Divergence of mitochondrial DNA in a population of sockeye salmon (Oncorhynchus nerka Walbaum) from Azabache'e lake (Kamchatka)

Variability of three PCR-amplified mtDNA regions was examined in five populations of sockeye salmon from Azabach'e Lake. Eighteen haplotypes were detected in 144 fish. Significant differences were found between seasonal races of sockeye salmon spawning in the lake. The short time of independent divergence between the seasonal races indicates that these races formed independently in each spawning region. No difference in mtDNA between lake samples of early sockeye salmon (subisolates) was revealed, which confirms the existence of gene flow between them. A high level of differences between the sockeye salmon spawning in the lake and spawning in the tributaries of the lake, the Bushuev and Lotnaya rivers, suggests that there were no migration between them during many generations and that the nature of spawning grounds (lake or river) is essential for within species differentiation in this species.     

Divergence of Mitochondrial DNA in Populations of Sockeye Salmon Oncorhynchus nerka Walbaum from Azabach'e Lake (Kamchatka)

Variability of three PCR-amplified mtDNA regions was examined in five populations of sockeye salmon from Azabach'e Lake. Eighteen haplotypes were detected in 144 fish. Significant differences were found between seasonal races of sockeye salmon spawning in the lake. The short time of independent divergence between the seasonal races indicates that these races formed independently in each spawning region. No difference in mtDNA between lake samples of early sockeye salmon (subisolates) was revealed, which confirms the existence of gene flow between them. A high level of differences between the sockeye salmon spawning in the lake and spawning in the tributaries of the lake, the Bushuev and Lotnaya rivers, suggests that there were no migration between them during many generations and that the nature of spawning grounds (lake or river) is essential for within-species differentiation in this species.     

Rheoreaction as a mechanism of formation of phenotypic groups of underyearlings of the Atlantic salmon <Emphasis Type="Italic">Salmo salar</Emphasis>

Experimental investigation on rheoreaction as a behavioral mechanism in the formation of phenotypic groups of underyearlings of the Atlantic salmon Salmo salar is performed. Juveniles of the Atlantic salmon are investigated at the age 0+ from the coastal group and from the tributary group in the period of its primary distribution from redds. The underyearlings from the tributary group differ from the coastal fish in increased critical current velocity, the fact that among them the most portion of individuals have a positive type of rheoreacrtion, and the fact that they prefer currents more often. The behavioral mechanism of spatial separation of the spreading juveniles at confluence of two currents is revealed: stronger individuals with the positive type of rheoreaction and the expressed rheopreferendum mainly move against the flow at a higher speed and manage to get into a tributary. The weaker fish with static and negative dynamic types of rheoreaction, having no expressed rheopreferendum, prefer the flow with lower current rate and turn out to be in the coastal zone of the mainstream.     

Polymorphism of smolts of pink salmon <Emphasis Type="Italic">Oncorhynchs gorbuscha</Emphasis> in the Indera River (Kola Peninsula)

Pink salmon introduced into the White Sea started to exploit as spawning grounds middle and upper reaches of the river 20 years after its appearance in the Indera River. As a result of this, the migration pathway of smolts and late smolts appeared in addition to early smolts. The intraspecies polymorphism of smolts is confirmed by differences of early and late smolts by body length and weight, migration dates, food spectrum, and indices of stomach fullness. The food spectra of late juveniles of pink salmon coincide with those of parr of Atlantic salmon Salmo salar and of brown trout S. trutta. Greater abundance of late migrants of pink salmon may cause competition of these species for food.     

Sea louse infection of juvenile sockeye salmon in relation to marine salmon farms on Canada's west coast

Background

Pathogens are growing threats to wildlife. The rapid growth of marine salmon farms over the past two decades has increased host abundance for pathogenic sea lice in coastal waters, and wild juvenile salmon swimming past farms are frequently infected with lice. Here we report the first investigation of the potential role of salmon farms in transmitting sea lice to juvenile sockeye salmon (Oncorhynchus nerka).

Methodology/Principal Findings

We used genetic analyses to determine the origin of sockeye from Canada''s two most important salmon rivers, the Fraser and Skeena; Fraser sockeye migrate through a region with salmon farms, and Skeena sockeye do not. We compared lice levels between Fraser and Skeena juvenile sockeye, and within the salmon farm region we compared lice levels on wild fish either before or after migration past farms. We matched the latter data on wild juveniles with sea lice data concurrently gathered on farms. Fraser River sockeye migrating through a region with salmon farms hosted an order of magnitude more sea lice than Skeena River populations, where there are no farms. Lice abundances on juvenile sockeye in the salmon farm region were substantially higher downstream of farms than upstream of farms for the two common species of lice: Caligus clemensi and Lepeophtheirus salmonis, and changes in their proportions between two years matched changes on the fish farms. Mixed-effects models show that position relative to salmon farms best explained C. clemensi abundance on sockeye, while migration year combined with position relative to salmon farms and temperature was one of two top models to explain L. salmonis abundance.

Conclusions/Significance

This is the first study to demonstrate a potential role of salmon farms in sea lice transmission to juvenile sockeye salmon during their critical early marine migration. Moreover, it demonstrates a major migration corridor past farms for sockeye that originated in the Fraser River, a complex of populations that are the subject of conservation concern.     

Ontogenetic Behavior and Migration of Gulf of Mexico Sturgeon, Acipenser oxyrinchus desotoi, with Notes on Body Color and Development

We observed Suwannee River Gulf sturgeon, Acipenser oxyrinchus desotoi, in the laboratory and found free embryos (first interval after hatching) hid under rocks and did not migrate. Thus, wild embryos should be at the spawning area. Larvae (first interval feeding exogenously) initiated a slow downstream migration, and some juveniles (interval with adult features) continued to migrate slowly for at least 5 months, e.g., a 1-step long larva-juvenile migration. No other population of sturgeon yet studied has this migration style. A conceptual model using this result suggests wild year-0 sturgeon have a variable downstream migration style with short-duration (short distance) migrants and long-duration (long distance) migrants. This migration style should widely disperse wild fish. The model is supported by field studies that found year-0 juveniles are widely dispersed in fresh water to river km 10. Thus, laboratory and field data agree that the entire freshwater reach of river downstream of spawning is nursery habitat. Foraging position of larvae and early juveniles was mostly on the bottom, but fish also spent hours holding position in the water column, an unusual feeding location for sturgeons. The holding position of fish above the bottom suggests benthic forage in the river is scarce and fish have evolved drift feeding. The unusual migration and foraging styles may be adaptations to rear in a river at the southern limit of the species range with poor rearing habitat (low abundance of benthic forage and high summer water temperatures). Suwannee River Gulf sturgeon and Hudson River Atlantic sturgeon, A. o. oxyrinchus, are similar for initiation of migration, early habitat preference, and diel migration. The two subspecies differ greatly for migration and foraging styles, which is likely related to major differences in the quality of rearing habitat. The differences between Atlantic sturgeon populations show the need for geographical studies to represent the behavior of an entire species.     

Thermal biology and bioenergetics of different upriver migration strategies in a stock of summer-run Chinook salmon

By combining biotelemetry with animal-borne thermal loggers, we re-created the thermal histories of 21 summer-run Chinook salmon (Oncorhynchus tshawytscha) migrating in the Puntledge River, a hydropower impacted river system on Vancouver Island, British Columbia, Canada. Daily maximum water temperatures in the Puntledge River during the summer-run adult Chinook salmon migration and residency period frequently exceeded 21 °C, a value that has been observed to elicit behavioral thermoregulation in other Chinook salmon populations. We therefore compared river temperatures to body temperatures of 16 fish that migrated through the river to understand if cool-water refuge was available and being used by migrants. In addition, we used thermal histories from fish and thermal loggers distributed in the river to model the effect of thermal habitat on energy density using a bioenergetics model. In general, we found no evidence that cool-water refuge existed in the river, suggesting that there is no opportunity for fish to behaviorally thermoregulate during upriver migration through the regulated portion of the river. Of the thermal histories used in the bioenergetics model, fish that reached an upstream lake were able to access cooler, deeper waters, which would have reduced energy consumption compared to fish that only spent time in the warmer river. Consequently, the Puntledge River water temperatures are likely approaching and in some cases exceeding the thermal limits of the summer-run Chinook salmon during the spawning migration. Further warming may cause more declines in the stock.     

The distribution of juvenile Pacific salmon and associated fish species in Lake Sopochnoye,Iturup Island

A single survey using a minnow seine net showed that juvenile chum and sockeye salmon are distributed extremely unevenly along the shoreline of Lake Sopochnoye, on Iturup Island. Young-of-the-year chum salmon aggregate mainly near the estuaries of the rivers that flow into the lake; young-of-the-year and 2-year-old sockeye salmon aggregate closer to the central part of the lake. The distribution of associated fish species is also very uneven, but none of them dominates within the zone of catches; the abundance of each of these species is comparable to that of the juvenile Pacific salmon.     

Effects of river temperature and climate warming on stock‐specific survival of adult migrating Fraser River sockeye salmon (Oncorhynchus nerka)

Mean summer water temperatures in the Fraser River (British Columbia, Canada) have increased by ～1.5 °C since the 1950s. In recent years, record high river temperatures during spawning migrations of Fraser River sockeye salmon (Oncorhynchus nerka) have been associated with high mortality events, raising concerns about long‐term viability of the numerous natal stocks faced with climate warming. In this study, the effect of freshwater thermal experience on spawning migration survival was estimated by fitting capture–recapture models to telemetry data collected for 1474 adults (captured in either the ocean or river between 2002 and 2007) from four Fraser River sockeye salmon stock‐aggregates (Chilko, Quesnel, Stellako‐Late Stuart and Adams). Survival of Adams sockeye salmon was the most impacted by warm temperatures encountered in the lower river, followed by that of Stellako‐Late Stuart and Quesnel. In contrast, survival of Chilko fish was insensitive to the encountered river temperature. In all stocks, in‐river survival of ocean‐captured sockeye salmon was higher than that of river‐captured fish and, generally, the difference was more pronounced under warm temperatures. The survival–temperature relationships for ocean‐captured fish were used to predict historic (1961–1990) and future (2010–2099) survival under simulated lower river thermal experiences for the Quesnel, Stellako‐Late Stuart and Adams stocks. A decrease of 9–16% in survival of all these stocks was predicted by the end of the century if the Fraser River continues to warm as expected. However, the decrease in future survival of Adams sockeye salmon would occur only if fish continue to enter the river abnormally early, towards warmer periods of the summer, as they have done since 1995. The survival estimates and predictions presented here are likely optimistic and emphasize the need to consider stock‐specific responses to temperature and climate warming into fisheries management and conservation strategies.     

Growth and migration patterns of juvenile temperate seabass Lateolabrax japonicus in the Yura River estuary,Japan—combination of stable isotope ratio and otolith microstructure analyses

It is important to know the characteristics of migration pattern and vital rates of juveniles to understand the early life history and its effect on the population dynamics of fishes. The relationship between growth and migration pattern of juvenile temperate seabass Lateolabrax japonicus in the Yura River estuary was examined by combination of stable carbon isotope ratio (δ¹³C) and otolith microstructure. Gut fullness indices were also examined to know the feeding condition of juveniles. δ¹³C values of seabass juveniles in the lower estuary and surf zone (LES) were enriched, while those in freshwater zone (FW) were depleted, consistent with δ¹³C differences in prey items. The back-calculated growth rates of juveniles in FW were significantly lower than those of juveniles that resided in the LES from 50 days to 90 days old, implying that juveniles with poor growth ascended the river while those with better growth remained in the LES. However, the growth rates of the juveniles, which resided in FW for more than 1 month, caught up with and even overtook those of juveniles in LES within 1 month after ascended the river. The higher water temperature and better feeding conditions would contribute to better growth rates of juveniles in FW than those in LES.     

Olfactory responses to natal stream water in sockeye salmon by BOLD fMRI

Many studies have shown that juvenile salmon imprint olfactory memory of natal stream odors during downstream migration, and adults recall this stream-specific odor information to discriminate their natal stream during upstream migration for spawning. The odor information processing of the natal stream in the salmon brain, however, has not been clarified. We applied blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging to investigate the odor information processing of the natal stream in the olfactory bulb and telencephalon of lacustrine sockeye salmon (Oncorhynchus nerka). The strong responses to the natal stream water were mainly observed in the lateral area of dorsal telencephalon (Dl), which are homologous to the medial pallium (hippocampus) in terrestrial vertebrates. Although the concentration of L-serine (1 mM) in the control water was 20,000-times higher than that of total amino acid in the natal stream water (47.5 nM), the BOLD signals resulting from the natal stream water were stronger than those by L-serine in the Dl. We concluded that sockeye salmon could process the odor information of the natal stream by integrating information in the Dl area of the telencephalon.     

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.     

Variation in smoltification age and its determinants in sockeye salmon of Lake Azabach’e

In this paper, we analyze scale samples of sexually mature sockeye salmon from Lake Azabach'e collected over many years and data on the abundance of zooplankton in this lake. For native juvenile sockeye salmon, the major limiting factor of growth and smoltification is food availability. During the observation period from 1977 to 1993, two-year-olds were the most numerous group among the downstream-migrating sockeye salmon. Short-term fluctuations in the proportion of one-year-old smolts during downstream migration are attributed to outbreaks of plankton due to the natural fertilization of the lake.     

Pacific salmon in hot water: applying aerobic scope models and biotelemetry to predict the success of spawning migrations

Concern over global climate change is widespread, but quantifying relationships between temperature change and animal fitness has been a challenge for scientists. Our approach to this challenge was to study migratory Pacific salmon (Oncorhynchus spp.), fish whose lifetime fitness hinges on a once-in-a-lifetime river migration to natal spawning grounds. Here, we suggest that their thermal optimum for aerobic scope is adaptive for river migration at the population level. We base this suggestion on several lines of evidence. The theoretical line of evidence comes from a direct association between the temperature optimum for aerobic metabolic scope and the temperatures historically experienced by three Fraser River salmon populations during their river migration. This close association was then used to predict that the occurrence of a period of anomalously high river temperatures in 2004 led to a complete collapse of aerobic scope during river migration for a portion of one of the sockeye salmon (Oncorhynchus nerka) populations. This prediction was corroborated with empirical data from our biotelemetry studies, which tracked the migration of individual sockeye salmon in the Fraser River and revealed that the success of river migration for the same sockeye population was temperature dependent. Therefore, we suggest that collapse of aerobic scope was an important mechanism to explain the high salmon mortality observed during their migration. Consequently, models based on thermal optima for aerobic scope for ectothermic animals should improve predictions of population fitness under future climate scenarios.     

Physiological mechanisms of imprinting and homing migration in Pacific salmon Oncorhynchus spp

After several years of feeding at sea, salmonids have an amazing ability to migrate long distances from the open ocean to their natal stream to spawn. Three different research approaches from behavioural to molecular biological studies have been used to elucidate the physiological mechanisms underpinning salmonid imprinting and homing migration. The study was based on four anadromous Pacific salmon Oncorhynchus spp., pink salmon Oncorhynchus gorbuscha, chum salmon Oncorhynchus keta, sockeye salmon Oncorhynchus nerka and masu salmon Oncorhynchus masou, migrating from the North Pacific Ocean to the coast of Hokkaido, Japan, as well as lacustrine O. nerka and O. masou in Lake Toya, Hokkaido, where the lake serves as the model oceanic system. Behavioural studies using biotelemetry techniques showed swimming profiles from the Bering Sea to the coast of Hokkaido in O. keta as well as homing behaviours of lacustrine O. nerka and O. masou in Lake Toya. Endocrinological studies on hormone profiles in the brain-pituitary-gonad axis of O. keta, and lacustrine O. nerka identified the hormonal changes during homing migration. Neurophysiological studies revealed crucial roles of olfactory functions on imprinting and homing during downstream and upstream migration, respectively. These findings are discussed in relation to the physiological mechanisms of imprinting and homing migration in anadromous and lacustrine salmonids.     

Going with the Flow: Spatial Distributions of Juvenile Coho Salmon Track an Annually Shifting Mosaic of Water Temperature

A critical challenge for ecologists is to understand the functional significance of habitat heterogeneity and connectivity for mobile animals. Here, we explore how a thermo-regulating fish responds to annual variation in the spatial patterning of thermal and trophic resources. In a third-order stream in coastal Alaska, juvenile coho salmon forage on sockeye salmon eggs at night in cold water and then move to warmer water to increase their digestive capacity. We mapped the spatial distributions of water temperature, juvenile coho salmon, and spawning sockeye salmon across a 5-year period during which summer discharge varied by greater than fivefold. In low flow years, warm water (9–12°C) was only available in thalweg (that is, main-channel) habitat at least approximately 400 m upstream of the cooler habitat (3–7°C) where sockeye salmon spawned. In high flow years, the entire stream thalweg was isothermal at 7–8°C, but inundated off-channel areas generated warm habitats (9–12°C) laterally adjacent to the downstream regions where sockeye salmon spawned. The daytime spatial distribution of juvenile coho salmon shifted from headwater thalweg habitats in low flow years, to downstream off-channel habitats in high flow years. In all years, the majority of juvenile coho salmon sampled during the daytime were found in warm habitat units without sockeye salmon present, yet they exhibited diet contents comprised virtually entirely of sockeye salmon eggs. Thus, thermoregulatory movements by coho salmon were able to track an annually shifting mosaic of water temperature. Our results demonstrate how the spatial habitat heterogeneity and connectivity of intact floodplains can in turn buffer aquatic organisms from high levels of temporal variation in habitat conditions and resource abundance.     

Population structure of lake‐type and river‐type sockeye salmon in transboundary rivers of northern British Columbia

The population structure of 'lake‐type' and 'river‐type' sockeye salmon Oncorhynchus nerka , primarily in transboundary rivers in northern British Columbia, was examined with a survey of microsatellite variation. Variation at 14 microsatellite loci was surveyed from c . 3000 lake‐type and 3200 river‐type sockeye salmon from 47 populations in six river drainages in British Columbia. The mean F _ST for the 14 microsatellite loci and 47 populations was 0·068, and 0·034 over all river‐type populations. River‐type sockeye salmon were more genetically diverse than lake‐type sockeye salmon, with expected heterozygosity of river‐type sockeye salmon 0·72 and with an average 12·7 alleles observed per locus, whereas expected heterozygosity of lake‐type sockeye salmon was 0·65 with and average 10·5 alleles observed per locus. River drainage of origin was a significant unit of population structure. There was clear evidence of genetic differentiation among river‐type populations of sockeye salmon from different drainages over a broad geographic range in British Columbia.     

A wide window of migration phenology captures inter‐annual variability of favourable conditions: Results of a whole‐lake experiment with juvenile Pacific salmon

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Reproductive biology of four large riverine fishes (Cyprinidae) in a man-made lake,Orange River,South Africa

The reproductive biology ofBarbus holubi, B. kimberleyensis, Labeo capensis andL. umbratus was examined in a large reservoir on the Orange River, South Africa. The findings are integrated into the existing knowledge on largeBarbus andLabeo species, which coexist in most river systems in Africa and Asia.LargeBarbus spawn on gravel beds within the river channel during floods in spring or summer. In continuously flowing regulated rivers, time of spawning is governed by water temperatures. They have moderate fecundity; large eggs, incubation time of several days and the larvae are initially immobile with large yolk sacs. In the impoundment, they spawn in the inflowing regulated river withB. kimberleyensis spawning four to six weeks later than the more cold-tolerantB. holubi, the dominant largeBarbus. Survival is generally good and the juveniles disperse throughout the lake, but unseasonal release of cold water from an upstream impoundment may cause poor reproductive success.In contrast,Labeo species generally spawn on newly flooded ground, usually leaving the main river channel. Spawning may or may not be preceded by a longitudinal migration. Labeos are relatively fecund with small (30%Barbus size) eggs which hatch quickly and the larvae swim in bursts up into the water column before sinking down again.L. capensis does not require a longitudinal spawning migration and breeds throughout the lake, depending on local conditions. Large temporal variation in gonadal development within the population can result in more than one spawning. Dispersal within the lake is poor.L. umbratus uses larger inflowing tributaries for spawning thanL. capensis and its juveniles have a much greater power of dispersal. Early dependence on external feeding and undependable occurrence of conditions for spawning and juvenile feeding makes for variable reproductive success.