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Salmon lice Lepeophtheirus salmonis infestation of sea trout Salmo trutta results in both additional marine mortality and behavioral changes which may contribute to sea trout population decline. For effective management of activities that increase exposure to salmon lice, such as salmon aquaculture, it is necessary to have a full understanding of how salmon lice may affect sea trout populations. An individual-based model (IBTRUTTA) was therefore developed to investigate the potential effects of salmon lice infestation on sea trout population abundance and dynamics based on data from the River Halselva and Altafjord system in northern Norway. This model allowed investigation of the effect of lice-induced mortality and also the compensatory salmonid behavioral mechanisms of premature return to freshwater, either persistent for overwintering or transitory after which sea trout could go back to sea. It was found that, in the absence of compensatory mechanisms, even low rates of lice infestation could lead to marked declines in sea trout abundance. Compensatory behavioral mechanisms had the potential to reduce these de - clines, but persistent premature return resulted in reduced body mass of returning adults. The shape of the stock-recruitment relationship was also shown to strongly affect how lice-induced mortality impacted the population. Individual-based model · Sea trout · Salmon lice · Lice-induced mortality · Premature return

The viability of wild Atlantic salmon populations is threatened by genetic introgression from escaped farmed salmon. Farmed Atlantic salmon are genetically improved for important commercial traits and a life in captivity but are poorly adapted to the natural environment. The rate of gene flow from escaped farmed to wild salmon depends on their spawning success and on offspring survival at various life stages. We here investigate relative survival of introgressed juvenile Atlantic salmon (parr) in a river in northern Norway. The studied population has experienced genetic introgression from farmed salmon for about four generations (20 years). We followed two cohorts of parr from the year of hatching (0+) to the age of 2 years (2+). Farmed genetic introgression was quantified at the individual level and on a continuous scale using diagnostic SNPs. Population-level genetic introgression decreased from 0+ to 2+ by 64% (2011 cohort) and 37% (2013 cohort). This change was driven by a 70% (2011 cohort) and 49% (2013 cohort) lower survival from age 0+ to 2+ in introgressed parr compared to parr of wild origin. Our observations show that there is natural selection against genetic introgression with a potential cost of lower productivity. aquaculture, Atlantic salmon, farmed salmon, genetic introgression, Salmo salar, survival

For successful evaluation of the overall effects of salmon louse infestation on brown trout population dynamics, it is crucial to have a realistic understanding of how lice infestation distributions are generated and how they should be interpreted. Here, we simulated the potential effects of spatio-temporal variance in lice larvae densities, temporal variance in sea trout marine migration timing and spatial variance in marine habitat use on lice infestation distributions. We show that, when sampling populations with individual variation in marine behaviour, e.g. from post-smolts to veteran migrants, we must expect multi-modal mixture lice infestation distributions. Applying standard statistical distributions, such as the Poisson, negative binomial or zeroinflated distributions, can be too simplistic and give biased results. Temporary increases in salmon lice load in a given area may have inconsistent effects among individuals of a population and may be critical for vulnerable groups such as post-smolts, dependent on timing. For many analyses, it will be necessary to resolve the contributions from groups of fish with different lice infestation expectations due to spatio-temporal differences in habitat use within the overall mixture distribution. Another consequence is that different data sources, obtained by different methods or sampled at different locations and periods, must be expected to give different lice infestation distributions, even when sampling the same population. We also discuss additional factors that may complicate the interpretation of salmon lice infestation distributions on sea trout, such as lice-induced mortality, and behavioural changes, such as premature return to less saline water for delousing. Salmo trutta · Lepeophtheirus salmonis · Anadromy · Marine migration · Aquaculture · Negative binomial distribution · Zero-inflated models © The authors 2020. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited.

Norway is the world’s largest producer of farmed Atlantic salmon and is home to ∼400 rivers containing wild salmon populations. Farmed escapees, a reoccurring challenge of all cage-based marine aquaculture, pose a threat to the genetic integrity, productivity, and evolutionary trajectories of wild populations. Escapees have been monitored in Norwegian rivers since 1989, and, a second-generation programme was established in 2014. The new programme includes data from summer angling, autumn angling, broodstock sampling, and snorkelling surveys in >200 rivers, and >25 000 scale samples are analysed annually. In 2014–2017, escapees were observed in two-thirds of rivers surveyed each year, and between 15 and 30 of the rivers had >10% recorded escapees annually. In the period 1989–2017, a reduction in the proportion of escapees in rivers was observed, despite a >6-fold increase in aquaculture production. This reflected improved escape prevention, and possibly changes in production methods that influence post-escape behaviour. On average, populations estimated to experience the greatest genetic introgression from farmed salmon up to 2014 also had the largest proportions of escapees in 2014–2017. Thus, populations already most affected are those at greatest risk of further impacts. These data feed into the annual risk-assessment of Norwegian aquaculture and form the basis for directing mitigation efforts.

Climate change is modifying the hydrological and thermal regimes of rivers worldwide, threatening the triggering of organisms’ key life-cycle processes. European eel (Anguilla anguilla) is a critically endangered fish species that migrates over several thousand kilometres between its rearing habitats in continental waters of Europe and North Africa and its spawning area in the Sargasso Sea. Downstream migration of adult eels occurs during periods of decreasing river water temperature associated with high discharge but changes in these environmental cues may affected eel migratory conditions. An innovative multivariate method was developed to analyse long-term datasets of daily water temperature, discharge and eel passage in two European rivers. Over the past 50 years, water temperature and discharge increased in both rivers during the downstream migration period from August to November. Silver eels preferentially migrated at temperatures between 10 and 20 °C combined with high discharge. Environmental changes have resulted in the migration of silver eels under warmer water temperatures. This example illustrates how the changes in environmental cues have led to a growing mismatch between the migratory conditions preferentially selected and those actually used, which may threaten the completion of the eel’s life cycle and ultimately the persistence of this already critically endangered species.

We have in this study analysed bird communities across Norway with a heterogeneous species abundance model, where dynamical parameters can vary among species. Similarity in community composition over time, used as a measure of temporal β-diversity or the turnover rate, was then estimated. When we account for heterogeneity in dynamical parameters among species it will affect how we estimate environmental stochasticity, and, subsequently, how the temporal dynamics is modelled. In addition, spatial variation in species abundance within a sampling area can obscure the temporal dynamics of communities. By inadvertently including small-scale spatial variation within sampling areas in the sample noise term, it will be difficult to correctly detect changes in community structure, or species abundance similarity, in time. Using Norwegian bird communities as a case study, we have shown how to interpret the sample correlation of the bivariate Poisson lognormal distribution, fitted to pairs of transects, and why separation of the transects into spatially similar subgroups can be beneficial. This approach also makes us able to account for sampling error and over-dispersion relative to Poisson sampling. The partitioning of the variance of the species abundance distributions showed that heterogeneity among species in temporal dynamics accounted for roughly 75% of the variation, close to estimates for other taxa. High temporal similarity can be interpreted as a low baseline turnover rate, which is important when studying changes to ecosystems due to e.g. anthropogenic effects. Furthermore, the environmental stochasticity was more realistically estimated in this heterogeneous model. This is essential for predicting the dynamics of species abundances forward in time. β-diversity Environmental stochasticity Heterogeneous species abundance models Over-dispersion Temporal community dynamics

The spawning migration of Atlantic salmon has been characterized by tracking salmon carrying electronic tags as they ascend rivers, but still little is known about how natural obstacles such as waterfalls influence migratory behaviour and how such behaviours are mediated by various biotic (e.g., fish size) and abiotic (e.g., discharge, water temperature, and barometric pressure) factors. The Norwegian river Numedalslagen is interrupted by natural waterfalls ranging in height from 2 to 6 m. We tagged 113 Atlantic salmon with radio transmitters in the estuary and used stationary radio telemetry stations to track fish. Ninety‐one salmon were recorded in Numedalslagen, 39 of which remained in the river for spawning. Large salmon moved farther and faster upriver but also delayed longer and had lower daily probability to pass the second waterfall. Delay below and passage probability at the final, largest waterfall was affected by water discharge, wherein passage occurred when discharge was declining. Barometric pressure also influenced daily probability of ascent, albeit in opposite directions for each waterfall. Importantly, we also found that salmon with surgically implanted radio transmitters moved farther upriver on average and delayed less time below one of the waterfalls than those with externally attached transmitters. Although there is variance in timing arising from individual decision‐making, we showed that natural waterfalls delay progress of Atlantic salmon on their spawning migration and that both biotic (i.e., size) and abiotic (i.e., barometric pressure and discharge) factors influenced the salmon's decisions to pass waterfalls that they encounter.

Freshwater metazoan biodiversity assessment using environmental DNA (eDNA) captured on filters offers new opportunities for water quality management. Filtering of water in the field is a logistical advantage compared to transport of water to the nearest lab, and thus, appropriate filter preservation becomes crucial for maximum DNA recovery. Here, the effect of four different filter preservation strategies, two filter types, and pre-filtration were evaluated by measuring metazoan diversity and community composition, using eDNA collected from a river and a lake ecosystem. The filters were preserved cold on ice, in ethanol, in lysis buffer and dry in silica gel. Our results show that filters preserved either dry or in lysis buffer give the most consistent community composition. In addition, mixed cellulose ester filters yield more consistent community composition than polyethersulfone filters, while the effect of pre-filtration remained ambiguous. Our study facilitates development of guidelines for aquatic community-level eDNA biomonitoring, and we advocate filtering in the field, using mixed cellulose ester filters and preserving the filters either dry or in lysis buffer. © The Author(s) 2018. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

European eel (Anguilla anguilla) recruitment has been declining at least since the early 1980s at the scale of its distribution area. Since the population is panmictic, its stock assessment should be carried out on a range-wide basis. However, assessing the overall stock during the continental phase remains difficult given its widespread distribution among heterogeneous and separate river catchments. Hence, it is currently considered by the International Council for the Exploration of the Sea (ICES) more feasible to use glass eel recruitment data to assess the status of the overall population. In this study, we used Glass Eel Recruitment Estimation Model (GEREM) to estimate annual recruitment (i) at the river catchment level, a scale for which data are available, (ii) at an intermediate scale (6 European regions), and (iii) at a larger scale (Europe). This study provides an estimate of the glass eel recruitment trend through a single index, which gathers all recruitment time-series available at the European scale. Results confirmed an overall recruitment decline to dramatically low levels in 2009 (3.5% of the 1960–1979 recruitment average) and highlighted a more pronounced decline in the North Sea area compared to elsewhere in Europe.

Downstream migration of 112 radio-tagged Atlantic salmon smolts was studied in the Diemel, Germany, to examine 1) mortality and migration speeds during riverine migration and at a hydropower station, 2) choice of migration routes at the power station, and 3) survival and transit speed through Archimedes screw and Francis turbines. Mortality was not elevated in the impounded stretch above the dam compared to a free-flowing control stretch (1.9 and 2.5% loss per km, respectively). Migration speeds did not differ among the control stretch, impounded stretch and in passing the power station, but there was large individual variation. Smolts reaching the power station (n = 101) could choose between six possible passage routes. Most smolts passed through the Archimedes screw (43%), or via a route where Francis turbines were installed (33%). Three percent migrated over the dam, 14% used a fishway at the Archimedes screw and 8% used a fishway at the Francis turbines. The smolts used the fishways (instead of the Archimedes and Francis turbines) more often than expected from the proportion of water discharge, especially larger smolts at lower discharge. Smolts passed the power station mainly in the evening and early night. Migration speed past the power station was faster for smolts passing via the Archimedes screw and associated fishway than for those using other routes. Smolts were not markedly delayed in their downstream migration by using the Archimedes screw. Immediate mortality of smolts passing through the Archimedes screw and Francis turbines was probably below 10% and 13%, respectively.

We studied downstream migration of 256 radio-tagged Atlantic salmon smolts passing a low-head power station where technical facilities have been improved to allow safe migration via several bypass routes. Extra mortality was 7 and 17% (two years) in the power station reservoir, and a minimum of 10 and 13% at the power station compared to in a control stretch. The majority of the smolts followed the main flow at the power station, towards the turbines. Sloped bar racks with 10 mm bar spacing hindered smolts from entering the turbines, hence there was no turbine mortality. Smolts used surface openings in the racks, which directed them to a bypass route outside the turbines. The extra mortality in the reservoir and at the power station was related to physical injuries in bypass routes and to predation. The mortality risk in the reservoir and at the power station decreased with increasing migration speed. Migration speeds increased with water discharge. Migration was slower when the smolts passed the power station than on other stretches. This study shows that hydropower regulation caused elevated mortality and delays for downstream migrating fish, even with improved technical facilities to reduce mortality.

Many animals perform long-distance migrations in order to maximize lifetime reproductive success. The European eel migrates several thousand kilometers between their feeding habitats in continental waters (fresh-,brackish, and sea water) and their spawning area in the Sargasso Sea. Eels residing in freshwaters usually initiate their spawning migration as silver eels during autumn, triggered by diverse environmental cues. We analyzed the time series of silver eel downstream migration in Burrishoole, Ireland (1971–2015), and Imsa, Norway (1975–2015), to examine factors regulating the silver eel migration from freshwater to the sea. The migration season (90% of the run) generally lasted from 1 August to 30 November. Environmental factors acting in the months before migration impacted timing and duration of migration, likely through influencing the internal processes preparing the fish for migration. Once the migration had started, environmental factors impacted the day-to-day variation in number of migrants, apparently stimulating migration among those eels ready for migration. Both the day-to-day variation in the number of migrants and the onset of migration were described by nearly identical models in the two rivers. Variables explaining day-to-day variation were all associated with conditions that may minimize predation risk; number of migrants was reduced under a strong moon and short nights and increased during high and increasing water levels. Presence of other migrants stimulated migration, which further indicates that silver eel migration has evolved to minimize predation risk. The onset of migration was explained mainly by water levels in August. The models for duration of the migration season were less similar between the sites. Thus, the overall migration season seems governed by the need to reach the spawning areas in a synchronized manner, while during the actual seaward migration, antipredator behavior seems of overriding importance. Anguilla anguilla, daily variation, environmental variables, freshwater migration, migration onset, silver eel

The effects of sea lice on the marine survival of wild salmonids are widely debated. In Norway this debate has reached a crescendo as the Norwegian government has recently ratified a management system where the growth in the salmonid aquaculture industry will be conditional on regional estimated impact of salmon lice on wild fish. Sea lice have thus become the most prominent obstacle to the stated political aim of quintupling aquaculture production in Norway by 2050. Scientific documentation that salmon lice impact the marine survival of salmon is robust. However, it is also evident that marine survival of salmon is strongly impacted by other factors, and that the effect of salmon lice is most likely an integral part of these other mortality factors. In this paper, our goal is to discuss and give advice on how managers and policy makers should handle this complexity, and to identify the greatest challenges in using scientific results to construct robust management rules. Inadequate extrapolation from the scale of known effects to the scale of management implementation may initially give a false impression of scientific certainty, but will eventually fuel upsetting disagreements among stakeholders as they gradually uncover the shaky foundation of the implemented policy. Thus, using a single model and parameter to determine management advice is not warranted, as no single data point reflects the natural complexity of nature. Furthermore, robust management rules should be based on unambiguous definitions of key concepts. Finally, despite the scientific consensus that salmon lice are a risk to salmon, studies on wild populations in situ that accurately quantify the impact of salmon lice are still urgently needed. We give advice on how this can be accomplished.

Downstream migration of radio-tagged Atlantic salmon smolts, Salmo salar L., was studied in the Kinzig, Germany, to examine effects of passing a run-of-river hydropower station with a movable bulb turbine. Immediate mortality for smolts passing the power station was low (3%–6%), probably facilitated by a curved rack in front of the turbine and the possibility to pass over it. Mortality in the impounded stretch above the power station was also low (1.5% extra mortality compared to a control stretch). The combined mortality due to hydropower was 5%–8%, excluding delayed effects. Most smolts followed the main flow passing through the turbine area (94%). Only few used a fishway (4%) or a nearby millstream (2%). Migration speed was slowed down at the power station, but the passage only caused a short delay (average/median 8.6/1.3 hr). However, even low mortality and short delays at several power stations and reservoirs may have considerable cumulative effects.

Consistent individual differences in behavior have been demonstrated for many animals, but there are few studies of consequences of such repeated behavior in the wild. We tested consistency in migration timing to and from the sea among anadromous Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta), using data from a study period of about 25 years, including more than 27,000 uniquely Carlin‐tagged individuals that migrated to sea for feeding in the spring and returned to the river in late summer for up to 13 successive years. Consistency was found between individuals across time in timing of the seaward migration. Individuals migrating early during their first migration tended to migrate early the following years, and late migrants tended to migrate late. The same pattern was found also at ascent to freshwater. Hence, this study demonstrated that individual fish in nature can differ in behavior related to migration timing and that these differences can be consistent during their lifetime. Early migrants increased their mass more than late migrants and had a higher specific growth rate. Early migrating Arctic char, but not brown trout, experienced a longer life after the first migration to sea than late migrants. In both species, maturity occurred earlier in individuals that migrated early. For brown trout, but not for Arctic char, fecundity was significantly correlated to the timing of smolt migration. Hence, the repeatable individual variation in migration timing seemed to have ecological and fitness consequences in terms of growth, longevity, timing of maturity, and lifetime fecundity., This 25‐year study tested consistency in migration timing to and from the sea among anadromous Arctic char and brown trout, including more than 27,000 uniquely tagged individuals that migrated to sea for feeding in the spring and returned to the river in late summer. Repeatable individual variation in migration was found between individuals across time in timing of the seaward migration. Individuals migrating early during their first migration continued to migrate early the following years, and late migrants continued to migrate late. The same pattern was found also at ascent to freshwater. The personality differences in migration timing seemed to have ecological and fitness consequences in terms of growth, timing of maturity, and lifetime fecundity.

The proportion of angled Atlantic salmon Salmo salar L. being caught and released has increased. If individuals are repeatedly captured, this may have fish welfare consequences. Of 995 Atlantic salmon tagged during catch and release in eight Norwegian rivers, 10% were captured twice, while 3% were captured three times within the same fishing season. The probability that released salmon were captured again decreased with decreasing time left of the fishing season, decreased for larger‐sized fish and varied among rivers/years. Increased exploitation rates within the river, indicating an increased fishing pressure, strongly increased the probability that fish would be recaptured. However, the proportion of salmon caught a second time was much lower than the total exploitation rates in the same rivers (which was on average 46%). For fish tagged in the sea, the likelihood of being angled decreased with time since entering the river, which may explain why the recapture rates of caught and released fish were lower than the total exploitation rates. © 2019 The Authors. Fisheries Management and Ecology published by John Wiley & Sons Ltd This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

We report on the data from an extensive monitoring programme for the occurrence of escaped farmed Atlantic salmon (Salmo salar) in Norwegian rivers for 25 years. This monitoring started as a 3-year research programme in 1989 and was followed by management authorities to cover the proportional occurrence of escaped farmed Atlantic salmon in rivers during summer and autumn before spawning. Farmed salmon were distinguished from wild salmon by growth patterns in the scales. More than 362 000 salmon were registered by this programme. Here we present the historical data on escaped farmed salmon in catches 1989–2013 and a methodology for calculating averages across summer and autumn capture in rivers, across years and in regions, using weighted and unweighted observations. Catches of escaped farmed salmon show large spatial and temporal variation, with the early 1990s and early 2000s being periods of large influxes of farmed fish. Western Norway and parts of middle and northern Norway have shown particularly high incidences of escaped farmed fish. Because escaped farmed Atlantic salmon are competing and interbreeding with wild Atlantic salmon, as well as increasing the spread of disease-causing agents, they have become a major force driving the abundance and evolution of Atlantic salmon. aquaculture, Atlantic salmon, escaped farmed salmon, fisheries management, Salmo salar.

Characterisation of freshwater benthic biodiversity using DNA metabarcoding may allow more cost-effective environmental assessments than the current morphological-based assessment methods. DNA metabarcoding methods where sorting or pre-sorting of samples are avoided altogether are especially interesting, since the time between sampling and taxonomic identification is reduced. Due to the presence of non-target material like plants and sediments in crude samples, DNA extraction protocols become important for maximising DNA recovery and sample replicability. We sampled freshwater invertebrates from six river and lake sites and extracted DNA from homogenised bulk samples in quadruplicate subsamples, using a published method and two commercially available kits: HotSHOT approach, Qiagen DNeasy Blood & Tissue Kit and Qiagen DNeasy PowerPlant Pro Kit. The performance of the selected extraction methods was evaluated by measuring DNA yield and applying DNA metabarcoding to see if the choice of DNA extraction method affects DNA yield and metazoan diversity results. The PowerPlant Kit extractions resulted in the highest DNA yield and a strong significant correlation between sample weight and DNA yield, while the DNA yields of the Blood & Tissue Kit and HotSHOT method did not correlate with the sample weights. Metazoan diversity measures were more repeatable in samples extracted with the PowerPlant Kit compared to those extracted with the HotSHOT method or the Blood & Tissue Kit. Subsampling using Blood & Tissue Kit and HotSHOT extraction failed to describe the same community in the lake samples. Our study exemplifies that the choice of DNA extraction protocol influences the DNA yield as well as the subsequent community analysis. Based on our results, low specimen abundance samples will likely provide more stable results if specimens are sorted prior to DNA extraction and DNA metabarcoding, but the repeatability of the DNA extraction and DNA metabarcoding results was close to ideal in high specimen abundance samples. Copyright Markus Majaneva et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Stocking of hatchery produced fish is common practise to mitigate declines in natural populations and may have unwanted genetic consequences. Here we describe a novel phenomenon arising where broodstock used for stocking may be introgressed with farmed individuals. We test how stocking affects introgression in a wild population of Atlantic salmon (Salmo salar) by quantifying how the number of adult offspring recaptured in a stocked river depend on parental introgression. We found that hatchery conditions favour farmed genotypes such that introgressed broodstock produce up to four times the number of adult offspring compared to non-introgressed broodstock, leading to increased introgression in the recipient spawning population. Our results provide the first empirical evidence that stocking can unintentionally favour introgressed individuals and through selection for domesticated genotypes compromise the fitness of stocked wild populations., Stocking of hatchery produced fish is widely used to supplement wild fish populations. Here, the authors show that supplementary stocking can unintentionally favour introgressed individuals with domestic genotypes and compromise the fitness of a wild population of Atlantic salmon.

The European eel (Anguilla anguilla) population has been in decline at least since the 1960s and reliable regional information, particularly on the spawner production and escapement (i.e. the silver eel life stage), is a requirement of the EU stock recovery regulation. Two comparable time series exist in Burrishoole (Ireland) and Imsa (Norway), with monitoring of total silver eel production since the early 1970s. Numbers of emigrating silver eels fell significantly (p < 0.0001) in the 1980s (breakpoints: Burrishoole 1982; Imsa 1988), in both catchments from >4000 eels per annum to ∼2000 eels per annum. The proportion of male eels dropped and the average size of female eels increased. Biomass of silver eels escaping has remained similar in Burrishoole (1.1/1.2 kg/ha), but not in Imsa (2.1/0.9 kg/ha) between the early period and the 2000s. Factors that govern the onset of eel maturation (silvering) and the annual production of silver eels are little understood. In this paper, the influence of time-lagged environmental variables on silver eel production is examined. Annual variation in the time series was partly (r2 Burrishoole = 0.43, Imsa = 0.46) explained by variation in water temperature and water level. Annual number of migrating eels in both catchments was positively related to summer temperature and summer water flow, negatively related to summer temperatures in the previous year, and in the Burrishoole, also negatively related to high water levels in September/October. The models did not transfer well between catchments, indicating likely catchment specific environmental factors impacting on eel production. The reduction in eel numbers observed in both catchments, accompanied by the change in sex ratio and mean weight of females that contribute to maintain biomass production, calls into question the advisability of basing a spawner escapement recovery target on biomass alone, while numbers and proportions of males decline. Locked until 9.5.2019 due to copyright restrictions. This is a pre-copyedited, author-produced version of an article accepted for publication in [ICES Journal of Marine Science] following peer review. The version of record is available online at: https://doi.org/10.1093/icesjms/fsy053

1. Climate change poses a challenge to wild fishes, yet little is known about the behavioural use and metabolic consequences of thermally heterogeneous water encountered by wild salmon during their energetically demanding upstream spawning migration. 2. Temperature, body size and activity levels were modelled to predict energy depletion of salmon during their spawning migration in rivers. Archival temperature loggers revealed the thermal habitat of adult migrating Atlantic salmon (Salmo salar Salmonidae), which we used to apply bioenergetics models that estimated size-dependent temperature-driven metabolic expenditures as part of the costs of the migration. 3. Between July 16 and August 19, the mean water temperature experienced by salmon (tFISH) ranged from 11.5 to 18.0°C (14.5 ± 1.2 SD °C) and closely followed the ambient surface water temperature (tRIVER) of the river (11.5–18.5°C; 14.8 ± 1.4°C) such that the regression equation tFISH = 3.24 + 0.76 (tRIVER) was highly correlated with observations (R2 = 0.94). 4. Although temperature increases were predicted and confirmed to increase energetic costs, rates of energy depletion were more sensitive to changes in swimming speed and body size than to temperature increases in the range explored for this system. 5. We conclude that warming could contribute to changing life history phenotypes of salmon in some rivers, for example, delayed river entry or reduced probability of iteroparity, with potentially more dire consequences for smaller individuals. bioenergetics, fisheries, iButton, iteroparity, telemetry

We evaluated the effect of the total number of passes used, and the application of block nets, on multi-pass electrofishing removal sampling for estimating juvenile Atlantic salmon (Salmo salar L.) abundance and body size distribution. Sites within selected salmon-bearing Norwegian rivers were enclosed by block nets and electrofished for multiple passes (range: 7–13), and capture probabilities and abundances were estimated using the Carle and Strub removal method. We examined for different body size classes: (1) bias in the estimated capture probability and abundance associated with the number of passes used; (2) the potential for bias to be minimized by the use of block nets; and (3) electrofishing-induced mortality. We found that the capture probability estimate was strongly dependent upon the number of passes used, tending to decline with successive pass, with the effect depending on size class. Thus, estimates made using the traditional three-pass approach would result in underestimates of abundance, and biased estimates of size distribution. Smaller juveniles were both more likely to impinge on the block nets and more likely to experience mortality than larger juveniles. Mortality was greatest when water temperature was high (> 18 °C). Our findings indicate that quantitative electrofishing for small juveniles may be unreliable, and that electrofishing at high temperatures should be avoided due to potential high mortality. Atlantic salmon Electrofishing Multi-pass removal Net capture Mortality Bias in estimates of electrofishing capture probability of juvenile Atlantic salmon

Anthropogenic activity can cause changes in the population dynamics of species. The changes can be modelled by density dependent models with time varying parameters. The following study looks at the accuracy of model parameter estimates using primarily simulations, in addition to a real data set of Grey Heron. A key point is the amount of data required to detect deterministic changes, either step-wise or gradual, in parameters for species with different population dynamics. The theta-logistic model is used to simulate the data and fitted to realizations of step-wise change in growth rate, and a linear model is fitted to gradual or step-wise changes in carrying capacity. Bayesian analysis is applied to study the effect of different prior distributions on the strength of density regulation. The range of the data is especially important when trying to detect step-wise changes in growth rate. Detection of changes in carrying capacity depends on the dynamics of the population, e.g. it is difficult to observe change for species with long return time to equilibrium within short time frames. The estimates of change in carrying capacity can become more accurate using a strong prior on the strength of density regulation. However, the prior may give more conservative estimates, if the prior assumes a weak density regulation. The results provide ecologists and decision makers with a general idea of what to expect of analyses of time series data of populations in changing environments.

A long-term study in the River Halselva in the Arctic region of Norway demonstrated that movements between watersheds were considerably higher in anadromous brown trout (Salmo trutta) than anadromous Arctic char (Salvelinus alpinus). Fourteen smolt year classes of both species were captured in a fish trap, individually tagged, and thereafter registered each time they passed the trap during their migration between the sea and fresh water every summer. Annual mean survival (i.e., recovery rate) after the first entry to sea as smolts was estimated as 31.4% in Arctic char and 26.6% in brown trout. Most surviving Arctic char returned to the River Halselva to overwinter after the same summer that they migrated to sea as smolts. However, several brown trout overwintered one to four times in other watersheds, mainly the considerably larger River Altaelva, before most eventually returned to the River Halselva upon maturation. The substantial difference in movement rate between watersheds between Arctic char (2.2%) and brown trout (39.6%) is expected to be a consequence of local geographic conditions combined with different habitat preferences of the two species.

A model that explains 48% of the annual variation in Atlantic salmon Salmo salar smolt production in the River Orkla, Norway, has been established. This variation could be explained by egg deposition, minimum daily discharge during the previous winter and minimum weekly discharge during the summer 3 years before smolt migration. All coefficients in the model were positive, which indicates that more eggs and higher minimum discharge levels during the winter before smolt migration and the summer after hatching benefit smolt production. Hence, when the spawning target of the river is reached, the minimum levels of river discharge, in both winter and summer, are the main bottlenecks for the parr survival, and hence for smolt production. The River Orkla was developed for hydropower production in the early 1980s by the construction of four reservoirs upstream of the river stretch accessible to S. salar. Although no water has been removed from the catchment, the dynamics of water flow has been altered, mainly by increasing discharges during winter and reducing spring floods. In spite of the higher than natural winter discharges, minimum winter discharge is still a determinant of smolt production. Hence, in regulated rivers, the maintenance of discharges to ensure that they are as high as possible during dry periods is an important means of securing high S. salar smolt production.

The prevalence and abundance (density 100 m−2) of European eel (Anguilla anguilla) were studied by means of electrofishing in 13 acidified rivers in Norway that had been limed to restore acceptable water quality for Atlantic salmon (Salmo salar). Status of Atlantic salmon in these rivers varied prior to liming, from being entirely lost in six highly acidified rivers and in different stages of decline in seven less acidified rivers. Four of the rivers are heavily affected by hydropower development. The abundance and prevalence of European eel increased significantly during the study period. The best model for predicting eel abundance was that with four explanatory variables: time after liming, time after liming squared, status of salmon stocks and hydropower regulation. The eel density was expected to increase by a factor of almost 5 after 10 years of liming. The model also predicts that a river with a formerly reduced Atlantic salmon stock has a 2.8 times higher density of eel than rivers with formerly lost salmon stocks. Before liming, European eel were on average recorded at 15 and 41% of the sampling stations in rivers with formerly lost and reduced Atlantic salmon populations, respectively, increasing to 49 and 68% in individual rivers, respectively, after 10 years of liming. The recovery of European eel in these formerly acidified rivers by means of liming took place during the same period as their abundance declined in other parts of their distribution area in Norway and elsewhere in Europe.

Short-term Al-exposure and moderate acidification increased initial marine mortality in migrating post-smolts, and can thereby reduce viability of Atlantic salmon stocks. The delayed impact of short-term aluminium (Al) exposure on hatchery-reared Atlantic salmon smolt in moderately acidified freshwater (pH 5.88–5.98) was investigated during the first 37 km of the marine migration. Smolts were tagged with acoustic tags and exposed to low (28.3 ± 4.6 μg l −1 labile Al, 90 h) or high (48.5 ± 6.4 μg l −1 labile Al, 90 or 48 h) Al concentrations within the hatchery. Thereafter their movements, together with a control group, were monitored throughout the marine fjord. Al-exposure resulted in increased gill-Al and compromised hypoosmoregulatory capacity, as shown by elevated mortality in laboratory seawater challenge tests and reduced Na + , K + -ATPase activity levels. Further, Al-exposure resulted in decreased plasma concentrations of growth hormone (GH), while the insulin-like growth factor (IGF-I) was unaffected. There was a significant mortality in the 90 h high-Al group during exposure, and those surviving until release died during the first 3.6 km of the marine migration. Physiological stress and mortality were not only a result of the Al-concentrations, but also dependent on exposure duration, as shown by results from the 48 h high-Al group. Elevated mortality was not recorded in freshwater or after entering the sea for this group, which highly contrasts to the 100% mortality in the 90 h high-Al group, despite both groups having similarly high gill-Al levels. The low-Al group showed a 20% higher mortality compared to the control group during the first 10 km of the marine migration, but during the next 28 km, mortality rates did not differ. Hence, post-smolts surviving the first 10 km subsequently showed no differences in mortality compared to controls. At least one third of the mortality in both the low-Al and control groups were due to predation by marine fishes, indicating that the proximate cause for elevated mortality due to Al-exposure may have been predation. Migration speeds over 3.6, 9.6 or 37.1 km from the release site was not affected by Al-exposure.

Estimates of fish abundance from electrofishing surveys depend on accurate estimation of capture probability. We examine in this paper how estimates of capture probability and abundance of Atlantic salmon from multi-pass removal sampling can be improved by comparing the results of an experimental programme of closed electrofishing sites within selected rivers in west-central Norway, and those obtained from open electrofishing sites established for monitoring long-term juvenile Atlantic salmon population abundance within the Burrishoole catchment, western Ireland. We first establish that the Carle & Strub method provides a more robust estimate of population abundance than the Zippin and Seber methods. We then show how prior information on capture probability may be used to improve the accuracy of the abundance estimate in open sites. We also show that the use of prior information with single-pass electrofishing may improve the accuracy of the abundance estimate so that it is comparable with that of multi-pass electrofishing in terms of stock prediction while requiring less sampling effort.

a b s t r a c t In this paper, we present a spatially explicit individual-based mechanistic model for predicting the freshwater population abundance of Atlantic salmon (Salmo salar L.). The model simulates the complete life-cycle at small spatial (∼50 m) and temporal (weekly) scales. Processes such as spawning, recruitment, mortality and movements are predicted using deterministic and stochastic functions, parameterized using relationships established from the literature and empirical observations. The model was used to simulate salmon population abundance within a river in western-central Norway (River Nausta). The sensitivity of population abundance to fry and parr carrying capacities, and parr and post-smolt densityindependent mortalities was analyzed. The optimally parameterized model predicted similar abundances and age compositions across the developmental stages of the population to those estimated from empirical observations within the river. The effect of carrying capacities and mortalities on abundance was strongest at the developmental stage at which they operated, but also affected the abundance of subsequent developmental stages or the progeny, suggesting negative (dampening) feedback mechanisms.

Interbreeding between domesticated and wild animals occurs in several species. This gene flow has long been anticipated to induce genetic changes in life-history traits of wild populations, thereby influencing population dynamics and viability. Here, we show that individuals with high levels of introgression (domesticated ancestry) have altered age and size at maturation in 62 wild Atlantic salmon Salmo salar populations, including seven ancestral populations to breeding lines of the domesticated salmon. This study documents widespread changes to life-history traits in wild animal populations following gene flow from selectively bred, domesticated conspecifics. The continued high abundance of escaped, domesticated Atlantic salmon thus threatens wild Atlantic salmon populations by inducing genetic changes in fitness-related traits. Our results represent key evidence and a timely warning concerning the potential ecological impacts of the globally increasing use of domesticated animals. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.

Communities with different phenotypic variation among species can have identical species abundance distributions, although their temporal dynamics may be very different. By using stochastic species abundance models, both the lognormal and beta prime abundance distributions can be obtained with either homogeneous or heterogeneous dynamics among species. Assuming that anthropogenic activity disturbs the communities such that species’ carrying capacities are decreasing deterministically, the structure of the communities are studied using simulations. In order to construct homogeneous communities with reasonable variation in abundance, the parameter values describing the dynamics of the species can be unrealistic in terms of long return times to equilibrium. Species in heterogeneous communities can have stronger density regulation, while maintaining the same variation in abundance, by assuming heterogeneity in one of the dynamical parameters. The heterogeneity generates variation in carrying capacity among species, while reducing the temporal stochasticity. If carrying capacity decreases, changes in community structure occur at a much slower rate for the homogeneous compared to the heterogeneous communities. Even over short time periods, the difference in response to deterministic changes in carrying capacity between homogeneous and heterogeneous community models can be substantial, making the heterogeneous model a recommended starting point for commu Community dynamics Lognormal species abundance model Beta prime species abundance distribution Beverton–Holt density regulation Time dependent parameters Environmental stochasticitynity analysis. © 2016 Elsevier Inc. All rights reserved. Author postprint

Anglers that release Atlantic salmon (Salmo salar) in recreational fisheries do so with the intention that the fish will survive and contribute to succeeding generations. In some instances, salmon that are released may be recaptured, but mechanisms associated with recapture are unclear. To test whether gear avoidance influences recapture rates, we analysed data from tagging programmes in major Norwegian Atlantic salmon fishing rivers to determine how frequently salmon were recaptu red by different gear than that by which they were initially captured (i.e. gear switch). Among 339 salmon captured, externally tagged and released in 2012 and 2013, 46 (14%) were recaptured; 70% of these recaptured salmon exhibited gear switch. To test whether this gear switch percentage could be expected in the absence of gear avoidance, a simulation was conducted, which accounted for variation in catch probability among rivers and across time with different gear types based on comprehensive catch data. Each simulation step provided a simulated rate of gear switch under the null hypothesis of no gear avoidance. A distribution was generated, which described the probability that we would observe 70% gear switch. The simulated results indicated that this rate of gear switch was highly unlikely (P = 0.003) if recapture gear is assumed to be independent of initial capture gear, suggesting that salmon avoided familiar gear types. Changes to behaviour after release, including learned hook avoidance, may explain our observation of gear avoidance by recaptured salmon. fisheries management; recreational fisheries; fish behaviour

Farmed Atlantic salmon (Salmo salar) escape from net pens and enter rivers to spawn, potentially resulting in genetic introgression and reduced fitness of wild salmon. Here, we quantify genetic introgression of farmed to wild salmon, using molecular genetic markers, in populations from 147 salmon rivers, representing three-quarters of the total wild salmon spawning population in Norway. For 109 rivers with adult modern samples and sample sizes of 20 or more, the average level of farmed genetic introgression was 6.4% (median = 2.3%), with a range between 0.0% and 42.2%. Fifty-one of these rivers showed significant farmed genetic introgression when compared with historical reference samples. We observed a highly significant correlation between estimated farmed introgression and average proportion of escaped farmed salmon. We quantify levels of introgression as unweighted averages or weighted by population sizes, to compare geographical regions and to compare levels of introgression in rivers and fjords designated as locations deserving a high level of protection. We found a generally lower level of introgression in National Salmon Rivers and National Salmon Fjords subjected to formal protection by parliament. We conclude that farmed to wild genetic introgression is high in a large proportion of Norwegian salmon rivers, with the highest levels found in the most intensive areas of salmon farming. The extensive genetic introgression documented here poses a serious challenge to the management of farmed and wild Atlantic salmon in Norway and, in all likelihood, in other regions where farmed-salmon escape events occur with regularity

Given most Atlantic salmon (Salmo salar) released by anglers survive (proportion = 0.97 in this study), eco-nomically and culturally important recreational Atlantic salmon fisheries are increasingly incorporatingcatch-and-release. Sublethal alterations to behaviour with potential individual fitness costs are a possibleconsequence of catch-and-release but are difficult to measure empirically relative to uncaptured fish. Totest for sublethal effects of angling on migratory movements, 39 salmon were captured by recreationalanglers, externally tagged with radio transmitters, and released. Data from the annual visual drift countof spawning salmon were used to calculate the probability of spawning in each pool of the river and inputinto simulation models. Simulation models were used to test the hypothesis that catch-and-release didnot affect the upriver movement of 30 salmon tracked to spawning grounds. Ten thousand simulationsteps selected a spawning pool for each of the tagged salmon, permitting a calculation of the averageexpected movement by salmon for comparison to the average movement observed with telemetry. Theaverage observed movement by the released salmon was significantly less than the average expectedmovement generated by all three null models, indicating a sublethal effect of catch-and-release on themigration of Atlantic salmon.© 2016 Elsevier B.V. All rights reserved.

In this study, the potential of Malaise traps to collect representative portions of an insect community was investigated. To do so, the complete catch (nearly 22 000 specimens) of male Chironomidae (Diptera) from five parallel Malaise traps along an alpine stream was identified and assigned to 108 different species. The traps were run for 4 weeks in June and July, 2008. The similarity in community composition between parallel samples, that is, from different traps the same week, was evaluated by fitting a bivariate Poisson-lognormal species abundance model. The estimated correlation in this bivariate distribution was used as a measure of similarity since this approach is utilising all the available species abundance information and accounts for the sampling process. Estimated similarities showed non-significant differences in chironomid community structure between parallel samples. The five Malaise traps sampled equally representative portions of the Chironomidae community present at the site, so the traps were found to be very reliable in the monitoring of Chironomidae community structure. Application of the bivariate correlation as a similarity measure offers advantages over traditional measures because it takes account of the complete species abundance distributions. This approach provides an approximately unbiased estimate of similarity despite varying sample sizes and detection/non-detection of species that are present, but rare.

The movement behaviour of juvenile dusky kob Argyrosomus japonicus (n = 25) was studied in the 12 km long Great Fish Estuary, South Africa, by collecting telemetry data in relation to tidal conditions over 6.5 mo. Two behavioural patterns were observed. Tagged fish either moved in circatidal rhythms over long stretches up and down the estuary, corresponding to the speed and direction of the rise and fall of the tide, or remained stationary, often in deeper or struc- tured habitats. All individuals alternated between moving (mean 61% of the time) and stationary behaviour. Moving periods occurred during both light and dark periods. However, up-estuary movements were initiated most frequently at night, while down-estuary movements were initi- ated most frequently at dawn and dusk. The mean distance of the unidirectional movements was approximately 3.2 km. Ground speed for up-estuary movements (0.29 m s �1 ) was faster than for down-estuary movements (0.22 m s �1 ). These findings suggest that juvenile A. japonicus adopt 2 distinct feeding strategies within their turbid estuarine nursery habitats. 'Riding the tide', with minimal energy expenditure, may be a successful strategy when feeding on prey that follow the tidal current. Alternatively, in periods when they adopt a stationary behaviour, they may fulfil their foraging requirements by feeding on stationary and/or passing prey, while at the same time reducing predation risk in sheltered, structured habitats.

In this study, cost effective (in terms of reducing loss of power production) measures for increasing bypass migration of Atlantic salmon Salmo salar were developed and tested by establishing statistical models for timing of smolt migration and favourable diversion of water to the bypass. Initial tracking of radio-tagged smolts showed very low bypass migration under normal hydropower operations. Bypass migration increased when bypass discharge was experimentally increased and a model was developed that described relationships between total river discharge, bypass diversion and smolt migration route. Further improvements were obtained by installing two strobe lights at the power-production tunnel entrance that increased bypass migration during the night, but not during daytime. According to the behaviour of radio-tagged fish, the implemented measures contributed to increasing the annual percentage of bypass migration from 11 to 64%, and according to model predictions to 60-74% when the hydropower facilities were operated according to the developed models. To ensure correct timing of discharge diversion a smolt migration model was developed based on environmental variables that could successfully predict the general pattern of migration timing. The concept presented for improving smolt migration past hydropower intakes should be applicable in many systems where migration past hydropower installations cannot easily be solved by screening systems.

This study explores the ecological and economic impacts of interactions between escaped farmed and wild Atlantic salmon (Salmo salar, Salmonidae) over generations. An age- and stage-structured bioeconomic model is developed. The biological part of the model includes age-specific life-history traits such as survival rates, fecundity and spawning successes for wild and escaped farmed salmon, as well as their hybrids, while the economic part takes account of use and non-use values of fish stock. The model is simulated under three scenarios using data from the Atlantic salmon fishery and salmon farming in Norway. The social welfare is derived from harvest and wild salmon while the economic benefits of fishing comprise both sea and river fisheries. The results reveal that the wild salmon stock is gradually replaced by salmon with farmed origin, while the total social welfare and economic benefit decline, although not at the same rate as the wild salmon stock.

The EU Water Framework Directive (WFD) is in need of a practical method and index suitable for comparing the ecological status of invertebrate fauna in rivers throughout Europe. The uncertainties that characterize lotic sampling methods can be omitted by increasing sampling effort up to a species detection probability threshold. We describe a statistical model which provides the background for applying a sampling protocol aiming to record the total number of common and abundant species. Methods, sample standards and sorting time become less significant to the result as long as the total sample is sufficiently large to detect common species. An index called the Intercalibrated Benthic Invertebrate Biodiversity Index - IBIBI - is proposed based on Observed / Expected species ratios for EPT groups. The Ecological Quality Ratio thus obtained may then be adjusted to WFD's ecological status scale within each region or river type across Europe, which then can be compared and intercalibrated. Although offering a possible solution to the problem of intercalibration, further studies are needed.

This work comprises the structural characterization of Eucalyptus and Pinus radiata pulp fibers and their corresponding fibrillated materials, based on quantitative electron microscopy techniques. Compared to hardwood fibers, the softwood fibers have a relatively open structure of the fiber wall outer layers. The fibrillation of the fibers was performed mechanically and chemi-mechanically. In the chemi-mechanical process, the pulp fibers were subjected to a TEMPO-mediated oxidation to facilitate the homogenization. Films were made of the fibrillated materials to evaluate some structural properties. The thicknesses and roughnesses of the films were evaluated with standardized methods and with scanning electron microscopy (SEM), in backscattered electron imaging mode. Field-emission SEM (FE-SEM) and transmission electron microscopy (TEM) were performed to quantify the nanofibril morphology. In this study, we give additional and significant evidences about the suitability of electron microscopy techniques for quantification of nanofibril structures. In addition, we conclude that standard methods are not suitable for estimating the thickness of films having relatively rough surfaces. The results revealed significant differences with respect to the morphology of the fibrillated material. The differences are due to the starting raw material and to the procedure applied for the fibrillation.

1. Red-listed species are species of great conservation concern, but they are inherently difficult to observe. Therefore, prediction models for hotspots of such species would be very useful for biodiversity monitoring and management. 2. Red-listed species are ecologically heterogeneous, and they may be associated with many different environmental variables that may be more or less correlated. To overcome these challenges, we introduce a new technique to species richness modelling: Partial Least Squares Regression (PLSR), a multivariate regression technique developed specifically for similar statistical problems in econometrics. 3. Partial Least Squares Regression models were developed for hotspots of red-listed beetles associated with oaks. In this system, environmental variables and the richness of red-listed species were often correlated. 4. Without exceptions, the PLSR performed better as prediction models than generalised linear models (GLM) and principal components regression (PCR). 5. Different combinations of variables associated with individual trees were important in continuous forest with a closed canopy and a natural understory vs. man-made wooded park landscapes. 6. Our results suggest that important variables related to hotspots for red-listed species in forests in forests are trees with cavities of intermediate size, as well as dead wood and broadleaved tree species other than oak in the surrounding forest. In parks, large trees with wood mould, but also other oak trees in the surroundings, seem to be important. 7. In conclusion, the PLSR models may be used to improve the prediction of species richness in the presence of many correlated predictors and thus improve biodiversity monitoring and management.

Eleven Arctic charr (Salvelinus alpinus) (370–512 mm) and eight sea trout (Salmo trutta) (370–585 mm in length) were tagged externally or internally with depthand temperature-measuring data-storage tags (DST) before they were released into the sea in the Alta Fjord in north Norway in June 2002. All sea trout were recaptured after they spent 1–40 days at sea, while all Arctic charr were recaptured after 0.5–33 days at sea. On average, trout preferred water about 0.6 m deeper and 1.3� C warmer than Arctic charr. Arctic charr spent >50% of their time between 0 and 1 m depth, while trout spent >50% of their time between 1 and 2 m depth. Both species spent >90% of their time in water no deeper than 3 m from the water surface. However, sea trout dove more frequently and to greater depths (max. 28 m) than Arctic charr (max. 16 m), and these deep dives were most frequently performed at the end of the sea migration. Arctic charr demonstrated a diel diving pattern, staying on average about 0.5 m deeper between 08:00 hours and about 15:00 hours than during the rest of the 24 h, even though there was continuous daylight during the experiments. When comparing data obtained from the DSTs with temperature measurements within the fjord system, the two species were observed to select different feeding areas during their sea migration, the sea trout choosing the inner and warmer parts of the fjord, in contrast to the Arctic charr that preferred the outer, colder parts of the fjord. The observed differences in migration behaviour between the two species are discussed in relation to species preferences for prey and habitat selection, and their optimal temperatures for growth.

Ecological monitoring programmes should provide precise data to inform management, but the data quality is often limited by methodological challenges and the need for cost-effective sampling. Parasite infestations are particularly challenging to monitor due to complex interactions among hosts, parasites and the environment. In Norway, salmon lice infestations on wild salmonid fish have been mon- itored since 1992 to survey the potential transmission between farmed and wild salmonids. Here, we com- pared spatiotemporal variation in salmon lice levels with variations in local fjord conditions, including salinity, temperature and infestation pressure from salmon farms (measured as mean abundance of ma- ture female lice × number of farmed fish). We tested 3 different measures of infestation with different statis- tical properties. Our results confirm that, even after correcting for temperature and salinity effects, in - festation pressure from salmon farms significantly increases the probability of lice infestation in wild salmonids. The probability of infestation increases with fish body length, salmon farm infestation pres- sure and tem perature, and decreases with increasing freshwater influence. Furthermore, we found a signif- icant interaction between temperature and infestation pressure from salmon farms. When the infestation pressure from farms is low, temperature has a strong increasing effect on the probability of infestation, but as the infestation pressure from farms increases, tem- perature gradually becomes less important. The exact results vary somewhat depending on the measure of lice infestations used, but the same trend can be seen in all models. We discuss the statistical and biological complexities that make monitoring of salmon lice in wild populations challenging.

Several studies have documented the genetic effects of intraspecific hybridization of cultured and wild Atlantic salmon (Salmo salar L.). However, the effect of salmon aquaculture on wild congeners is not so well understood. Diseases, introduced or increased in incidence by salmon aquaculture activities, may have an impact on co-occurring wild sea trout (Salmo trutta L.), as implied by the steep decline in sea trout numbers in many Irish, Scottish, and Norwegian rivers since the late 1980s, which may be linked to sea lice infestations associated with marine salmonid farming. Our data suggest that salmon farming and ocean ranching can indirectly affect, most likely mediated by disease, the genetics of cohabiting sea trout by reducing variability at major histocompatibility class I genes. We studied samples of DNA extracted from scales of sea trout in the Burrishoole River, in the west of Ireland, before and at intervals during aquaculture activities. In these samples, allelic variation at a microsatellite marker, tightly linked to a locus critical to immune response (Satr-UBA), was compared with variation at six neutral microsatellite loci. A significant decline in allelic richness and gene diversity at the Satr-UBA marker locus, observed since aquaculture started and which may indicate a selective response, was not reflected by similar reductions at neutral loci. Subsequent recovery of variability at the Satr-UBA marker, seen among later samples, may reflect an increased contribution by resident brown trout to the remaining sea trout stock.

Hindar, K., Fleming, I. A., McGinnity, P., and Diserud, O. 2006. Genetic and ecological effects of salmon farming on wild salmon: modelling from experimental results. � ICES Journal of Marine Science, 63: 1234e1247. Cultured salmonids are released or escape into the wild in large numbers and may make up significant proportions of wild salmonid populations in fresh- and saltwater, causing considerable concern for the fitness and productivity of these populations. This paper focuses on the effects of escaped farmed Atlantic salmon (Salmo salar) on wild salmon. Farmed salmon have been under artificial selection for growth and other economically important traits for 30 years and are genetically different in their origin at the molecular and quantitative genetic levels. Escaped farmed salmon spawn in the wild with limited success. Their offspring outgrow those of wild origin but suffer higher mortality. Whole-river experiments in Ireland and Norway have shown that the lifetime success of farmed salmon is reduced relative to wild salmon. Based on data from these experiments, we model the future of wild salmon populations experiencing invasions of escaped farmed salmon. Simulations with a fixed intrusion rate of 20% escaped farmed salmon at spawning suggest that substantial changes take place in wild salmon populations within ten salmon generations (w40 years). Low-invasion scenarios suggest that farmed offspring are unlikely to become established in the population, whereas high-invasion scenarios suggest that populations are eventually mixtures of hybrid and farmed descendants. Recovery of the wild population is not likely under all circumstances, even after many decades without further intrusion. Managers of wild salmon will have difficulty in obtaining broodstock of the original wild population after a few generations of high intrusion. We conclude that further measures to reduce escapes of farmed salmon and their spawning in wild populations are urgently needed.

Current methods for measuring similarity among phytophagous insect communities fail to consider the phylogenetic relationship between host plants. We analysed this relation based on 3580 host observations of 1174 beetle species associated with 100 species of angiosperms in two different forest types in Panama. We quantified the significance of genetic distance as well as taxonomic rank among angiosperms in relation to species overlap in beetle assemblages. A logarithmic model describing the decrease in beetle species similarity between host-plant species of increasing phylogenetic distance explains 35% of the variation. Applied to taxonomic rank categories the results imply that except for the ancient branching of monocots from dicots, only adaptive radiations of plants on the family and genus level are important for host utilization among phytophagous beetles. These findings enable improvements in estimating host specificity and species richness through correction for phylogenetic relatedness between hosts and consideration of the host-specific fauna associated with monocots.

When comparing samples to evaluate changes in community structure, there are several uncertainties that must be taken into consideration. Sampling inevitably induces randomness in observed species composition and abundance. Even if they come from exactly the same community, two samples may show considerable differences. If the sampling effort varies, differences will increase even more. Finally, when time has elapsed between samples, we would like to correct for variations in true species abundance occurring naturally due to fluctuating environmental conditions. In this paper we develop a test method that corrects for sampling in general, as well as for differential sampling efforts. The species abundances are also allowed to vary in time, enabling us to test for additional changes in community structure due to some extraordinary event. The method will be useful when analyzing consequences of human-induced disturbances, such as pollution, but also natural catastrophes, such as fire, flooding, extreme weather, or arrival of new species. Here, our method will be applied to a pair of samples from an insect community. We found that the result was affected by the way we chose to measure the community structure, and that the conclusion depended heavily on the estimate of the environmental variation.

Estimates of the global number of arthropod species range from 2 million to more than 30 million species. One of the most critical assumptions affecting the higher of these estimates is the assumed magnitude of host specificity of phytophagous insects, which varies considerably. Difficulties in estimating this value are caused by both lack of satisfactory data sets and lack of methods for its objective calculation. We provide a new method for predicting host specificity for phytophagous insects at a local scale based on the concept of ef- fective specialization. When the insect-plant host associations of a restricted number of plant species are known, we can predict the magnitude of host specificity when more plant species are included. Based on 2561 host observations of 697 beetle species on 50 plant species in the canopies of a tropical dry forest in Panama, we predict that host specificity for adult phytophagous beetles in this forest range from 7% to 10%. These values suggest that the higher estimates of global species richness are not tenable.