Fraser River Sockeye Salmon Research Articles

Pink salmon (Oncorhynchus gorbuscha) migratory energetics: response to migratory difficulty and comparisons with sockeye salmon (Oncorhynchus nerka)

Pink salmon (Oncorhynchus gorbuscha) are generally considered weak upriver migrants relative to sockeye salmon (Oncorhynchus nerka), though this assertion is largely anecdotal. To assess energy-use patterns during migration, we collected pink salmon from two major Fraser River stocks (Weaver and Seton in British Columbia, Canada) in 1999 at three times and locations: (1) at the start of freshwater migration, (2) at the end of migration before spawning, and (3) immediately after spawning. We calculated the energy content of somatic and reproductive tissues, recorded several body measurements, and conducted both intraspecific (between pink stocks) and interspecific analyses with co-migrating Fraser River sockeye salmon collected during the same season. We found that between pink salmon stocks, there were no significant energetic or morphological differences either at river entry or upon arrival at spawning areas regardless of the level of migratory difficulty encountered. When compared with sockeye salmon, however, we found that pink salmon began upriver migration with significantly smaller somatic energy reserves but made up for this deficiency by minimizing absolute transport and activity costs, presumably by seeking out migratory paths of least resistance. This energetic efficiency comes at a cost to reproductive output: relative to sockeye salmon, pink salmon diverted less absolute energy to egg production, producing smaller ovaries and fewer eggs. We speculate that fundamental differences in behaviour shape the migratory energetic tactics employed by pink salmon.

Epizootiology of Parvicapsulaminibicornis in Fraser River sockeye salmon, Oncorhynchusnerka (Walbaum)

Late‐spawning Fraser River sockeye salmon, Oncorhynchus nerka, stocks have suffered significant prespawn mortality associated with an unusually early freshwater migration pattern and the myxosporean parasite Parvicapsula minibicornis. Surveys of migrating adult salmon from several spawning populations were conducted in 1999 and 2000 to determine the extent of infection with P. minibicornis, when and where the parasite first becomes detectable during migration, and whether early migrating stocks might be used as sentinels to assess risk of infection in late‐spawning stocks. Posterior kidney, preserved in 95% ethanol, was examined for P. minibicornis in stained histological sections and using a polymerase chain reaction (PCR) test. The prevalence of this parasite in all Fraser River sockeye salmon stocks examined was high (range 47–100% infected). In contrast, P. minibicornis was not detected in the fish tested from the two sockeye salmon stocks outside the Fraser River drainage in either 1999 or 2000. The parasite was also not detected histologically or by PCR in the kidney tissue of the fish from the Fraser River that were sampled in salt water or early during their freshwater migration up the river. These findings and the progression in the prevalence and intensity of infection as the fish from three stocks (early Stuart, Weaver Creek and Cultus Lake) were monitored over time, suggest salmon acquired the parasite either in the lower Strait of Georgia or in the lower Fraser River before the confluence of the Harrison River. In both 1999 and 2000 the parasite was present in all Fraser River sockeye salmon stocks sampled, which suggests that early Stuart salmon may be valuable as a sentinel stock for the presence of the parasite in later‐spawning stocks.

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.

Assessing the northern diversion of sockeye salmon returning to the Fraser River, BC

We examine the oft‐quoted relationship between the migration of Fraser River sockeye salmon around the northern end of Vancouver Island and sea surface temperatures. We examine the methods used to estimate the northern diversion and conclude that the estimates have a sufficiently low expected error to form a useful representation of sockeye salmon behaviour. The well‐known relationship with Kains Island sea surface temperature is explored and problems are pointed out. In particular, we explore why Kains Island temperatures are good predictors of salmon behaviour in May when the sockeye can be over 1000 km away, but the coastal temperatures are poor predictors in July to September when the salmon are actually close by. We show that a more robust predictor can be developed using open ocean temperature fields and we show why Kains Island fails as a predictor during the summer months. Finally, we show by cross‐validation that the northern diversion is predictable with an r.m.s. error of about 0.1.

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 <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.

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...

Changes in size at maturity of Fraser River sockeye salmon (Oncorhynchus nerka) (1952–1993) and associations with temperature

Unlike other Canadian Pacific salmon (Oncorhynchus spp.), long-term declines in the size at maturity of Fraser River sockeye salmon (O. nerka) have not been reported in past studies. Using data specific for 10 Fraser River sockeye stocks, we demonstrate that size at maturity has generally declined over the past 42 yr for females in all stocks and for males from eight stocks. Independent of this temporal trend, we found that size at maturity of both sexes in all stocks was smaller in years when sea surface temperatures were relatively warm. Slower growth in warmer years may be caused directly by increased metabolic demand, or indirectly by oceanic changes that influence food acquisition. We speculate that fitness of Fraser River sockeye will be reduced in the future if sea surface temperature increases and salmon abundance remains near present levels.

A reappraisal of the ocean migration patterns of Fraser River sockeye salmon (Oncorhynchus nerka) by individual-based modelling

Although sockeye salmon (Oncorhynchus nerka) spend 1-4 years in the ocean and accumulate 99% of adult body weight during this period, their migratory patterns in the Northeast Pacific are not yet well understood. A model of ocean migration based on conjecture from limited catch and tagging data has influenced work in sockeye ecology for the past 20 years. To evaluate this model, we constructed a spatially explicit individual-based model that used ocean surface currents and simple behavioural rules to simulate migration patterns for sockeye from the Fraser River system. We explored several modelled behaviours, including random swimming and swimming with a directional bias during some months. The simulations begin at the time when juveniles leave inside coastal waters and end when return migration begins (a few months before river reentry). We determined that simple undirected swimming for most of the ocean phase (except the first 4 months when smolts are near the coast) provided results that challenged the prevailing model but did not require complex assumptions. The migration patterns generated by these rules compare well both qualitatively and quantitatively with the existing empirical data on British Columbia sockeye distribution and migrations in the ocean.

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.

A reappraisal of the ocean migration patterns of Fraser River sockeye salmon (<I>Oncorhynchus nerka</I>) by individual-based modelling

A reappraisal of the ocean migration patterns of Fraser River sockeye salmon (<I>Oncorhynchus nerka</I>) by individual-based modelling

Changes in size at maturity of Fraser River sockeye salmon (<I>Oncorhynchus nerka</I>) (1952–1993) and associations with temperature

Changes in size at maturity of Fraser River sockeye salmon (<I>Oncorhynchus nerka</I>) (1952–1993) and associations with temperature

Comments on ‘Computer simulations of homeward‐migrating Fraser River sockeye salmon: is compass orientation a sufficient direction‐finding mechanism in the north‐east Pacific ocean?’ by C. G. Dat et al. (1995)

Comments on ‘Computer simulations of homeward‐migrating Fraser River sockeye salmon: is compass orientation a sufficient direction‐finding mechanism in the north‐east Pacific ocean?’ by C. G. Dat et al. (1995)

Potential effects of climate change on marine growth and survival of Fraser River sockeye salmon

Simulation results from the Canadian Climate Centre's atmospheric general circulation model (CCC GCM) coupled to a simplified mixed-layer ocean model predict that doubled atmospheric CO2 concentrations would increase northeast Pacific Ocean sea surface temperatures and weaken existing north–south air pressure gradients. On the basis of predicted changes to air pressure and an empirical relationship between wind-driven upwelling and zooplankton biomass, we calculate that production of food for sockeye salmon (Oncorhynchus nerka) may decrease by 5–9%. We developed empirical relationships between sea surface temperature, zooplankton biomass, adult recruitment, and terminal ocean weight for the early Stuart stock of Fraser River sockeye salmon. Our analyses show that warmer sea surface temperatures, larger adult recruitment, and lower zooplankton biomass are correlated with smaller adult sockeye. Bioenergetics modeling suggests that higher metabolic costs in warmer water coupled with lower food availability could cause the observed reductions in size. Warmer sea surface temperatures during coastal migration by juveniles were correlated with lower recruitment 2 yr later. Warmer sea surface temperatures may be a surrogate for increased levels of predation or decreased food during the juvenile stage. We speculate that Fraser sockeye will be less abundant and smaller if the climate changes as suggested by the Canadian Climate Centre's general circulation model.

Computer simulations of homeward‐migrating Fraser River sockeye salmon: is compass orientation a sufficient direction‐finding mechanism in the north‐east Pacific Ocean?

ABSTRACTComputer simulations were used to investigate whether compass orientation is a sufficient guidance mechanism for sockeye salmon migrating to the Fraser River from their ocean foraging grounds in the north‐east Pacific Ocean. Daily surface ocean currents, simulated by the ocean surface current simulations (OSCURS) model, were used to test the influence of currents on the return oceanic migration of Fraser River sockeye salmon. High seas tagging and coastal recover data of Fraser River sockeye salmon were used for the migration simulations. Surface currents were shown to increase the speed of the homeward‐migrating sockeye salmon, as well as to deflect the fish in a north‐eastward direction. In spite of ocean currents, all Fraser River sockeye salmon were able to reach their destination with a fixed direction and bioenergetically efficient swimming speed when migration was delayed until the last month at sea. Compass orientation alone was shown to be a sufficient direction‐finding mechanism for Fraser River sockeye salmon.

Simulation of juvenile sockeye salmon (Oncorhynchus nerka) migrations in the Strait of Georgia, British Columbia

ABSTRACTPrevious research has documented two main migratory routes of juvenile sockeye salmon (Oncorhynchus nerka) through the Strait of Georgia, British Columbia, Canada, and large interannual variability in marine survival rates of the Chilko Lake stock. Simulation models were used to explore the influence of surface currents on the migratory route of juvenile sockeye salmon (smolts) through the Strait of Georgia. We used a model of downstream migration to generate daily numbers of Chilko Lake sockeye salmon smolts entering the Strait of Georgia, based on daily counts of smolts leaving the rearing lake. A numerical hydrodynamic model (driven by surface wind, tide, and Fraser River discharge) hindcasted surface currents in the Strait of Georgia on a 2 km × 2 km grid. A smolt migration model simulated fish moving through the Strait with different compass‐oriented migratory behaviours (i.e. swimming speed and directional orientation) within the time‐varying surface advection field. Results showed that surface currents within the Strait of Georgia can affect the migratory route of sockeye salmon smolts in spite of their large size (8 cm). Wind is the forcing mechanism primarily responsible for determining which migratory route would be used. Under prevailing wind conditions (i.e. toward the north‐west), most sockeye salmon smolts would use the eastern migratory route; however, relatively brief south‐eastward wind events (lasting about 2 days) would force most smolts into the western migratory route. Given the heterogeneity of food for salmon within the Strait, we hypothesize that wind‐driven variability in the annual proportion of smolts that use the western and eastern migratory routes in the Strait of Georgia affects early marine survival rates of Fraser River sockeye salmon.

Cooperative Fisheries Management Involving First Nations in British Columbia: An Adaptive Approach to Strategy Design

In 1991, a substantial program of cooperative salmon fishery management involving First Nations was initiated in British Columbia. This paper considers how ongoing cooperative management initiatives in this fishery could be designed and implemented. The process discussed in the paper could be viewed as an adaptive management experiment in institutional design for cooperative management. First, sets of fundamental objectives for cooperative management and strategies for achieving these objectives are developed. The methods for structuring objectives and developing strategies are drawn from decision analysis practice. Then the actual experience in implementing a version of one of the strategies during the 1992 Fraser River sockeye salmon First Nations fishery is discussed. The highly publicized and controversial events of the 1992 season are instructive about how cooperative management should be implemented in other contexts.

Evaluation of the Depensatory Fishing Hypothesis as an Explanation for Population Cycles in Fraser River Sockeye Salmon (Oncorhynchus nerka)

Causes of cyclic fluctuations in the abundance of Fraser River sockeye (Oncorhynchus nerka) have been the focus of considerable debate for much of this century. Most hypotheses to explain cyclic behaviour in Fraser River sockeye centre on identifying agents of depensatory mortality, and several recent papers argue that sockeye cycles are maintained primarily by depensatory fishing patterns. We assess the evidence for depensatory fishing as an explanation for these cycles. Using simulations, we demonstrate that empirical evidence for depensatory fishing is likely an artifact caused by bias in estimating stock composition of catches in mixed-stock fisheries. Moreover, recent trends in harvest rates among comigrating stocks with asynchronous cycles are inconsistent with the depensatory fishing hypothesis. It also seems very unlikely that aboriginal and early commercial fisheries were intensive enough to maintain cycles that persisted prior to 1860. Only during the unregulated, early commercial fishery prior to the collapse of the upriver runs following the 1913–14 disaster at Hell's Gate is there any convincing evidence of depensatory fishing.

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.