The Scottish brown trout (Salmo trutta L.) is identified as an important resource which requires responsible and continual management. This study was divided into two parts; an electrophoretic survey of wild trout populations in Scotland, and a quantitative assessment of the genetic component to growth rate in various stocks, grown under hatchery and farm conditions. Sixty wild populations were sampled by various methods. All fish were typed using brain, eye, heart, liver and muscle tissue and starch gel electrophoresis for thirty four enzyme loci, thirteen of which were found to be polymorphic. Gene diversity analysis was conducted on the data collected, 33% of the diversity being attributed to differences between populations, much of the variation was thought to be due to founder effects. Evidence is presented to support a hypothesis that the trout in Scotland are derived from two main post glacial invasion stocks. Future management strategies for wild stocks of Scottish brown trout are discussed. Growth trials were conducted at Howietoun fish farm in order to calculate heritability estimates for growth rate. Hierarchical and factoral crossing schemes were employed, using broodstock from three stocks. Heritability estimates for growth rate were found to be high and it was concluded, significant genetic gains could be achieved if growth rate was the only trait of commercial interest and truncated mass selection was adopted. Attempts were made to investigate the relationship between heterozygosity and growth rate in the hatchery populations. It was concluded that more data were required to make a meaningful assessment, but from this study little evidence exists for a positive correlation between heterozygosity and growth rate. Correlations between early life cycle stages and subsequent growth are discussed.

Thesis (Ph.D.)--Pennsylvania State University, 2005. / Mode of access: World Wide Web.

Thesis (Ph.D. )--Memorial University of Newfoundland, 1997. / Bibliography: leaves 118-145.

Abstract Maintaining connectivity in boreal streams by rehabilitation procedures is a challenging task that requires ecological understanding based on empirical research. In this thesis, I examined the effects of stream rehabilitation on densities and growth of brown trout (Salmo trutta L.), as well as on benthic biodiversity. As streams are known to be closely connected to their watersheds, I also examined the effects of watershed drainage activities on stream organisms. The results of this thesis have implications for enhancing salmonid populations, as well for maintaining stream biodiversity. First, regional climatic variability was shown to override local impacts of watershed management on stream biota. This highlights the importance of placing results from local studies in a regional context. Second, increased sedimentation that typically follows anthropogenic actions in the watershed did not only cause direct mortality on the early life stages of brown trout, but also forced them to emerge earlier from gravel and constrained their development. Thus, sedimentation may have far-reaching fitness consequences on juvenile salmonids. Third, while instream rehabilitation did enhance habitat diversity for salmonid fish, there were only marginal effects on juvenile fish and benthic biodiversity. Therefore, the factors limiting stream biota, and obscuring positive effects of rehabilitation, are to be found elsewhere. For this purpose, my thesis offers at least three potential, not mutually exclusive explanations: (i) land use changes have altered watersheds and this can be seen as decreased stream biodiversity that cannot be corrected through local-scale restoration efforts; (ii) a habitat-forming organism group, stream bryophytes, is dispersal limited, slowing down any positive responses to restoration by fish or invertebrates that depend strongly on bryophytes; and (iii) changes to stream habitat heterogeneity caused by channelization for timber floating were rather modest to start with, and therefore any effects of stream habitat rehabilitation on stream biota are likely to be subtle. Based on these findings, I suggest that future restoration efforts should be prioritized according to a comprehensive watershed assessment. Also, monitoring of projects should be more rigorous and preferably multidisciplinary, documenting the ecological as well as hydrological and socioeconomic outcomes of rehabilitation projects.

Abstract For effective management of stream salmonids, it is essential to (i) assess the productive potential of a stream in relation to species-specific habitat requirements, and to (ii) identify the key factors underlying any bottleneck periods during the life cycle of a fish. For this purpose, this PhD-thesis focuses on the mechanisms of habitat selection by juvenile salmonids in boreal streams. Habitat preference curves for depth, water velocity, substrate and instream cover for brown trout (Salmo trutta L.) in river Kuusinkijoki, northeastern Finland, indicated that larger trout preferred deeper stream areas than age-0 trout did. In summer, all size-classes of trout preferred small substrates, whereas in winter, areas with cobble-boulder substrates were preferred. Winter presents a bottleneck period for trout in boreal streams; therefore winter habitat curves should be incorporated into habitat-hydraulic models when estimating habitat suitable for riverine trout in areas with severe winter conditions. The preference curves of age-0 trout were validated by correlating age-0 trout density with habitat availability at multiple sites in two boreal rivers where trout densities were monitored in 1988-1995. Substrate preference curve was effective in predicting trout densities among sites, whereas among-year variation in trout densities was best predicted by depth-related preference curves. The responses of age-0 brown trout and grayling (Thymallus thymallus (L.)) to enhancement structures were investigated in artificial stream flumes. For both species a crucial habitat factor was the availability of flow refuges, especially in winter. In another experiment, age-1 trout dominated over age-0 trout when competing for velocity and overhead cover they both found suitable, emphasizing the role of intraspecific interactions in habitat selection by trout. These results suggest that the provision of a broad diversity of microhabitats should be a major goal in rehabilitation programs for fishery purposes. A new method, combining GIS-assisted (Geographical Information System) approach with geostatistical tools, facilitated the detection of fish distribution patterns in a spatially heterogenous stream habitat. The method will likely prove valuable when determining appropriate sampling scale(s) for future studies of fish habitat selection in relation to benthic prey. Unlike Arctic bullhead (Cottus poecilopus, Heckel), trout did not show any aggregation with their benthic prey according to spatially-referenced data on the distribution of lotic fishes and benthic macroinvertebrates within a stream reach.

The genes of the Major Histocompatibility Complex (MHC) represent the most diverse genomic region in vertebrates, and has become a paradigm both for adaptively important genetic variation and how balancing selection can act to retain diversity in the face of gene flow. Within this thesis I examined how the natural mating system of a population of sea trout (Salmo trutta) located in a stream in N E Scotland, affected levels of genetic diversity at both neutral microsatellite loci and at the MHC. High levels of multiple mating were observed for both males and females whereby females mated with as many as nine males during one spawning event and often spawned at multiple nests and males mated with as many as nine females. Repeat spawning events including the same mate pairs was common, perhaps indicating mate choice. Indeed majority males (those which sired the highest number of offspring within a nest) sired more MHC divergent offspring than expected under random mating i.e. individual offspring's maternally and paternally inherited MHC sequences contained a higher number of polymorphic sites than expected under random mating. This may indicate a mating strategy whereby disassortative MHC mate choice increases offspring diversity. Although, MHC played a significant role in mate selection¸ no selective effect of MHC diversity or genotype was found to influence offspring survival in c.8 month old parr. However, any affect may be masked by the strong family group structure within the offspring population with clustering of highly related individuals. Selective mating resulting in high individual diversity and high diversity across the offspring cohort may act as a bet hedging mechanism maximising the chances that at least some offspring will be genetically equipped to deal with selective pressures in the environment. The findings of this thesis highlight the complexity of individual mating systems and the implications that mating practices such as multiple mating and mate choice can have on offspring genetic diversity.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2005. / Thesis documentation sheet inserted. Appendix includes six papers and manuscripts co-authored with others. Also issued electronically via World Wide Web in PDF format; online version lacks appendix of papers.

<p>Populationer av öring består av både migrerande och stationära individer, och det tycks vara både genetiska och miljömässiga faktorer som påverkar en individs beslut att vandra eller ej. Syftet med denna studie var att testa vilken effekt tillgång på föda har på tillväxt och smoltifieringsprocess hos öring (Salmo trutta). Min hypotes var att öring med hög tillförsel av mat växer bättre och smoltifieras därmed inte till samma grad som öring med låg tillförsel av mat. Som en konsekvens av skillnader i mattillgång förväntades att ATPas-aktiviteten, vilken indikerar smoltstatus, var lägre vid god tillförsel av mat än vid låg tillförsel. Experimentet utfördes från november 2003 till april 2004 vid fiskeodlingen i Brattfors, Värmland, där 2+ Klarälvsöringar utsattes för tre olika födonivåer, med fyra replikat av varje födonivå. Var 4-5 vecka fångades fisken för att vägas och mätas och slutligen togs biopsi på öringens gälar för en analys av Na+,K+ -ATPas aktivitet. I slutet av experimentet klassificerades fiskarna som parr eller smolt.</p><p>Parr hade en signifikant lägre Na+, K+ -ATPas aktivitet än smolt i de tre olika födonivåerna. Na+, K+ -ATPas aktiviteten visade dock ingen signifikant skillnad mellan födonivåerna. Parr hade ökat sin vikt och längd mest i samtliga födonivåer och störst skillnad var det i den lägsta födonivån, parr hade ökat i genomsnitt 17 g och 3,5 mm mer än smolt. Av de två högsta födonivåerna var andelen klassificerade som smolt 37 % och vid den lägsta födonivån var andelen smolt 76 %.</p> / <p>Populations of brown trout consist of both migratory and resident individuals, and it is likely that both genetic and environmental factors influence the decision to migrate. The purpose of this study was to test the effect of food availability on growth and the smolting process in brown trout (Salmo trutta). My hypothesis was that brown trout subjected to a high food supply grows better and smoltifies to a lesser degree than brown trout subjected to a low food supply. As a consequence of differences in food supply I expected that ATPase-activity, which indicates smoltification status, would be lower with a high food supply than with a low supply. The experiment was run from November 2003 until April 2004 in a fish hatchery in Brattfors, Värmland, where 2+ brown trout from the river Klarälven were exposed to three food levels, each replicated four times. Every 4-5 weeks the fish were weighed and measured and a biopsy was taken from the gills for analysis of Na+, K+ -ATPase activity at the end of the experiment. At the end of the experiment the fish were classified as parr or smolt.</p><p>Parr had a significantly lower Na+, K+ -ATPase activity than smolt for the three different food treatments. Na+, K+ -ATPase activity did not differ significantly between food levels. Parr grew faster (both weight and length) than smolt at all food levels, and the largest difference between parr and smolt was observed at the lowest food level, where parr increased on average 17 g and 3,5 mm more than smolt. At the two highest food levels the proportion classified as smolt was 37 % and at the lowest foodlevel the proportion of smolt was 76 %.</p>

Brown trout (Salmo trutta), one of the world’s most successful introduced species, negatively impacts native aquatic communities through predation, competition, and ecosystemlevel effects. Thus, there is a need to understand factors controlling the distribution of exotic brown trout in river systems, in order to prioritize and develop conservation and management strategies. Within the context of invasion success, I investigated how the physical template of the Logan River influences the distribution of brown trout along a longitudinal gradient, and the potential for brown trout predation on the native mottled sculpin (Cottus bairdi). The Logan River, Utah USA, is a high-elevation, mountain river exhibiting a wide range of physical habitat characteristics along the altitudinal (or elevational) gradient. In chapter 1, I evaluated whether longitudinal trends in geomorphology contribute to higher potential mortality of brown trout fry at high elevations due to flood-caused streambed scour. High-elevation spawning gravels did not exhibit higher scour compared to low elevations, because brown trout locally chose low-scour areas for spawning. In chapter 2, I investigated the importance of gravel availability, versus other habitat factors, in controlling the spatial distribution of brown trout redd densities. Using a Bayesian hierarchical modeling approach, I demonstrated that anchor ice, distance from high-quality backwater habitat, and to a lesser-extent gravel availability, best explained redd densities. Finally, in chapter 3, I evaluated the potential predatory effects of exotic brown trout on native mottled sculpin (Cottus bairdi). High rates of sculpin consumption contrasted to previously documented low rates of predation by native Bonneville cutthroat (Oncorhynchus clarkii) and depended on abiotic factors controlling the distribution of both species. Collectively, my research suggests that both abiotic factors and source-population dynamics structure brown trout distributions on the Logan River, and ultimately the potential impacts of this invasive fish. Specifically, the distribution of anchor ice and distance from dam backwaters are important drivers of the brown trout distribution, which may extend to other systems. These drivers, including how they may be influenced by future climate change and habitat alteration, should be considered in management efforts to control brown trout expansion and to limit the predatory impacts of brown trout.

The introduction of exotic species is one of the greatest threats to freshwater biodiversity. Brown trout are native to Eurasia, but have been introduced to much of the rest of the world, including the United States. In other parts of their introduced range, brown trout have caused substantial negative effects to native species‟ abundances and distributions, and have altered the structure of some aquatic communities. In the United States, studies of some streams and watersheds have shown that brown trout can negatively affect native species, but I found no study that considers the effect of brown trout across a large portion of their introduced range. For this study, I examined if (1) the abundance and distribution of two ecologically different native fish taxa (sculpins and speckled dace) and (2) the structure of entire stream vertebrate assemblages were negatively associated with the presence and abundance of brown trout. I based my analyses on existing, standardized survey data collected across streams of the western United States. I found no relationship between brown trout and the abundance, presence-absence, or probability of detection of sculpins or speckled dace. I also found that brown trout were not associated with the structure of native stream vertebrate assemblages. My results imply that native stream vertebrates in western US streams are able to coexist with brown trout across the western United States, despite the negative effects brown trout can have on some taxa in individual watersheds or rivers.