River Sockeye Salmon Oncorhynchus Nerka Research Articles

Stock Identification of Fraser River Sockeye Salmon Using Microsatellites and Major Histocompatibility Complex Variation

The utility of DNA-based variation for stock identification was evaluated for Fraser River sockeye salmon Oncorhynchus nerka. For this evaluation, the variation at 14 microsatellite loci and one major histocompatibility complex (MHC) locus was determined from approximately 13,000 fish from 47 populations in the drainage. Genetic differentiation among the populations was observed, the overall FST value for the 14 microsatellite loci surveyed being 0.054 and that for the MHC locus being 0.215. The variation among regions and populations within regions was approximately 20 times as great as that of the annual variation within populations for the microsatellite loci and 28 times as great for the MHC locus. The power of a microsatellite locus for population-specific identification in simulated mixture samples was positively correlated with the number of observed alleles at the locus. Analysis of simulated mixtures indicated that the mean percentage error of estimated stock compositions was less than 1% per population, with a standard deviation of approximately 3% for a mixture sample size of 150 fish. Estimated stock compositions of a known sample of radio-tagged sockeye salmon indicated that the mean percentage error was 1% per population and 1% per run-time group. The use of DNA variation to estimate stock compositions in the management of the 2002 Fraser River sockeye salmon fisheries indicated the early arrival of the late run in the Fraser River. Stock identification based on DNA-level variation will probably become the preferred method in Pacific salmon applications in the near future.

Energetics and morphology of sockeye salmon: effects of upriver migratory distance and elevation

Depending on population, wild Fraser River sockeye salmon Oncorhynchus nerka travel distances of <100 km to >1100 km and ascend elevations ranging from near sea‐level to 1200 m to reach spawning areas. Populations embarking on distant, high elevation migrations (i.e. Early Stuart, Chilko and Horsefly populations) began their upriver spawning migrations with higher densities of somatic energy (c. 9·2 to 9·8 MJ kg−1) and fewer eggs (c. 3200 to 3800) than populations making shorter, low elevation migrations (i.e. Weaver and Adams; c. 7·1 to 8·3 MJ kg−1 gross somatic energy and c. 4300 to 4700 eggs). Populations making difficult upriver migrations also had morphologies that were smaller and more fusiform than populations making less difficult migrations, traits that may facilitate somatic energy conservation by reducing transport costs. Indeed, fish travelling long distances expended less somatic energy per unit of migratory difficulty than those travelling shorter distances (2·8 to 3·8 kJ v. 10–1400 kJ). Consistent with evolutionary theory, difficult migrations appear to select for energy efficiency but ultimately fish making more difficult migrations produce fewer eggs, even when differences in body length have been accounted for. Despite large among‐population differences in somatic energy at the start of upriver migration, all populations completed migration and spawning, and subsequently died, with c. 4 MJ kg−1 of energy remaining, a level which may reflect a threshold to sustain life.

The effect of exercise and captivity on energy partitioning, reproductive maturation and fertilization success in adult sockeye salmon

Releasing a population of adult Fraser River sockeye salmon Oncorhynchus nerka from an energetically more expensive non‐feeding natural migration (1089 km, natal groups) and allowing them to sexually mature in either a moderate flow (captive exercise group) or a no flow (captive non‐exercise group) environment resulted in significant differences in body energy densities (MJ kg−1) among groups (ranked: initial natural migrator > non‐exercise > exercise > natal arrivals). Similarly, per cent body lipids were significantly lower in exercise females compared with non‐exercise females, experimentally confirming the central role lipid catabolism has in powering swimming. Although restricting exercise did result in greater body energy reserves at spawning, this did not result in a reallocation of energy to reproduction, as fecundity, egg size and gonad composition were unchanged among the groups. Furthermore, non‐exercise females had delayed maturity, lower egg deposition rates, and were more likely to die prior to egg ovulation than exercise females and natal spawners. Eggs from captive exercise adult females were more likely to survive to the eyed stage than eggs from captive non‐exercise females, but both captive groups had significantly lower egg fertilization success than natal spawners suggesting that confinement stress played a role in some of results presented. There were no significant differences in plasma levels of glucose, lactate, cortisol and reproductive hormones among the groups, but correlations among acute and chronic indicators of stress were significant among individuals. These results indicate that exercise during the late stages of maturation, as might occur normally, may be required for optimizing reproductive maturation and maximizing reproductive success.

Abnormal Migration Timing and High en route Mortality of Sockeye Salmon in the Fraser River, British Columbia

Abstract Since 1995, several stocks of Fraser River sockeye salmon (Oncorhynchus nerka) have begun upriver spawning migrations significantly earlier than previously observed. In some years, the timing of peak migration has shifted more than 6 weeks. Coincident with this early migration are high levels of en route and pre-spawning mortality, occasionally exceeding 90%. These phenomena pose risks to the perpetuation of these fisheries resources. At present, although there are many competing hypotheses (e.g., energetics, osmoregulatory dysfunction, oceanic conditions, parasites) that may account for early migration and high mortality, there are no definitive answers, nor any causal evidence that link these issues. With poor predictive ability in the face of uncertainty, fisheries managers have been unable to effectively allocate harvest quotas, while ensuring that sufficient fish are able to not only reach the spawning sites, but also successfully reproduce. If trends in mortality rates continue, several imp...

Impact and Adaptation Responses of Okanagan River Sockeye Salmon (Oncorhynchus nerka) to Climate Variation and Change Effects During Freshwater Migration: Stock Restoration and Fisheries Management Implications

We summarized existing knowledge on behavioural and physiological responses of Okanagan sockeye salmon (O. nerka) adults to annual and seasonal variations in aquatic thermal regimes during migration. This enabled us to identify an underlying set of ’decision rules’ as a biophysical model of how temperature mediates en-route delays as a specific element of annual migrations by sockeye salmon. Several sets of results indicate that adult sockeye migrations stop as seasonal water temperatures increase and exceed 21 °C and then restart when temperatures decrease and fall below 21 °C. Model predictions of annual variations in the duration of migratory delay exhibited close agreement with independent estimates of observed delays available from a subset of years (predicted delay = 1.23 observed delay + 2.08, r2 = 0.92, p < 0.001, n = 10). We applied the model in a retrospective analysis of the likely impacts of climate variation and change events on adult sockeye migrations in freshwater over the 70 plus year interval between 1924 and 1998. Results indicate that migration delays for a significant portion of the sockeye population averaged 29 days per year (range 0–55). Average annual migration delays roughly equal the 33 day estimate of time required, given continuous migration, to traverse the 986 km distance from the Columbia River mouth to terminal spawning grounds near Osoyoos Lake, BC. Alternating intervals of above-average and below-average migration delays corresponded closely with ’warm-phase’ and then ’cold-phase’ periods of the Pacific Interdecadal Oscillation. Circumstantial evidence suggests alternating periods of sub-average and above-average productivity for salmon on the southern end of their range are linked to climate variation and change events in both freshwater and marine environments. Climate impact and adaptation responses that register first at the level of salmon, propagate rapidly through both salmon resource users and fisheries managers. Consequently, future climate warming episodes will complicate the manageability and threaten the sustainability of many salmon populations in the southern end of their range (Georgia Basin and the Pacific Northwest). This requires strategies that minimize the impact of uncertain climate variability and change scenarios on the resilience of the salmon resource, and maximize our adaptive capacity for both short- and long-term fisheries planning and management decisions.

A Bayesian decision analysis to set escapement goals for Fraser River sockeye salmon (Oncorhynchus nerka)

This paper illustrates a complete Bayesian decision analysis for evaluating multistock harvest goals in the fishery on Fraser River sockeye salmon (Oncorhynchus nerka). We identify four key steps necessary to assess a resource production system. Each step entails choices that can alter the perceived consequences of management decisions. A Markov chain Monte Carlo sample captures uncertainty in the population dynamics. The Bayesian formalism then translates this uncertainty into uncertain policy outcomes. We examine a relatively simple control law, designed to protect stocks at low abundance. We restrict our attention to retrospective policy analysis by investigating what might have happened to sockeye stocks if management had proceeded differently during years for which historical data are available. A formal objective function quantifies societal values associated with a range of policy options. To confine the paper to manageable scope, we consider only relatively simple assumptions. Our analytical framework offers an iterative route to policy design, where managers play an active role in formulating policy options and evaluating their consequences.

Swim speeds and energy use of upriver-migrating sockeye salmon (Oncorhynchus nerka): simulating metabolic power and assessing risk of energy depletion

We simulated metabolic power consumed by Fraser River sockeye salmon (Oncorhynchus nerka) during upriver migration based on direct measures of activity from physiological field telemetry. The most accurate prediction of energy expenditure was obtained by expressing activity as a fine time scale (5 s) stochastic process. By imposing a daily time step, predictions of energy use were considerably lower than observed energy use, suggesting that the practice of modeling field energetics at a daily time scale, particularly for relatively active fish, may render dubious results. Daily mean power consumption through the Fraser River Canyon by the average migrant was about 20 W, about fourfold higher than for less constricted reaches. Power consumption predicted at fine time scales ranged from &lt;1 W (0.1 body length·s-1) during periods of reduced activity to 1700 W (8 body lengths·s-1) during bursts while navigating through turbulent canyon reaches. Through Monte Carlo simulations representing environmental variability observed during 1950-1994, we determined that 8% of the salmon runs during this time resulted in high risk of exhaustion for the average migrant that could lead to elevated in-river mortality. Reducing harvest levels on sockeye salmon that may be exposed to these unfavourable conditions may assist agencies in achieving a risk-averse management strategy.

Adding Nutrients to Enhance the Growth of Endangered Sockeye Salmon: Trophic Transfer in an Oligotrophic Lake

Snake River sockeye salmon Oncorhynchus nerka listed under U.S. law as endangered in 1991 in response to a decline in anadromous adult numbers, spend their first 1–2 years in Redfish Lake, Idaho, before migrating to the sea. To determine how nutrient enhancement might influence phytoplankton, zooplankton, and fish production, we performed fertilization experiments in large enclosures in this oligotrophic lake using juvenile kokanee (lacustrine O. nerka) as analogues for endangered sockeye salmon. Fertilization of the metalimnion substantially increased chlorophyll a (150%), phytoplankton biovolume (75%), primary productivity (250%), and zooplankton biomass (200%), and moderately increased fish growth (12%) over our control enclosures. Community composition of phytoplankton and zooplankton changed little, and water transparency declined less than 15% compared with controls. Thus, we concluded that metalimnetic fertilization could maintain the aesthetic value of these lakes while increasing zooplankton food resources for juvenile salmon. Our results suggest that whole-lake fertilization would aid in the recovery of Snake River sockeye salmon.

NerkaSim: A Research and Educational Tool to of Pacific Salmon in a Dynamic Environment

Abstract This paper introduces NerkaSim, a computer program used to simulate and visualize the life history of Pacific salmon in a dynamic ocean environment. The computer program enables users to (1) archive and visualize biophysical oceanographic data; (2) execute a spatially explicit, individually based Pacific salmon model that can include migration, growth, and mortality processes; and (3) produce images of simulated migration trajectories and bioenergetic variables in both space and time. We anticipate a demand for the model for basic and applied research applications, where it can serve as a platform to explore hypotheses concerning migration, growth, and mortality processes for salmon in coastal and high-seas environments. Although designed to address issues related to British Columbia's Fraser River sockeye salmon (Oncorhynchus nerka), the model can easily be customized to accommodate different salmon species across the eastern Pacific Rim. Distributed as freeware, we hope that NerkaSim will becom...

Adjusting for missed tags in salmon escapement surveys

One of the assumptions in mark-recapture studies is that all tags recovered are correctly identified. In some cases, tags are overlooked, and a subsample of fish previously classified as untagged is examined to look for missed tags. In this paper, a method for estimating the salmon escapement using a mark-recapture methodology after correcting for missed tags is developed. The variance of the revised estimator is derived and the loss of efficiency compared with a Petersen estimate, where no tags are overlooked, is found. Optimal allocation of effort between the initial and second examination is considered. Finally, a numerical example using actual data from the 1994 Fraser River sockeye salmon (Oncorhynchus nerka) season is used to illustrate the results.

Production of Fraser River sockeye salmon (Oncorhynchus nerka) in relation to decadal-scale changes in the climate and the ocean

The abundance of Fraser River sockeye salmon (Oncorhynchus nerka) stocks was low in the 1960s, increased to high levels in the 1980s, and possibly entered a period of low abundance in recent years. The abundance changes of the combined stocks can be separated into productivity regimes that correspond to changes in climate trends. The most distinct change occurred when there was a major change in the climate over the Pacific Ocean in the winter of 1976-1977. The existence of natural shifts in abundance trends means that the high returns that occur during periods of high productivity would not be expected to occur during the low-productivity periods. The response of Fraser River sockeye to climate changes may be a specific example of a more general response by a number of species of fishes in the Pacific and perhaps in other oceans. Because the shift from one regime to the other occurred quickly in the 1970s, future shifts could also occur quickly. It is necessary to detect natural shifts in productivity when attempting to manage fishing impacts to ensure that economic expectations are sound and that overfishing does not occur.

Simulated Growth and Production of Endangered Snake River Sockeye Salmon: Assessing Management Strategies for the Nursery Lakes

Abstract We examined the potential of employing a series of lake management strategies to enhance production of endangered Snake River sockeye salmon (Oncorhynchus nerka) in its historical nursery lakes in central Idaho. We used a combination of limnological sampling, experimentation, and simulation modeling to assess effects of lake fertilization and kokanee reduction on growth and survival of juvenile sockeye salmon. Juvenile sockeye salmon from a broodstock of this endangered species are being introduced into the lakes from 1995 to 1998. Results of our analyses indicated that several lakes were suitable for receiving broodstock progeny. Field experimentation and simulation modeling indicated that lake fertilization, coupled with a program of kokanee reduction, provided the management option most likely to enhance the survival of stocked juvenile sockeye salmon. Simulation models that encompass physiological requirements, ecological interactions, and life-history consequences could be used as templates ...

A Preseason Simulation Model for Fisheries on Fraser River Sockeye Salmon (Oncorhynchus nerka)

Using a preseason fishery simulation model that refines previous reconstruction models, we explored the effects of various fishing regimes on annual catch and escapement of the major stocks of Fraser River sockeye salmon (Oncorhynchus nerka). To obtain harvest rate parameters for the model, we analyzed historical fishery catches to develop a theory of fish movement through time and space. Harvest parameters were then calculated using run reconstruction techniques. The model uses a daily time step to move fish sequentially through the major fishing areas. Fishing scenarios may be examined in the preseason to aid in developing annual management plans. Inputs of run size, timing, and diversion rate via Johnstone Strait are used to calculate run-timing curves which are normally distributed. The proportion of sockeye migrating via the northern approach or Johnstone Strait diversion, is shown to be a major factor in the sensitivity of fishing plans to altered input parameters. Clearly stated goals and objectives for spawning escapement and allocation of catch by stock groups are essential in the modelling process. The model permits managers to examine underlying assumptions and biological, economic, and social requirements centred on the harvest of these stocks.

Computer Simulations of the Influence of Ocean Currents on Fraser River Sockeye Salmon (Oncorhynchus nerka) Return Times

We hypothesized that the interannual variability of the northeast Pacific Ocean circulation affects the return times of Fraser River sockeye salmon (Oncorhynchus nerka). Homeward migrations were simulated for 1982 (with a relatively weak Alaska Gyre circulation) and 1983 (with a relatively strong circulation) in the context of three sequential return migration phases: a nondirected oceanic phase, a directed oceanic phase, and a directed coastal phase. Passive drifters were simulated to examine the influence of ocean currents during the nondirected oceanic phase: model fish south of 48°N were advected closer to Vancouver Island in 1983 compared with 1982; those north of 48°N were advected closer to Vancouver Island in 1982 than in 1983. Fish were simulated during the directed oceanic phase using a variety of behaviour scenarios: model fish starting south of 50°N had earlier return times in 1983 than in 1982; those starting north of 50°N had return times in 1983 that were generally the same as or later than in 1982. We inferred that ocean currents would modulate the environmental influences on return times during the directed coastal migration phase, by deflecting sockeye salmon into different oceanographic domains along the British Columbia coast.

Genetic Models for Cyclic Dominance in Sockeye Salmon (Oncorhynchus nerka)

A simple genetic mechanism may be partly responsible for maintaining violent cycles in abundance of some Fraser River sockeye salmon (Oncorhynchus nerka) stocks. If age at maturity is highly heritable, spawning runs in low cycle lines may have high percentages of age 5 spawners that tend to produce offspring that will return at age 5, due to production of low percentages of such spawners by preceding high cycle lines. Then even if each low cycle line has a high productivity per spawner, a large fraction of this productivity may be "lost" to the cycle line, in the form of age 5 recruits to other cycle lines. In the face of high fishing mortality, even a small relative loss from any cycle line may cause it to remain small relative to other lines. This model explains several observations, such as high productivity per spawner in low cycle lines, that cannot be explained by previous hypotheses involving depensatory predation or food supply. However, it is unlikely that genetic effects alone are responsible for the stability of cyclic patterns, unless low offcycle runs consist entirely of "temporal colonizer" genotypes that produce a high proportion of age 5 offspring as a dominant trait.

Evaluation of Alternative Models of the Coastal Migration of Adult Fraser River Sockeye Salmon (Oncorhynchus nerka)

A set of stochastic discrete step models of individual fish movement was developed to investigate the efficiency of compass orientation as a migratory mechanism in the coastal homeward migration of Fraser River sockeye salmon (Oncorhynchus nerka). Ultrasonic tracking data provided empirical values for the required parameters. Alternative movement models were validated by comparing the results of Monte Carlo simulations and known features of sockeye migration: general aspect of individual trajectories, timing, success in reaching the goal, and spatial occurrence. The effect of different headings and directional precisions on the probability of success in reaching the goal were considered. The more complex models captured the essence of observed movement patterns, but the number of fish getting to the goal was lower than expected. Many "modeled" fish were lost in the complex web of channels and inlets characteristic of this area. We conclude that the preference of a compass direction is not a sufficient mechanism to explain the observed migratory behavior of Fraser River sockeye salmon in coastal areas. Other mechanisms, such as negative kinetic responses to water from nonnatal rivers or short-term learning, may prevent the fish from being trapped in complex areas.

Using a Numerical Model of the Northeast Pacific Ocean to Study the Interannual Variability of the Fraser River Sockeye Salmon (Oncorhynchus nerka)

The hypothesis that numerical ocean circulation models could benefit fishery management was tested by first simulating the interannual variability of the northeast Pacific Ocean from 1955 to 1979 with the Bryan–Cox–Semtner ocean model (from the Geophysical Fluid Dynamics Laboratory, Princeton, NJ) and then relating the model output to the interannual variability found in the Fraser River sockeye salmon (Oncorhynchus nerka). Empirical orthogonal function (EOF) analysis was first used to condense the model output fields as well as the atmospheric forcing data. Next, the amplitude of the EOF's were regressed with the annual values of the sockeye variables (return migration route and timing, marine survival, and fork length) by stepwise multiple regression, with various time lags between the physical and the sockeye variables. The EOF modes associated with interannual variability (usually mode 2) were more often correlated with the sockeye variables than the other modes thought to contain mainly the seasonal cycle (mode 1) or else noise. The correlations between the physical variables and the sockeye variables were highest in the first and final few months of the sockeye marine life.

Optimal Harvest Rate Policies for Rebuilding the Adams River Sockeye Salmon (Oncorhynchus nerka)

This paper examines how a currently depressed population, the Adams River sockeye salmon (Oncorhynchus nerka), should be rebuilt over time in order to maximize the economic benefit. We use dynamic optimization techniques to answer two questions which previous static optimization work on the Adams River sockeye controversy did not address: (1) what changes from current management policies are required over time to maximize the net economic yield from the population and (2) just how much economic benefit can accrue from following such a policy? We find that following the optimal policy identified by this methodology could contribute more than $600 million to the net value of the Adams River stock. Examination of various confounding factors (co-migrating stocks, parameter uncertainty, and the discount rate applied) indicates that the optimal harvest policy is remarkably robust to these sources of uncertainty. The study also lays the basis for repeating such numerical analysis on other populations of interest.

Cyclic Dominance and Optimal Escapement of Adams River Sockeye Salmon (Oncorhynchus nerka)

We examined escapement policies for a stock-recruitment model with negative between-year interactions. Regardless of the degree of interaction present, the optimal policy is to always equalize escapement. Parameter estimates obtained for the Adams River sockeye salmon (Oncorhynchus nerka) indicate that between-year interactions may occur, but confidence regions include the null hypothesis of no interaction at all (the Ricker model). We conclude that the extreme amplitude of the current recruitment cycle in this stock frustrates statistical identification of interaction. It seems unlikely that between-year interactions will be measurable until the off year runs increase by at least two to three orders of magnitude. Comparison of total yields for the Adams River sockeye shows that an equal escapement policy could increase yields by at least 35% over that obtained by the current cyclic escapement pattern. This is equivalent to obtaining an additional $27 million in total yield per annum from the Adams River stock alone and, assuming a discount rate of 4%, translates into an increase in net present value of $675 million. If between-year interactions do not exist, the potential benefits of moving to an equal escapement policy are even larger, on the order of $3 to $4 billion.

Predicting the Return Migration Routes of the Fraser River Sockeye Salmon (Oncorhynchus nerka)

The Johnstone Strait diversion rate (i.e. the percentage of homeward migrating Fraser River sockeye salmon (Oncorhynchus nerka) travelling around Vancouver Island via the northern route of Johnstone Strait) is statistically predicted using the March values of the Kains Island sea surface temperature T and the Fraser River runoff R. The prediction formula incorporates nonlinear terms such as T2 and RT, as well as the diversion rate 2 yr ago. We tested the forecasting performance by constructing a prediction formula using only data from 1953–78, and making predictions for 1979–88. The mean absolute error of our prediction of the diversion rate was 8% which compared favourably with the prediction by a linear temperature scheme and a linear runoff scheme where the errors were respectively 13 and 29%. Unlike the latter two schemes where T and R data from April–June are needed, our scheme with the use of data no later than March allows much earlier forecasts to be made.