Brown Trout (brown + trout)

Distribution by Scientific Domains
Life Sciences51%
Earth and Environmental Science44%
2 Other Domains5%
Distribution within Life Sciences
Ecology & Organismal Biology66%
Conservation Science7%
Evolution3%
6 Other Subdomains24%

Kinds of Brown Trout

  • anadromous brown trout
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  • juvenile brown trout
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  • resident brown trout
    		•

    Terms modified by Brown Trout

  • brown trout population
    		•
  • brown trout salmo trutta
    		•
  • brown trout salmo trutta l.
    		•

    Selected Abstracts

    Role of Genetic Refuges in the Restoration of Native Gene Pools of Brown Trout

    CONSERVATION BIOLOGY, Issue 4 2009
    ROSA M. ARAGUAS
    introgresión de piscifactoría; pautas de manejo; acervos génicas nativas; refugios genéticos; repoblación de peces Abstract:,Captive-bred animals derived from native, alien, or hybrid stocks are often released in large numbers in natural settings with the intention of augmenting harvests. In brown trout (Salmo trutta), stocking with hatchery-reared non-native fish has been the main management strategy used to maintain or improve depleted wild brown trout populations in Iberian and other Mediterranean regions. This measure has become a serious threat to the conservation of native genetic diversity, mainly due to introgressive hybridization. Aware of this risk, the agency responsible for management of brown trout in the eastern Pyrenees (Spain) created "brown trout genetic refuges" to preserve the integrity of brown trout gene pools in this region. Within refuge areas, the prerefuge status with respect to fishing activities has been maintained, but hatchery releases have been banned completely. We evaluated this management strategy through a comparison of the stocking impact on native populations that accounted for stocking histories before and after refuge designations and fishing activities. In particular we examined the relevant scientific, cultural, and political challenges encountered. Despite agency willingness to change fishery policies to balance exploitation and conservation, acceptance of these new policies by anglers and genetic monitoring of refuge populations should also be considered. To improve management supported by genetic refuges, we suggest focusing on areas where the public is more receptive, considering the situation of local native diversity, and monitoring of adjacent introgressed populations. We recommend the use of directional supportive breeding only when a population really needs to be enhanced. In any case, management strategies should be developed to allow for protection within the context of human use. Resumen:,Animales criados en cautiverio derivados de individuos nativos, exóticos o híbridos a menudo son liberados en grandes cantidades en ambientes naturales con la intención de incrementar su explotación. En la trucha común (Salmo trutta), la repoblación con peces no nativos criados en granjas ha sido la principal estrategia de manejo utilizada para mantener o mejorar poblaciones naturales de trucha común en la Peninsula Ibérica y otras regiones Mediterráneas. Esta medida se ha convertido en una seria amenaza para la conservación de la diversidad genética nativa, debido principalmente a la hibridación introgresiva. Consciente de este riesgo, la agencia responsable del manejo de la trucha común en los Pirineos orientales (España) creó"refugios genéticos de trucha común" para preservar la integridad de las acervos genéticos de trucha común en esta región. Dentro de las áreas de refugio, se ha mantenido el estatus previo al refugio con respecto a las actividades pesqueras pero las liberaciones de peces de piscifactoría han sido completamente prohibidas. Evaluamos esta estrategia de manejo mediante la comparación del impacto de la repoblación sobre las poblaciones nativas que registraron historias de repoblación antes y después de la designación de refugios y de actividades pesqueras. En particular, examinamos los significativos retos científicos, culturales y políticos que encontramos. A pesar de la disponibilidad de la agencia para cambiar las políticas de pesca hacia un equilibrio entre la explotación y la conservación, también se debe considerar la aceptación de estas nuevas políticas por los pescadores y el monitoreo genético de las poblaciones en los refugios. Para mejorar el manejo en los refugios genéticos sugerimos centrarse en las áreas donde el público es más receptivo, considerando la situación de la diversidad nativa local y el monitoreo de las poblaciones introgresadas adyacentes. Recomendamos la utilización de la cría de apoyo direccional solo cuando una población realmente requiera ser mejorada. En cualquier caso, se deberían desarrollar estrategias de manejo para permitir la protección en el contexto del uso por el hombre. [source]

    Sex-Specific Aggression and Antipredator Behaviour in Young Brown Trout

    ETHOLOGY, Issue 7 2001
    Jörgen I. Johnsson
    Sex differences in adult behaviour are often interpreted as consequences of sexual selection and/or different reproductive roles in males and females. Sex-specific juvenile behaviour, however, has received less attention. Adult brown trout males are more aggressive than females during spawning and juvenile aggression may be genetically correlated with adult aggression in fish. We therefore tested the prediction that immature brown trout males are more aggressive and bolder than immature females. Because previous work has suggested that precocious maturation increases dominance in salmonids, we included precocious males in the study to test the prediction that early sexual maturation increase male aggression and boldness. Aggression and dominance relations were estimated in dyadic contests, whereas boldness was measured as a response to simulated predation risk using a model heron. Independent of maturity state, males initiated more than twice as many agonistic interactions as females in intersexual contests. However, males were not significantly more likely to win these contests than females. The response to a first predator attack did not differ between sex categories, but males reacted less to a second predator attack than females. Sexual maturity did not affect the antipredator response in males. Since there is no evidence from field studies that stream-living immature male and female salmonids differ in growth rate, it appears unlikely that the sex differences demonstrated are behavioural consequences of sex-specific investment in growth. It seems more likely that sex-specific behaviour arises as a correlated response to sexually selected gene actions promoting differential behaviour in adult males and females during reproduction. Alternatively, sex differences may develop gradually during juvenile life, because a gradual developmental program should be less costly than a sudden behavioural change at the onset of sexual maturity. [source]

    Growth-enhanced fish can be competitive in the wild

    FUNCTIONAL ECOLOGY, Issue 5 2001
    J. I. Johnsson
    Summary 1,The widespread commercial interest in producing growth-enhanced organisms has raised concerns about ecological consequences, emphasizing the need to understand the costs and benefits associated with accelerated growth in nature. Here, sustained-release growth hormone (GH) implants were used to estimate the competitive ability of growth-enhanced fish in the wild. Growth rate, movements and survival over winter were compared between GH-implanted and control Brown Trout in a natural stream. The study was repeated over two consecutive years. 2,GH treatment had no effect on recapture rates, indicating that mortality rates did not differ between GH-treated and control fish. More GH-treated trout (63%) than control fish (41%) were recaptured within their 10 m section of release. Thus, GH-treated fish were more stationary than control fish over winter. 3,GH-treated fish grew about 20% faster than control fish. This was mainly because of a three-fold growth rate increase in GH-treated fish in late summer, whereas growth rates over winter did not differ significantly between treatment groups. These results were consistent over both replicate years. 4,This first study of growth-enhanced fish in the wild shows that they can survive well and therefore may out-compete normal fish with lower growth rates. Although selection against rapid growth may be more intense at other life-history stages and/or during periods of extreme climate conditions, our findings raise concerns that released or escaped growth-enhanced salmonids may compete successfully with resident fish. It is clear that the potential ecological risks associated with growth-enhanced fish should not be ignored. [source]

    Do dams increase genetic diversity in brown trout (Salmo trutta)?

    ECOLOGY OF FRESHWATER FISH, Issue 4 2006
    Microgeographic differentiation in a fragmented river
    Abstract , Local genetic differentiation may potentially arise in recently fragmented populations. Brown trout is a polytypic species exhibiting substantial genetic differentiation, which may evolve in few generations. Movement (semi-)barriers in rivers may cause fragmentation, isolation and genetic differentiation in fish. In the Måna River (28 km) flowing from the alpine Lake Møsvatn to the boreal Lake Tinnsjø, construction of four hydropower dams during the period 1906,1957 have fragmented the previously (since last Ice Age) continuous wild resident brown trout population. Samples from the two lakes (N = 40) and six sites in the river (N = 30) isolated at different times were analysed at nine microsatellite loci. All populations showed substantial genetic variation (mean number of alleles per locus 5.3,8.9, observed heterozygosity 0.57,0.65 per population, overall Fst = 0.032). Pairwise multilocus Fst estimates indicated no significant differentiation between populations in the two lakes, and no or little differentiation in the lower river (Fst = 0.0035,0.0091). The microgeographic differentiation among wild resident trout at these sites was less than expected based on similar previous studies. However, results from the upper river, in particular the site immediately below the Lake Møsvatn outlet and dam, indicated isolation (Fst > 0.035). Calculation of genetic distances and assignment tests corroborated these results, as did a significant correlation between years of isolation (since dam construction) and Fst. The population structuring is most likely a result of fragmentation by dams, which has increased overall genetic diversity. This increased local differentiation may be caused by natural selection, but more likely by genetic drift in small, recently fragmented populations. Increased local genetic diversity by genetic drift does not justify conservation measures aiming at preserving genetic diversity. [source]

    Long-term variation in brown trout, Salmo trutta L., stocking success in a large lake: interplay between availability of suitable prey and size at release

    ECOLOGY OF FRESHWATER FISH, Issue 4 2005
    P. Hyvärinen
    Abstract , Factors affecting long-term variation in brown trout, Salmo trutta L., stocking success were examined in a large lake, Lake Oulujärvi, in central Finland. Brown trout were stocked in spring (late May to early June) in 1974,1991 and in summer (late June to early July) in 1992,2001. The biomass of the vendace, Coregonus albula (L.), population (prey) at release time had the largest positive effect on stocking success within both periods: biomass of adult vendace in spring and both 0+ and adult vendace in summer. Increasing the size of stocked fish had a positive effect if the vendace available at release were only adults. The increasing trend of predator-catch-per-unit-effort (CPUE) [combined CPUE of northern pike Esox lucius L., burbot Lota lota (L.), and pike-perch Stizostedion lucioperca (L.)] through the study period and its negative effect on trout stocking success suggested an increasing effect of predation within the entire time series. Resumen 1. Dado lo impredecible que son los resultados de las repoblaciones, se hace necesario conocer los mecanismos que afectan el éxito de los peces soltados para minimizar los riesgos de error en altas inversiones de repoblaciones. Podría existir una ventana óptima para las sueltas que produzca las condiciones más favorables - tales como la ausencia de predadores en la zona de suelta y la disponibilidad de presas apropiadas - bajo las que cualquier pez soltado pueda sobrevivir y generar una producción máxima. El fin de este estudio fue examinar como factores tales como la abundancia de las poblaciones de presas y predadores, y las tasas, tamaños y estaciones de repoblación pueden explicar las variaciones anuales a largo plazo (años 1974,1991) en el éxito de repoblación de Salmo trutta L. en el Lago Oulujärvi (928 km2, Finlandia central). 2. Individuos de S. trutta fueron repoblados en primavera (finales de Mayo , principios de Junio) durante los años 1974,1991 y en verano (finales de Junio , principios de Julio) durante los años 1992,2001. Los resultados de análisis de regresión por pasos mostró que la biomasa de Coregonus albula (L.) adultos (i.e., presas) en el momento de la suelta tuvieron el mayor efecto positivo sobre el éxito de la repoblación en dos períodos: la biomasa de adultos de C. albula en primavera y ambos dos, juveniles 0+ y adultos en verano. Incrementar el tamaño de los peces repoblados tuvo un efecto positivo si los C. albula disponibles en el momento de la suelta fueron solamente adultos (repoblaciones primaverales). La tendencia a incrementar los CPUE-predadores (CPUE combinadas de Esox lucius L., Lota lota (L.), y Stizostedion lucioperca (L.)) a lo largo del periodo de estudio y su efecto negativo sobre el éxito de las repoblaciones de S. trutta sugirió un mayor efecto de la predación sobre la series temporales completas. 3. Concluimos que el momento de la repoblación juega un papel más importante como determinante de la mejor ventana para la repoblación de S. trutta de lagos. Individuos de S. trutta de tamaños <200 g deberían ser repoblados solo si presas de pequeño tamaño (individuos 0+ de C. albula en verano) son también abundantes en el momento y en el área de la suelta. Si las presas disponibles son solos grandes (adultos de C. albula en primavera), el tamaño de repoblación debería ser mayor con individuos de S. trutta claramente mayores de 200 g porque el mayor tamaño amplia el rango de tamaños de las presas disponibles. [source]

    Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life histories

    ECOLOGY OF FRESHWATER FISH, Issue 1 2003
    A. Klemetsen
    Abstract ,,,Among the species in the family Salmonidae, those represented by the genera Salmo, Salvelinus, and Oncorhynchus (subfamily Salmoninae) are the most studied. Here, various aspects of phenotypic and life-history variation of Atlantic salmon Salmo salar L., brown trout Salmo trutta L., and Arctic charr Salvelinus alpinus (L.) are reviewed. While many strategies and tactics are commonly used by these species, there are also differences in their ecology and population dynamics that result in a variety of interesting and diverse topics that are challenging for future research. Atlantic salmon display considerable phenotypic plasticity and variability in life-history characters ranging from fully freshwater resident forms, where females can mature at approximately 10 cm in length, to anadromous populations characterised by 3,5 sea-winter (5SW) salmon. Even within simple 1SW populations, 20 or more spawning life-history types can be identified. Juveniles in freshwater can use both fluvial and lacustrine habitats for rearing, and while most smolts migrate to sea during the spring, fall migrations occur in some populations. At sea, some salmon undertake extensive oceanic migrations while other populations stay within the geographical confines of areas such as the Baltic Sea. At the other extreme are those that reside in estuaries and return to freshwater to spawn after spending only a few months at sea. The review of information on the diversity of life-history forms is related to conservation aspects associated with Atlantic salmon populations and current trends in abundance and survival. Brown trout is indigenous to Europe, North Africa and western Asia, but was introduced into at least 24 countries outside Europe and now has a world-wide distribution. It exploits both fresh and salt waters for feeding and spawning (brackish), and populations are often partially migratory. One part of the population leaves and feeds elsewhere, while another part stays as residents. In large, complex systems, the species is polymorphic with different size morphs in the various parts of the habitat. Brown trout feed close to the surface and near shore, but large individuals may move far offshore. The species exhibits ontogenetic niche shifts partly related to size and partly to developmental rate. They switch when the amount of surplus energy available for growth becomes small with fast growers being younger and smaller fish than slow growers. Brown trout is an opportunistic carnivore, but individuals specialise at least temporarily on particular food items; insect larvae are important for the young in streams, while littoral epibenthos in lakes and fish are most important for large trout. The sexes differ in resource use and size. Females are more inclined than males to become migratory and feed in pelagic waters. Males exploit running water, near-shore and surface waters more than females. Therefore, females feed more on zooplankton and exhibit a more uniform phenotype than males. The Arctic charr is the northernmost freshwater fish on earth, with a circumpolar distribution in the Holarctic that matches the last glaciation. Recent mtDNA studies indicate that there are five phylogeographic lineages (Atlantic, Arctic, Bering, Siberian and Acadian) that may be of Pleistocene origin. Phenotypic expression and ecology are more variable in charr than in most fish. Weights at maturation range from 3 g to 12 kg. Population differences in morphology and coloration are large and can have some genetic basis. Charr live in streams, at sea and in all habitats of oligotrophic lakes, including very deep areas. Ontogenetic habitat shifts between lacustrine habitats are common. The charr feed on all major prey types of streams, lakes and near-shore marine habitats, but has high niche flexibility in competition. Cannibalism is expressed in several cases, and can be important for developing and maintaining bimodal size distributions. Anadromy is found in the northern part of its range and involves about 40, but sometimes more days in the sea. All charr overwinter in freshwater. Partial migration is common, but the degree of anadromy varies greatly among populations. The food at sea includes zooplankton and pelagic fish, but also epibenthos. Polymorphism and sympatric morphs are much studied. As a prominent fish of glaciated lakes, charr is an important species for studying ecological speciation by the combination of field studies and experiments, particularly in the fields of morphometric heterochrony and comparative behaviour. [source]

    Creation of artificial upwelling areas for brown trout, Salmo trutta, spawning in still water bodies

    FISHERIES MANAGEMENT & ECOLOGY, Issue 5 2006
    Å. BRABRAND
    Abstract, Brown trout, Salmo trutta L., spawning sites were constructed by creating areas of artificial upwelling water, 252 ± 37 mL m,2 min,1 (95% CL), through appropriately sized spawning gravel substrate in 3 m2 vessels buried in the bottom of a 150-m2 pond. Natural spawning occurred in the vessels during autumn 2001,2004, with hatching and alevin swim up the following spring. In areas of upwelling, egg survival was 85,95%, while no live eggs were observed in areas without upwelling. In areas with upwelling, the maximum density of live eggs at the eyed stage was 570,1510 eggs m,2. In spring 2004 and 2005, the density of alevins was estimated at 322 (±187) m,2 and 567 (±217) m,2, respectively, in areas with upwelling water, compared with 35.2 ± 25.4 m,2 in areas without upwelling water in 2004. [source]

    Genetic structure in Atlantic brown trout (Salmo trutta L.) populations in the Iberian peninsula: evidence from mitochondrial and nuclear DNA analysis

    JOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 3 2000
    S. Dunner
    Summary Brown trout (Salmo trutta L.) was sampled in rivers belonging to three different Spanish basins in order to analyse the distribution of genetic variability. The genetic analysis was performed by using two systems and techniques: nuclear DNA was screened through random amplified polymorphic DNAs (screening 2 × 105 bp of the whole genome), and mitochondrial DNA (mtDNA) through sequencing of the hypervariable control region. Genetic distances between the populations were similar using either analysis although some differences arise. For example, some populations of the Tajo basin were very close through nuclear analysis but more distant using mtDNA. Differences between the two DNA sources could be the result of a different evolutionary rate, and the fact that mtDNA is maternally transmitted and differences in sex migration rates will influence the patterns of genetic variation between the transmitted DNAs. Total variation was partitioned using amova showing a clear subdivision among basins although intrapopulation variation remained as high as 62%. A correspondence analysis defined the differences in a three-dimensional way, clustering the populations according to their common basin. When mtDNA was sequenced, higher variability was noted in the segment between 400 and 600bp of the whole D-loop sequence, suggesting that these 200bp improved the analysis of the variability more than sequencing the t-RNA ends of the control region. A comparison was made between the t-RNAPro ends of the 10 populations screened here and the rest of the published sequences found in the literature, leading to a concentration of these populations in group IV which includes all trouts which originate in the Atlantic. The analyses performed suggest that a high genetic variability is present in all populations and that although there has been a probable interference from stocked strains introduced to increase population density, this was only detectable through the variance between rivers which reflect different policies according to the region where the basin is located. However, the genetic analysis using the two approaches allows the control of the natural populations avoiding a loss of their genetic potential. Zusammenfassung In drei verschiedenen spanischen Wassersystemen wurden Bachforellen (Salmo trutta L.) gesammelt, um die genetische Variabilität zu analysieren. Zur Analyse wurden zwei Systeme und zwei Techniken genutzt: Kern-DNA wurde mittels RAPD analysiert (2.105bp des Gesamtgenoms), mitochondriale DNA durch das Sequenzieren der hypervariablen Kontrollregion. Beide Techniken ergaben ähnliche genetische Distanzen zwischen den Populationen, obwohl Unterschiede bei Populationen aus dem Tajo-Gebiet auftraten, deren Kern-DNA eine sehr geringe Distanz aufwiesen, während die über Sequenzierung von mtDNA ermittelte Distanz auf größere Unterschiede hinwies. Diese Differenz könnte das Ergebnis unterschiedlicher Mutationsraten während der Evolution sein, oder auf dieTatsache zurückzuführen sein, daß mtDNA über die Mutterlinien weitergegeben wird, und Migrationsunterschiede zwischen den Geschlechtern die Muster der genetischen Variation der weitergegebenen DNA-Stücke beeinflußt. Die Gesamtvarianz wurde mit Hilfe von AMOVA analysiert, wobei zwischen den Wassersystemen eine eindeutige Unterteilung festgestellt werden konnte, obwohl die Varianz innerhalb der Population bei 62% liegt. Eine Korrespondenzanalyse erklärt die Distanzen dreidimensional, wodurch die Populationen gleicher Herkunft in Cluster zusammenfallen. Bei der Sequenzierung von mtDNA wurde eine größere Variabilität im Sequenzbereich zwischen 400 und 600 bp der gesamten D-Loop Sequenz festgestellt, was darauf schließen läßt, daß diese 200 bp für eine Analyse der Variabilität geeigneter sind als eine Sequenzierung der t-RNA Enden der Kontrollregion. Ein Vergleich der t-RNAPro Enden der zehn hier untersuchten Populationen und der bereits publizierten Sequenzen führen zu einer Konzentration dieser in der Gruppe IV, zu der alle Forellenpopulationen zählen, die aus dem Atlantik stammen. Die Untersuchung deutet auf eine hohe genetische Variabilität in allen Populationen hin und auf Interferenzen durch Aufstockungsmaßnahmen zur Erhöhung der Populationsdichten hin. Dies ist nur durch die Varianz zwischen den Flußsystemen aufzuklären, die von Region zu Region unterschiedliche Maßnahmen wiederspiegelt. Die genetische Analyse mittels dieser zwei Ansätze erlaubt eine Kontrolle der natürlichen Populationen zwecks Vermeidung eines Verlustes ihres genetischen Potentials. [source]

    Reproductive migration of brown trout in a small Norwegian river studied by telemetry

    JOURNAL OF FISH BIOLOGY, Issue 1 2004
    A. Rustadbakken
    The movement of 34 large (39,73 cm standard length) brown trout Salmo trutta was monitored using radio telemetry for up to 74 days in Brumunda, a small Norwegian river (mean annual discharge 3·3 m3 s,1) flowing into the large Lake Mjøsa. The maximum range of movement in the river was 20 km. No clear relationships existed between individual movement and water discharge, temperature and barometric pressure. Brown trout migrated at all levels of water discharge. At low discharge (<2 m3 s,1) movements were nocturnal. A weir 5·3 km from the outlet restricted ascending brown trout at low (c. 6° C), but not at high (c. 8° C) water temperatures. Spawning occurred in September to October and tagged individuals spent 2,51 days at the spawning sites. Mean migration speed from tagging to when the fish reached the spawning area, and from when they left the spawning areas and reached the lake was 1·0 and 2·3 km day,1, respectively. All tagged brown trout that survived spawning returned to the lake after spawning. [source]

    Role of Genetic Refuges in the Restoration of Native Gene Pools of Brown Trout

    CONSERVATION BIOLOGY, Issue 4 2009
    ROSA M. ARAGUAS
    introgresión de piscifactoría; pautas de manejo; acervos génicas nativas; refugios genéticos; repoblación de peces Abstract:,Captive-bred animals derived from native, alien, or hybrid stocks are often released in large numbers in natural settings with the intention of augmenting harvests. In brown trout (Salmo trutta), stocking with hatchery-reared non-native fish has been the main management strategy used to maintain or improve depleted wild brown trout populations in Iberian and other Mediterranean regions. This measure has become a serious threat to the conservation of native genetic diversity, mainly due to introgressive hybridization. Aware of this risk, the agency responsible for management of brown trout in the eastern Pyrenees (Spain) created "brown trout genetic refuges" to preserve the integrity of brown trout gene pools in this region. Within refuge areas, the prerefuge status with respect to fishing activities has been maintained, but hatchery releases have been banned completely. We evaluated this management strategy through a comparison of the stocking impact on native populations that accounted for stocking histories before and after refuge designations and fishing activities. In particular we examined the relevant scientific, cultural, and political challenges encountered. Despite agency willingness to change fishery policies to balance exploitation and conservation, acceptance of these new policies by anglers and genetic monitoring of refuge populations should also be considered. To improve management supported by genetic refuges, we suggest focusing on areas where the public is more receptive, considering the situation of local native diversity, and monitoring of adjacent introgressed populations. We recommend the use of directional supportive breeding only when a population really needs to be enhanced. In any case, management strategies should be developed to allow for protection within the context of human use. Resumen:,Animales criados en cautiverio derivados de individuos nativos, exóticos o híbridos a menudo son liberados en grandes cantidades en ambientes naturales con la intención de incrementar su explotación. En la trucha común (Salmo trutta), la repoblación con peces no nativos criados en granjas ha sido la principal estrategia de manejo utilizada para mantener o mejorar poblaciones naturales de trucha común en la Peninsula Ibérica y otras regiones Mediterráneas. Esta medida se ha convertido en una seria amenaza para la conservación de la diversidad genética nativa, debido principalmente a la hibridación introgresiva. Consciente de este riesgo, la agencia responsable del manejo de la trucha común en los Pirineos orientales (España) creó"refugios genéticos de trucha común" para preservar la integridad de las acervos genéticos de trucha común en esta región. Dentro de las áreas de refugio, se ha mantenido el estatus previo al refugio con respecto a las actividades pesqueras pero las liberaciones de peces de piscifactoría han sido completamente prohibidas. Evaluamos esta estrategia de manejo mediante la comparación del impacto de la repoblación sobre las poblaciones nativas que registraron historias de repoblación antes y después de la designación de refugios y de actividades pesqueras. En particular, examinamos los significativos retos científicos, culturales y políticos que encontramos. A pesar de la disponibilidad de la agencia para cambiar las políticas de pesca hacia un equilibrio entre la explotación y la conservación, también se debe considerar la aceptación de estas nuevas políticas por los pescadores y el monitoreo genético de las poblaciones en los refugios. Para mejorar el manejo en los refugios genéticos sugerimos centrarse en las áreas donde el público es más receptivo, considerando la situación de la diversidad nativa local y el monitoreo de las poblaciones introgresadas adyacentes. Recomendamos la utilización de la cría de apoyo direccional solo cuando una población realmente requiera ser mejorada. En cualquier caso, se deberían desarrollar estrategias de manejo para permitir la protección en el contexto del uso por el hombre. [source]

    Individual, Population, Community, and Ecosystem Consequences of a Fish Invader in New Zealand Streams

    CONSERVATION BIOLOGY, Issue 1 2003
    Colin R. Townsend
    But because invaders can have unexpected indirect effects in food webs, invasion ecologists need to integrate processes at the population level and other ecological levels. I describe a series of coordinated studies in New Zealand streams that address the effect of an exotic fish on individual behavior, population, community, and ecosystem patterns. Such case studies are important as an aid to the formulation of policy about invasions that are especially likely to become problematic. At the individual level, grazing invertebrates showed changes in behavior as a result of the introduction of brown trout ( Salmo trutta), a predator that exerts a very different selection pressure than do native fish. At the population level, trout have replaced nonmigratory galaxiid fish in some streams but not others, and have affected the distributions of crayfish and other large invertebrates. At the community level, trout have suppressed grazing pressure from invertebrates and are thus responsible for enhancing algal biomass and changing algal species composition. Finally, at the ecosystem level, essentially all annual production of invertebrates is consumed by trout ( but not by galaxiids), and algal primary productivity is six times higher in a trout stream. This leads, in turn, to an increased flux of nutrients from the water to the benthic community. The trout invasion has led to strong top-down control of community structure and ecosystem functioning via its effects on individual behavior and population distribution and abundance. Particular physiological, behavioral, and demographic traits of invaders can lead to profound ecosystem consequences that managers need to take into account. Resumen: Para desarrollar procedimientos y políticas de manejo efectivos a menudo será necesario conocer la biología de la población de especies invasoras. Sin embargo, debido a que los invasores pueden tener efectos indirectos inesperados en las redes alimenticias, ecólogos de invasión necesitan integrar procesos en la población y otros niveles ecológicos. Describo una serie de estudios coordinados en arroyos de Nueva Zelanda que enfocan el impacto de un pez exótico sobre los patrones de comportamiento individual, de la población, la comunidad y el ecosistema. Tales estudios de caso son importantes como un auxiliar para la formulación de políticas sobre invasiones que pueden ser especialmente problemáticas. Al nivel individual, los invertebrados que pastorean mostraron cambios de conducta como resultado de la introducción de la trucha café ( Salmo trutta), un depredador que ejerce una presión de selección muy diferente a la de los peces nativos. En el nivel de población, las truchas han reemplazado a peces galaxídos no migratorios en algunos arroyos pero no en otros y han afectado las distribuciones de cangrejos de río y otros invertebrados mayores. Al nivel de comunidad, las truchas han suprimido la presión de pastoreo por invertebrados y por lo tanto son responsables del incremento de la biomasa de algas y del cambio en la composición de especies de algas. Finalmente, a nivel de ecosistema, la producción anual de invertebrados esencialmente es consumida por las truchas ( pero no por galaxídos), y la productividad primaria de algas es seis veces mayor en arroyos con truchas. A su vez, esto conduce a incrementos en el flujo de nutrientes del agua hacia la comunidad béntica. La invasión de truchas ha conducido a un fuerte control de arriba hacia abajo de la estructura de la comunidad y del funcionamiento del ecosistema por medio de sus efectos sobre la conducta individual y la distribución y abundancia de la población. Las características fisiológicas, de conducta y demográficas particulares de los invasores pueden llevar a consecuencias profundas en los ecosistemas que los administradores necesitan tomar en consideración. [source]

    Environmentally induced migration: the importance of food

    ECOLOGY LETTERS, Issue 6 2006
    Ivan C. Olsson
    Abstract The decision to migrate or not is regarded as genetically controlled for many invertebrate and vertebrate taxa. Here, we show that the environment influences this decision. By reciprocally transplanting brown trout (Salmo trutta L.) between two sections in a river, we show that both migratory and non-migratory behaviour can be environmentally induced; migratory behaviour developed in a river section with high brown trout densities and low specific growth rates, whereas non-migratory behaviour developed in a section with low brown trout densities and high specific growth rates. In a laboratory experiment, we tested the effect of food availability on the development of migratory and non-migratory body morphologies and found that most brown trout became migrants when food levels were low but fewer did so at high food levels. Thus, the decision to migrate seems to be a plastic response, influenced by growth opportunities. [source]

    Functional response and size-dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.)

    ECOLOGY OF FRESHWATER FISH, Issue 2 2010
    P. Gustafsson
    Gustafsson P, Bergman E, Greenberg LA. Functional response and size-dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.).Ecology of Freshwater Fish 2010: 19: 170,177. © 2010 John Wiley & Sons A/S Abstract ,, Terrestrial invertebrate subsidies are believed to be important energy sources for drift-feeding salmonids. Despite this, size-specific use of and efficiency in procuring this resource have not been studied to any great extent. Therefore, we measured the functional responses of three size classes of wild brown trout Salmo trutta (0+, 1+ and ,2+) when fed either benthic- (Gammarus sp.) or surface-drifting prey (Musca domestica) in laboratory experiments. To test for size-specific prey preferences, both benthic and surface prey were presented simultaneously by presenting the fish with a constant density of benthic prey and a variable density of surface prey. The results showed that the functional response of 0+ trout differed significantly from the larger size classes, with 0+ fish having the lowest capture rates. Capture rates did not differ significantly between prey types. In experiments when both prey items were presented simultaneously, capture rate differed significantly between size classes, with larger trout having higher capture rates than smaller trout. However, capture rates within each size class did not change with prey density or prey composition. The two-prey experiments also showed that 1+ trout ate significantly more surface-drifting prey than 0+ trout. In contrast, there was no difference between 0+ and ,2+ trout. Analyses of the vertical position of the fish in the water column corroborated size-specific foraging results: larger trout remained in the upper part of the water column between attacks on surface prey more often than smaller trout, which tended to seek refuge at the bottom between attacks. These size-specific differences in foraging and vertical position suggest that larger trout may be able to use surface-drifting prey to a greater extent than smaller conspecifics. [source]

    A patch perspective on summer habitat use by brown trout Salmo trutta in a high plains stream in Wyoming, USA

    ECOLOGY OF FRESHWATER FISH, Issue 3 2009
    R. R. O'Connor
    Abstract,,, We quantified the use of habitat patches by brown trout, Salmo trutta, during summer conditions in a plains stream in the western United States. A Global Positioning System was used to map discrete habitat patches (2,420 m2) consisting of macrophytes, wood accumulation, or deep water. Habitat use by brown trout was monitored by radio telemetry. Brown trout used habitat in a nonrandom manner with 99% of all daytime observations and 91% of all nighttime observations occurring in patches that consisted of combinations of deep water, wood accumulations or macrophytes even though such patches constituted only 9.8% of the available habitat. Brown trout used deep water almost exclusively during the day but broadened their habitat use at night. Most fish stayed within a large plunge pool created by a low-head dam. This pool supplemented the deep-water habitat that was naturally rare in our study area and illustrates how human modifications can sometimes create habitat patches important for stream fishes. [source]

    Tagging effects on three non-native fish species in England (Lepomis gibbosus, Pseudorasbora parva, Sander lucioperca) and of native Salmo trutta

    ECOLOGY OF FRESHWATER FISH, Issue 2 2009
    S. Stak
    Abstract,,, To address the dearth of information on tagging effects and long-term survivorship of tagged fish in native and introduced species, laboratory and field investigations were undertaken on three non-native fish species (pumpkinseed Lepomis gibbosus; topmouth gudgeon Pseudorasbora parva; pikeperch Sander lucioperca) tagged with coded-wire (CW), passive integrated transponder (PIT), radio (RT) telemetry and/or acoustic tags (AT), with survivorship of native brown trout (Salmo trutta) examined in the field. Laboratory results revealed high survivorship following tag attachment/insertion and resumption of feeding within 24,48 h of tagging (all mortalities could be attributed to an unrelated outbreak of fungal infection), with retention rates being high in both pumpkinseed and pikeperch but low in topmouth gudgeon (excluded from field studies). In the field, short-term post-operation survival was high in pikeperch, pumpkinseed and brown trout. In pumpkinseed and trout, 100% of RT fish survived a 24,30 day tracking study, with 60% and 80%, respectively, recaptured alive at least 3 months post-tagging. Of PIT tagged pumpkinseed, 44% were recaptured (after 6,18 months), with small-sized, CW-tagged fish (0.38 g weight) captured up to 1 year after tagging. In pikeperch, all AT fish except one (the smallest specimen) survived their full expected tracking period (i.e. tag life) , the single lost specimen survived at least half of its expected tracking period (i.e. 6 month battery life). Overall, the tagging methods used were highly effective in pumpkinseed and pikeperch, showing good retention and survival, but PIT tagging of topmouth gudgeon was plagued by low survivorship and tag rejection. [source]

    What can otolith examination tell us about the level of perturbations of Salmonid fish from the Kerguelen Islands?

    ECOLOGY OF FRESHWATER FISH, Issue 4 2008
    F. Morat
    Abstract,,, Otoliths preserve a continuous record of the life cycle from the natal through the adult stage. For that reason, the morphological and chemical characteristics of otoliths of two nonnative Salmonids, brown trout (Salmo trutta) and brook charr (Salvelinus fontinalis) from populations on the Kerguelen Islands were compared. Several approaches were used to study the relationships between otolith morphometry, crystal morph and chemical elemental composition. These salmonids sampled in Kerguelen are well differentiated in terms of species through their otolith shape. The results indicate that ecotypes and river populations can be reasonably well differentiated on the basis of otolith shape. The crystallisation study has revealed the presence of a particular form: the vaterite, present at a high rate: 45% of S. fontinalis and 18% from Salmo trutta fario. Moreover, vaterite and aragonite otoliths presented differences in chemical composition. [source]

    Different longitudinal distribution patterns of native white-spotted charr and non-native brown trout in Monbetsu stream, Hokkaido, northern Japan

    ECOLOGY OF FRESHWATER FISH, Issue 1 2008
    K. Hasegawa
    Abstract, This study focused on longitudinal distribution patterns of native white-spotted charr and non-native brown trout in a mountainous stream in Hokkaido, Japan. Brown trout ratio, which is the proportion of brown trout in the catch of salmonids, was decreasing from downstream to upstream. Brown trout ratio correlated negatively with water temperature. Thus, our results suggested that temperature may influence the possible competition between native white-spotted charr and non-native brown trout. [source]

    Do dams increase genetic diversity in brown trout (Salmo trutta)?

    ECOLOGY OF FRESHWATER FISH, Issue 4 2006
    Microgeographic differentiation in a fragmented river
    Abstract , Local genetic differentiation may potentially arise in recently fragmented populations. Brown trout is a polytypic species exhibiting substantial genetic differentiation, which may evolve in few generations. Movement (semi-)barriers in rivers may cause fragmentation, isolation and genetic differentiation in fish. In the Måna River (28 km) flowing from the alpine Lake Møsvatn to the boreal Lake Tinnsjø, construction of four hydropower dams during the period 1906,1957 have fragmented the previously (since last Ice Age) continuous wild resident brown trout population. Samples from the two lakes (N = 40) and six sites in the river (N = 30) isolated at different times were analysed at nine microsatellite loci. All populations showed substantial genetic variation (mean number of alleles per locus 5.3,8.9, observed heterozygosity 0.57,0.65 per population, overall Fst = 0.032). Pairwise multilocus Fst estimates indicated no significant differentiation between populations in the two lakes, and no or little differentiation in the lower river (Fst = 0.0035,0.0091). The microgeographic differentiation among wild resident trout at these sites was less than expected based on similar previous studies. However, results from the upper river, in particular the site immediately below the Lake Møsvatn outlet and dam, indicated isolation (Fst > 0.035). Calculation of genetic distances and assignment tests corroborated these results, as did a significant correlation between years of isolation (since dam construction) and Fst. The population structuring is most likely a result of fragmentation by dams, which has increased overall genetic diversity. This increased local differentiation may be caused by natural selection, but more likely by genetic drift in small, recently fragmented populations. Increased local genetic diversity by genetic drift does not justify conservation measures aiming at preserving genetic diversity. [source]

    Egg size differentiation among sympatric demes of brown trout: possible effects of density-dependent interactions among fry

    ECOLOGY OF FRESHWATER FISH, Issue 3 2006
    F. Gregersen
    Abstract,,, This study investigates differentiation in egg size among five sympatric brown trout (Salmo trutta (L.)) demes. We explore a hypothesis predicting high density-dependent interactions among juveniles to favour large eggs by sampling closely located (<100 m) deme pairs with low and high fry abundances. A mancova model fitted the egg size versus egg number relationship as a function of large-scale spatial habitat heterogeneity (basin) and maternal phenotype revealed that demes have significantly different egg size versus fecundity relationships and that the differentiation is mainly due to interdeme variation in egg size. Fry density was significantly and positively associated with egg size and a post-hoc test indicated egg size to be significantly greater in high-density than low-density tributaries. The data is consistent with the density-dependent hypothesis and suggest that reproductive investment can diverge over small geographic distances, potentially in response to environments favouring greater investment in offspring quality. [source]

    Effect of habitat fragmentation on spawning migration of brown trout (Salmo trutta L.)

    ECOLOGY OF FRESHWATER FISH, Issue 3 2006
    C. Gosset
    Abstract , Human-induced habitat alteration is one of the main causes of the decline of freshwater fish populations. The watershed of the River Bidasoa (Spain) is an example of heavily fragmented habitat. The local brown trout (Salmo trutta L.) population is disturbed, with evidence of poor recruitment as well as low adult densities in the main stem. Forty male and female adult migratory trout were tagged with external or internal radio transmitters and released. Fixed stations with data loggers and mobile antennae were used with daily surveys to track fish movements during the migration and spawning period (3 months). Migration distances did not exceed 10 km, and half of the fish never entered a tributary in the study area. Fragmentation because of weirs on the main stem apparently prevented fish from reaching their spawning destination. Fish that entered the tributaries were first confronted with an accessibility problem because of low discharge. However, each fish chose one tributary, without making attempts to run up in other tributaries. Once in the tributary, fish were restrained in their upstream movements by dams. The study area appeared to be isolated from the vast upper part of the watershed. Within the study area, upper parts of tributaries also seemed strongly disconnected from the main stem. This study illustrates the negative impact of river fragmentation on S. trutta migration pattern. Population sustainability can be directly affected through the low availability of spawning grounds for migratory fish. Long-term effects of fragmentation may cause reproductive isolation within watersheds, which in the case of trout also means isolated phenotypic population units. [source]

    Long-term variation in brown trout, Salmo trutta L., stocking success in a large lake: interplay between availability of suitable prey and size at release

    ECOLOGY OF FRESHWATER FISH, Issue 4 2005
    P. Hyvärinen
    Abstract , Factors affecting long-term variation in brown trout, Salmo trutta L., stocking success were examined in a large lake, Lake Oulujärvi, in central Finland. Brown trout were stocked in spring (late May to early June) in 1974,1991 and in summer (late June to early July) in 1992,2001. The biomass of the vendace, Coregonus albula (L.), population (prey) at release time had the largest positive effect on stocking success within both periods: biomass of adult vendace in spring and both 0+ and adult vendace in summer. Increasing the size of stocked fish had a positive effect if the vendace available at release were only adults. The increasing trend of predator-catch-per-unit-effort (CPUE) [combined CPUE of northern pike Esox lucius L., burbot Lota lota (L.), and pike-perch Stizostedion lucioperca (L.)] through the study period and its negative effect on trout stocking success suggested an increasing effect of predation within the entire time series. Resumen 1. Dado lo impredecible que son los resultados de las repoblaciones, se hace necesario conocer los mecanismos que afectan el éxito de los peces soltados para minimizar los riesgos de error en altas inversiones de repoblaciones. Podría existir una ventana óptima para las sueltas que produzca las condiciones más favorables - tales como la ausencia de predadores en la zona de suelta y la disponibilidad de presas apropiadas - bajo las que cualquier pez soltado pueda sobrevivir y generar una producción máxima. El fin de este estudio fue examinar como factores tales como la abundancia de las poblaciones de presas y predadores, y las tasas, tamaños y estaciones de repoblación pueden explicar las variaciones anuales a largo plazo (años 1974,1991) en el éxito de repoblación de Salmo trutta L. en el Lago Oulujärvi (928 km2, Finlandia central). 2. Individuos de S. trutta fueron repoblados en primavera (finales de Mayo , principios de Junio) durante los años 1974,1991 y en verano (finales de Junio , principios de Julio) durante los años 1992,2001. Los resultados de análisis de regresión por pasos mostró que la biomasa de Coregonus albula (L.) adultos (i.e., presas) en el momento de la suelta tuvieron el mayor efecto positivo sobre el éxito de la repoblación en dos períodos: la biomasa de adultos de C. albula en primavera y ambos dos, juveniles 0+ y adultos en verano. Incrementar el tamaño de los peces repoblados tuvo un efecto positivo si los C. albula disponibles en el momento de la suelta fueron solamente adultos (repoblaciones primaverales). La tendencia a incrementar los CPUE-predadores (CPUE combinadas de Esox lucius L., Lota lota (L.), y Stizostedion lucioperca (L.)) a lo largo del periodo de estudio y su efecto negativo sobre el éxito de las repoblaciones de S. trutta sugirió un mayor efecto de la predación sobre la series temporales completas. 3. Concluimos que el momento de la repoblación juega un papel más importante como determinante de la mejor ventana para la repoblación de S. trutta de lagos. Individuos de S. trutta de tamaños <200 g deberían ser repoblados solo si presas de pequeño tamaño (individuos 0+ de C. albula en verano) son también abundantes en el momento y en el área de la suelta. Si las presas disponibles son solos grandes (adultos de C. albula en primavera), el tamaño de repoblación debería ser mayor con individuos de S. trutta claramente mayores de 200 g porque el mayor tamaño amplia el rango de tamaños de las presas disponibles. [source]

    Population genetics of the European trout (Salmo trutta L.) migration system in the river Rhine: recolonisation by sea trout

    ECOLOGY OF FRESHWATER FISH, Issue 1 2005
    A. Schreiber
    Abstract , Allozyme genetics (34 loci) is studied in up to 1010 European trout (Salmo trutta) from the Rhine, Meuse, Weser, Elbe and Danube river systems in Central Europe. Population samples from single collection sites, chiefly small streams (GCG = 0.2126), rather than the divergence of the trout from Atlantic and Danubian drainages (GSG = 0.0711), contributed to the overall gene diversity of GST = 0.2824. Sea trout (n = 164) and brown trout (n = 767) in Atlantic rivers adhere to the same biogeographical stock, but anadromous trout from the Rhine and the Elbe display more genetic cohesion than resident brown trout from the Rhine system alone. Strayers from the Elbe could have founded the recently re-established sea trout population of the Rhine, after a few decades of absence or precarious rarity. Migrants may even connect the Rhine and Elbe stocks by ongoing gene flow. A release,recapture study confirms that all trout in the Rhine belong to one partly migratory population network: Six of 2400 juvenile sea trout released into a tributary of the Rhine were later recorded as emigrants to the Rhine delta, against three of 1600 released brown trout. One migrant had entered the open North Sea, but the other dispersers were recorded in fresh waters of the Rhine delta (Ijsselmeer, Amstelmeer). Stocking presumably elevated both heterozygosity and fixation indices of brown trout, but this effect is subtle within the range of the Atlantic population group. Improved sea trout management in the Rhine, and modifications to brown trout stocking in the upper Danubian area are recommended. [source]

    Migration of landlocked brown trout in two Scandinavian streams as revealed from trap data

    ECOLOGY OF FRESHWATER FISH, Issue 3 2004
    J. Carlsson
    Abstract,,, Anthropogenic barriers that may interfere or prevent fish migration are commonly found in streams throughout the distribution of salmonids. Construction of fish passages in streams is a common solution to this problem. However, the goal with fish passages is often, at least in Scandinavia, to allow Atlantic salmon (Salmo salar L.) and migratory brown trout (S. trutta L.) to get access to spawning areas above these barriers. Hence, the fish passages may often only be open during the spawning migration of salmonids (late summer to autumn). We present data, on wild brown trout migration, from two trapping systems in two Scandinavian streams showing that intra- and interstream migrations are common throughout the summer and autumn. Moreover, differences in size were found between trap-caught trout and electrofished trout where trapped trout were generally larger than electrofished trout. We suggest that the current regime with fish passages only open parts of the year can have negative effects on populations by depriving trout from the possibility to perform migrations throughout the year. Resumen 1. Barreras de origin antrópico que pueden interferer o prevenir las migraciones de los peces son frecuentes a lo largo de las áreas de distribución de los salmónidos. Una solución común a este problema es la construcción de pasos. Si embargo, el fin general de estos pasos es, por lo menos en Escandinavia, permitir el acceso a las áreas de reproducción por encima de las barreras tanto a salmones (Salmo salar L.) como a truchas migratorias (S. trutta L.). Frecuentemente, estos pasos están solamente abiertos durante el período de migración reproductiva (final del verano y otoño) porque se piensa que este régimen no tiene consecuencias negativas ya que estas especies muestran movimientos muy limitados en otros periodos del año. 2. Presentamos datos sobre migraciones de truchas colectados en dos sistemas de trampas de dos ríos escandinavos. Un río localizado por encima de una catarata inaccesible. El segundo, con una población migratoria de truchas. Los datos indicaron claramente migraciones intensivas a lo largo de todo el período en el que las trampas estuvieron operativas. Ambos ríos mostraron un pico de migración aguas arriba a mediados de Julio. Migraciones aguas abajo fueron raramente observadas en la población por encima de la catarata aunque migraciones aguas abajo en la población del río fueron intensivas al final del otoño. 3. Sugerimos que el régimen actual de pasos de peces que abren solamente partes del año puede tener efectos negativos sobre las poblaciones, al privar a las truchas de la posibilidad de migrar a lo largo del año. Esto puede extenderse a otros sistemas con barreras ya que observamos también migraciones intensivas en la población localizada por encima de la catarata. [source]

    Effect of brown trout body size on post-stocking survival and pike predation

    ECOLOGY OF FRESHWATER FISH, Issue 2 2004
    P. Hyvärinen
    Abstract,,, A total of 40 (20 age-3 + 20 age-4) radio-tagged hatchery-reared brown trout (Salmo trutta L.) and 40 wild radio-tagged northern pike (Esox lucius L.) were released into a regulated river. Age-3 brown trout were predicted and observed to be highly vulnerable to predation by pike (50% mortality), whereas age-4 brown trout were predicted and observed to enjoy an almost absolute size refuge from predation (5% mortality). Almost half of the fish from both age groups similarly emigrated and survived from the river within 3 days of the release. However, there was a considerable difference in survival between age groups for fish that remained in the river for a longer period. Of these, all except one age-3 brown trout were eaten by pike, whereas all but one age-4 fish survived predation. Resumen 1. Un total de 40 individuos de Salmo trutta (20 de edad-3 y 20 de edad-4) procedentes de piscifactoría fueron marcados con radio-transmisores y 40 individuos de Esox lucius también marcados con radio-transmisores, fueron soltados en un río regulado. Predecimos y observamos que los individuos de edad-3 de S. trutta fueron altamente vulnerables a la predación por Esox lucius (50 % de mortalidad) mientras que los individuos de edad-4 gozaron de refugio de tamaño casi absoluto de la predación (5% de mortalidad). 2. Casi la mitad de los peces de ambos grupos de edad sobrevivieron y emigraron del río durante los tres días siguientes a la suelta. Sin embargo, hubo una considerable diferencia en la supervivencia entre grupos de edad para los peces que permanecieron en el río por un período mayor de tiempo. De estos, todos excepto 1 individuo de S. trutta de edad-3 fueron comidos por E. lucius mientras que todos excepto un individuo de edad-4 sobrevivieron a la predación. [source]

    Effects of size and morphology on swimming performance in juvenile brown trout (Salmo trutta L.)

    ECOLOGY OF FRESHWATER FISH, Issue 4 2003
    A. F. Ojanguren
    Abstract,,, Our study assesses swimming capacity (speed and stamina) and possible morphometric determinants of locomotor performance of juvenile brown trout (Salmo trutta L.). We addressed these issues at the individual level to have an approach of the functional significance of intraspecific variation in morphological design. Both swimming speed and endurance time showed significant positive relationships with fish length. Size-corrected values of speed and endurance time were negatively correlated suggesting a phenotypic trade-off between burst and prolonged swimming. Size was also highly correlated with all the morphological variables measured. Therefore, we used the residuals of the regressions of those variables on fish length to remove the effect of body size. A principal components analysis (PCA) summarised the 12 morphological variables into two factors, which accounted for 44.3% of the variance. PC1 combined several measures of body depth and width, whereas PC2 represented mainly postanal length relative to abdomen length. Relationships between the scores of the two factors and size-corrected values of maximum swimming speed and endurance time were weak. PC2 showed a significant positive relationship with endurance time; that is, individuals with longer caudal regions were able to swim against water flow for longer periods of time. Stoutness (PC1) showed a marginally significant negative correlation with endurance time. The lack of stronger relationships could be because of the low morphometric variability among the test individuals, all proceeding from the same population, reared in a common environment, and measured at the same ontogenetic stage. [source]

    Stream habitat use and diet of juvenile (0+) brown trout and grayling in sympatry

    ECOLOGY OF FRESHWATER FISH, Issue 4 2000
    E. Degerman
    Abstract , Electrofishing survey data and experiments carried out in a semi-natural stream were used to test the hypothesis that interactions between underyearling (0+) trout and grayling during their first summer affect habitat use and diet. The survey data revealed a general difference in habitat use, with 0+ grayling being more common than 0+ trout in large streams and deeper sections. It was also found that in the presence of trout, finer substrate and shallower sections were utilised more by grayling. Field experiments were carried out with three treatments; trout alone, grayling alone and the two species together. In both the July and September experiments grayling tended to occupy deeper sections than trout. Trout abundance was higher in shallow areas in sympatry, while no such difference was found in allopatry. The rate of disappearance of grayling from the study sections was significantly higher in sympatry in July, while no difference was found in September. In July the size difference between species and the degree of dietary overlap were small and non-significant, respectively, indicating that the two species were strongly competing., [source]

    Resource partitioning between lake-dwelling Atlantic salmon (Salmo salar L.) parr, brown trout (Salmo trutta L.) and Arctic charr (Salvelinus alpinus (L.))

    ECOLOGY OF FRESHWATER FISH, Issue 4 2000
    L. Jørgensen
    Abstract , Resource partitioning between Atlantic salmon parr, brown trout and Arctic charr was studied throughout the ice-free season in a north Norwegian lake. Juvenile salmon and trout (,160 mm) utilized the littoral zone and juvenile charr the profundal, while adult trout and charr (>160 mm) were found in both. Juvenile salmon and trout had a similar diet, although trichopteran larvae were more important for the trout and chironomid pupae and three-spined sticklebacks for the salmon parr. Small salmon and trout parr (,120 mm) had a higher diet overlap than larger parr (121,160 mm). The feeding habits of adult trout were similar to that of juvenile trout, but the former took larger prey items. At the population level, both salmon and trout were generalistic feeders with a broad diet, but at the individual level, both species had specialized on a single or a few prey categories. Juvenile charr were segregated from salmon and trout in both habitat and food utilization; they had a narrow diet consisting of chironomids and zooplankton, possibly reflecting their confinement to the profundal habitat which have a low diversity of potential prey. Larger charr also took zoobenthos and sticklebacks in the littoral zone., [source]

    Threatened obligatory riverine fishes in human-modified Polish rivers

    ECOLOGY OF FRESHWATER FISH, Issue 1-2 2000
    T. Penczak
    Abstract , The fate of obligatory riverine fish species (rheophils), which are the objects of anglers' exploitation (chub ,Leuciscus cephalus, nase ,Chondrostoma nasus, barbel ,Barbus barbus, gudgeon ,Gobio gobio), and brown trout (Salmo trutta m. fario) and grayling (Thymallus thymallus) (in the Gwda River basin only), were investigated in large alluvial rivers (Pilica and Warta) and in the medium-sized Gwda River basin. The Pilica (1973) and the Warta (1986,1987) were divided by large dams without fish ladders in their middle courses. The Gwda River was divided by only a few dams along its course, but its tributaries carrying pure water had numerous small dams that supplied water for fish farms. Other stresses influencing fish populations in these rivers were: pollution, overfishing, hydroelectric plants and bank revetments. Because the listed stresses occurred alternately and at various periods of time in these rivers, this enabled attributing the cause for extinction and reduction of the abundance and distribution. In the salmon Gwda River basin, a drastic decrease in spatial distribution and reduction of occurrence ranges of brown trout, grayling and barbel was evident in respect to the first study period (1980s) in the 1990s. In the large, alluvial Pilica River, nase, barbel and dace are on the edge of extinction and chub and gudgeon are vulnerable. In the Warta's tailwater, barbel is an extinct species, and chub, dace and gudgeon are vulnerable ones. In a site in the backwater, none of the above mentioned species became extinct, but their abundance and occurrence frequency decreased a bit in respect to the pre-impoundment period. Roach-generalist, which was used in this research as a "control" species, increased in abundance in all 3 rivers. These investigations univocally proved that the dams cause catastrophic stress for obligatory riverine species., [source]

    The Bold and the Variable: Fish with High Heterozygosity Act Recklessly in the Vicinity of Predators

    ETHOLOGY, Issue 1 2008
    Sampsa Vilhunen
    Variation in the innate behavioral response to predation threat is often assumed to reflect genetic differences among the prey individuals. To date, no published results, however, exist that would offer explanation for the origin of this behavioral variation within populations. Using microsatellites as markers, we estimated the genetic variability of juvenile brown trout (Salmo trutta) individuals whose behavior had been individually recorded in a trade-off situation where both predator chemical cues and food were present. Mean overall heterozygosity and the internal relatedness of fish associated significantly with their activity and foraging, so that the genetically more variable individuals showed more risk-prone behavior under predation risk. No association between genetic variability and behavior was found in trials where predator odors were not present. These results were consistent over the three study populations of brown trout with different backgrounds, suggesting that the phenomenon is of general nature in this species. Of the possible mechanisms suggested to enable the existence of the positive association between neutral microsatellite variation and fitness-related trait, the local effect hypothesis gained more support from our data than the general effect hypothesis. [source]

    Gillnet fishing drives lake-migrating brown trout to near extinction in the Lake Päijänne region, Finland

    FISHERIES MANAGEMENT & ECOLOGY, Issue 2 2010
    J. SYRJÄNEN
    Abstract, Wild stocks of brown trout, Salmo trutta L., collapsed in Finnish inland waters during the 20th Century because dams prevented upstream migration, and low water quality and stream dredging weakened reproduction. The demise in migratory stocks was coupled with overfishing, mainly by gillnetting on lakes. Consequently, the migratory spawning stocks have diminished to negligible levels. The remaining stocks exhibit restricted immigration and emigration, are supplemented by continuous stocking, and their natural genetic diversity is affected by human activities. In recent years, various recovery actions have been implemented including stream channel restorations, fish passage facilities constructed and stocking of eggs and smolts. Gillnetting has also been regulated by banning certain mesh sizes, and catch-and-release of wild trout is spreading amongst sport fishers. However, these measures seem to be inadequate and almost no recovery of migratory populations has been reported. The problem of by-catch in intensive gillnetting continues to threaten stocks and creates disputes between stakeholders. [source]