Stream-dwelling Salmonids Research Articles

Does recruitment trigger negative density-dependent feedback loops in stream-dwelling salmonids?

I explored the hypothesis that recruitment may stabilize the numerical dynamics of stream-dwelling salmonids by triggering density-dependent feedback loops through the operation of recruitment dependence on individual growth, mortality, life span and maximum size and their effects on fecundity. I examined 98 cohorts of two Salmo trutta populations of northern Spain and a population of Jutland (Denmark) located 2400 km apart. Recruitment, growth, mortality, life span and maximum size were inter-related, were recruitment-dependent and described negative power trajectories. In the Spanish populations, faster-growing individuals of weakly recruited cohorts with lower mortality attain longer life span and larger size. Hence, larger females spawning more abundant, larger eggs that, in turn, induce stronger cohorts of higher spawners’ abundance, recruitment and mortality. The mortality patterns match the self-thinning patterns, an ultimate expression of competition. Significant relationships among self-thinning slopes and mortalities rates with increasing recruitment demonstrate that the rate at which density-driven mortality is higher, the stronger the intensity of intraspecific competition. Space-limited habitat and size-dependent resource availability underpinning site-specific carrying capacities suggest that interference competition is the primary mechanism underpinning population regulation.

Wintertime growth in Atlantic salmon under changing climate: the importance of ice cover for individual growth dynamics

Understanding the dynamic nature of individual growth in stream-dwelling salmonids may help forecast consequences of climate change on northern fish populations. Here, we performed an experimental capture–mark–recapture study in Atlantic salmon (Salmo salar) to quantify factors influencing wintertime growth variation among juveniles under different scenarios for ice-cover reduction. We applied multiple imputation to simulate missing size observations for unrecaptured fish and to account for individual-level variation in growth rates. The salmon parr exhibited substantial body length shrinkage in early winter, suppressed growth through midwinter, and increased growth rates in late winter and particularly in spring. Unexpectedly, the presence of ice cover had no direct effects on wintertime growth. Instead, our results implied increasing energetic costs with reducing ice cover; individuals exposed to absent or shortened ice-covered period gained mass at a lowered rate in spring, whereas the present, long ice-covered period was followed by rapid growth. This study emphasizes natural resilience of Atlantic salmon to wintertime environmental variation, which may help the species to cope with the reductions in ice-cover duration due to climate change.

Advantages and insights from a hierarchical Bayesian growth and dynamics model based on salmonid electrofishing removal data

Growth is a fundamental ecological process of stream-dwelling salmonids which is strongly interrelated to critical life history events (emergence, mortality, sexual maturity, smolting, spawning). The ability to accurately model growth becomes critical when making population predictions over large temporal (multi-decadal) and spatial (meso) scales, e.g., investigating the effect of global change. Body length collection by removal sampling is a widely-used practice for monitoring fish populations over such large scales. Such data can be efficiently integrated into a Hierarchical Bayesian Model (HBM) and lead to interesting findings on fish dynamics. We illustrate this approach by presenting an integrated HBM of brown trout (Salmo trutta) growth, population dynamics, and removal sampling data collection processes using large temporal and spatial scales data (20 years; 48 sites placed along a 100 km latitudinal gradient). Growth and population dynamics are modelled by ordinary differential equations with parameters bound together in a hierarchical structure. The observation process is modelled with a combination of a Poisson error, a binomial error, and a mixture of Gaussian distributions. Absolute fit is measured using posterior predictive checks, those results indicate that our model fits the data well. Results indicate that growth rate is positively correlated to catchment area. This result corroborates those of other studies (laboratory, exploratory) that identified factors besides water temperature that are related to daily ration and have a significant effect on stream-dwelling salmonid growth at a large scale. Our study also illustrates the value of integrated HBM and electrofishing removal sampling data to study in situ fish populations over large scales.

Profitability of stocking to enhance populations of ayu and stream-dwelling salmonids for Japanese inland fishery cooperatives

Profitability of stocking to enhance populations of ayu and stream-dwelling salmonids for Japanese inland fishery cooperatives

Modelling the factors influencing ontogenetic dietary shifts in stream-dwelling brown trout (Salmo trutta)

Biotic and abiotic variables shape ontogenetic trajectories of animals. This study modelled (i) the body length related timing of the ontogenetic switch from aquatic to surface prey and (ii) the impacts of habitat characteristics, prey availability, and fish densities on the relative contribution of surface prey to the overall diet of native brown trout (Salmo trutta). We used individual-based models of dietary data for 170 fish (length range 48–343 mm). There was a high degree of individual variation in the use of surface prey, but logistic regression suggested that the shift from aquatic to surface prey was established at a body length of 81 mm (range 36–127 mm). Results of linear mixed-effects models highlighted the importance of fish length, benthic invertebrates, brown trout density, and water current velocity to the switch to surface prey by riverine brown trout, with fish length being the most influential variable. Our study provides evidence of the importance of ontogeny (intrinsic features of individuals linked to fish length) and individual differences in feeding behaviour to understand water-column use for feeding by stream-dwelling salmonids.

河川性サケ科魚類のメタ個体群動態 : 個人レベルの大規模長期研究( 大規模長期生態学研究とは何か?)

河川性サケ科魚類のメタ個体群動態 : 個人レベルの大規模長期研究( 大規模長期生態学研究とは何か?)

Brown trout (Salmo trutta) growth and condition along a winter thermal gradient in temperate streams

Winter harshness and the degree to which it can impact stream-dwelling salmonid populations has received considerable attention from fisheries biologists, although some debate exists regarding the importance of winter severity for local populations. Groundwater input may buffer stream water temperature and benefit fish in buffered versus unbuffered streams. Overwinter growth and condition of individual brown trout were measured in 24 groundwater-dominated streams, and the relations between winter growth and condition to stream thermal regime (quantified by regressions of air and water temperature) and diet quality (amount and caloric density of prey) were examined in a subset of 16 streams. Brown trout (Salmo trutta) growth rate (mg·g−1·day−1) was positive overwinter in 18 of 24 streams, and there was no significant change in condition between early and late winter. Juvenile fish grew faster than adults, but there was no significant difference in condition between adults and juveniles. Thermal regime positively influenced winter growth for both adults and juveniles, likely mediated through moderation of water temperature by groundwater, whereas diet had no significant effect on growth.

Ontogenetic shifts in terrestrial reliance of stream-dwelling brown trout

<p>This study focuses on terrestrial reliance of brown trout (<em>Salmo trutta</em>) and compared it to the potential prey available (macrozoobenthos and drifting invertebrates) in three temperate rivers (Galicia, NW Spain), with special emphasis on variations in terrestrial energy intake through the ontogeny of brown trout. Additionally, we paid particular attention to individual variation of terrestrial resource use within and between age classes. Prey items were grouped in four categories: i) aquatic invertebrates; ii) imagoes of aquatic invertebrates; iii) terrestrial invertebrates; and iv) fish prey. Next, energy composition was measured according to dry weight-energy equations for each individual in line with above-mentioned prey categories. Our findings illustrate that terrestrial invertebrates appeared to be scarce in the environment, whereas aquatic food resources were rather abundant and accessible. The use of terrestrial invertebrates tended to increase with age, but with a high degree of inter-individual variation in resource use. In fact, the individual reliance of brown trout on terrestrial invertebrates may vary considerably (between 0% and 76.9%). Besides, the frequency of terrestrial foragers, <em>i.e</em>., individuals with terrestrial invertebrates in their stomachs, increased with age, except in one population which had the maximum value in the age-2 class. The acquisition of terrestrial invertebrates thus appears to be a process strongly dependent upon the actual food availability in the environment, but with a high degree of individual variance in resource use within the same age class. Finally, we discuss that terrestrial invertebrates may largely contribute to cover the energy intake of the species, highlighting the interface between terrestrial and aquatic ecosystems, and thereby the importance of riparian canopy cover as a key factor for food supply of stream-dwelling salmonids species.</p>

Efficiency of Portable Antennas for Detecting Passive Integrated Transponder Tags in Stream-Dwelling Salmonids.

Portable antennas have become an increasingly common technique for tracking fish marked with passive integrated transponder (PIT) tags. We used logistic regression to evaluate how species, fish length, and physical habitat characteristics influence portable antenna detection efficiency in stream-dwelling brown trout (Salmo trutta), bull trout (Salvelinus confluentus), and redband trout (Oncorhynchus mykiss newberrii) marked with 12-mm PIT tags. We redetected 56% (20/36) of brown trout, 34% (68/202) of bull trout, and 33% (20/61) of redband trout after a recovery period of 21 to 46 hours. Models indicate support for length and species and minor support for percent boulder, large woody debris, and percent cobble as parameters important for describing variation in detection efficiency, although 95% confidence intervals for estimates were large. The odds of detecting brown trout (1.5 ± 2.2 [mean ± SE]) are approximately four times as high as bull trout (0.4 ± 1.6) or redband trout (0.3 ± 1.8) and species-specific differences may be related to length. Our reported detection efficiency for brown trout falls within the range of other studies, but is the first reported for bull trout and redband trout. Portable antennas may be a relatively unbiased way of redetecting varying sizes of all three salmonid species.

Net rate of energy intake predicts reach-level steelhead (Oncorhynchus mykiss) densities in diverse basins from a large monitoring program

Substantial research effort has been devoted to understanding stream-dwelling salmonids’ use of summer rearing and growth habitat, with a subset of studies focusing on foraging position selection and the energetic trade-offs of differential habitat use. To date, however, cost–benefit analyses for most foraging model studies have focused on small sampling areas such as individual habitat units. To address this knowledge gap, we applied a mechanistic foraging model to 22 stream reaches (100–400 m) from two watersheds within the Columbia River Basin. We found a strong, positive correlation (R2= 0.61, p < 0.001) between predicted carrying capacities and observed fish densities. Predicted proportion of suitable habitat was weakly correlated with observed fish density (R2= 0.18, p = 0.051), but the mean net rate of energy intake prediction in sampling reaches was not a significant predictor of observed fish biomass. Our results suggest spatial configuration of habitat, in addition to quantity and quality, is an important determinant of habitat use. Further, carrying capacity predicted by the model shows promise as a habitat metric. We also evaluated the feasibility of applying this data-intensive modeling approach in a large-scale monitoring program to examine habitat quality and quantity. Though the approach can be computationally expensive, we feel the model’s ability to integrate physical habitat metrics (e.g., depth, velocity) with important biological considerations like food availability and temperature is a benefit that far outweighs associated costs. We feel this modeling approach has great potential as a tool to help understand habitat use in drift-feeding fishes.

Demogenetic structure of brown troutSalmo truttaLinnaeus, 1758 populations in mountain headwaters: implications for conservation management

A demogenetic analysis based on 7 years of observation (2005–2011) was conducted to examine the population structure of brown trout Salmo trutta in pristine dendritic headwaters. The value of genetic divergence (FST) among sampling units ranged from −0.03 to 0.16. Demographic synchrony was low or moderate, and the average correlation coefficient of population growth between sampling units () ranged from 0.28 to 0.66. No isolation by distance was observed, but genetic divergence was negatively correlated with demographic synchrony among sampling units. Variance in the population growth rate (i.e. local extinction probability) increased with distance from the mainstream and from other sampling units. In contradiction with the usual model of stream-dwelling salmonids, the upstream sections of headwaters holds only ephemeral subpopulations, whereas the mainstream played a role in the source area of the metapopulation. These findings stress the importance of the mainstream in management conservation for brown trout in low productive mountain headwaters.

Fall–winter collection of two salmonid species: seasonal changes in population densities in four tributaries of the Kushiro river system

The environmental conditions faced by stream-dwelling fish in many regions are highly variable during fall and winter, and may include very low water temperatures or ice formation (Brown et al. 2011). Such extremes can result in increased overwinter mortality (Hurst 2007). To minimize this, stream-dwelling fish have developed phenology responses to cope with the variable conditions seen during winter (Huusko et al. 2007; Shuter et al. 2012). In the absence of direct behavioral observation, seasonal changes in population density provide indirect evidence of behavioral repertoires in fish response. Moreover, the seasonal changes in population density may influence population processes via a density-dependent effect (Bailey et al. 2010). Numerous studies have evaluated the seasonal change in population densities in stream-dwelling salmonids between spring and fall (e.g., Niemela et al. 2001). However, few studies have investigated seasonal changes in population density during fall and winter, especially at the community level. Morita et al. (2011) examined the annual seasonal change in the densities of three salmonid species (white-spotted charr Salvelinus leucomaenis leucomaenis, masu salmon Oncorhynchus masou, and rainbow trout Oncorhynchus mykiss) in the Shoro river system. The authors noted that the density of white-spotted charr decreased in both tributaries between fall and winter, whereas the densities of masu salmon and rainbow trout increased in the warmer of the two streams during this period. Unfortunately, however, the study lacked spatial replication as the authors were only able to compare seasonal changes in population densities between two tributaries. Thus, the relationship between salmonid densities and water temperature in winter remains poorly understood. To address this, we evaluated the seasonal changes in the population density and ratio of two salmonid species, white-spotted charr and masu salmon, between fall and winter in four tributaries of the Kushiro river system, eastern Hokkaido, Japan. White-spotted charr (hereafter charr) and masu salmon (hereafter salmon) are the dominant species within the Kushiro river system and generally occur sympatrically (Hariu 2010). The field study was conducted in four tributaries: Hitominai Stream, Oriyomappu Stream, Ooshima Stream, and Minamitawa Stream (see Sahashi and Morita 2013: fig. 1). The sampling reaches included the typical biotopes of the two species in each tributary (see abiotic characteristics of the four tributaries in the electronic supplementary material of Sahashi and Morita 2013). The length of the study reaches was 80 m in Hitominai Stream, Ooshima Stream, and Minamitawa Stream. The length of the reaches at Oriyomappu Stream was 55 m in fall and 27.5 m in winter. In each tributary study reach, we deployed fixed data loggers (Stow-Away TidbiT; Onset Computer Corp., Bourne, Massachusetts, USA) on the stream bed to measure water temperature at hourly intervals between 1 June and 4 September 2010, and 1 November and 1 February 2011. G. Sahashi Division of Marine Bioresource and Environmental Science, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate 041-8611, Japan

Winter feeding, growth and condition of brown trout Salmo trutta in a groundwater-dominated stream

Winter can be a stressful period for stream-dwelling salmonid populations, often resulting in reduced growth and survival. Stream water temperatures have been identified as a primary mechanism driving reductions in fitness during winter. However, groundwater inputs can moderate water temperature and may reduce winter severity. Additionally, seasonal reductions in prey availability may contribute to decreased growth and survival, although few studies have examined food webs supporting salmonids under winter conditions. This study employed diet, stable isotope, and mark-recapture techniques to examine winter (November through March) feeding, growth, and condition of brown trout Salmo trutta in a groundwater-dominated stream (Badger Creek, Minnesota, USA). Growth was greater for fish ≤ 150 mm (mean = 4.1 mg g−1 day−1) than for those 151–276 mm (mean = 1.0 mg g−1 day−1) during the winter season. Overall condition from early winter to late winter did not vary for fish ≤150 mm (mean relative weight (Wr) = 89.5) and increased for those 151–276 mm (mean Wr = 85.8 early and 89.4 late). Although composition varied both temporally and by individual, brown trout diets were dominated by aquatic invertebrates, primarily Amphipods, Dipterans, and Trichopterans. Stable isotope analysis supported the observations of the dominant prey taxa in stomach contents and indicated the winter food web was supported by a combination of allochthonous inputs and aquatic macrophytes. Brown trout in Badger Creek likely benefited from the thermal regime and increased prey abundance present in this groundwater-dominated stream during winter.

Individual variability in the movement behaviour of juvenile Atlantic salmon

Stream-dwelling salmonid populations are generally thought to be composed of both relatively mobile and sedentary individuals, but this conclusion is primarily based on results obtained from recapture methods with low temporal resolution. In this study, the mobility of 50 juvenile Atlantic salmon (Salmo salar) was monitored using a large array of passive integrated transponder antennas buried in the bed of a natural stream. Fish locations were recorded at a high frequency for a period of 3 months in a 65 m reach. Four types of daily behaviour were identified: stationary (detected primarily at one location), sedentary (limited movement between a few locations), floater (frequent movements in a restricted home range), and wanderer (movements across the reach). Most individuals exhibited low mobility on most days, but also showed occasional bouts of high mobility. Between-individual variability accounted for only 12%–17% of the variability in the mobility data. High mobility was more frequent at low flow, but no difference was observed between the summer (12–18 °C) and the autumn (4–12 °C). Individual variation on a daily basis suggested that movement behaviour is a response to changing environmental conditions rather than an individual behavioural trait.

Distribution and growth of brown trout in pristine headwaters of Central Europe

AbstractThe majority of stream-dwelling salmonid populations in Europe are affected by artificial stocking and the fragmentation of riverine ecosystems. The present study was performed in the unique pristine headwaters of the Otava River in the Elbe catchment area of the Czech Republic. The aim was to investigate the spatial distribution and individual growth pattern of brown trout, Salmo trutta, populations. Twenty sites in two main streams and their tributaries were sampled twice a year (spring and autumn) during the period 2005–2011. The sampling sites were grouped into fourteen so-called synchronised population units within the boundaries of three populations, according to analyses of synchrony in population abundance. The individual growth of juveniles (age-0, age-1) varied between all three spatial units (sampling sites, synchronised population units and populations), while the individual growth of adults (age-2 and older) did not. The distinctiveness regarding individual growth and demographic independence among the synchronised population units and populations indicates their suitability for use as population units for management purposes.

Effect of food abundance on aggressiveness and territory size of juvenile rainbow trout, Oncorhynchus mykiss

How food abundance affects (1) whether or not individuals defend territories and (2) what size of territory is defended are crucial to understanding the role that territoriality plays in regulating the population size of stream-dwelling salmonids. The threshold model of feeding territoriality predicts that territorial defence will be most intense at intermediate levels of food abundance, whereas optimal territory-size models predict that territory size will decrease with increasing food abundance. While the latter prediction has been supported by several studies of stream salmonids, too few levels of food abundance were typically used to describe the exact relationship between territory size and food abundance. Hence, to quantify the relation between the intensity of defence, territory size and food abundance, we manipulated food abundance over a broad range of values (0.62, 1.25, 2.5, 5, 10 and 20% of the fish wet body weight in dry food per day) in artificial stream channels (1.92 × 0.77 m), while monitoring the territorial behaviour of juvenile rainbow trout. As predicted by the threshold model of feeding territoriality, the frequency of territorial aggression was highest at intermediate levels of food abundance, but fish never ceased defending territories entirely, particularly at food densities likely found in the wild. Also as predicted, the aggressive radius of rainbow trout decreased significantly, but only by 30% over a 32-fold increase in food abundance, equivalent to a 51% decrease in territory size. Our results suggest that territory size is relatively insensitive to changes in food abundance and may have a regulatory effect on population density.

Effect of acclimation temperature on the upper thermal tolerance of Colorado River cutthroat trout Oncorhynchus clarkii pleuriticus: thermal limits of a North American salmonid

In an effort to explore the thermal limitations of Colorado River cutthroat trout Oncorhynchus clarkii pleuriticus, the critical thermal maxima (T(cmax) ) of 1+ year Lake Nanita strain O. c. pleuriticus were evaluated when acclimated to 10, 15 and 20° C. The mean ±s.d.T(cmax) for O. c. pleuriticus acclimated to 10° C was 24·6 ± 2·0°C (n = 30), for 15° C-acclimated fish was 26·9 ± 1·5° C (n = 23) and for 20° C-acclimated fish was 29·4 ± 1·1° C (n = 28); these results showed a marked thermal acclimation effect (Q₁₀ = 1·20). Interestingly, there was a size effect within treatments, wherein the T(cmax) of larger fish was significantly lower than that of smaller fish acclimated to the same temperature. The critical thermal tolerances of age 0 year O. c. pleuriticus were also evaluated from three separate populations: Lake Nanita, Trapper Creek and Carr Creek reared under 'common-garden' conditions prior to thermal acclimation. The Trapper Creek population had significantly warmer T(cmax) than the Lake Nanita population, but that of the Carr Creek fish had T(cmax) similar to both Trapper Creek and Lake Nanita fish. A comparison of these O. c. pleuriticus T(cmax) results with those of other stream-dwelling salmonids suggested that O. c. pleuriticus are less resistant to rapid thermal fluctuations when acclimated to cold temperatures, but can tolerate similar temperatures when acclimated to warmer temperatures.

Pacific salmon (Oncorhynchus spp.) runs and consumer fitness: growth and energy storage in stream-dwelling salmonids increase with salmon spawner density

We examined how marine-derived nutrients (MDN), in the form of spawning Pacific salmon, influenced the nutritional status and δ15N of stream-dwelling fishes. We sampled juvenile coho salmon ( Oncorhynchus kisutch ) and Dolly Varden ( Salvelinus malma ) during spring and fall from 11 south-central Alaskan streams that ranged widely in spawning salmon biomass (0.1–4.7 kg·m–2). Growth rate (as indexed by RNA–DNA ratios), energy density, and δ15N enrichment in spring-sampled fishes increased with spawner biomass, indicating the persistence of spawner effects more than 6 months after salmon spawning. Point estimates suggest that spawner effects on nutrition were substantially greater for coho salmon than Dolly Varden (268% and 175% greater for growth and energy, respectively), indicating that both species benefitted physiologically, but that juvenile coho salmon accrued more benefits than Dolly Varden. Although the data were less conclusive for fall- than spring-sampled fish, they do suggest spawner effects were also generally positive during fall, soon after salmon spawned. In a follow-up analysis where growth rate and energy density were modeled as a function of δ15N enrichment, results suggested that both increased with MDN assimilation, especially in juvenile coho salmon. Our results support the importance of salmon runs to the nutritional ecology of stream-dwelling fishes.

Spatial and temporal scale of density-dependent body growth and its implications for recruitment, population dynamics and management of stream-dwelling salmonid populations

Density-dependent variations in body growth and size have important consequences for the population dynamics of stream-dwelling salmonid populations, since body size is related to a variety of ecologically relevant characteristics. These include survival and fecundity, competitive and predatory abilities, and foraging behavior. However, little work has been done to understand how density-dependent body growth varies across temporal and spatial scales and when this compensatory process is relevant for recruitment and population dynamics of stream- dwelling salmonids. Increased intra- or inter-cohort competition reduces growth rates of juveniles. Both within- and among-cohort differences at the juvenile stage are likely to be maintained through the lifetime. Limited movement or dispersal can lead to subdivision of a population into several local populations with independent dynamics. The spatial and temporal variation in movement and the patchy distribution of resources make fish likely to experience density- dependence across location, life-stage, and season. The relaxation of density-dependent suppression of body growth at low densities constitutes a potential mechanism for salmonids to persist in the face of environmental perturbation and may contribute to explaining the peculiar resilience to population col- lapses often showed by salmonids. The inclusion of density-dependent growth in population models may increase the usefulness of model predictions in management contexts. Models not accounting for density-dependent growth may underestimate the recovery potential of resident salmonid populations when they collapse to low densities.

Shape of Single and Multiple Central-Place Territories in a Stream-Dwelling Fish

Territory shape yields important insights into how animals exploit local resources. Territories of stream-dwelling salmonids are typically (1) mapped around a single central-place, (2) described as circular, elliptical or teardrop-shaped, and (3) believed to reflect their exploitation of drifting invertebrate prey. In this study, we tested the current view of territory shape by mapping multiple central-place territories for 50 young-of-the-year Atlantic salmon. Multiple central-place areas were more elongated (eccentricity: median = 1.301, range = 1.043–2.784) than the foraging patterns around each central place (eccentricity: median = 1.135, range = 1.014–1.385). In addition, multiple central-place areas were elongated along the stream length (33 of 50 fish), whereas the foraging areas around each station tended to be elongated along the stream width (32 of 50 fish). These findings may be explained by the way that stream salmonids interact with drifting prey. At each central place, a wider foraging area should provide an increased access to prey drifting downstream. Similarly, by regularly patrolling a large multiple central-place area along the stream axis, a territorial fish may increase its access to drifting prey by excluding competitors from upstream areas. Further studies are needed on the ecological factors that determine territory shape in stream fish and multiple central-place foragers.