Adult Brown Trout Research Articles

Physical habitat assessment in the Tajuna river (Spain) by means of the MesoHABSIM approach

Physical habitat assessment in the Taju˜ na river (Spain) by means of the MesoHABSIM approach Physical habitat was assessed in the Taju˜ na river (Tagus basin, Spain) by means of the MesoHABSIM approach. Long reaches of the Taju˜ na river are altered by agricultural use of the riverside. The main impacts are river rectification (straightening), channel entrenchment and incision, and degradation of riparian vegetation, along with importantflow depletion and regulation. To our knowledge, this is the first application in Spain of MesoHABSIM, which is a physical habitat model based on the identification of habitat attributes -depth, water velocity, substrate, types of hydromorphologic units (HMU), and types of cover- on the mesohabitat scale. The river was stratified into 16 segments with similar habitat characteristics. Mesohabitats were mapped in one representative site (1-2 km long) within each segment to provide a hydromorphologic model of the river. Biological models were developed for fry, juvenile, and adult brown trout. To do this, preliminary models were generated based on literature about trout habitat requirements, and then they were calibrated with electrofishing data. These models were applied to the hydromorphologic model of the river to quantify the available habitat for brown trout in the current conditions. Finally, restoration action was designed to decrease channel entrenchment, increase river sinuosity, and recover its riparian vegetation. The physical changes after restoration were estimated by expert opinion, and the quantification of the available habitat was done with MesoHABSIM at each site. These results can be used to select the segments that are the best candidates for restoration.

Demography of Juvenile and Adult Brown Trout in Streams of Southeastern Minnesota

AbstractWe assessed recruitment, survival, emigration, and immigration of brown trout Salmo trutta in six interconnected stream reaches to quantitatively estimate how much immigrants contributed to population size in reaches in southeastern Minnesota. We also examined the influence of reach and season on estimates of survival and emigration via mark and recapture of individual trout representing three groups (age‐0 juveniles, age‐1 and age‐2 adults, and age‐3+ large adults). Immigration was calculated as 1 minus emigration. Recruitment varied among the six reaches and 3 years of this study (range, 0–1,292 fish/km). Survival of the age‐0 group and that comprising ages 1 and 2 varied by season but not reach. Survival was highest in winter for both groups but lowest in spring for age‐0 trout and in fall for age‐1 and age ‐2 trout. Emigration varied by season for age‐0 trout but by reach for trout of ages 1 and 2. For age‐3+ trout, survival and emigration only varied by reach. Survival was highest and emigration was lowest in reaches with the most cover, including deep pools. From these demographic characteristics we estimated the proportions of the population that consisted of brown trout that had survived within a reach, recruited into it, or immigrated into it from some other reach. Immigration was predicted to contribute the most for the youngest age‐group (35% or more of the predicted abundance of age‐0 trout in most reaches) and is probably important for genetic purposes or to bolster population units in adjacent reaches. Our results for adult brown trout suggest that within‐reach recruitment and survival contribute a larger proportion of trout to population units in many reaches than do immigrants. This confirms the appropriateness of current management approaches and suggests that maintenance of the exceptional recreational brown trout fishery in southeastern Minnesota is at least solidly dependent on factors promoting recruitment and survival within most managed stream reaches.

INFLUENCE OF THE MORPHOLOGICAL AND HYDRAULIC CHARACTERISTICS OF MOUNTAIN STREAMS ON FISH HABITAT SUITABILITY CURVES

ABSTRACTMicrohabitat preferences of adult brown trout (Salmo trutta m. fario) were monitored for the purpose of determining design parameters for river restoration. The habitat preferences were evaluated during the summer period of minimum flows. Since 1995, field measurements have been performed in 52 reaches in 43 mountain and piedmont streams. The relationship between hydraulic characteristics and the values of maximum habitat suitability derived from velocity and depth habitat suitability curves (HSCs) was statistically determined. Trout in natural stream reaches showed a strong degree of dependence on depths, but in regulated streams, they were dependent on velocities.The representative habitat suitability curves for four depth intervals were extrapolated. From these outputs, the optimum depths of a microhabitat for river restoration measures and/or assessment of the influence of water withdrawals can be derived. The influence of geological regions on the shape of HSCs has not been proved; therefore, it is conceivable that after verification, the generalized HSCs may also be valid in other mountain and piedmont regions. Copyright © 2011 John Wiley & Sons, Ltd.

Movement and Survival of Brown Trout and Rainbow Trout in an Ozark Tailwater River

AbstractWe evaluated the movement of adult brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss in relation to a catch‐and‐release area in the White River downstream from Beaver Dam, Arkansas. Nine fish of each species were implanted with radio transmitters and monitored from July 1996 to July 1997. The 1.5‐km river length of a catch‐and‐release area (closed to angler harvest) was greater than the total linear range of 72% of the trout (13 of 18 fish), but it did not include two brown trout spawning riffles, suggesting that it effectively protects resident fish within the catch‐and‐release area except during spawning. The total detected linear range of movement varied from 172 to 3,559 m for brown trout and from 205 to 3,023 m for rainbow trout. The movements of both species appeared to be generally similar to that in unregulated river systems. The annual apparent survival of both trout species was less than 0.40, and exploitation was 44%. Management to protect fish on spawning riffles may be considered if management for wild brown trout becomes a priority.Received August 31, 2010; accepted January 20, 2011

Evaluación del lavado gástrico como herramienta para el análisis de la dieta en trucha común

Evaluation of the gastric lavage as a tool for the analysis of the brown trout diet The efcacy of the method of extracting stomach content, by means of the procedure of stomach washing through a pump, based on Seaburg's original model (1957), has been studied. The effectiveness of the method is not related to the size of thesh, but rather to the prey's own morphological characteristics, the degree of repletion of the stomach and the extent of digestion of the food. Thus, the effectiveness of the method is inversely related to the degree of repletion. Furthermore, bigger prey having rigid structures, such as Aeshnidae and Caddisies with cases are more difcult to expel. However, the observed differences in the effectiveness of expulsion between preys with similar characteristics are due to the extent of their digestion. Nevertheless, the average effectiveness of the method is high and in excess of 80 %. It is therefore a relatively simple and effective methodology and the reason why its use is appropriate for obtaining stomach content samples in young and adult brown trout.

Recapture rate and growth of hatchery-reared brown trout (Salmo trutta v. fario, L.) in Blanice River and the effect of stocking on wild brown trout and grayling (Thymallus thymallus, L.)

Summary Hatchery-reared adult brown trout, Salmo trutta v. fario L., [215–335 mm standard length (LS), n = 82] were individually tagged and released into three sections of the Blanice River in May 2007. Wild populations of brown trout and grayling, Thymallus thymallus, L., in these sections and three nonstocked control sections were also tagged. The recapture rate of hatchery-reared adult brown trout after 6 months (18%, n = 15) was comparable to that of wild adult brown trout in stocked (15%, n = 14) and control (14%, n = 11) sections. The recapture rates of wild brown trout and grayling after 6 months were higher in control sections than in stocked sections, but the differences were not significant. The movement of recaptured large juvenile wild brown trout from stocked sections was significantly higher (36%) than from control sections (9%). Wild brown trout growth and grayling growth were unaffected by stocking with adult hatchery-reared brown trout.

Influence of Drought Conditions on Brown Trout Biomass and Size Structure in the Black Hills, South Dakota

AbstractWe evaluated the influence of drought conditions on the biomass of brown trout Salmo trutta in Spearfish Creek, upper Rapid Creek, and lower Rapid Creek in the Black Hills of western South Dakota. Stream discharge, mean summer water temperature, the biomass of juvenile and adult brown trout, and brown trout size structure were compared between two time periods: early (2000–2002) and late drought (2005–2007). Mean summer water temperatures were similar between the early‐ and late‐drought periods in Spearfish Creek (12.4°C versus 11.5°C), lower Rapid Creek (19.2°C versus 19.3°C), and upper Rapid Creek (9.8°C in both periods). In contrast, mean annual discharge differed significantly between the two time periods in Spearfish Creek (1.95 versus 1.50 m3/s), lower Rapid Creek (2.01 versus 0.94 m3/s), and upper Rapid Creek (1.41 versus 0.84 m3/s). The mean biomass of adult brown trout in all three stream sections was significantly higher in the early‐drought than in the late‐drought period (238 versus 69 kg/ha in Spearfish Creek, 272 versus 91 kg/ha in lower Rapid Creek, and 159 versus 32 kg/ha in upper Rapid Creek). The biomass of juvenile brown trout was similar (43 versus 23 kg/ha) in Spearfish Creek in the two periods, declined from 136 to 45 kg/ha in lower Rapid Creek, and increased from 14 to 73 kg/ha in upper Rapid Creek. Size structure did not differ between the early‐ and late‐drought periods in lower Rapid and Spearfish creeks, but it did in upper Rapid Creek. In addition to drought conditions, factors such as angler harvest, fish movements, and the nuisance algal species Didymosphenia geminata are discussed as possible contributors to the observed changes in brown trout biomass and size structure in Black Hills streams.

Seasonal movement patterns of Credit River brown trout (Salmo trutta)

Zimmer M, Schreer JF, Power M. Seasonal movement patterns of Credit River brown trout (Salmo trutta). Ecology of Freshwater Fish 2010: 19: 290–299. © 2010 John Wiley & Sons A/SAbstract – Movement habits in riverine populations of brown trout vary among watersheds. Thus it is important to identify factors influencing differences in individual behaviour so as to improve the information resource base available for the design of river‐specific management strategies. Such information is particularly needed in the rapidly urbanising watersheds of eastern North America where relatively little is known about anthropogenic influences on brown trout populations. In this study, we examined the influence of water temperature on brown trout behaviour in the Credit River in south‐central Ontario, Canada with respect to seasonal movement patterns. Observed patterns of movement were also correlated with variations in river discharge and habitat quality. Forty‐three radio‐tagged, adult brown trout were tracked in a confined 39.8 km portion of the Credit River from 15 May 2002 to 28 July 2003. Fish were captured in three sections of the river that differed in distance downstream and habitat quality. Fish size had little impact on movement patterns. However, there was considerable variation in seasonal movement with upstream movements to summer positions, maintenance of summer positions, downstream and often extensive movements in fall. Also observed was maintenance of winter positions and repeated upstream movements in late spring‐early summer to previously used summer positions. The elaborate movement behaviour in the Credit River population was attributed to seasonal changes in thermal habitat quality. Fish tagged in less suitable thermal habitats moved significantly more than fish from more suitable thermal habitats.

Movement and Mortality of Adult Brown Trout in the Motupiko River, New Zealand: Effects of Water Temperature, Flow, and Flooding

AbstractManagement of the effects of water quality and flow on fisheries requires an understanding of the factors that control fish movements. We used radiotelemetry to monitor the movements of adult brown trout Salmo trutta in a New Zealand river over 11 months (September 2004 to August 2006) and linked those movements to the changes in flow and water temperature. Individual fish moved up to 41 km during the study. However, most fish moved less than 1 km. All of the trout that showed little movement throughout the summer were living in relatively deep pools that presumably provided cover. The rates of movement declined steadily over the spring–summer period, as flow decreased and water temperature increased. The percentage of fish moving was positively related to the average daily flow during the interval between tracking occasions and negatively related to the average daily water temperature, less than 20% of the tagged fish moving once temperatures were above 19°C. A severe, 50‐year flood occurred in March 2005 and was associated with the mortality of 60–70% of the remaining tagged fish, confirming that flood‐induced mortality can affect a substantial proportion of an adult brown trout population.

Interspecific competition and predation: relative effects on foragers and their densities

Predation and competition are both strong structuring forces in community dynamics, but their relative importance is disputed. In a laboratory experiment, we evaluated the relative importance of competition and predation from juvenile and adult brown trout, respectively, on foraging performance of groups of three stone loaches. We observed loach consumption rate, time spent inactive, and aggressive interactions between juvenile trout and loach in artificial stream sections. The controlled experiments were complemented by examining stone loach population densities in natural systems as functions of juvenile and adult trout. In the laboratory experiments, increasing numbers of competitors decreased prey availability, which ultimately led to lower consumption rates for loach. Loach responded to predation risk by increasing time being inactive, thereby decreasing consumption rates. However, there were no effects of juvenile trout competitors on loach consumption rates in treatments with adult trout presence, suggesting no additive effect of predation and competition on loach foraging success. Partial regressions of loach and trout densities in natural streams revealed a positive relationship between juvenile trout and loach, and a negative relationship between adult trout and loach. Our laboratory and field data thus suggest that predation is a limiting factor for loach success, and predator presence could mediate species coexistence at high interspecific densities.

Energy Densities of Brown Trout (Salmo trutta) and Its Main Prey Items in an Alpine Stream of the Slizza Basin (Northwest Italy)

ABSTRACT In the present study, energy densities of 80 adult brown trout (Salmo trutta), seasonally sampled in an alpine stream in the eastern Alps and energy densities of their main prey items, were determined. The energy density (J/g wet mass) and dry weight content (%) of fish were highly correlated (p<0.00 1) and averaged 5, 611.6 ± 857.9 J/g wet mass and 25.3 ± 2.1% dry weight, respectively. Energy density values were significantly higher in fish sampled in spring than in other seasons. No major changes in the energy content were observed due to age or sex. Macroinvertebrates. particularly Ephemeroptera and Diptera, were the major food source of brown trout in the sampled area. Their gross energy content varied within a wide range of values (1, 654–5, 110 J/g wet weight), depending on the taxa and family or genus within a given taxon.

Application of GIS modelling to quantify fish habitats in lakes

AbstractQuantitative measures of fish habitat in lakes and impoundments have seldom been proposed. The availability of Geographic Information Systems (GIS), however, now provides a means for researchers to assess fish habitat on a whole‐lake scale. GIS modelling was used in this study to quantify the impacts of stratification on the amount and distribution of brown trout (Salmo trutta) habitat in a large reservoir in Victoria, Australia. Species‐specific temperature and dissolved oxygen tolerance ranges for brown trout were applied to the hydrological profile and lake bathymetry. The model predicted that brown trout habitat was reduced by 82% in the summer, and the model was validated with position data from acoustically tagged adult brown trout. This study demonstrated that a quantifiable assessment of fish habitat on a whole‐lake spatial scale can be made. It also could be applied to a range of fish species, with applications in ecosystem monitoring and fisheries management.

Interactive effects of cover and hydraulics on brown trout habitat selection patterns

AbstractHabitat modelling results are extremely sensitive to the habitat suitability criteria (HSC) used in the simulations. HSCs are usually expressed as univariate habitat suitability curves, although such univariate approach has been long questioned, since overlooking interactions between hydraulic variables may misrepresent the complexity of fish behaviour in habitat selection. It could lead to adopt erroneous flow management decisions based on misleading results. Furthermore, the interactive effects of hydraulic variables on habitat selection may be driven by the structural features of the channel, which determine cover availability. Therefore, we compared brown trout habitat selection patterns through multivariate resource selection functions (RSFs) in structurally contrasting rivers to unveil the interactive effects of hydraulics and cover elements and their consequences in univariate HSC results. Microhabitat preferences of young‐of‐the‐year (0+) trout were similar across fast and slow waters, meanwhile juvenile (1+) and adult (&gt;1+) preferences significantly changed. RSFs for young‐of‐the‐year trout were consistent with univariate results and did not differ among water types. However, RSFs for older trout varied among water types and revealed complex interactions among hydraulic variables and between hydraulics and structural elements, which were not described accurately by univariate curves. Therefore, results suggest that interactions between water depth and current velocity have a significant effect on habitat selection patterns in juvenile and adult brown trout, this effect being controlled by cover availability. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Exploring the relative influence of biotic interactions and environmental conditions on the abundance and distribution of exotic brown trout (Salmo trutta) in a high mountain stream

Abstract – In the Logan River, UT, USA, exotic brown trout demonstrate a strong allopatric distribution and occur at high densities at low‐elevation sites and in tributaries, and in low densities at native trout dominated, high‐elevation sites. Summer temperatures and discharge do not appear limiting for growth; adult growth rates were high overall and were greatest when fish were held experimentally at high elevation where they do not occur naturally. Brown trout are superior competitors; competition for space or food was stronger with their own con‐specifics than with other species. Evidence of density dependence was not observed at the juvenile life stage; no consistent relationships were detected between brown trout density and age‐1 condition or lagged, age‐0 weight (g). In contrast, adult brown trout demonstrated density‐dependent effects on condition and growth when reared experimentally. Field estimates of adult growth rates (g·day−1), although variable, declined subtly with increasing density, and annual survival was significantly greater in the mainstem sites (mean = 52%) relative to a high‐density tributary site (mean = 22%). Annual predicted age‐0 brown trout growth potential was four‐times greater at the lowermost site, compared with the highest elevation site, although fish lost weight over winter months at all sites. While adult density dependence may influence population abundance at some sites, extreme spring–winter conditions may ultimately limit the upper elevational extent of brown trout in this system. With changing climatic conditions and the potential for habitat degradation in the future, these results have important implications for native fish conservation.

Distribution of calretinin during development of the olfactory system in the brown trout, Salmo trutta fario: Comparison with other immunohistochemical markers

Immunocytochemical techniques were used to investigate the appearance and distribution of calretinin in the olfactory system of developing and adult brown trout ( Salmo trutta fario L.). The earliest calretinin-immunoreactive (CR-ir) cells were detected in the olfactory placode of 5-mm embryos. In 8-mm embryos, a CR-ir olfactory nerve was observed. The number of CR-ir olfactory receptor cells increased rapidly, and in fry and adults they were characterized by light and electron microscopy as pertaining to three morphological types of receptor cell, called microvillous, ciliated and rod-like cells or crypt cells. Comparisons of the cells labeled with CR and with more general olfactory markers (acetylated tubulin and keyhole limpet haemocyanin) in alevins and fry revealed that CR-ir cells represent only a subpopulation of olfactory receptor cells. Large cells located in the primordial mitral cell layer were the first CR-ir neuronal population of the olfactory bulbs and were observed in 7-mm embryos. These cells express high HuC/D immunoreactivity and were negative for glutamic acid decarboxylase and tyrosine hydroxylase. CR immunoreactivity diminished with development and most large cells of the mitral cell layer were CR-negative in fry. In later embryos and in alevins, CR-ir granule-like cells were observed in the olfactory bulbs. Comparisons of the terminal fields of primary olfactory fibers labeled with CR and with a more general olfactory marker in the olfactory bulbs of fry and adults revealed significant differences, with most glomeruli of the dorsomedial field receiving CR-negative olfactory fibers. These results suggest new criteria for understanding the organization of the olfactory system of the trout, and hence of teleosts. Our results also suggest that CR is involved in specific functions in the olfactory system during development.

Process-based modelling of invertebrate drift transport, net energy intake and reach carrying capacity for drift-feeding salmonids

We present an overview of a process-based modelling approach for predicting how change in flow affects drift density, net rate of energy intake (NREI) and numbers of drift-feeding salmonids. It involves linking an existing two-dimensional flow model (River2D) with models of invertebrate drift transport and drift-foraging which we have developed. We describe, demonstrate and partially test our models in an application on a 80 m × 20 m pool on a New Zealand river. We show how these models realistically capture hydraulic, drift dispersion and bioenergetics drift-foraging processes to predict the relationship between stream flow, habitat quality and quantity (in terms of NREI), and carrying capacity for drift-feeding salmonids. Overall, the 2D hydraulic model made good predictions of water levels, depths and water velocity at the calibration flow and a lower (validation) flow. The drift transport model made good predictions of the spatial distribution of invertebrate drift density throughout the pool at low flow after it was calibrated against observed drift density at the higher flow. The model correctly predicted that drift density would decline downstream and into the margins due to the process of settling dominating over entry from the stream bed, and that drift would be carried further downstream and laterally as flow increased. The foraging model made a reasonable prediction (6–7) of the numbers of 0.5 m adult brown trout observed (5) in the pool. It accurately predicted that trout should be distributed down the thalweg where net rate of energy intake (NREI) was highest, but when NREI was adjusted for depletion by feeding fish the predicted drift-feeding locations were more closely spaced (bunched) than observed fish locations. Our process-based modelling approach has important implications for improving biological realism in predictions of the response of drift-feeding fishes to flow change within the context of the IFIM.

Influence of genetic dissimilarity in the reproductive success and mate choice of brown trout – females fishing for optimal MHC dissimilarity

We examined the reproductive success of 48 adult brown trout (Salmo trutta L.) which were allowed to reproduce in a stream that was controlled for the absence of other trout. Parentage analyses based on 11 microsatellites permitted us to infer reproductive success and mate choice preferences in situ. We found that pairs with intermediate major histocompatibility complex (MHC) dissimilarity mated more often than expected by chance. It appears that female choice was the driving force behind this observation because, compared with other individuals, males with intermediate MHC dissimilarity produced a larger proportion of offspring, whereas female reproductive output did not show this pattern. Hence, rather than seeking mates with maximal MHC dissimilarity, as found in several species, brown trout seemed to prefer mates of intermediate MHC difference, thus supporting an optimality-based model for MHC-dependent mate choice.

Benefits of repeated stocking with adult, hatchery‐reared brown trout, Salmo trutta, to recreational fisheries?

Abstract Recaptures of adult, hatchery‐reared, brown trout, Salmo trutta L., and fishing time from anglers were used to evaluate the benefits of stocking programmes with repeated releases of adult brown trout. The recapture rate varied between 17% and 29%. The time between stocking and capture (referred to as residence time) varied between 1 and 160 days (median 3–49 days). Between 67% and 84% of trout caught in the river were recently released fish. Fishing effort increased after stocking, thereby increasing the impact of angling on wild stocks. Stocking with adult brown trout decreases the impact of angling on wild trout only if the time spent fishing by all anglers is kept stable. Furthermore, because of the short residence time of stocked trout, long‐term impacts through competition for space and food, or genetic impact through introgression, are limited.

Field protocol for assessing small obstacles to migration of brown trout Salmo trutta, and European grayling Thymallus thymallus: a contribution to the management of free movement in rivers

Abstract Between 1996 and 2004, adult brown trout, Salmo trutta L. (n = 40) and European grayling, Thymallus thymallus (L.) (n = 39) were radio‐tracked in three southern Belgium rivers to assess their capabilities to bypass various obstacles. During their upstream migrations individuals encountered different types of physical obstacles and successfully passed some under variable environmental conditions. The obstacles cleared by the fish were characterised based on a simple topographical description protocol and compared with tracking data. The ability of trout and grayling to pass different typologies of physical obstacles in natural river systems is discussed in the context of enabling their free movement in rivers.

A Bioenergetic Analysis of Factors Limiting Brown Trout Growth in an Ozark Tailwater River

We examined prey utilization and energy consumption by brown trout, Salmo trutta, in a cold tailwater (Little Red River, Arkansas, USA; LRR) having low biodiversity and low availability of fish as prey. Stomach content analysis and age estimation were performed on thirty brown trout (10 each of three size classes for a total of 710 trout) collected monthly from an upstream and downstream site over a 1-year period. Diet diversity was low at both sites, as 80% and 70% of all prey consumed by upstream and downstream brown trout, respectively, were isopods. Piscivory ( < 0.5% of individuals sam- pled) and consumption of terrestrial invertebrates were rare. There was no relation between diet diversity and trout age, and a very small ontoge- netic shift in brown trout diet. Second, we inves- tigated brown trout growth rates relative to prey consumption and temperature. Temperatures and availability of prey were less than required for maximal trout growth. However, prey availability limited trout growth directly, but sub-optimal temperatures probably buffered the effect of this reduced energy consumption by reducing meta- bolic energy expenditures. Brown trout growth was 54.8-57.0% of the maximum predicted by a bioenergetics model. Instantaneous growth rates for age 1 and adult brown trout were slightly higher for those downstream (0.195) versus those upstream (0.152). Although isopods are abundant within this tailwater to serve as a forage base, the displacement of native fish fauna and subsequent lack of establishment of cold-tolerant forage fish species due to the thermal regime of hypolimnetic release from Greers Ferry Reservoir probably serves as a major barrier to brown trout growth.