Abundance Of Juvenile Salmon Research Articles

Beavers (Castor canadensis) influence habitat for juvenile salmon in a largeAlaskan river floodplain

SummaryOur aim was to determine how beavers affect habitats and food resources for juvenile salmon in theKwethlukRiver in westernAlaska.Habitat modification by beavers was quantified using 3 years of satellite imagery to assess the amount and spatial distribution of potential juvenile rearing habitat. Macroinvertebrate community composition and juvenile salmon abundance in beaver ponds, spring brooks with and without upstream beaver dams, and main channel shorelines were quantified to determine beaver influence. Presence of beaver dams and time‐series measures of water levels were used to assess hydrological connectivity and fish access between the sites and the river as modified by beavers.Of the off‐channel aquatic habitat, 87.5% was altered by beavers damming spring brooks. All beaver‐free and beaver‐influenced juvenile salmon habitats had similar physical characteristics [by non‐metric multidimensional scaling (NMDS) ordination], indicating that all are suitable as juvenile salmon rearing habitat.Aquatic macroinvertebrate community composition differed between beaver ponds and spring brooks (byNMDSordination) with differences driven by larval stoneflies in spring brooks compared to cladocerans, copepods and freshwater clams in beaver ponds.Chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon were predominant in all habitat types except late‐successional ponds. Total fish species and salmon species richness was 2–3× higher, the proportion of young‐of‐the‐year salmon was over 50% compared to <5%, and densities of juvenile salmon were 5–7× higher in spring brooks and early‐successional ponds compared to late‐successional ponds.Early‐successional ponds had high hydrological synchrony values (closely tracking water fluctuations in the main channel), while mid‐ and late‐successional ponds, being farther from the main channel and with more dams blocking flow paths, had lower and highly variable synchrony values. Almost no movement of juvenile salmon occurred past dams at base flow. However, summer and autumn flooding mediated movement past dams, allowing individuals to ‘escape’ or enter early‐successional ponds.Beavers reduced habitat connectivity and added variability to macroinvertebrate assemblages within habitats by damming floodplain spring brooks. Nonetheless, juvenile salmon were able to effectively inhabit and move between early‐successional ponds and spring brooks in theKwethlukRiver, although the presence of beaver dams strongly limited the use of late‐successional ponds on the large alluvial river floodplain.

Spatial variations in the distribution of yearling spring Chinook salmon off Washington and Oregon using COZIGAM analysis

Yearling Chinook salmon Oncorhynchus tshawytscha were sampled off Washington and Oregon, USA, along with environmental factors, every June from 1998 to 2010. The abundance of yearling Chinook salmon varied over space with a high proportion of zero catches. Positive catches were more numerous north of the Columbia River, likely because most yearling Chinook salmon turn north after leaving the Columbia River. Using the latitude of the Columbia River mouth as a geographical border, the survey area was divided into 2 regions: north and south of the Colum- bia River. We hypothesized that (1) the spatial distribution pattern within each region was related to local environmental factors and (2) the difference between north and south was related to large- scale ocean processes. A constrained zero-inflated generalized additive model (COZIGAM) was applied to examine the non-linear relationships between juvenile salmon abundance and environ- mental factors. Results from the COZIGAM suggested that water temperature, chlorophyll a (chl a) concentration, copepod biomass and spatial factors were significantly correlated with the density of salmon in the northern region, and only chl a concentration was correlated significantly with year- ling Chinook density in the southern region. The difference between the abundances north and south of the Columbia River was significantly correlated with alongshore ocean currents, with weaker alongshore currents leading to greater difference between north and south. Results sug- gest that salmon distribution is determined not only by standard habitat parameters (local biotic and abiotic factors) but by ocean conditions such as the strength of alongshore coastal currents.

Distribution of the freshwater pearl mussel (Margaritifera margaritifera) in the Republic of Karelia (North-West Russia)

Data are presented on the distribution and state of populations of a rare species, the European freshwater pearl mussel, in the rivers of Karelia. Populations of Atlantic salmon in the rivers surveyed, and pearl mussel glochidial infection in salmon juveniles were analyzed. It is demonstrated that timber floating, hydropower engineering, pearl harvesting and deforestation have resulted in extinction of the pearl mussel in several rivers. Decline in juvenile salmon abundance has negative influence on the pearl mussel recruitment. However, our data prove that Karelia, both the White Sea and the Baltic Sea catchments, still possesses viable populations of the pearl mussel.

Copepods and salmon: characterizing the spatial distribution of juvenile salmon along the Washington and Oregon coast, USA

Yearling Chinook (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) were sampled concurrently with physical variables (temperature, salinity, depth) and biological variables (chlorophyll a concentration and copepod abundance) along the Washington and Oregon coast in June 1998–2008. Copepod species were divided into four different groups based on their water-type affinities: cold neritic, subarctic oceanic, warm neritic, and warm oceanic. Generalized linear mixed models were used to quantify the relationship between the abundance of these four different copepod groups and the abundance of juvenile salmon. The relationships between juvenile salmon and different copepod groups were further validated using regression analysis of annual mean juvenile salmon abundance versus the mean abundance of the copepod groups. Yearling Chinook salmon abundance was negatively correlated with warm oceanic copepods, warm neritic copepods, and bottom depth, and positively correlated with cold neritic copepods, subarctic copepods, and chlorophyll a concentration. The selected habitat variables explained 67% of the variation in yearling Chinook abundance. Yearling coho salmon abundance was negatively correlated with warm oceanic copepods, warm neritic copepods, and bottom depth, and positively correlated with temperature. The selected habitat variables explained 40% of the variation in yearling coho abundance. Results suggest that copepod communities can be used to characterize spatio-temporal patterns of abundance of juvenile salmon, i.e., large-scale interannual variations in ocean conditions (warm versus cold years) and inshore-offshore (cross-shelf) gradients in the abundance of juvenile salmon can be characterized by differences in the abundance of copepod species with various water mass affinities.

The Response of Salmon Populations to Geomorphic Measurements at Three Scales

AbstractProtocols to assess stream channel response to disturbances often focus on physical aspects of the stream at the reach scale without measurements of fish populations. In this study, estimates of juvenile salmon abundance in 511 habitat units within 25 reaches of 12 streams were made over 4 years and juxtaposed with measurements of physical habitat at the habitat unit, reach, and watershed scales. Fish ranged in size from about 50 to 160 mm fork length. The amount of variation among densities differed by species and geographic scale. For most species, the habitat unit scale accounted for the most variation. Relationships between salmon density and measurements at the habitat unit scale varied. At the reach scale, we observed a negative relationship between abundance of coho salmon Oncorhynchus kisutch parr and number of pools. A positive relationship appeared between coho salmon parr and large wood. At the watershed scale, a positive relationship was observed between coho salmon parr and valley morphology. Valley morphology also entered the model for cutthroat trout O. clarkii. Differences in salmonid densities observed between northern and southern watersheds were attributed to differences in landforms, geology, and soils among islands in southeast Alaska. Simple habitat measures, such as pool counts, were not good predictors of fish abundance. However, geomorphic measures from multiple scales that are accompanied by estimates of fish abundance can provide managers with an integrated picture of watershed productivity and a better means to evaluate features that influence productivity.

Sablefish Predation on Juvenile Pacific Salmon in the Coastal Marine Waters of Southeast Alaska in 1999

AbstractAt‐sea observations of predation by age‐1 and older (age‐1+) sablefish Anoplopoma fimbria on juvenile Pacific salmon Oncorhynchus spp. were combined with laboratory studies to determine gastric evacuation rates and were used to estimate summer predation impact in the northern region of Southeast Alaska. In June and July 1999, up to 63% of sablefish examined from trawl catches in strait habitat had each consumed one to four juvenile pink salmon O. gorbuscha, chum salmon O. keta, or sockeye salmon O. nerka. In two laboratory experiments, field‐captured sablefish were acclimated without food in compartmentalized flow‐through tanks with conditions manipulated to reflect the photoperiod and temperature regimes of summer. These sablefish were each offered one whole, preweighed juvenile chum salmon; consumption events were observed, and the sablefish were then sacrificed at predetermined time intervals. Prey biomass remaining in the stomach of each sablefish predator was weighed, and an exponential model of the decline in percent biomass over time was used to yield instantaneous evacuation rates of 0.049 at 12°C and 0.027 at 7°C. From field data combined with model‐derived estimates of meal frequency, we estimated that 0.8‐6.0 million juvenile salmon were consumed by age‐1+ sablefish in the 500‐km2 area of Icy Strait during a 33‐d period. Moreover, a 10‐year time series of catches indicated that 1999 was a year of unusually high age‐1+ sablefish abundance and relatively low juvenile salmon abundance. We speculate that sablefish predation in 1999 could have affected abundance of out‐migrating juveniles and contributed to low harvests of returning adult pink salmon in 2000 and adult chum salmon in 2002. Our results suggest that sablefish predation on juvenile Pacific salmon can occur during episodic strong year‐classes of sablefish and may affect adult salmon returns.

Juvenile masu salmon in a regulated river

AbstractWe examined the relationship between the physical environment and habitat use of juvenile masu salmon, Oncorhynchus masou, in the Nobori River in Hokkaido, Japan to provide a perspective for the conservation of fish habitat in regulated streams. The study was undertaken during the autumn and winter, with an emphasis on the hierarchy of three spatial scales: microhabitat, channel‐unit and reach scales. The microhabitat‐scale analysis indicated juvenile masu salmon preferred a midstream habitat type, with a greater depth (Avg. ± SD: 35.4 ± 14.2 cm) and high (43.4 ± 23.1 cm s−1) and uniform current velocities during the autumn, and a channel margin habitat type with a moderate current (about 20 cm s−1) and submerged cover during winter. In addition, different cover types have different roles in determining juvenile salmon distributions during winter. Grass cover had extremely high carrying capacities, whereas coarse substrate cover provided winter habitat for larger juvenile salmon. Channel‐unit scale analyses showed that abundance of juvenile salmon tended to be higher in pools than runs in the autumn through winter. Reach‐scale analysis showed that abundance and mean body length of juvenile salmon significantly differed between differently regulated reaches during winter, associated with the dominant cover type in each reach. This study demonstrated that the habitat conditions determining juvenile masu salmon distribution differ according to the season and scale of analysis. Therefore, for conservation of fish communities, it is important to evaluate and conserve or create fish habitats in regulated reaches, with a focus on the hierarchy of spatial scales and seasonal differences. Copyright © 2007 John Wiley & Sons, Ltd.

Interannual changes in recruitment of the Atlantic salmon (Salmo salar) population in the River Oir (Lower Normandy, France): relationships with spawners and in-stream habitat

Abstract Since 1985, the dynamics of the Atlantic salmon (Salmo salar) population in the River Oir, a spawning tributary of the River Sélune (Lower Normandy, France), have been studied from a data set of parr density and the number and the age structure of migrating fish (smolts and adults). Parr densities (1.5–17.4 per 100 m2) and smolt production (0.25–9.2 per 100 m2) varied considerably from year to year. Migrating juveniles were mainly 1 year old. Abundance of parr and smolts was strongly correlated with 0+ densities. Egg-to-smolt survival rates were highly variable year on year (0.044–1.07%). During the juvenile freshwater phase, mortality was highest between the egg and the 0+ stage (97.5–99.9%). The fluctuations in abundance of juvenile salmon appear to be linked to the number and distribution of spawners within the stream during spawning, and also to the amount of silt deposition on the spawning beds. As a result, mortality was highest during the under-gravel phase, and the mean survival rate from egg to smolt was much lower than in rivers less impacted by human activities. Therefore, during the study period, the low production of smolts during some years might lead to a low renewal rate of the salmon population.

Is juvenile salmon abundance related to subsequent and preceding catches? Perspectives from a long-term monitoring programme

AbstractThe abundance of wild Atlantic salmon in the River Teno system has been monitored since the 1970s by estimating salmon catches and juvenile salmon densities at permanent electrofishing sites. Analysis of the time-series has shown significant relationships between juvenile densities (0+ and 1+) and subsequent 1SW and 2SW catches. Corresponding significant relationships have been detected between 1SW and 2SW female salmon in the catches and subsequent fry and parr densities. Monitoring juvenile densities allows evaluation of spawning escapement 1 and 2 years earlier, confirming the stock status information provided by catch statistics. These relationships between juvenile abundance and catches suggest that the monitoring programme has included feasible and biologically relevant variables and proper methodologies. Increasing trends were detected in the numbers of 1SW and 2SW salmon in catches between 1977 and 2003. Similarly, fry abundance indicated long-term increasing trends at most sites. Significant relationships were detected between abundances of subsequent sea-age groups in catches (1SW vs. 2SW 1 year later, etc.), indicating that strong smolt year classes influence the abundance of several subsequent sea-age groups, and that such relationships permit forecasting future catches of multi-sea-winter salmon by 1SW salmon catches.

Atlantic salmon (Salmo salar) in winter: "the season of parr discontent"?

Winter is a dynamic period. Effects of the winter regime on northern streams and rivers is extremely variable and characterized by dramatic alterations in physical habitat to which Atlantic salmon (Salmo salar) must acclimate and adapt to survive. In this paper, we synthesize recent advances in the biological and hydrologic/ geomorphic disciplines, with specific reference to Atlantic salmon overwintering in the freshwater portions of those running waters subject to freezing water temperatures. The specific requirements and adaptations for surviving winter at the three distinct life-stages in freshwater (egg, parr, kelt) are identified in relation to the characteristics of three biophysical phases: early winter (temperature decline and freeze-up), midwinter (ice growth and habitat reduction), and the break-up/warming phase. In a case study of Catamaran Brook (New Brunswick), a hydro-ecological analysis was used to explain interannual variability in juvenile abundance, especially for young-of-the-year salmon. A strong relation was found between winter discharge and interstage survival (egg to 0+, 0+ to 1+, 1+ to 2+) in 5 of 6<~>years. That is, juvenile salmon abundance in summer was highest following winters with high streamflow, presumably a function of habitat availability, especially beneath ice cover. However, the lowest measured egg-0+ survival (9.2%) was related to an atypical midwinter, dynamic ice break-up triggered by a rain-on-snow event that resulted in severe scouring of the stream-bed and redds. Thus, interannual variability in Atlantic salmon parr abundance from 1990 to 1996 was largely explained by density-independent (environmental) constraints to winter survival. The complexity of stream processes during winter underscores the need for interdisciplinary research to quantify biological change.