory phases during the historic California drought of 2012–2016. Survival to the ocean in this river system is already lower relative to Chinook Salmon populations in North American. Survival to the Pacific Ocean ranged from 0.0–9.1% over the course of this three-year study. Use of four migratory routes through the Delta was variable, both within and between years. We documented extensive use and relatively high survival in Steamboat Slough (up to 41.5% routing through and up to 39.8% survival), part of the Sacramento River’s distributary network. Migration through this pathway precludes juvenile salmon from encountering junctions leading to low survival routes. Results from this modeling effort provide valuable information and highlight opportunities for directing management actions to benefit these ecologically and economically valuable runs of Chinook Salmon.

Effect of release timing on apparent survival of juvenile fall run Chinook Salmon from Coleman National Fish Hatchery

Hatchery production of Pacific salmon for release into the environment is a common tool for conservation and supplementation of depleted stocks. Hatchery conditions are controlled to support high survival rates; however, once released into the environment, managers have little control over conditions experienced by juveniles. Thus, release timing is a critical decision in hatchery operations. This 3-year study used acoustic telemetry to estimate release timing effects on migration survival of fall run Chinook Salmon from the largest hatchery in California: the Coleman National Fish Hatchery. Juvenile Chinook Salmon implanted with JSATS transmitters were released in two or more groups each year, concomitant with the regular hatchery production. Arrays of acoustic monitors were deployed at six locations within the 517 km migration route to estimate reach-specific survival of each release. Mark-recapture models identified both year and release timing effects on reach-specific survival. In years when release effects were well-supported, survival was higher in the earlier release group. Survival in subsequent releases was similar or significantly lower indicating that conditions in the river may decline or stay the same but improvement was not observed. Survival was consistently high in the first 92 km of the migration route and may be related to predator swamping from the release of millions of hatchery fish. Survival declined, and became more variable, within the lower 425 km of the river with the lowest rates observed in the tidal bay-delta. These results indicate that both year and release timing can strongly influence survival and that time between releases likely influences the magnitude of the effect.

Density‐dependent marine survival of hatchery‐origin Chinook salmon may be associated with pink salmon

AbstractUnderstanding how protected species influence the population dynamics of each other is an essential part of ecosystem‐based management. Chinook salmon (Oncorhynchus tshawytscha) are critical prey for endangered southern resident killer whales (SRKWs; Orcinus orca), and increasing releases of hatchery Chinook salmon has been proposed to aid SRKW recovery. We analyzed 30 yr of data and found that density‐dependent survival of hatchery Chinook salmon released into the central and southern parts of the Salish Sea (Washington, USA; and British Columbia, Canada) may be associated with the presence of naturally produced pink salmon (O. gorbuscha), which are highly abundant as juveniles only in even‐numbered years. We first modeled hatchery Chinook salmon marine survival as a function of the numbers of juvenile Chinook released and the presence of emigrating juvenile pink salmon between 1983 and 2012. Then, we related reconstructed numbers of hatchery Chinook salmon returning to Puget Sound to the abundance of juvenile Chinook released in even (pink emigration) and odd (non‐pink emigration) years from 1980 to 2010. We found that in some regions of the Salish Sea, both hatchery Chinook salmon marine survival and adult Chinook returns varied depending on the number of hatchery Chinook released and the presence of juvenile pink salmon. Specifically, in some regions survival of hatchery Chinook salmon decreased when greater numbers of juveniles were released into the Salish Sea in even years, when large numbers of pink salmon were present, but increased or remained stable when pink salmon were not present in large numbers (in odd years). This suggests lower, density‐dependent survival of juvenile Salish Sea Chinook salmon during even outmigration years. Our analyses suggest that scientists and managers should further investigate potential mechanisms for density‐dependent survival of hatchery Chinook salmon from Salish Sea hatcheries when designing strategies to maximize adult returns.

Rethinking Strategies for Increasing Salmon Survival

It’s a long-held belief that a series of dams in the Snake River in Northwest USA constructed nearly 50 years ago has led to serious declines in Chinook salmon populations. However, new research by Dr David Welch and his team from Kintama Research Services Ltd shows that survival of Chinook salmon measured by a wide range of government agencies has fallen by 65% along the whole North American West Coast over this period. These results have significant implications for informing conservation strategies to protect and restore this important species.

Density-dependent Marine Survival of Hatchery-origin Chinook Salmon may be Mediated by Pink Salmon

Density-dependent Marine Survival of Hatchery-origin Chinook Salmon may be Mediated by Pink Salmon

Spatial variation of juvenile Chinook Salmon (Oncorhynchus tshawytscha) survival in a modified California river

Spatial variation in habitat structure is a well-recognized characteristic of lotic ecosystems. The resulting patchwork mosaic provides opportunities for growth and survival as well as mortality risks for fish migrating through these systems. Dam construction within a watershed has numerous downstream tail water effects that alter creation and evolution of habitat features used by anadromous fishes that spawn and rear in these reaches. California Central Valley Pacific salmon (Oncorhynchus spp) are largely restricted to areas below impassable dams and these populations are undergoing widespread declines. High mortality of juvenile salmon in these reaches is thought to be a limitation to recovery. We conducted a radio telemetry study to evaluate spatial variation in juvenile Chinook Salmon (O. tschawytscha) survival and survival-environment relationships in three reaches of a Central Valley tail water. Additionally, we used mobile surveys to identify the location of last known detections to elucidate areas of disproportionate mortality. Our results indicated variation in flow and salmon size had greater explanatory power than year effects. However, relationships between flow, salmon size and survival were reach-specific indicating drivers of survival are spatially heterogeneous. Significant clumping of last known detections in the two lower reaches of the river suggests that mortality may be more frequent in these locations. Our results suggest that there is substantial spatial variation in migration mortality and both environmental conditions (flow) and salmon characteristics (size) have a strong influence on observed mortality. This information should be used to target actions that can support Chinook Salmon recovery.

Relating survival of fall-run Chinook Salmon through the San Joaquin Delta to river flow

Survival of juvenile fall-run Chinook Salmon Oncorhynchus tshawytscha from the San Joaquin River (SJR) during their migration through the Sacramento-San Joaquin Delta of California has been low in recent years, and there is uncertainty about the role of river flow on survival. Five years (2010–2014) of acoustic telemetry data from juvenile hatchery-reared salmon offer spatially detailed survival information through this region. Multinomial regression and generalized linear models were used to relate survival to river flow in the SJR and its distributary, Old River (OR), on various spatial and temporal scales. Higher survival to Delta exit (rkm 77 from Golden Gate Bridge) was associated with higher root mean square of OR flow in the strongly tidal interior Delta (rkm 123; P < 0.0001), but not with higher SJR flow either entering the Delta from upstream (rkm 196; P = 0.2795) or measured in the Delta near the riverine/tidal interface (rkm 150; P = 0.3845). Survival in the upstream, more riverine region of the Delta was positively associated with SJR flow measured at rkm 150 and average net flow in the interior Delta (P ≤ 0.0001 for each), suggesting different mechanisms driving survival in the upstream versus downstream reaches of the Delta. The spatial complexity of the survival-flow relationship suggests that efforts to maximize total Delta survival should focus on a sequence of smaller regions, tailoring management strategies to each region rather than a single strategy for the Delta as a whole. Highly variable environmental conditions in this region combined with very low survival require more data to fully address the complex survival-flow relationship, both more years of data on various spatial scales and larger sample sizes of acoustic-tagged fish.

Evaluation of Growth, Survival, and Recruitment of Chinook Salmon in Southeast Alaska Rivers

AbstractRecent reductions in the run sizes of Chinook Salmon Oncorhynchus tshawytscha in Southeast Alaska have resulted in social and economic hardships within the region. For Pacific salmon, including Chinook Salmon, brood year (BY) strength may be determined by size‐selective processes that occur during early marine residence. However, the relative importance of freshwater versus marine growth in determining recruitment success is unknown. We conducted a scale‐based retrospective analysis to examine the relative effects of freshwater and marine growth on survival to the age of reproduction for female Chinook Salmon by BY in the Taku (BYs 1979–1985, 1990–1999, 2002–2004) and Unuk (BYs 1981–1983, 1986–1988, 1994–2003, 2005–2006) rivers located in Southeast Alaska. First‐year marine growth of Chinook Salmon was positively related to total return, productivity (returns per spawner), and marine survival for stocks from both systems. In the Taku River, growth during the third year at sea was positively related to marine survival. Annual growth of Taku River Chinook Salmon was correlated with previous growth through the second year at sea; however, no correlations were detected between adjacent growth zones of Unuk River fish. These findings suggest that current declines in Chinook Salmon abundance in Southeast Alaska is attributed to changes in growth conditions during the first year at sea.