Adult Sockeye Salmon Oncorhynchus Nerka Research Articles

Resumption of Anadromy or Straying? Origins of Sockeye Salmon in the Elwha River

AbstractWhen barriers to migration are removed, anadromous fishes from other rivers may colonize newly accessible habitat or landlocked forms of the species may resume anadromy if conditions allow. For example, two large hydroelectric dams on the Elwha River, Washington, were removed between 2011 and 2014 to restore populations of Pacific salmon Oncorhynchus spp. after a century of isolation. Immediately prior to and following dam removal (2010–2017), upstream‐migrating adult Sockeye Salmon Oncorhynchus nerka were sampled, and DNA was extracted and compared with samples from the local Lake Sutherland population (above the lower dam’s former location) and a coastwide genetic baseline to determine the probable origin of each fish. Genetic analysis indicated that none of the 45 Sockeye Salmon sampled had originated from the local population or other populations nearby in the genetic baseline, and only a single fish originated from the abundant and proximate Fraser River populations. The strays reflected two different sources and processes: 22 were from the west coast of Vancouver Island (all in 2015, when these populations were very abundant and encountered conditions unfavorable for upstream migration in their natal system) and another 22 assigned to more northerly populations, mostly to riverine populations from the Stikine River. Test fishery samples collected in the Strait of Juan de Fuca contained very few fish with assignments similar to these northern rivers. It is not clear whether these individuals originated from the distant riverine populations or from a closer population not in the baseline that resembles them genetically. Taken together, the findings indicate that the genetic composition of any future population in the Elwha River may reflect signatures from diverse sources and subsequent selection in the new habitat.

Stable Isotopes Reveal Variation in Consumption of Pacific Salmon by Brown Bears, Despite Ready Access in Small Streams

AbstractBrown bears Ursus arctos consume a wide range of organisms, including ungulates and plants, but Pacific salmon Oncorhynchus spp. are especially important to their diet where their ranges overlap. Although some brown bears minimize antagonistic encounters with other brown bears or infanticide by avoiding streams where salmon spawn, studies generally assume that brown bears with ready access to salmon feed heavily on them. To test this assumption, and the hypothesis that male brown bears would feed more heavily on salmon than females (owing to their sexual size dimorphism), we collected hair samples from brown bears by using barbed wire placed on six small tributaries of Lake Aleknagik, Alaska, USA, where adult Sockeye Salmon Oncorhynchus nerka are readily accessible and frequently consumed by brown bears. Analysis of DNA distinguished among the different brown bears leaving the hair samples, some of which were sampled multiple times within and among years. We assessed the contribution of salmon to the diet of individual brown bears by using carbon and nitrogen stable isotope signatures. The 77 samples analyzed from 31 different bears over 4 y showed isotopic ratios consistent with reliance on salmon, but the wide range of isotopic signatures included values suggesting variable, and in one case considerable, use of terrestrial resources. Stable isotope signatures did not differ between male and female brown bears, nor did they differ between two sides of the lake, despite marked differences in Sockeye Salmon density. We collected the hair samples when salmon were present, so there was some uncertainty regarding whether they reflected feeding during the current or previous season. Notwithstanding this caveat, the results are consistent with the hypothesis that salmon were sufficiently available to provide food for the brown bears and that the considerable isotopic variation among brown bears with access to salmon reflected their age, status, and behavior.

Trace element content in tissues of sockeye salmon from several waterbodies of the Kamchatka Peninsula

The results of the study of macro- (Ca, Mg) and micro- (Mn, Zn, Cu, Fe) elements content in the pectoral fin tissue of adult sockeye salmon Oncorhynchus nerka from the rivers Bolshaya and Kamchatka as well as from Azabachye Lake (Kamchatka Peninsula) are presented. The significant differences in the contents in samples from the three waterbodies were found. It was ascertained that the largest ash proportion (and the mass fraction of trace elements) in dry matter contained in the tissues of sockeye salmon from Kamchatka River, the smallest in the sample of Azabachye Lake. The Ca content was 98 % of the ash mass in all samples; Mg accounted for slightly less than 2 %. The proportion of the remaining elements varied within 0.1 %, and exactly in this range the differences in the microelement composition between the samples were revealed. In sockeye salmon tissues from the Kamchatka River, the content of heavy metals as well as Ca and Mg was higher than in other samples, and their percentage ratio considerably differed from the others. Obviously, the water bodies studied sufficiently distinguish in hydrochemical indices, and that is the cause of differences in bioaccumulation intensities of trace elements in fish tissues at the freshwater life stage.

Adult Sockeye Salmon Assessment in a Tidal, Turbid River: A Comparison of Sonar and Test Fishing Methods

AbstractThe feasibility of using sonar in Alaska's lower Kvichak River, a region with a 3.8 m tidal flux, to assess the abundance of adult Sockeye Salmon Oncorhynchus nerka was evaluated as a replacement for an in‐river gill‐net test fishery. Test fish indices are one tool that is used to manage commercial and subsistence fisheries in Bristol Bay. On this river, an observation tower project near the clear headwaters provides accurate abundance estimates for this species, but fishery managers require timelier estimates for in‐season daily management. The lower‐river test fish index is timelier, but it is less precise than tower estimates are. We had to determine whether to replace the test fish project with sonar based on how well each compared with tower estimates and an assessment of their cost and effort. Two dual‐frequency identification sonars (DIDSONs) were deployed along one bank of the lower river (one pointed toward shore and one away from shore) to assess salmon passage across all tidal stages in an attempt to produce an index with higher precision. Compared with the tower estimates, the test fish index showed a slightly stronger correlation in each of the three study years than the sonar index did, despite the stronger sampling power of the sonar. The test fish and sonar indices were strongly correlated. In the lower river, upriver salmon migration (85–98%) occurred primarily during ebb tides and downriver passage (97–100%) during flood tides, indicating that salmon do not use selective tidal stream transport to minimize their energy expenditures in this river. We were able to successfully use fixed‐location sonar in a tidal nearshore region to produce an index of fish abundance. Our recommendation was to continue the test fishing project rather than to replace it with sonar because of the similarity between their indices and the higher cost of the sonar project.

Olfactory gene expression in migrating adult sockeye salmon Oncorhynchus nerka.

Expression of 12 olfactory genes was analysed in adult sockeye salmon Oncorhynchus nerka nearing spawning grounds and O. nerka that had strayed from their natal migration route. Variation was found in six of these genes, all of which were olfc olfactory receptors and had lower expression levels in salmon nearing spawning grounds. The results may reflect decreased sensitivity to natal water olfactory cues as these fish are no longer seeking the correct migratory route. The expression of olfactory genes during the olfactory-mediated spawning migration of Pacific salmon Oncorhynchus spp. is largely unexplored and these findings demonstrate a link between migratory behaviours and olfactory plasticity that provides a basis for future molecular research on salmon homing.

Global Warming of Salmon and Trout Rivers in the Northwestern U.S.: Road to Ruin or Path Through Purgatory?

AbstractLarge rivers constitute small portions of drainage networks but provide important migratory habitats and fisheries for salmon and trout when and where temperatures are sufficiently cold. Management and conservation of coldwater fishes in the current era of rapid climate change require knowing how riverine thermal environments are evolving and the potential for detrimental biological impacts. Robust estimates of warming rates, however, are lacking due to limited long‐term temperature monitoring, so we compiled the best available multidecadal records and estimated trends at 391 sites in the 56,500‐km river network of the northwestern USA. Warming trends were prevalent during summer and early fall months in recent 20‐ and 40‐year periods (0.18–0.35°C per decade during 1996–2015 and 0.14–0.27°C per decade during 1976–2015), paralleled air temperature trends, and were mediated by discharge trends at regional and local levels. To illustrate the biological consequences of warming later in this century, trend estimates were used to inform selection of river temperature scenarios and assess changes in thermal exposure of adult Sockeye Salmon Oncorhynchus nerka migrating to four population areas as well as thermal habitat shifts for resident Brown Trout Salmo trutta and Rainbow Trout O. mykiss populations throughout the region. Future warming of 1–3°C would increase Sockeye Salmon exposure by 5–16% (3–143 degree‐days) and reduce thermally suitable riverine trout habitats by 8–31% while causing their upstream shift. Effects of those changes on population persistence and fisheries are likely to be context dependent, and strategic habitat restoration or adaptation strategies could ameliorate some biological impairments, but effectiveness will be tempered by the size of rivers, high costs, and pervasiveness of thermal effects. Most salmon and trout rivers will continue to provide suitable habitats for the foreseeable future, but it also appears inevitable that some river reaches will gradually become too warm to provide traditional habitats.

Short‐term Physiological Response Profiles of Tagged Migrating Adult Sockeye Salmon: A Comparison of Gastric Insertion and External Tagging Methods

AbstractA variety of electronic tag types are routinely applied to fish to better understand migration biology. However, tagging procedures have the potential to affect the postrelease behaviour and survival of tagged individuals. In this study, wild adult Sockeye Salmon Oncorhynchus nerka from the Harrison River, British Columbia, were radio‐tagged by gastric insertion or external attachment techniques immediately after capture to understand the short‐term physiological response to these two tagging methods. Plasma cortisol, glucose, lactate, sodium, and potassium levels, as well as white muscle lactate and glycogen concentrations, were measured in samples obtained from fish upon capture (0 h) as well as 1 or 4 h after the tagging treatment. The effects of key biological variables, such as sex and proximity to spawn, on the physiological response to the tagging events were also evaluated. Tagging occurred during two distinct time periods representing fish of different maturation states and durations of freshwater residency. Overall, the physiological response to the tagging scenarios was characteristic of the disturbance associated with exhaustive exercise. There were no significant differences detected in the response profiles following gastric or external tagging procedures. This was despite procedural differences such as stomach perforations observed in 68% of the gastric insertions in the late sampling period, and external attachments taking three times longer (43 s) than gastric insertion (15 s). Moreover, the tagged fish showed similar response profiles to control fish that were handled but not tagged. These results suggest that the capture and handling associated with a tagging event induced physiological disturbance, and that the addition of a quick tagging procedure appeared to be nonadditive over the 4‐h assessment period. Sex and proximity to spawn had significant main and interaction effects on some of the physiological response variables, indicating that biological context is important for interpreting physiological assessments in experiments that manipulate exercise and stress responses in migrating adult Pacific salmon.

Influence of ocean and freshwater conditions on Columbia River sockeye salmonOncorhynchus nerkaadult return rates

In recent years, returns of adult sockeye salmon Oncorhynchus nerka to the Columbia River Basin have reached numbers not observed since the 1950s. To understand factors related to these increased returns, we first looked for changes in freshwater production and survival of juvenile migrants. We then evaluated productivity changes by estimating smolt-to-adult return rates (SAR) for juvenile migration years 1985–2010. We found SAR varied between 0.2 and 23.5%, with the highest values coinciding with recent large adult returns. However, the largest adult return, in 2012, resulted not from increased survival, but from increased smolt production. We evaluated 19 different variables that could influence SARs, representing different facets of freshwater and ocean conditions. We used model selection criteria based on small-sample corrected AIC to evaluate the relative performance of all two- and three-variable models. The model with April upwelling, Pacific Northwest Index (PNI) in the migration year, and PNI in the year before migration had 10 times the AICc weight as the second-best-supported model, and R2 = 0.82. The variables of April ocean upwelling and PNI in the migration year had high weights of 0.996 and 0.927, respectively, indicating they were by far the best of the candidate variables to explain variations in SAR. While our analyses were primarily correlative and limited by the type and amount of data currently available, changes in ocean conditions in the northern California Current system, as captured by April upwelling and PNI, appeared to play a large role in the variability of SAR.

Dead fish swimming: a review of research on the early migration and high premature mortality in adult Fraser River sockeye salmon Oncorhynchus nerka

Adult sockeye salmon Oncorhynchus nerka destined for the Fraser River, British Columbia are some of the most economically important populations but changes in the timing of their homeward migration have led to management challenges and conservation concerns. After a directed migration from the open ocean to the coast, this group historically would mill just off shore for 3-6 weeks prior to migrating up the Fraser River. This milling behaviour changed abruptly in 1995 and thereafter, decreasing to only a few days in some years (termed early migration), with dramatic consequences that have necessitated risk-averse management strategies. Early migrating fish consistently suffer extremely high mortality (exceeding 90% in some years) during freshwater migration and on spawning grounds prior to spawning. This synthesis examines multidisciplinary, collaborative research aimed at understanding what triggers early migration, why it results in high mortality, and how fisheries managers can utilize these scientific results. Tissue analyses from thousands of O. nerka captured along their migration trajectory from ocean to spawning grounds, including hundreds that were tracked with biotelemetry, have revealed that early migrants are more reproductively advanced and ill-prepared for osmoregulatory transition upon their entry into fresh water. Gene array profiles indicate that many early migrants are also immunocompromised and stressed, carrying a genomic profile consistent with a viral infection. The causes of these physiological changes are still under investigation. Early migration brings O. nerka into the river when it is 3-6° C warmer than historical norms, which for some late-run populations approaches or exceeds their critical maxima leading to the collapse of metabolic and cardiac scope, and mortality. As peak spawning dates have not changed, the surviving early migrants tend to mill in warm lakes near to spawning areas. These results in the accumulation of many more thermal units and longer exposures to freshwater diseases and parasites compared to fish that delay freshwater entry by milling in the cool ocean environment. Experiments have confirmed that thermally driven processes are a primary cause of mortality for early-entry migrants. The Fraser River late-run O. nerka early migration phenomenon illustrates the complex links that exist between salmonid physiology, behaviour and environment and the pivotal role that water temperature can have on population-specific migration survival.

Physiological and molecular endocrine changes in maturing wild sockeye salmon, Oncorhynchus nerka, during ocean and river migration

Maturing adult sockeye salmon Oncorhynchus nerka were intercepted while migrating in the ocean and upstream in freshwater over a combined distance of more than 1,300 km to determine physiological and endocrine changes associated with ionoregulation. Sockeye migrating through seawater and freshwater showed consistent declines in gill Na+/K+ -ATPase (NKA) activity, plasma osmolality and plasma chloride concentration. In contrast, plasma sodium concentration became elevated in seawater as fish approached the river mouth and was then restored after sockeye entered the river. Accompanying the movement from seawater to freshwater was a significant increase in mRNA for the NKA α1a subunit in the gill, with little change in the α1b subunit. Potential endocrine signals stimulating the physiological changes during migration were assessed by measuring plasma cortisol and prolactin (Prl) concentrations and quantifying mRNA extracted from the gill for glucocorticoid receptors 1 and 2 (GR1 and GR2), mineralocorticoid receptor (MR), growth hormone 1 receptor (GH1R), and prolactin receptor (PrlR). Plasma cortisol and prolactin concentrations were high in seawater suggesting a preparatory endocrine signal before freshwater entry. Generally, the mRNA expression for GR1, GR2 and MR declined during migration, most notably after fish entered freshwater. In contrast, PrlR mRNA increased throughout migration, particularly as sockeye approached the spawning grounds. A highly significant association existed between gill PrlR mRNA and gill NKA α1a mRNA. GH1R mRNA also increased significantly, but only after sockeye had migrated beyond tidal influence in the river and then again just before the fish reached the spawning grounds. These findings suggest that cortisol and prolactin stimulate ionoregulation in the gill as sockeye salmon adapt to freshwater.

The effect of the infectious hematopoietic necrosis virus on the population of sockeye salmon Oncorhynchus nerka (Salmoniformes, Salmonidae) from Lake Nachikinskoe

The results of virological examination of adult sockeye salmon Oncorhynchus nerka in Lake Nachikinskoe from 2003 to 2008 demonstrated high values of prevalence of the infectious hematopoietic necrosis virus (IHNV) in the fish population (up to 100%). In the studied water reservoir there are optimal conditions for the development and revealing of the epizootic of infectious hematopoietic necrosis (IHN). In Lake Nachikinskoe, two natural epizootics of IHN in juvenile sockeye salmon were recorded in 2003 and 2006. The tendencies for change of prevalence of IHNV by years were analyzed, and their relation to the numbers of adult sockeye salmon at the spawning grounds of Lake Nachikinskoe was determined. The correlation of IHNV prevalence with the numbers of adult sockeye salmon in the studied water reservoir is direct but insignificant (r s = 0.695, p < 0.05). It was shown that the epizootic of 2003 could affect the fact that fish return in 2007 and 2008 was minimum for the considered time interval while the numbers of their parents were, on the other hand, very high.

The influence of maternal condition on offspring performance in sockeye salmon Oncorhynchus nerka

Eggs were taken from adult sockeye salmon Oncorhynchus nerka that had reached their journey's end in spawn-ready and moribund condition, and fertilized by healthy males. Egg number, size, hatching success and offspring growth did not differ with maternal condition, which suggests the absence of any persisting physiological maternal effects. Differences were noted in the swimming behaviour and physiology of the offspring at parr stage. In a 30 min schooling test conducted using groups of five in a flume, parr from moribund females were more likely to fatigue, were not as tightly schooled, and had a diminished startle response, both in the per cent responding and the burst distance. In individual, confined swimming tests conducted within a tube, post-exercise plasma lactate concentration, which is an indicator of white muscle use, was greater for parr from moribund adult females. The moribund females also had elevated lactate following exercise (their migration), which suggests heritable differences may exist in muscle use. This study shows that juvenile O. nerka artificially propagated from females exhausted by their return migration can exhibit swimming performance differences, indicating that maternal condition may need to be considered in breeding programmes.

Physiological, energetic and behavioural correlates of successful fishway passage of adult sockeye salmon Oncorhynchus nerka in the Seton River, British Columbia

Electromyogram (EMG) radio telemetry was used in conjunction with physiological biopsy to relate prior physiological condition and subsequent swimming energetics and behaviours to passage success of 13 wild adult sockeye salmon Oncorhynchus nerka at a vertical-slot fishway on the Seton River, British Columbia. At the time of capture, plasma lactate, glucose and cortisol levels indicated that fish were not exhibiting unusually high levels of physiological stress. Very few differences existed between successful and unsuccessful fish in body size, initial plasma physiology and energy state and mean swim speed and energy use during passage. Generally, fish did not employ burst swimming during successful or failed attempts at passage, indicating that failure was probably not related to metabolic acidosis. Plasma Na(+) concentration was significantly lower in unsuccessful fish (P < 0.05), which is suggestive of a depressed ionic state or a possible stress component, although values in all fish were within an expected range for migrant adult O. nerka. Nevertheless, six of 13 fish failed to reascend the fishway and remained in the tailrace of the dam for more than a day on average before moving downstream and away from the dam. During this time, fish were observed actively seeking a means of passage, suggesting that there may have been other, undetermined causes of passage failure.

The Influence of Water Temperature on Time to Surface for Adult Sockeye Salmon Carcasses and the Limitations in Estimating Salmon Carcasses in the Fraser River, British Columbia

AbstractWe determined the postmortem specific gravity and examined the relationship between water temperature and the time to surface for carcasses of adult sockeye salmon Oncorhynchus nerka. These results, in conjunction with other biophysical factors, were used to explain the difficulties associated with the detection of the carcasses of sockeye salmon that die during upstream migration in the Fraser River. Large negative differences have occurred between the sockeye salmon estimates at the river entry and spawning escapement (&gt;0.5 million in 8 of the past 15 years), but relatively few carcasses are observed. Without confirmation of mortality, managers are left with the dilemma of how to partition these differences among lower river escapement, spawning ground escapement, catch, en route mortality, and unreported catch. We investigated the reasons for the paucity of carcass observations by experimentally testing the influence of water temperature on carcass buoyancy and by examining hydrological factors that may affect carcass visibility. Because the Fraser River is turbid (Secchi depth, &lt;40 cm), only carcasses on the surface can be observed. Initially, all fish had specific gravity estimates of greater than 1 (mean ± SD, 1.057 ± 0.010) and were negatively buoyant when placed in tanks at different water temperatures. The time for a sockeye salmon carcass to surface was inversely related to water temperature and ranged from 1–3 d at 20°C to 12–18 d at 6°C. Annual counts of dead fish floating on the surface were positively correlated with river water temperature. Fisheries managers should not always expect to see large numbers of dead salmon in years of high estimated en route losses, given the factors that influence the visibility of salmon carcasses in a large river system. We recommend alternative methods for achieving more accurate and precise estimates of en route mortalities.

A Bayesian Analysis of Biological Uncertainty for a Whole-Lake Fertilization Experiment for Sockeye Salmon in Chilko Lake, British Columbia, and Implications for the Benefit–Cost Ratio

Chilko Lake in British Columbia, Canada, was fertilized with nitrogen and phosphorus in the late 1980s and early 1990s to increase abundance and harvests of adult sockeye salmon Oncorhynchus nerka. Because of the short, 5-year duration of this program and the large inherent natural variation in adult recruits produced per spawner both before and during lake fertilization, there is considerable uncertainty about the efficacy of that fertilization. Recent analyses suggest a high probability that more adult sockeye salmon were produced per spawner from fertilization than would have been produced without fertilization, but the confidence interval on that increase is large. Furthermore, no economic analysis has been done to determine the effect of the large biological uncertainties on the benefit–cost (BC) ratio of the project. We filled this need by using Bayesian statistical analysis to estimate uncertainty in the parameters of four models that reflected different hypotheses about the biological effects of fertilization on sockeye salmon. We then used those estimated posterior probability distributions for (1) additional sockeye salmon recruits that were attributable to fertilization and (2) the resulting economic BC ratio. This ratio took into account costs of fertilization as well as costs and benefits of harvesting additional fish. We found evidence of biological and net economic benefits for the Chilko Lake fertilization project. Depending on the model, the posterior probability was at least 81% that the abundance of adult sockeye salmon increased owing to fertilization and at least 84% that the BC ratio was greater than 1.0 (mean BC ratio = 27). Nevertheless, considerable uncertainty remains because the 95% probability interval was large for the BC ratio. The breadth of the distribution for the BC ratio was probably underestimated because of uncertainties (omitted here) concerning various economic components of our analysis as well as the costs and benefits of the indirect effects of fertilization.

Ionoregulatory changes in different populations of maturing sockeye salmonOncorhynchus nerkaduring ocean and river migration

We present the first data on changes in ionoregulatory physiology of maturing, migratory adult sockeye salmon Oncorhynchus nerka. Fraser River sockeye were intercepted in the ocean as far away as the Queen Charlotte Islands (approximately 850 km from the Fraser River) and during freshwater migration to the spawning grounds; for some populations this was a distance of over 700 km. Sockeye migrating in seawater toward the mouth of the Fraser River and upriver to spawning grounds showed a decline in gill Na+,K+-ATPase activity. As a result, gill Na+,K+-ATPase activity of fish arriving at the spawning grounds was significantly lower than values obtained from fish captured before entry into freshwater. Plasma osmolality and chloride levels also showed significant decreases from seawater values during the freshwater migration to spawning areas. Movement from seawater to freshwater increased mRNA expression of a freshwater-specific Na+,K+-ATPase isoform (alpha1a) while having no effect on the seawater-specific isoform (alpha1b). In addition, gill Na+,K+-ATPase activity generally increased in active spawners compared with unspawned fish on the spawning grounds and this was associated with a marked increase in Na+,K+-ATPase alpha1b mRNA. Increases in gill Na+,K+-ATPase activities observed in spawners suggests that the fish may be attempting to compensate for the osmotic perturbation associated with the decline in plasma chloride concentration and osmolality.

Coupling non‐invasive physiological assessments with telemetry to understand inter‐individual variation in behaviour and survivorship of sockeye salmon: development and validation of a technique

Approximately 200 km from the mouth of the Fraser River, British Columbia, Canada, adult sockeye salmon Oncorhynchus nerka, were gastrically implanted with radio transmitters without anaesthetic. Subsets of the transmitter implanted fish were also biopsied which included drawing blood from the caudal peduncle (3 ml), removal of gill tissue (0·03 g) and quantification of energetic status using a microwave fat meter. Several experiments were used to test the hypothesis that the biopsy had a negligible effect on the subsequent survival and migratory behaviour of transmitter implanted fish. In the first experiment, no difference was found in the survival (both 100%) or tag retention (both 100%) between the two treatment groups (transmitter implanted with and without biopsy) when fish were held in pens for 24 h in the marine environment. Similarly, in other experiments where fish were released to the ocean to resume their migratory journey, no statistical differences were found in the travel times of fish in the two treatment groups, or in the proportion of fish that passed in‐river telemetry checkpoints. These results indicated that the handling and biopsy methods produced similar levels of mortality and tag retention as the telemetry treatment alone and that any changes in behaviour between the two treatment groups did not adversely affect migration time. Based upon the evidence provided from the biotelemetry of &gt;300 adult sockeye salmon, it was felt that this general type of approach could be applicable to other fish species.

Radio Tag Retention and Tag-Related Mortality among Adult Sockeye Salmon

Abstract Tag retention and tag-related mortality are concerns for any tagging study but are rarely estimated. We assessed retention and mortality rates for esophageal radio tag implants in adult sockeye salmon Oncorhynchus nerka. Migrating sockeye salmon captured at the outlet of Lake Clark, Alaska, were implanted with one of four different radio tags (14.5 × 43 mm (diameter × length), 14.5 × 49 mm, 16 × 46 mm, and 19 × 51 mm). Fish were observed for 15 to 35 d after tagging to determine retention and mortality rates. The overall tag retention rate was high (0.98; 95% confidence interval (CI), 0.92-1.00; minimum, 33 d), with one loss of a 19-mm × 51- mm tag. Mortality of tagged sockeye salmon (0.02; 95% CI, 0-0.08) was similar to that of untagged controls (0.03 (0-0.15)). Sockeye salmon with body lengths (mid-eye to tail fork) of 585-649 mm retained tags as large as 19 × 51 mm and those with body lengths of 499-628 mm retained tags as small as 14.5 × 43 mm for a minimum of 33 d with no increase in mortali...

Effects of Swim Speed and Activity Pattern on Success of Adult Sockeye Salmon Migration through an Area of Difficult Passage

We used electromyogram telemetry to examine swim speeds and passage success for 12 adult sockeye salmon Oncorhynchus nerka migrating through Hell's Gate, a reach in the Fraser River canyon that is notorious for creating conditions that impede salmon migrations. Fishways exist in one segment; however, the approach immediately downstream of the fishways is also very challenging to migration. Average swim speeds (in body lengths per second; BL/s) were slower (P = 0.017) and residency times shorter (P = 0.058) in the approach for fish that successfully entered the fishways (mean = 1.85 BL/s, SE = 0.71; mean = 34.57 min, SE = 17.39; n = 7) compared with those of fish that were unsuccessful (mean = 4.23 BL/s, SE = 0.85; mean = 1,742 min, SE = 1,367; n = 5). Migrant-specific swim-speed patterns revealed that fish alternated at different time scales between relatively fast and slow speeds. Continuous swimming at greater than maximum sustained speeds (Ucrit) never exceeded 3 min in the case of any of the successful migrants, but unsuccessful migrants exhibited one or more periods (each of >10 min duration) of continuous swimming at speeds greater than Ucrit. Unsuccessful fish disappeared downstream and died without passing Hell's Gate. Hyperactivity seems to have played a significant role in lack of passage success. It is unclear why some fish swam at relatively fast speeds for extended periods of time while others did not. It is possible that unsuccessful migrants swam fast because they used relatively turbulent and fast-flowing migration paths. Some individuals may also be prone to swim at relatively fast speeds regardless of migration path.

Use of Electromyogram Telemetry to Assess Difficult Passage Areas for River-Migrating Adult Sockeye Salmon

Abstract We conducted laboratory respirometry trials using adult sockeye salmon Oncorhynchus nerka implanted with electromyogram (EMG) radio transmitters to investigate the relationship between oxygen consumption and EMG pulse interval. The strong association that was observed suggested that EMG telemetry could be used to assess activity and, thus, relative energy expenditure in freely migrating sockeye salmon. Using EMG telemetry, we then assessed the relative energy costs of upstream migration by adult sockeye salmon through specific reaches of the Fraser River, British Columbia. Greatest energy costs were incurred during migration through Hell's Gate fishways, a known point of difficult passage. Another energetically demanding area was a gravel bar that had not been previously identified as difficult for passage. Three other areas that historically had been identified as difficult for passage were energetically less expensive to migrate through during our study. Our results demonstrate that EMG telemet...