Aquaculture Impacts

This guidebook is written to help local governments and the communities whom they govern, address the negative environmental impacts associated with aquaculture. Fish kills, red tide, eutrophication, and other forms of aquatic pollution are among the negative impacts of aquaculture which should be managed, avoided, and mitigated.

Here we critically review the scale and extent of adaptive genetic variation in Atlantic salmon (Salmo salar L.), an important model system in evolutionary and conservation biology that provides fundamental insights into population persistence, adaptive response and the effects of anthropogenic change. We consider the process of adaptation as the end product of natural selection, one that can best be viewed as the degree of matching between phenotype and environment. We recognise three potential sources of adaptive variation: heritable variation in phenotypic traits related to fitness, variation at the molecular level in genes influenced by selection, and variation in the way genes interact with the environment to produce phenotypes of varying plasticity. Of all phenotypic traits examined, variation in body size (or in correlated characters such as growth rates, age of seaward migration or age at sexual maturity) generally shows the highest heritability, as well as a strong effect on fitness. Thus, body size in Atlantic salmon tends to be positively correlated with freshwater and marine survival, as well as with fecundity, egg size, reproductive success, and offspring survival. By contrast, the fitness implications of variation in behavioural traits such as aggression, sheltering behaviour, or timing of migration are largely unknown. The adaptive significance of molecular variation in salmonids is also scant and largely circumstantial, despite extensive molecular screening on these species. Adaptive variation can result in local adaptations (LA) when, among other necessary conditions, populations live in patchy environments, exchange few or no migrants, and are subjected to differential selective pressures. Evidence for LA in Atlantic salmon is indirect and comes mostly from ecological correlates in fitness-related traits, the failure of many translocations, the poor performance of domesticated stocks, results of a few common-garden experiments (where different populations were raised in a common environment in an attempt to dissociate heritable from environmentally induced phenotypic variation), and the pattern of inherited resistance to some parasites and diseases. Genotype x environment interactions occur for many fitness traits, suggesting that LA might be important. However, the scale and extent of adaptive variation remains poorly understood and probably varies, depending onhabitat heterogeneity, environmental stability and the relative roles of selection and drift. As maladaptation often results from phenotype-environment mismatch, weargue that acting as if populations are not locally adapted carries a much greater risk of mismanagement than acting under the assumption for local adaptations when there are none. As such, an evolutionary approach to salmon conservation is required, aimed at maintaining the conditions necessary for natural selection to operate most efficiently and unhindered. This may require minimising alterations to native genotypes and habitats to which populations have likely become adapted, but also allowing for population size to reach or extend beyond carrying capacity to encourage competition and other sources of natural mortality.Key words: adaptive variation, local adaptation, heritabilities, phenotypic plasticity, genotype-by-environment interaction, fitness, conservation, Atlantic salmon,salmonids.

Exotic fishes are a principal threat to global freshwater biodiversity. Rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta are the world's two most widespread exotic fishes, dominate the fish communities of most cold-temperate waters in the southern hemisphere and are implicated in the decline and extirpation of native fish species. Here we provide the first direct comparison of the impacts of rainbow and brown trout on populations of a native fish by quantifying three components of exotic species impact-range, abundance, and effect. We surveyed 54 small streams on the island of Chiloé in Chilean Patagonia and found rainbow trout has colonized significantly more streams and has a wider geographic range and than brown trout. The two species had similar post-yearling abundances in allopatry and sympatry, and their abundances depended similarly on reach-level variation in physical habitat. The species appeared to have dramatically different effects on the native drift-feeding Aplochiton sp., which was virtually absent from streams invaded by brown trout but shared a broad sympatric range with rainbow trout. Within this range the species' post-yearling abundances varied independently before and after controlling for variation in physical habitat. In the north of the island Aplochiton inhabited streams uninvaded by exotic trout. Our results provide a context for investigating the processes responsible for apparent differences in rainbow and brown trout invasion biology and can help inform conservation strategies for native fishes on Chiloé and elsewhere. Keywords: non-native species; invasion; fishes; freshwater; Chile; Oncorhynchus mykiss; Salmo trutta; Aplochiton zebra.

The well being of fish populations is directly affected by a number of interconnected environmental parameters such as dissolved oxygen, temperature, eutrophication of the water column that affects the qualitative and quantitative composition of phytoplankton and zooplankton (the food web). The main impacts to the environment are from nutrients supplied as fish feed that are not utilised by the fish for maintenance and growth and so are released to the environment which has to assimilate them or they will build up.
he MERAMOD model was used to predict benthic impact from a seabass cage farm for existing and increased production. To assess the GHG emissions associated with aquaculture systems, Life Cycle Assessment (LCA) is the selected analytical tool to evaluate the potential impacts from the compiling of inputs and outputs of the whole life cycle stages of product covering from raw material production, manufacturing, distribution, consumption and final disposal.

Exotic salmonids were deliberately introduced to the Southern Hemisphere during the last part of the 20th century, initially to boost sport fishing and later to develop an aquaculture industry. Early introductions were justified by governments on purely utilitarian arguments as it was felt that translocated salmonids would capitalize on otherwise 'underutilized' aquatic niches. A century later, exotic salmonids are established in nearly all places where they were originally introduced and beyond, and constitute one of the main threats to endemic fish fauna, amongst which galaxiid fishes have perhaps been impacted the most. We screened the literature to document the changing perspectives on exotic salmonids in the Southern Hemisphere, and employed SWOT analysis to assess the conservation prognosis of native galaxiids in the face of salmonid invasions. Our analysis indicates that opinions differ - and contradictions abound - as to how to prevent further salmonid encroachment. This is largely due to lack of information on the impact of exotics but, more importantly, because the problem is often approached merely from a socio-economic perspective. Sport fishermen, for example, actively support the stocking of rivers to enhance sport fisheries and argue in favour of considering established salmonids as part of the native biodiversity, but also want to see an end to salmonids escaping from fish farms. The salmon industry tends to stress the social and economic benefits brought about by aquaculture, but continues to demand the right to expand and self-regulate. Governments, on the other hand, have not always had consistent or clear policies on exotic salmonids, and have tended to favour some stakeholders and penalized others. Our analysis emphasizes the need to consider biologically meaningful time scales when assessing impacts on biodiversity, and stresses the need to anticipate shifts in public opinion and stakeholder support in conservation. Key words: aquaculture, conservation, Convention on Biological Diversity, galaxiids, impacts, invasive species, salmonids, sport fishing, stocking, SWOT.

In Chilean Patagonia relatively pristine aquatic environments are being modified by the introduction of exotic salmonids, initially through their deliberate release for sport fishing since the early 20th century, and more recently via the accidental escape from fish farms. There is therefore a need to reliably distinguish between naturally reproducing and fugitive salmonids associated with the Chilean salmonid farming industry, the second largest in the world. We tested the ability of stable isotope analysis (SIA) and analysis of scale growth profiles to discriminate between farmed and free-living salmonids sampled around the Island of Chiloé. Juvenile Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) from aquaculture facilities were significantly more enriched in ä15N and lipid-corrected ä13C than river-caught individuals. Scale growth slopes during the first year in freshwater were significantly higher in farmed than in wild-caught rainbow trout, indicating faster somatic growth under hatchery conditions. Stable isotopes analysis classified 94% of juvenile Atlantic salmon and rainbow trout to their correct farm or free-living groups. Our results, therefore, can help to elucidate the origin and spread of exotic invasive salmonids in Chile, and address one of the biggest threats to native freshwater fishes in Patagonia and other temperate zones of the Southern Hemisphere. Keywords: stable isotope analysis, invasive species, salmonids, aquaculture

Aquaculture is a major source of invasive aquatic species, despite the fact that cultured organisms often have low genetic diversity and tend to be maladapted to survive in the wild. Yet, to what extent aquaculture escapees become established by means of high propagule pressure and multiple origins is not clear. We analysed the genetic diversity of 15 established populations and four farmed stocks of non-native rainbow trout in Chile, a species first introduced for recreational fishing around 1900, but which has in recent decades escaped in large numbers from fish farms and become widespread. Aquaculture propagule pressure was a good predictor of the incidence of farm escapees, which represented 16% of all free-ranging rainbow trout and were present in 80% of the study rivers. Hybrids between farm escapes and established trout were present in all rivers at frequencies ranging between 7 and 69%, and population admixture was positively correlated with genetic diversity. We suggest that non-native salmonids introduced into the Southern Hemisphere could benefit from admixture because local adaptations may not have yet developed, and there may be initially little fitness loss resulting from outbreeding depression.

This paper is written to present the current situation of the Philippine aquaculture industry, focusing on the impacts of feed wastage and inappropriate feeding to the environment, as well as its effects to the operators economically in particular, and to the
whole feed miller industry in general. This paper will also provide recommendations, which are the result of the series of consultation meetings and workshop with the different stakeholders which primary aims on addressing these issues and concerns

The project TCP/RAS/3203 "Reducing the dependence on the utilization of trash fish/ low-value fish as an aquaculture feed for marine finfish in the Asian region" involved assessing and comparing the environmental impacts between fish fed pellet or trash fish/low-value fish in trial cage farms across four countries.

The exploitation of Atlantic salmon, Salmo salar, in food and recreational fisheries has a long history in the rivers and coastal waters of the species range. Fortunately, prior to the last few centuries, when river stocks were largely healthy, exploitation was not a serious management concern. However, increasingly with many populations in decline, fisheries exploitation has come to be a major concern for managers of salmon fisheries, both in rivers and in the sea. Until recently, most of this concern focused on the direct threat posed by the reduction in numbers. However, recent research suggests that the impacts are likely to be more complex and insidious through effects on the genetic structure of the affected populations.

The tendency of salmon, Salmo salar, to return from the sea to the river of hatching and form 'local populations' has apparently been known for a long time (Calderwood 1908). Writing in 1653, Izaak Walton described how juveniles marked with ribbons tied to their tails were later recaptured as adults in their home river. Since no two rivers are completely identical, salmon returning to spawn in different rivers will, with time, give rise to different strains or 'races'(Huntsman 1941). Those races, so the story goes, are presumably the ones best 'adapted' to the local river conditions. But, is this really the case? And if so, what are local salmon adapted to? And perhaps more importantly, why should we care about it? In this chapter we will examine the evidence for (and against) the existence of local adaptations in Atlantic salmon, in particular those studies that have become available during the last decade, since Taylor (1991) reviewed this subject. We will also consider the implications of adaptive variation for the management and conservation of Atlantic salmon populations. But first we must define what we mean by 'adaptation'.

Electrophoretic studies of proteins remain a primary source of insight into genetic diversity in many species including the Atlantic salmon Salmo salar, one of the most culturally and economically important fish species of the North Atlantic region. Since 1966, >350 scientific papers on protein variation have been published encompassing 25 000þ salmon from over 400 locations in >200 river systems across the species' distribution. Variation has been detected at 30% of the 110 protein loci screened, though most studies examine <40. The method has been applied largely to the investigation of population structure and differentiation, but work has also led to the systematic revision of the genus Salmo and remains the primary source of insight into hybridization in the wild with brown trout Salmo trutta. Spatial patterns of differentiation show temporal stability, both within and among river systems, and strongly support structuring of the species into river and tributary specific populations and the designation of European and North American populations as distinct sub-species. They also show widespread regional differentiation within both continents, beyond the marked subcontinental differences between Baltic Sea and Atlantic Ocean populations in Europe. Most of the differentiation probably reflects gene flow and founder events associated with colonization following the retreat of the glaciers from much of the species' modern range. However, variation at MEP-2* shows strong correlations with environmental temperature, both within and among rivers, and associations with phenotypic performance. This suggests selection is acting on the locus and provides †Author to whom correspondence should be addressed. Tel.: þ44 (0) 796 472060; fax: þ44 (0) 1796 473523; # 2005 Crown copyright compelling evidence for the local adaptation of populations. Protein studies have led to more population centred management of the species and have been exploited in the discrimination of regional stocks in mixed stock analysis in high seas fisheries, particularly in the Baltic Sea, and as markers for the assessment of stocking success. They have also advanced insight into how the genetic character of populations can be changed in cultivation and the potential impact of salmon aquaculture and stocking on wild populations. The method has been largely superseded by DNA based analyses, but the results remain highly relevant to Atlantic salmon management and conservation and are an irreplaceable data set for studying genetic stability of populations over time. # 2005 Crown copyright

Aquaculture is a major source of invasive aquatic species, despite the fact that cultured organisms often have low genetic diversity and tend to be maladapted to survive in the wild. Yet, to what extent aquaculture escapees become established by means of high propagule pressure and multiple origins is not clear. We analysed the genetic diversity of 15 established populations and 4 farmed stocks of non-native rainbow trout in Chile, a species first introduced for recreational fishing around 1900, but which has in recent decades escaped in large numbers from fish farms and become widespread. Aquaculture propagule pressure was a good predictor of the incidence of farm escapees, which represented 16% of all free-ranging rainbow trout and were present in 80% of the study rivers. Hybrids between farm escapes and established trout were present in all rivers at frequencies ranging between 7 and 69%, and population admixture was positively correlated with genetic diversity. We suggest that non-native salmonids introduced into the Southern Hemisphere could benefit from admixture because local adaptations may not have yet developed and there may be initially little fitness loss resulting from outbreeding depression.

Aplochiton zebra (peladilla, zebra trout) is a galaxiid fish endemic to Patagonia and the Falkland Islands, where populations are threatened by salmonid introductions. Here we describe the isolation and characterization of 13 polymorphic microsatellite DNA markers that can be used for assessing the genetic variation and conservation status of this species. The variability of these markers was assessed in six rivers in Chilean Patagonia. The number of alleles ranged from 5 to 80 per locus and observed heterozygosities varied between 0.168 and 0.910. A protocol for multiplexing these markers is described.

This paper examines two areas to be considered in developing conservation plans for Atlantic salmon (Salmo salar): goal statements and the general framework for the implementation of a conservation plan. From a biological perspective, the appropriate conservation unit for Atlantic salmon is the Evolutionary Significant Unit (ESU). As conservation decisions will rarely be based solely on biological information, the Operational Conservation Unit (OCU) is defined as resulting from the interplay between biological requirements and socio-economic issues. A multi-scale habitat inventory of Atlantic salmon rivers to know what their status is relative to historical conditions is the first step in a functional conservation plan. The viability of salmon populations may be assessed according to 6 variables: abundance, resilience, age and size structure, sex ratio, spatial and geographical distribution. A genetically viable population possesses the species' evolutionary legacy and the genetic variation on which future evolutionary potential depends. Four factors important to monitoring changes in a population's genetic health are genetic diversity, effective population size, genetic bottlenecks and founder effects and gene flow. Implementation of a conservation plan must be proactive to maintain the quality of the OCUs. Commercial and recreational fisheries need to be limited and several case studies are reviewed. The importance of avoiding the introduction of exotics and minimizing the impact of sampling methodology, as well as the pitfalls of planting eggs, fry, or parr, are addressed. Finally, the importance of fostering public awareness of the value of conservation is essential to apply the political pressure necessary to preserve natural resources.

Electrophoretic studies of proteins remain a primary source of insight into genetic diversity in many species including the Atlantic salmon Salmo salar, one of the most culturally and economically important fish species of the North Atlantic region. Since 1966, >350 scientific papers on protein variation have been published encompassing 25 000+ salmon from over 400 locations in >200 river systems across the species' distribution. Variation has been detected at 30% of the 110 protein loci screened, though most studies examine <40. The method has been applied largely to the investigation of population structure and differentiation, but work has also led to the systematic revision of the genus Salmo and remains the primary source of insight into hybridization in the wild with brown trout Salmo trutta. Spatial patterns of differentiation show temporal stability, both within and among river systems, and strongly support structuring of the species into river and tributary specific populations and the designation of European and North American populations as distinct sub-species. They also show widespread regional differentiation within both continents, beyond the marked subcontinental differences between Baltic Sea and Atlantic Ocean populations in Europe. Most of the differentiation probably reflects gene flow and founder events associated with colonization following the retreat of the glaciers from much of the species' modern range. However, variation at MEP-2* shows strong correlations with environmental temperature, both within and among rivers, and associations with phenotypic performance. This suggests selection is acting on the locus and provides compelling evidence for the local adaptation of populations. Protein studies have led to more population centred management of the species and have been exploited in the discrimination of regional stocks in mixed stock analysis in high seas fisheries, particularly in the Baltic Sea, and as markers for the assessment of stocking success. They have also advanced insight into how the genetic character of populations can be changed in cultivation and the potential impact of salmon aquaculture and stocking on wild populations. The method has been largely superseded by DNA based analyses, but the results remain highly relevant to Atlantic salmon management and conservation and are an irreplaceable data set for studying genetic stability of populations over time

Natural (parasite-driven) and sexual selection are thought to maintain high polymorphism in the genes of the major histocompatibility complex (MHC), but support for a link between mate choice, MHC variation, and increased parasite resistance is circumstantial. We compared MHC diversity and Anisakis loads amongst anadromous Atlantic salmon returning to four rivers to spawn which had originated from natural spawning (parents allowed to mate freely) or from artificial crosses (parents deprived from the potential benefits of mate choice). We found that the offspring of artificially-bred salmon had higher parasite loads and were almost 4 times more likely to be infected than free-mating salmon, despite having similar levels of MHC diversity. Moreover, the offspring of wild salmon were more MHC-dissimilar than the offspring of artificially-crossed salmon, and uninfected fish were more dissimilar for MHC than infected fish. Thus, our results suggest a link between disassortative mating and offspring benefits, and indicate that MHC-mediated mate choice and natural (parasite-driven) selection act in combination to maintain MHC diversity, and hence fitness. Therefore, artificial breeding programmes that negate the potential genetic benefits of mate choice may result in inherently inferior offspring, regardless of population size, rearing conditions, or genetic diversity. Keywords: MHC, mate choice, good genes, compatible genes, parasite resistance, salmon

From 1983 to 1986 the Rivers Asón and Nansa (northern Spain) were stocked with over 100 000 eyed ova year-1 from a Scottish hatchery in an effort to increase angling catches of Atlantic salmon. An inherent genetic marker was used to estimate the contributions of stocked and wild fish from these year-classes to the 1988 rod-and-line fishery. Stocking with foreign ova yielded 0.9 fish per 10 000 ova in the R. Asón and zero fish in the R. Nansa. Natural egg deposition yielded 4.1and 4.9 fish per 10 000 ova, respectively. Reasons for the difference in performance between stocked and wild fish are examined. Key words: stocking success; genetic marker; Salmo salar; Spain.

We used an invaded stream fish community in southern Chile to experimentally test whether the diversity of exotic species affects their competitive impact on a native species. In artificial enclosures an established invasive, rainbow trout, Oncorhynchus mykiss, and a potential invader, Atlantic salmon, Salmo salar, reduced the growth rate of native peladilla, Aplochiton zebra, by the same amount. In enclosures with both exotic salmonids, the growth rates of all three species were the same as in single exotic treatments. While neither species identity nor diversity appeared to affect competitive interactions in this experiment, the impact of salmonid diversity may vary with the type of interspecific interaction and/or the species identity of the exotics. Our experiment links two prominent concepts in invasion biology by testing whether the result of invasional meltdown, an increase in the diversity of exotic species, affects their impact through interspecific competition, the mechanism invoked by the biotic resistance hypothesis. Keywords  Exotic species diversity - Interspecific competition - Salmonids - Galaxiids - Stream enclosure experiment - Aquaculture

Exotic salmonids were deliberately introduced to the southern hemisphere during the last part of the 20th century, initially to boost sport fishing and later to develop an aquaculture industry. Early introductions were justified by governments on purely utilitarian arguments as it was felt that translocated salmonids would capitalize on otherwise 'underutilized' aquatic niches. A century later, exotic salmonids are established in nearly all places where they were originally introduced and beyond, and constitute one of the main threats to endemic fish fauna, amongst which galaxiid fishes have perhaps been impacted the most. We screened the literature to document the changing perspectives on exotic salmonids in the southern hemisphere, and employed SWOT analysis to assess the conservation prognosis of native galaxiids in the face of salmonid invasions. Our analysis indicates that opinions differ and contradictions abound as to how to prevent further salmonid encroachment. This is largely due to lack of information on the impact of exotics but, more importantly, because the problem is often approached merely from a socio-economic perspective. Sport fishermen, for example, actively support the stocking of rivers to enhance sport fisheries and argue in favour of considering established salmonids as part of the native biodiversity, but also want to see an end to salmonids escaping from fish farms. The salmon industry tends to stress the social and economic benefits brought about by aquaculture, but continues to demand the right to expand and self-regulate. Governments, on the other hand, have not always had consistent or clear policies on exotic salmonids, and have tended to favour some stakeholders and penalized others. Our analysis emphasizes the need to consider biologically meaningful time scales when assessing impacts on biodiversity, and stresses the need to anticipate shifts in public opinion and stakeholder support in conservation.

Over the last 50 years, Spanish Atlantic salmon (Salmo salar) populations have been in decline.  In order to bolster these populations, rivers were stocked with fish of northern European origin during the period 1974-1996, probably also introducing the furunculosis-inducing pathogen, Aeromonas salmonicida.  Here we assess the relative importance of processes influencing mitochondrial (mt)DNA variability in these populations from 1948-2002.  Genetic material collected over this period from four rivers in northern Spain (Cantabria) was used to detect variability at the mtDNA ND1 gene. Before stocking, a single haplotype was found at high frequency (0.980).  Following stocking, haplotype diversity (h) increased in all rivers (mean h before stocking was 0.0411, and 0.2453 afterwards). These increases were due principally to the dramatic increase in frequency of a previously very low frequency haplotype, reported at higher frequencies in northern European populations proximate to those used to stock Cantabrian rivers.  Genetic structuring increased after stocking: among-river differentiation was low before stocking (1950s/1960s ÖST = –0.00296-0.00284), increasing considerably at the height of stocking (1980s ÖST = 0.18932) and decreasing post-stocking (1990s/2002 ÖST = 0.04934-0.03852).  Gene flow from stocked fish therefore seems to have had a substantial role in increasing mtDNA variability.  Additionally, we found significant differentiation between individuals that had probably died from infectious disease and apparently healthy, angled fish, suggesting a possible role for pathogen-driven selection of mtDNA variation.  Our results suggest that stocking with non-native fish may increase genetic diversity in the short term, but may not reverse population declines.Keywords: Salmo salar, stocking, mitochondrial DNA, conservation genetics, foreign gene introgression

Exotic salmonids were deliberately introduced to the southern hemisphere during the last part of the 20th century, initially to boost sport fishing and later to develop an aquaculture industry. Early introductions were justified by governments on purely utilitarian arguments as it was felt that translocated salmonids would capitalize on otherwise 'underutilized' aquatic niches. A century later, exotic salmonids are established in nearly all places where they were originally introduced and beyond, and constitute one of the main threats to endemic fish fauna, amongst which galaxiid fishes have perhaps been impacted the most. We screened the literature to document the changing perspectives on exotic salmonids in the southern hemisphere, and employed SWOT analysis to assess the conservation prognosis of native galaxiids in the face of salmonid invasions. Our analysis indicates that opinions differ and contradictions abound as to how to prevent further salmonid encroachment. This is largely due to lack of information on the impact of exotics but, more importantly, because the problem is often approached merely from a socio-economic perspective. Sport fishermen, for example, actively support the stocking of rivers to enhance sport fisheries and argue in favour of considering established salmonids as part of the native biodiversity, but also want to see an end to salmonids escaping from fish farms. The salmon industry tends to stress the social and economic benefits brought about by aquaculture, but continues to demand the right to expand and self-regulate. Governments, on the other hand, have not always had consistent or clear policies on exotic salmonids, and have tended to favour some stakeholders and penalized others. Our analysis emphasizes the need to consider biologically meaningful time scales when assessing impacts on biodiversity, and stresses the need to anticipate shifts in public opinion and stakeholder support in conservation.

A previous analysis of proportions of stocked and wild Atlantic salmon among angled fish in the Rivers Ason and Nansa in northern Spain based on the analysis of MEP-2* genotypes is extended. The results reinforce the initial conclusion that returns of stocked Scottish salmon are significantly lower than returns for wild fish. Key words: malic enzyme; MEP-2*; Salmo salar; introductions.

Here we critically review the scale and extent of adaptive genetic variation in Atlantic salmon (Salmo salar L.), an important model system in evolutionary and conservation biology that provides fundamental insights into population persistence, adaptive response and the effects of anthropogenic change. We consider the process of adaptation as the end product of natural selection, one that can best be viewed as the degree of matching between phenotype and environment. We recognise three potential sources of adaptive variation: heritable variation in phenotypic traits related to fitness, variation at the molecular level in genes influenced by selection, and variation in the way genes interact with the environment to produce phenotypes of varying plasticity. Of all phenotypic traits examined, variation in body size (or in correlated characters such as growth rates, age of seaward migration or age at sexual maturity) generally shows the highest heritability, as well as a strong effect o...

Rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta are the world's two most widespread exotic fishes, dominate the fish communities of most coldtemperate waters in the southern hemisphere and are implicated in the decline and extirpation of native fish species. Here, we provide the first direct comparison of the impacts of rainbow and brown trout on populations of a native fish by quantifying three components of exotic species impact: range, abundance and effect. We surveyed 54 small streams on the island of Chilo´e in Chilean Patagonia and found that the rainbow trout has colonized significantly more streams and has a wider geographic range than brown trout. The two species had similar postyearling abundances in allopatry and sympatry, and their abundances depended similarly on reach-level variation in the physical habitat. The species appeared to have dramatically different effects on native drift-feeding Aplochiton spp., which were virtually absent from streams invaded by brown trout but shared a broad sympatric range with rainbow trout. Within this range, the species' post-yearling abundances varied independently before and after controlling for variation in the physical habitat. In the north of the island, Aplochiton spp. inhabited streams uninvaded by exotic trouts. Our results provide a context for investigating the mechanisms responsible for apparent differences in rainbow and brown trout invasion biology and can help inform conservation strategies for native fishes in Chilo´e and elsewhere.

This paper examines two areas to be considered in developing conservation plans for Atlantic salmon (Salmo salar): goal statements and the general framework for the implementation of a conservation plan. From a biological perspective, the appropriate conservation unit for Atlantic salmon is the Evolutionary Significant Unit (ESU). As conservation decisions will rarely be based solely on biological information, the Operational Conservation Unit (OCU) is defined as resulting from the interplay between biological requirements and socio-economic issues. A multi-scale habitat inventory of Atlantic salmon rivers to know what their status is relative to historical conditions is the first step in a functional conservation plan. The viability of salmon populations may be assessed according to 6 variables: abundance, resilience, age and size structure, sex ratio, spatial and geographical distribution. A genetically viable population possesses the species' evolutionary legacy and the genetic variation on which future evolutionary potential depends. Four factors important to monitoring changes in a population's genetic health are genetic diversity, effective population size, genetic bottlenecks and founder effects and gene flow. Implementation of a conservation plan must be proactive to maintain the quality of the OCUs. Commercial and recreational fisheries need to be limited and several case studies are reviewed. The importance of avoiding the introduction of exotics and minimizing the impact of sampling methodology, as well as the pitfalls of planting eggs, fry, or parr, are addressed. Finally, the importance of fostering public awareness of the value of conservation is essential to apply the political pressure necessary to preserve natural resources.