Fraser River Sockeye Salmon Research Articles

Assessing the impacts of environmental and ecological variables on the performance of Fraser sockeye salmon forecast

The Canadian Fraser River sockeye salmon ( Oncorhynchus nerka) is one of the largest stock complexes in North America, supporting major commercial, recreational, and First Nations fisheries. Sockeye fisheries management relies on an annual pre-season forecast of adult returns. In this study, we developed a comprehensive framework for visualization with a Taylor diagram to evaluate pre-season forecast models annually and identify external drivers important for forecasting sockeye returns. Specifically, we incorporated five new covariates, including sea surface temperature in the Gulf of Alaska and the abundance of salmon species, into the existing forecast models. Results revealed better performances by both the Ricker and Power models when coupled with the newly included covariates. Moreover, models selected over a decade ago underperformed compared to those selected based on our recent retrospective analysis from 2009 to 2020. We advocate for continuous evaluation of forecast models in the face of environmental change, emphasizing the necessity of developing models that incorporate non-stationary processes and assess the impacts of environmental and ecological factors on Fraser sockeye dynamics.

Using repeat injury assessments in adult sockeye salmon (Oncorhynchus nerka) to predict spawning success and describe severity of migration conditions

Pacific salmon (Oncorhynchus spp.) are semelparous and anadromous, and during their up-river migration to spawn can experience injuries and mortality from fisheries interactions and adverse environmental conditions. There is the potential to improve models used to predict those losses by including information on surficial fish condition, but for this information to be useful, we need to understand how injuries change over time, and how injury type influences this change. To do this, we used repeated individual assessments to examine whether injuries accrued during migration on Fraser River sockeye salmon (O. nerka), assessed in the last leg of their migration or on arrival at the spawning grounds, could be used to predict their final injury score at death after spawning. We found that injury scores increased over the spawning period, but this was not driven by any specific type of migration-related injury, and fish initially scored as ‘uninjured’ had the largest increase in injury score, indicating a ceiling effect to our scoring method. Females with higher migration-related injury scores were more likely to experience pre-spawn mortality. Initial injury score accrued during migration was positively correlated with final injury score after spawning but only when initially assessed 45 km from the spawning grounds, and females that spawned accrued more injuries than females that did not spawn. Thus our method was able to use pre-spawn injury scores to predict spawning success but was limited in its ability to use post-spawn injury scores to describe severity of migration conditions. This highlights the need to better understand injury and disease dynamics and further refine injury assessment and scoring methods at the individual level if information on surficial fish condition is to be used to either describe or predict migration severity or pre-spawn mortality at the population level.

Migration timing affects the foraging ecology of Fraser River sockeye salmon stocks in coastal waters of British Columbia, Canada

Coastal migrations of juvenile Pacific salmon Oncorhynchus spp. have evolved to take advantage of optimal ocean foraging conditions and maximize early marine growth and survival. The growth and survival of salmon during the early marine period is affected by both the diversity of encountered coastal habitats, with varying productivity and plankton phenology, and stock-specific migration timings that determine the match-mismatch with their prey. In 2015 and 2016, we investigated temporal and spatial patterns in environmental conditions and zooplankton prey as well as diets and stock composition of juvenile Fraser River sockeye O. nerka during their outmigration through the tidally mixed Discovery Islands and Johnstone Strait in British Columbia (Canada). Three groups of sockeye diet profiles reflected variations in environmental conditions and prey communities. First, in the Discovery Islands, earlier migrating stocks primarily encountered and foraged on small, energy-poor zooplankton prey (barnacles and cladocerans). Second, later migrating stocks foraged mainly on larger, more energy-rich copepod and larvacean prey. And third, in the highly mixed waters of Johnstone Strait, large energy-rich calanoid copepods dominated diets irrespective of migration timing and year. Foraging success was typically low throughout the areas sampled and across the migration period, which may amplify the importance of prey nutritional quality. Our findings highlight the importance of accounting for spatial and temporal differences in foraging environments for migrating species such as juvenile salmon. Furthermore, we demonstrate that the timing of stock migration affects the foraging conditions experienced.

Atlantic salmon farms are a likely source of Tenacibaculum maritimum infection in migratory Fraser River sockeye salmon

Juvenile sockeye salmon (Oncorhynchus nerka) in British Columbia migrate past numerous Atlantic salmon (Salmo salar) farms from which they may acquire infectious agents. We analyse patterns of molecular detection in juvenile sockeye for the bacterium Tenacibaculum maritimum, known to cause disease in fish globally and to cause mouthrot disease in farmed Atlantic salmon in British Columbia. Our data show a clear peak in T. maritimum detections in the Discovery Islands region of British Columbia, where sockeye migrate close to salmon farms. Using well-established differential equation models to describe sockeye migration and bacterial infection, fit to detection data, we assessed support for multiple hypotheses describing farm- and background-origin infection. Our best models (with 99.8% empirical support) describe constant background infection pressure, except around Discovery Islands salmon farms, where farm-origin infection pressure peaked at 12.7 (approximate 95% CI: 4.5 to 31) times background levels. Given the severity of associated disease in related species and the imperilled nature of Fraser River sockeye, our results suggest the need for a more precautionary approach to managing farm–wild interactions in sockeye salmon.

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.

Covariability of Fraser River sockeye salmon productivity and phytoplankton biomass in the Gulf of Alaska

AbstractUsing satellite ocean color measurements and sockeye salmon stock–recruit data from 1995 to 2016, our analysis reveals a significant, positive relationship between Fraser River sockeye productivity and summer chlorophyll a concentrations (Chl‐a) in the northwestern Gulf of Alaska. The correlation is the strongest for the area adjacent to the continental shelf near Kodiak Island (northern Gulf of Alaska), during midsummer of the juvenile sockeye salmon ocean entry year. The inclusion of (Chl‐a) data from this region significantly improved the performance of Ricker stock–recruitment models for ten out of eighteen Fraser River stocks. We discuss the potential oceanographic processes driving the correlation between (Chl‐a) and sockeye productivity. During midsummer, positive sea‐level anomalies in the offshore waters near Kodiak Island suggest the presence of mesoscale eddies, which can transport nutrients to this region and concentrate phytoplankton and zooplankton biomass, thus supporting enhanced sockeye salmon prey abundance. These results suggest a mechanism linking mesoscale oceanographic dynamics to sockeye salmon productivity, and identify a potentially important region for future studies of Fraser River sockeye salmon survival.

Exceptionally high mortality of adult female salmon: a large-scale pattern and a conservation concern

In recent decades, the relative proportion of female sockeye salmon (Oncorhynchus nerka) on spawning grounds of several British Columbia populations has declined. Coincident with the decline has been large changes to oceanic, estuarine, and river migration environments. Over the past 30 years, numerous telemetry tracking and laboratory studies have examined mortality of adult Fraser River sockeye salmon during ocean and freshwater migrations. We reviewed 19 studies that provided 40 situations where male and female mortality could be directly compared. Female mortality averaged 2.1 times greater than that of males and up to eightfold higher. High female mortality was also evident in migrating coho salmon (Oncorhynchus kisutch) and Chinook salmon (Oncorhynchus tshawytscha) and for sockeye salmon in other systems. Female mortality was highest when migration conditions were challenging (e.g., high or turbulent flows, high temperatures, confinement, or handling) and towards end of river migration. We review mechanisms for differential mortality, including energy exhaustion, cardiac performance, physiological stress, and immune factors. Female-specific mortality will become even more pronounced in coming years as ocean and riverine conditions continue to change.

Importance of sample size for estimating prevalence: a case example of infectious hematopoietic necrosis viral RNA detection in mixed-stock Fraser River sockeye salmon (Oncorhynchus nerka), British Columbia, Canada

Proper sample size must be considered when designing infectious-agent prevalence studies for mixed-stock fisheries, because bias and uncertainty complicate interpretation of apparent (test)-prevalence estimates. Sample size varies between stocks and are often smaller than expected during wild-salmonid surveys. Our case example of 2010–2016 survey of sockeye salmon (Oncorhynchus nerka) from different stocks of origin in British Columbia, Canada, illustrated the effect of sample size on apparent-prevalence interpretation. Molecular testing (viral RNA RT-qPCR) for infectious hematopoietic necrosis virus (IHNv) revealed large differences in apparent prevalence across wild salmon stocks (much higher from Chilko Lake) and sampling location (fresh water or marine), indicating differences in both stock and host life-stage effects. Ten of the 13 marine non-Chilko stock–years with IHNv-positive results had small sample sizes (<30 samples per stock–year), which, with imperfect diagnostic tests (particularly lower diagnostic sensitivity), could lead to inaccurate apparent-prevalence estimation. When calculating sample size for expected apparent prevalence using different approaches, smaller sample sizes often led to decreased confidence in apparent-prevalence results and decreased power to detect a true difference from a reference value.

Has Steller Sea Lion Predation Impacted Survival of Fraser River Sockeye Salmon?

The commercially, recreationally, and culturally important Fraser River Sockeye Salmon Oncorhynchus nerka has experienced a productivity decline over the past 3 decades, which—along with greater temporal variation in annual abundance (i.e., cyclic dominance)—may at least partly be due to Steller sea lion Eumetopias jubatus (SSL) predation on returning adult salmon. This assumes that SSLs residing around northern Vancouver Island (British Columbia, Canada) target Sockeye Salmon for just a few weeks during the peak of their run. It is a reasonable enough assumption to warrant immediate priority for field research on SSL behavior and diets during the migration period. We evaluated the plausibility of the assumption with a variety of approaches ranging from simple estimates of maximum SSL consumption to partitioning of observed marine mortality rates and analysis of SSL foraging behavior to show that SSLs could have caused the decline in productivity and abundance of Fraser River Sockeye Salmon.

Running the trophic gauntlet: Empirical support for reduced foraging success in juvenile salmon in tidally mixed coastal waters

AbstractThe productivity of Fraser River sockeye salmon has declined in recent years, with 2019 being the lowest return on record. The cause of the decline is still not fully understood; however, bottom‐up drivers and trophic interactions during the early marine migration are considered to be important contributing factors. McKinnell et al. (Fisheries Oceanography, 23, 2014 and 322) developed a “trophic gauntlet hypothesis,” proposing that low biological productivity leads to an energy deficit from poor foraging opportunities in migrating salmon. When combined with poor foraging conditions in typically productive waters elsewhere on the migration, low marine survival may result. Our study examined prey availability and stomach fullness of juvenile sockeye salmon along the 120 km stretch of the coastal migration through the Discovery Islands and Johnstone Strait to determine whether this section of the migration is indeed food limited. We observed low stomach fullness throughout tidally mixed waters, providing empirical support for the trophic gauntlet hypothesis. Zooplankton abundance was high in these regions so it appeared that unfavourably small prey size may have been the cause of low foraging success. We also observed foraging hotspots at both ends of the gauntlet, indicating that such areas may be key feeding grounds for migratory salmon.

Impact of time-varying productivity on estimated stock–recruitment parameters and biological reference points

Models with time-varying parameters are increasingly being considered in the assessment of fish stocks, but their reliability when used to derive biological reference points or benchmarks has not been thoroughly evaluated. Here, we evaluated stock–recruitment models with and without time-varying productivity in a simulation framework for sockeye salmon (Oncorhynchus nerka) under different scenarios of productivity and exploitation. Ignoring trends in productivity led to overestimates of productivity and underestimates of capacity when both exploitation rates and productivity declined over time, resulting in an underestimation on average of benchmarks of biological status. Despite being less biased, time-varying models had relatively poor fit based on AICc and BIC model selection criteria. Our simulation results were compared with empirical analyses of 12 Fraser River sockeye salmon stocks in British Columbia, Canada. Although benchmarks were less biased when based on time-varying models, underlying true benchmarks based on spawner abundances at maximum sustainable yield, SMSY, trend downwards when productivity declines, which may not be aligned with conservation objectives. We conclude with best practices when adapting biological benchmarks to time-varying productivity.

What can We Learn About the Return Migration of Fraser River Sockeye Salmon from Catches in Alaska?

What can We Learn About the Return Migration of Fraser River Sockeye Salmon from Catches in Alaska?

Weakened portfolio effects constrain management effectiveness for population aggregates.

Population diversity can reduce temporal variability in aggregate population abundances in a process known as the portfolio effect. Portfolio effects may weaken, however, due to greater synchrony among component populations. While weakened portfolio effects have been previously documented, the consequences of reduced stability on meeting conservation goals for population aggregates that are harvested (e.g., stock aggregates in fisheries) are rarely quantified. Here, we demonstrate how changes in variability within components, synchrony among components, and population productivity interact to influence the probability of achieving an array of management objectives for Fraser River sockeye salmon: a stock aggregate of high economic, ecological, and cultural value. We first present evidence that component variability and synchrony have increased over the last two decades, consistent with a weakening portfolio effect. We then parameterize a stochastic, closed‐loop model that simulates the population dynamics of each stock, the fishery that harvests the stock aggregate, and the management framework used to establish mixed‐stock exploitation rates. We find that while median aggregate abundance and catch through time were relatively insensitive to greater aggregate variability, catch stability and performance metrics associated with achieving management targets generally declined as component variability and synchrony increased. A notable exception we observed is that harvest control means that scale exploitation rates based on aggregate abundance may be more effective as synchrony increases. Reductions in productivity led to broad declines in performance, but also moderated the impacts of component variability and synchrony on the proportion of component stocks above management targets and catch stability. Our results suggest that even precautionary management strategies that account for declines in productivity may underestimate risk, particularly to socioeconomic objectives, if they fail to consider changes in aggregate variability. Adequately incorporating changes in portfolio effect strength may be particularly relevant when developing recovery strategies that are robust to climate change, which is likely to increase synchrony and component variability.

In-season assessment and management of salmon stocks using a Bayesian time–density model

We document a time–density model for in-season assessment of salmon stocks that integrates both relative and absolute indicators of abundance and incorporates preseason information on run size and migration timing using a Bayesian framework. We evaluate different data collection programs for Fraser River sockeye salmon (Oncorhynchus nerka) by examining the precision, bias, and timeliness of resulting run-size estimates with a retrospective analysis of 20 years of data. We quantify the run-size bias if migration was early versus late and evaluate the impact of run-size uncertainty on the ability to reach management objectives. In-season assessments greatly improve the accuracy and precision of run-size estimates compared with preseason forecasts. For the in-season assessment of Fraser River sockeye, catch-per-unit-effort (CPUE) data from seaward marine test fisheries, although less precise, were more informative at the peak marine migration than more precise terminal, in-river hydroacoustic data obtained on the same date due to the time lag associated with migration from the marine test fishing locations to the lower river. Throughout the season, the best fisheries management results were obtained by relying on in-season assessments using both marine CPUE data as well as marine reconstructed abundance estimates derived from in-river hydroacoustic estimates, thereby taking advantage of the benefits of both sources of information.

The Influence of Smolt Age on Freshwater and Early Marine Behavior and Survival of Migrating Juvenile Sockeye Salmon

AbstractSockeye Salmon Oncorhynchus nerka smolts typically experience high mortality during out‐migration through freshwater and the early marine environment. Due to tag burden (tag mass relative to fish mass) constraints, telemetry studies investigating migration survival have focused on tracking hatchery smolts or larger individuals within wild populations. However, hatchery and larger wild smolts may not represent the majority of migrants. We used miniaturized acoustic transmitters (VEMCO V4) to track age‐1 Sockeye Salmon smolts (n = 200) for the first time over approximately 950 km from Chilko Lake, British Columbia, Canada, through the coastal environment by using large‐scale receiver arrays. We compared their survival with that of concomitantly tracked age‐2 smolts (n = 100) by using VEMCO V7 acoustic transmitters. Freshwater survival of tagged age‐1 smolts was double the age‐2 survival (56% versus 28%), potentially due to higher proportional tag burdens on age‐2 smolts. Age‐1 smolt cumulative survival was 16% to the last array capable of detecting age‐1 smolts (944 km from release) and was within the range of cumulative survival reported for age‐2 Chilko Lake Sockeye Salmon smolts in previous telemetry studies. Age‐2 smolt minimum cumulative survival to the final arrays (944 and 1,041 km) was about 2% and was lower than survival in previous years. Although survival differed between age‐classes in 2016, both experienced similar trends in landscape‐specific survival relative to age‐2 smolts tracked in previous years. Survival was particularly low in the upper Fraser River tributaries for age‐1 and age‐2 smolts (76% and 53%, respectively, over 13 km from release) and after ocean entry for age‐1 smolts (36% over 217 km). Migration rates of both age‐classes among landscapes were within the range observed for age‐2 smolts in earlier studies. Our study highlights the importance of expanding research to include smaller age‐1 smolts and provides survival estimates for an indicator population of Fraser River Sockeye Salmon.

Detection and Assessment of the Distribution of Infectious Agents in Juvenile Fraser River Sockeye Salmon, Canada, in 2012 and 2013.

Infectious diseases may contribute to declines in Fraser River Sockeye salmon (Oncorhynchus nerka) stocks, but a clear knowledge gap exists around which infectious agents and diseases are important. This study was conducted to: (1) determine the presence and prevalence of 46 infectious agents in juvenile Fraser River Sockeye salmon, and (2) evaluate spatial patterns in prevalence and burden over initial seaward migration, contrasting patterns between 2 years of average and poor productivity. In total, 2,006 out-migrating Sockeye salmon were collected from four regions along their migration trajectory in British Columbia, in 2012 and 2013. High-throughput microfluidics quantitative PCR was employed for simultaneous quantitation of 46 different infectious agents. Twenty-six agents were detected at least once, including nine with prevalence >5%. Candidatus Brachiomonas cysticola, Myxobolus arcticus, and Pacific salmon parvovirus were the most prevalent agents. Infectious agent diversity and burden increased consistently upon smolts entry into the ocean, but they did not substantially change afterwards. Notably, both freshwater- and saltwater-transmitted agents were more prevalent in 2013 than in 2012, leading to an overall higher infection burden in the first two sampling regions. A reduction in the prevalence of two agents, erythrocytic necrosis virus and Paraneuclospora theridion, was observed between regions 2 and 3, which was speculated to be associated with mortality during the 1st month at sea. The most prevalent infectious agents were all naturally occurring. In a small number of samples (0.9%), seven agents were only detected around and after salmon farming regions, including four important pathogens: piscine orthoreovirus, Piscirickettsia salmonis, Tenacibaculum maritimum, and Moritella viscosa. As the first synoptic survey of infectious agents in juvenile Sockeye salmon in British Columbia, this study provides the necessary baseline for further research on the most prevalent infectious agents and their potential pathogenicity, which may adversely affect the productivity of valuable Sockeye salmon stocks. In addition, our findings are informative to the decision makers involved in conservation programs.

Coherent population dynamics associated with sockeye salmon juvenile life history strategies

Although the importance of diversity to maintaining metapopulation stability is widely recognized, the ecological characteristics that lead to synchronous dynamics within population aggregates are often unclear. We used a constrained dynamic factor analysis to explore patterns of covariance in productivity among 16 Fraser River sockeye salmon (Oncorhynchus nerka) conservation units (CUs). Specifically, we tested whether coherent trends in productivity covaried with five distinct ecological attributes: physical characteristics of nursery lakes, large-scale management interventions, genetic similarity, adult migration phenology, or juvenile migratory traits. The top-ranked model had two trends based on nursery lake characteristics and juvenile migratory traits. One trend represented the dynamics of CUs that rear in nursery lakes prior to ocean entry and undergo relatively rapid marine migrations. The second included a sea-type CU, Harrison River, which enters the marine environment without rearing in a nursery lake and migrates more slowly. The uniform response of lake-type CUs, as well as Harrison River CU’s unique life history, suggests that coherent trends are structured by traits that covary with broad life history type, rather than fine-scale characteristics. Furthermore, we document substantial temporal variability in the strength of synchronous dynamics among Fraser River CUs. Greater synchrony in recent years suggests that the importance of shared regional drivers, relative to local processes, may have increased.

Thiamine Levels in Muscle and Eggs of Adult Pacific Salmon from the Fraser River, British Columbia.

Multiple species and stocks of Pacific salmon Oncorhynchus spp. have experienced large declines in the number of returning adults over a wide region of the Pacific Northwest due to poor marine survival (low smolt-to-adult survival rates). One possible explanation for reduced survival is thiamine deficiency. Thiamine (vitamin B1 ) is an essential vitamin with an integral role in many metabolic processes, and thiamine deficiency is an important cause of salmonid mortality in the Baltic Sea and in the Laurentian Great Lakes. To assess this possibility, we (1) compared muscle thiamine content over time in a holding experiment using Fraser River (British Columbia) Sockeye Salmon O. nerka to establish whether adults that died during the holding period had lower thiamine levels than survivors, (2) measured infectious loads of multiple pathogens in held fish, and (3) measured egg thiamine content from four species of Pacific salmon collected on Fraser River spawning grounds. Chinook Salmon O. tshawytscha had the lowest egg thiamine, followed by Sockeye Salmon; however, egg thiamine concentrations were above levels known to cause overt fry mortality. Thiamine vitamers in the muscle of Fraser River adult Sockeye Salmon shifted over a 13-d holding period, with a precipitous decline in thiamine pyrophosphate (the active form of thiamine used in enzyme reactions) in surviving fish. Survivors also carried lower loads of Flavobacterium psychrophilum than fish that died during in the holding period. Although there is no evidence of thiamine deficiency in the adults studied, questions remain about possible thiamine metabolism-fish pathogen relationships that influence survival.

The influence of water temperature on sockeye salmon heart rate recovery following simulated fisheries interactions.

Selective harvest policies have been implemented in North America to enhance the conservation of Pacific salmon (Oncorhynchus spp.) stocks, which has led to an increase in the capture and release of fish by all fishing sectors. Despite the immediate survival benefits, catch-and-release results in capture stress, particularly at high water temperatures, and this can result in delayed post-release mortality minutes to days later. The objective of this study was to evaluate how different water temperatures influenced heart rate disturbance and recovery of wild sockeye salmon (Oncorhynchus nerka) following fisheries interactions (i.e. exhaustive exercise). Heart rate loggers were implanted into Fraser River sockeye salmon prior to simulated catch-and-release events conducted at three water temperatures (16°C, 19°C and 21°C). The fisheries simulation involved chasing logger-implanted fish in tanks for 3 min, followed by a 1 min air exposure. Neither resting nor routine heart rate differed among temperature treatments. In response to the fisheries simulation, peak heart rate increased with temperature (16°C = 91.3 ± 1.3 beats min-1; 19°C = 104.9 ± 2.0 beats min-1 and 21°C = 117 ± 1.3 beats min-1). Factorial heart rate and scope for heart rate were highest at 21°C and lowest at 16°C, but did not differ between 19°C and 21°C. Temperature affected the initial rate of cardiac recovery but not the overall duration (~10 h) such that the rate of energy expenditure during recovery increased with temperature. These findings support the notion that in the face of climate change, efforts to reduce stress at warmer temperatures will be necessary if catch-and-release practices are to be an effective conservation strategy.

Stock-Recruit Analyses of Fraser River Sockeye Salmon

Stock-Recruit Analyses of Fraser River Sockeye Salmon