Sea Trout Populations Research Articles

Negative associations between parasite avoidance, resistance and tolerance predict host health in salmonid fish populations.

Genetic variation in defence against parasite infections is fundamental for host-parasite evolution. The overall level of defence of a host individual or population includes mechanisms that reduce parasite exposure (avoidance), establishment (resistance) or pathogenicity (tolerance). However, how these traits operate and evolve in concert is not well understood. Here, we investigated genetic variation in and associations between avoidance, resistance and tolerance in a natural host-parasite system. Replicated populations of Atlantic salmon (Salmo salar) and sea trout (an anadromous form of brown trout, Salmo trutta) were raised under common garden conditions and infected with the eye fluke Diplostomum pseudospathaceum. We demonstrate significant genetic variation in the defence traits across host populations and negative associations between the traits, with the most resistant populations showing the weakest avoidance and the lowest infection tolerance. These results are suggestive of trade-offs between different components of defence and possibly underlie the genetic variation in defence traits observed in the wild. Because the three defence mechanisms affect host-parasite evolution in profoundly different ways, we emphasize the importance of studying these traits in concert.

Ecology and movement of juvenile salmonids in beaver‐influenced and beaver‐free tributaries in the Trøndelag province of Norway

AbstractThere is concern that expanding beaver (Castor fiber) populations will negatively impact the important economic, recreational and ecological resources of Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) populations in Europe. We studied how beaver dams influenced habitat, food resources, growth and movement of juvenile Atlantic salmon and trout on three paired beaver‐dammed and beaver‐free (control) tributaries of important salmon rivers in central Norway. Lotic reaches of beaver‐dammed and control sites were similar in habitat and benthic prey abundance, and ponds were small (<3,000 m2). Though few juvenile salmonids were detected in ponds, trout and salmon were present in habitats below and above ponds (comprising 9%–31% and 0%–57% of the fish collected respectively). Trout dominated control sites (79%–99%), but the greatest proportion of Atlantic salmon were upstream of beaver ponds (0%–57%). Growth rates were highly variable, with no differences in growth between lotic reaches of beaver‐dammed and control sites. The condition and densities of juvenile salmon and trout were similar in lotic reaches of beaver‐dammed and control sites, though one beaver‐dammed site with fine sediment had very few juvenile salmonids. Beaver dams did not block the movement of juvenile salmonids or their ability to use upstream habitats. However, the degree of repeated movements and the overall proportion of fish moving varied between beaver‐dammed and control sites. The small scale of habitat alteration and the fact that fish were able to move past dams makes it unlikely that beaver dams negatively impact the juvenile stage of salmon or trout populations.

Genetic Differentiation in Hatchery and Stocked Populations of Sea Trout in the Southern Baltic: Selection Evidence at SNP Loci.

The impacts and interactions between hatchery-bred fish and wild fish populations has been a topic of active investigation in recent decades. In some instances, the benefits of stocking can be overshadowed by negative effects such as genetic introgression with natural populations, loss of genetic diversity, and dilution of local adaptations. Methods that facilitate the identification of stocked fish enable us to estimate not only the effectiveness of stocking but also the level of natural reproduction and the degree of hybridization. The longest Baltic river, the Vistula, also has the second highest discharge. Historically, it hosted numerous populations of the anadromous form of brown trout (sea trout); however, dam construction has since interfered with and reduced spawning migration to a rate that is much lower than before. Reduced spawning has resulted in a population collapse and a negative flow-on effect on commercial catches. In response, Poland (along with many other Baltic countries) initiated an intensive stocking program which continues today and which sees the average annual release of 700,000 smolts. As a consequence, today’s main-river and inshore catches come from stock-enhanced populations. High-throughput single-nucleotide polymorphism (SNP) genotyping was performed on samples of sea trout from southern Baltic populations; results suggest that a significant portion of the sea trout catches in the Vistula mouth region have direct hatchery origin and indicate the presence of Pomeranian specimens. SNP loci identified as outliers indicate a potential selection pressure that may be related with effects of hatchery breeding and mixing with natural populations. The brown trout SNP array applied in this study showed high effectiveness not only for population differentiation, but more importantly, it emerged as a sensitive tool to provide evidence of detection selection.

Mortality of Baltic sea trout (Salmo trutta) after release from gillnets

We explore the mortality rate of disentangled sea trout in whitefish fishery using gillnets with a 35–43 mm bar length. The study was conducted during the main fishing seasons in the Gulf of Bothnia in the northern Baltic Sea. Overall 59.5% of the sea trout were alive at the end of a 2–7 day observation period following release from the gillnets. Altogether, 12.1% of the captured fish were found dead in gillnets and 28.4% died due to injuries during an extended observation period. The average length of the captured sea trout was 435 mm, indicating that the majority were spending their first or second year at sea. The proportion of the survived and not injured (no observed damage) fish was highest in larger fish, >450 mm. The injured and not injured fish died equally frequently. Post capture survival was not connected to the removal time from gillnets or type of observed injuries but to the type of entanglement. Most of the fish were entangled by a mesh around the body, which caused extensive scale loss and open sores on the skin. The smallest fish may have had internal wounds that were not registered in this study. These results can be used in fisheries management to estimate the mortality of multi‐species gillnet fishing to sea trout populations in relation to management actions.

Mark-recapture estimation of mortality and migration rates for sea trout (Salmo trutta) in the northern Baltic sea

Knowledge of current fishing mortality rates is an important prerequisite for formulating management plans for the recovery of threatened stocks. We present a method for estimating migration and fishing mortality rates for anadromous fishes that combines tag return data from commercial and recreational fisheries with expert opinion in a Bayesian framework. By integrating diverse sources of information and allowing for missing data, this approach may be particularly applicable in data-limited situations.Wild populations of anadromous sea trout (Salmo trutta) in the northern Baltic Sea have undergone severe declines, with the loss of many populations. The contribution of fisheries to this decline has not been quantified, but is thought to be significant. We apply the Bayesian mark-recapture model to two reared sea trout stocks from the Finnish Isojoki and Lestijoki Rivers. Over the study period (1987–2012), the total harvest rate was estimated to average 0.82 y–1 for the Isojoki River stock and 0.74 y−1 for the Lestijoki River stock. Recreational gillnet fishing at sea was estimated to be the most important source of fishing mortality for both stocks, particularly during the 1980s and 1990s. Our results indicate a high probability of unsustainable levels of fishing mortality for both stocks, and illustrate the importance of considering the effect of recreational fisheries on fish population dynamics.

Recent genetic changes in enhanced populations of sea trout (Salmo truttam.trutta) in the southern Baltic rivers revealed with SNP analysis

The genetic structure of a fish population is usually thought to be stable over time. In the southern Baltic, Salmo trutta m. trutta (sea trout) populations have been characterized by low degree of genetic differentiation. All studied populations had been heavily stocked with mixed material for many years prior to the sampling period, including releases of Pomeranian sea trout to the Vistula River in Poland, Southern Baltic. However, the strategy of stocking became river based a few years before the sampling began. Juveniles from artificial reproduction are released only to their parental river, which reduces the mixing of the gene pool of fish from different populations. Changes in sea trout populations in the southern Baltic over time were studied using single nucleotide polymorphisms (SNPs). Genetic composition of populations of sea trout in the Vistula and Drwȩca river system were found to increasingly resemble the non-admixed hatchery population from Aquamar (Miastko, Poland), whereas the Pomeranian populations were stable. The implementation of a new stocking strategy for the restoration and protection of Vistula sea trout was noted as possible explanation. With the increase of natural breeding, artificial enhancement of sea trout populations should be reduced.

Effects of Cold Winters on the Genetic Diversity of an Estuarine Fish, the Spotted Seatrout

AbstractSpotted Seatrout Cynoscion nebulosus are recreationally important fish that have been harvested in South Carolina for centuries. The Spotted Seatrout in South Carolina suffered substantial declines in estuarine abundance during the cold winters of 2000, 2009, and 2010, when water temperatures dropped below their tolerance threshold. As these population declines may result in genetic bottlenecks and their repetitive occurrence over a short timescale could reduce the population’s adaptive potential, we estimated the genetic diversity and effective population size (Ne) of the Charleston Harbor Spotted Seatrout population at six time points related to recent cold winters using a suite of 13 microsatellite markers. Grouping individuals by year-class (fish spawned in the same year) was the most appropriate and effective method for measuring interannual fluctuations in observed and expected heterozygosity and allelic richness, superior to partitioning fish by collection year. The genetic diversity of Spo...

Large-scale use of fish traps for monitoring sea trout (Salmo trutta) smolts and sea lice (Lepeophtheirus salmonis) infestations: efficiency and reliability

ABSTRACTLice-infected sea trout populations were monitored using fish traps in the Romsdalsfjord (Norway). The reliability and efficiency of this capture technique, which allows estimation of lice infestation rates without killing the fish, was evaluated through a mark–recapture study. A total of 2447 sea trout smolts were captured, tagged and released over a three-year period. There was a considerable variation in capture rates (range: 0.4–17.7 fish per day) and sea lice numbers (number of lice per fish: 2.8–30.3; number of lice per gram body weight: 0.02–0.69) among localities, sampling times and years. Recapture rates of tagged fish with traps, which were low (2% or 0.11 fish per day), showed that the risk for pseudoreplication was minor, in terms of counting lice on the same fish several times. Most of the tagged sea trout (90%) were recaptured within the first two months after release, and no significant variations in lice numbers were found between tagging and recapture. The lack of differences in lice levels between tagging and recapture during the first week after tagging indicated that the method most likely would not significantly underestimate the lice infestations due to loss of lice during handling. Therefore, our results confirm that the use of fish traps is a suitable method for estimation of lice numbers on wild salmonids.

Effects of salmon lice Lepeophtheirus salmonis on wild sea trout Salmo trutta—a literature review

Salmon farming increases the abundance of salmon lice, which are ectoparasites of salmonids in the sea. Here we review the current knowledge on the effects of salmon lice on wild sea trout. Salmon lice feed on host mucus, skin and muscle, and infestation may induce osmoreg- ulatory dysfunction, physiological stress, anaemia, reduced feeding and growth, increased sus- ceptibility to secondary infections, reduced disease resistance and ultimately mortality of individ- ual sea trout. Wild sea trout in farm-free areas generally show low lice levels. In farm-intensive areas, lice levels on wild sea trout are typically higher, and more variable than in farm-free areas. Lice on wild sea trout are found at elevated levels particularly within 30 km of the nearest farms but can also extend to further ranges. Salmon lice in intensively farmed areas have negatively impacted wild sea trout populations by reducing growth and increasing marine mortality. Quan- tification of these impacts remains a challenge, although population-level effects have been quan- tified in Atlantic salmon by comparing the survival of chemically protected fish with control groups, which are relevant also for sea trout. Mortality attributable to salmon lice can lead to an average of 12�29% fewer salmon spawners. Reduced growth and increased mortality will reduce the benefits of marine migration for sea trout, and may also result in selection against anadromy in areas with high lice levels. Salmon lice-induced effects on sea trout populations may also extend to altered genetic composition and reduced diversity, and possibly to the local loss of sea trout, and establishment of exclusively freshwater resident populations.

Genetic baseline for conservation and management of sea trout in the northern Baltic Sea

The genetic structure of nine wild, seven hatchery-reared, and one presumably mixed, sea trout (Salmo trutta L.) populations sampled from watersheds along the Swedish Baltic Sea coast was analysed using ten microsatellite loci. DNA-information was evaluated as a baseline for mixed stock analysis (MSA) and individual assignment (IA). A clear genetic structure with distinct populations was identified (global F ST = 0.066), with significant regional differentiation. Average gene diversity (H e) was similar among samples of wild and reared trout, whereas levels of heterozygote deficiency differed significantly (wild: H e = 0.70, F IS = 0.075; reared: H e = 0.69, F IS = 0.022). The high F IS found in wild samples indicates presence of within-river sub-structuring. Evaluation with realistic-fishery simulations indicated that the baseline resolution was sufficient for MSA, at least at a regional level. Hierarchical MSA and IA analyses of real catches from two coastal fisheries showed that populations from the northern region contributed about 90 % to the catch. Analysed individually, the two fisheries differed in catch compositions despite a short geographic distance among sites. One fishery mainly caught sea trout from a small wild population whereas the other fishery was dominated by reared sea trout. Stock composition analysis is a valuable tool for refining exploitation rate estimates for individual sea trout populations in mixed coastal fisheries, as well as for investigating migration patterns in the Baltic Sea.

Genetic Variation of <I>Salmo trutta</I> L. Populations from the Catchment Areas of the Rega, Parseta and Wieprza Rivers Evaluated by RAPD and SSR Markers

By using simple sequence repeats (SSR) and random amplification of polymorphic DNA (RAPD) markers, the genetic variability of three Salmo trutta L. populations from three rivers, the Wieprza, the Rega and the Parseta, was determined. The investigated populations showed a high level of genetic variability. Microsatellites showed that observed heterozygosity (Ho) was higher than the expected heterozygosity (He), with most heterozygotes found in the population from the Parseta river and the fewest in the Wieprza population. The F(IS) coefficient in all investigated populations of the sea trout indicate a high excess of heterozygotes. The highest genetic differentiation was observed between the sea trout from the Rega river and those from the Wieprza (0.366). The obtained results based on microsatellite and RAPD analysis showed that the investigated populations formed two groups. The first group consisted of the sea trout populations from the Wieprza and the Parseta rives, while the second group was formed solely by the Rega river population.

Lice pressure from salmon farms on wild sea trout (Salmo trutta) in a Norwegian fjord

Event Abstract Back to Event Lice pressure from salmon farms on wild sea trout (Salmo trutta) in a Norwegian fjord Pablo Arechavala-Lopez1*, Marius Berg2, Ingebrigt Uglem2, Pal Arne Bjorn3 and Bengt Finstad2 1 University of Alicante, Department of Marine Science and Applied Biology, Spain 2 Norwegian Institute for Nature Research, Norway 3 Institute of Marine Research, Norway Salmon lice Lepeophtheirus salmonis are external parasites on salmonids in the marine environment. However, during recent years, salmon lice abundance has increased due to the presence of salmon farming. Scientific studies shows that salmon farming increases the abundance of lice in the marine habitat and that salmon lice in the most intensively farmed areas have negatively affected wild fish populations. The present study assesses the spatiotemporal distribution of salmon lice infestations on wild sea trout population in the Romsdalsfjord region (Norway), and the potential relationship with fish-farming activity and environmental parameters in this area. Salmon lice at farms varied among localities or farming areas, although infestation levels were under the safety established thresholds (max: 0.5 adult females per fish) in most of the cases. However, salmon farms with these levels might produce and release millions of copepods, potentially infecting wild salmonids. In accordance, low lice loads were recorded on wild sea trout captured in areas with low farming activity, while higher mean loads were recorded in areas with higher farming activity. A clear seasonal pattern and a positive correlation between lice on sea trout and sea water temperature were observed throughout the study period. The estimated production of copepods at farms and the mobile lice counted on wild sea trout one month later were correlated, suggesting the potential use of lice monitoring on sea trout as a proxy indicator of salmon lice infestation risks. Image 1 Keywords: sea lice, parasite, Aquaculture, Environmental effects, salmonids, Norway Conference: XV European Congress of Ichthyology, Porto, Portugal, 7 Sep - 11 Sep, 2015. Presentation Type: Poster Presentation Topic: Ecology, Conservation and Invasive Species Citation: Arechavala-Lopez P, Berg M, Uglem I, Bjorn P and Finstad B (2015). Lice pressure from salmon farms on wild sea trout (Salmo trutta) in a Norwegian fjord. Front. Mar. Sci. Conference Abstract: XV European Congress of Ichthyology. doi: 10.3389/conf.fmars.2015.03.00111 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 19 Nov 2015; Published Online: 22 Nov 2015. * Correspondence: Dr. Pablo Arechavala-Lopez, University of Alicante, Department of Marine Science and Applied Biology, Alicante, 03690, Spain, pablo.arechavala@ua.es Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Pablo Arechavala-Lopez Marius Berg Ingebrigt Uglem Pal Arne Bjorn Bengt Finstad Google Pablo Arechavala-Lopez Marius Berg Ingebrigt Uglem Pal Arne Bjorn Bengt Finstad Google Scholar Pablo Arechavala-Lopez Marius Berg Ingebrigt Uglem Pal Arne Bjorn Bengt Finstad PubMed Pablo Arechavala-Lopez Marius Berg Ingebrigt Uglem Pal Arne Bjorn Bengt Finstad Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Wild Estonian and Russian sea trout (Salmo trutta) in Finnish coastal sea trout catches: results of genetic mixed-stock analysis.

For responsible fisheries management of threatened species, it is essential to know the composition of catches and the extent to which fisheries exploit weak wild populations. The threatened Estonian, Finnish and Russian sea trout populations in the Gulf of Finland are targets of mixed-stock fisheries. The fish may originate from rivers with varying production capacities, from different countries, and they may also have either a wild or hatchery origin. In order to resolve the composition of Finnish coastal sea trout catches, we created a standardized baseline dataset of 15 DNA microsatellite loci for 59 sea trout populations around the Gulf of Finland and tested its resolution for mixed-stock analysis of 1372 captured fish. The baseline dataset provided sufficient resolution for reliable mixture analysis at regional group level, and also for most of the individual rivers stocks. The majority (76-80%) of the total catch originated from Finnish sea trout populations, 6-9% came from Russian and 12-15% from Estonian populations. Nearly all Finnish trout in the catch were of hatchery origin, while the Russian and Estonian trout were mostly of wild origin. The proportion of fish in the Finnish catches that originated from rivers with natural production was at least one fifth (22%, 19-23%). Two different spotting patterns were observed among the captured trout, with a small and sparsely spotted form being markedly more common among individuals of Russian (28%) and Estonian origin (22%) than among fish assigned to a Finnish origin (0.7%).

Genetic diversity within sea trout population from an intensively stocked southern Baltic river, based on microsatellite DNA analysis

AbstractSea trout, Salmo trutta L., populations in the Slupia River basin have been affected by mass stocking with smolts and fry. This work is focused on a small‐scale differentiation in sea trout populations from one basin with a strong emphasis on the relationship between wild and hatchery origin fish. A total of 216 sea trout were genotyped at 10 microsatellite loci. Global FST obtained by amova was low at 0.0165. Pairwise FST were significant for all tests except wild and stocked adults. The highest pairwise difference was found between the hatchery sample and Kwacza (FST = 0.038). Analysis of the genetic structure revealed micro‐geographical differentiation with four subpopulations. The quality of the artificial spawning was found not to be adequate with a high risk of adverse effects to the whole population. All future stocking actions in the basin should consider the existing population structures.

Regional population structure and management of aquaculture for stock enhancement of the spotted seatrout (Cynoscion nebulosus)

Abstract The spotted seatrout, Cynoscion nebulosus is one of the most popular game fish in coastal waters of the north central Gulf of Mexico. An aquaculture-based stock enhancement program that aims to supplement native wild populations in Mississippi was initiated in 2004 as part of management efforts to sustain stocks and provide additional fishing opportunities to anglers. A genetic program associated with stock enhancement is in development and seeks to assess the effects of stocking on genetic diversity and fitness of wild populations, and design and implement genetic management to monitor and minimize those impacts. In this work, the structure of spotted seatrout populations in the region was investigated in order to assist with the development of a sustainable spatial management of stocking operations. Spotted seatrout specimens were collected during 2010 and 2011 from the four major bay systems in Mississippi and from reference populations in Louisiana (Grand Isle), and West Florida (Pensacola and Apalachicola). Sample size per locality ranged from 53 to 105 specimens. All samples were assayed at 15 microsatellite markers. Divergence among bay systems from Grand Isle (Louisiana) to Grand Bay (Mississippi–Alabama border) was low and non-significant. However, significant divergence between these localities and the Apalachicola location (West Florida) was detected (0.0214 ST 0.0264, P 0.001), consistent with an isolation-by-distance model of population structure. Estimates of local effective population size by the linkage disequilibrium method were very large or infinite in most localities within the Western part of the sampled range (Mississippi and Louisiana) suggesting current population density is high in that region. While the lack of divergence among Mississippi bay systems supports genetic management as a single unit, further work is needed to determine the spatial scale of natural dispersal and assess the degree of local adaptation of regional populations.

Erratum

Animal GeneticsVolume 45, Issue 1 p. 155-155 ErratumFree Access Erratum This article corrects the following: Genetic differentiation of southeast Baltic populations of sea trout inferred from single nucleotide polymorphisms A. Poćwierz-Kotus, R. Bernaś, P. Dębowski, M. P. Kent, S. Lien, M. Kesler, S. Titov, E. Leliūna, H. Jespersen, A. Drywa, R. Wenne, Volume 45Issue 1Animal Genetics pages: 96-104 First Published online: November 15, 2013 First published: 10 January 2014 https://doi.org/10.1111/age.12130Citations: 2AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL The Publisher would like to extend our sincerest apologies for the erroneous copyright line in Poćwierz-Kotus et al (2014). The copyright line was corrected on 16 December 2013 and as follows, after first online publication: © 2013 Stichting International Foundation for Animal Genetics References Poćwierz-Kotus A., Bernaś R., Debowski P., Kent M.P., Lien S., Kesler M., Titov S., Leliuna E., Jespersen H., Drywa A. & Wenne R (2014) Genetic differentiation of southeast Baltic populations of sea trout inferred from single nucleotide polymorphisms. Animal Genetics 45, 96– 104. Citing Literature Volume45, Issue1February 2014Pages 155-155 ReferencesRelatedInformation

Sea-trout populations in small coastal streams

Sea-trout populations in small coastal streams

Sea-trout populations in small coastal streams

In recent years there has been increasing interest in the conservation and management of small streams. They are essential to the health of the wider aquatic ecosystem and of fish populations throughout river catchments. Because of their size, small streams are particularly at risk from the predicted changes in temperature and flow regimes resulting from climate change. This paper deals with small coastal streams, which to date have received little if any attention from researchers, local authorities or fisheries management bodies. It seeks to summarise the information currently available on small coastal streams, to outline the potential importance of such streams from both an ecological and biodiversity perspective and suggest research topics that could help to conserve these sensitive biotopes and underpin the requirement to assess and categorise their role as producers of juvenile seatrout (Salmo trutta L.). It is argued that recruitment from such streams may be of critical importance to the abundance of sea-trout in the neighbouring coastal margins.

Genetic differentiation of southeast Baltic populations of sea trout inferred from single nucleotide polymorphisms

Sea trout (Salmo trutta m. trutta) is a migratory form of brown trout common in the Baltic Sea. Nine populations from the southeast Baltic (Poland; Lithuania; Denmark, Bornholm; Estonia and Russia) were genotyped using iPLEX Gold technology (Sequenom) with 62 informative SNPs. A diagnostic panel of 23 SNPs was applied to estimate genetic differentiation and assess the population structure of Baltic sea trout. The highest level of pairwise FST differences was observed between the Russian (East Gulf of Finland) and Polish (Baltic main basin) populations. The lowest differences were between the two Polish and the Polish and Lithuanian populations. A genetic similarity was noted between the Estonian Riguldi River and Danish Bornholm populations, and this finding was supported by a Bayesian and factorial correspondence analysis. Diversity within populations was highest for populations from Estonia and lowest for the Lithuanian population. Genetic structure analysis indicated that individuals from the nine populations were clustered into four groups.

Can the river location within a fjord explain the density of Atlantic salmon and sea trout?

The rivers that drain into the Hardangerfjord were historically known to have numerous populations of both sea trout (Salmo trutta) and Atlantic salmon (Salmo salar). After a decline in catches during the last decades many of the rivers have been closed for fishing. In this study we use snorkelling observations from rivers and catch statistics from 2004 to 2011 to describe the current situation and analyse the patterns of density of wild salmon, sea trout and escaped farmed salmon in the Hardangerfjord rivers. We hypothesize that some of the variance in density of salmon and sea trout can be explained by the location of the river in the fjord, with fish from rivers with a longer fjord exposure having a lower density. A median number of 3.5 salmon×ha−1 and 14.9 sea trout×ha−1 were observed in the rivers. Farmed salmon were observed in all rivers and constituted on average 23.3% of the total number of observed salmon. For salmon, there was an inverse log-linear relationship between density in the river and migration distance to coast, with a higher density in rivers with a shorter migration distance. For sea trout there was no evident relationship with location within the fjord. We suggest that the spatial patterns observed for salmon and sea trout can be related to the species-specific differences in habitat use within the fjord system.