Institute of Freshwater Research

Swedish, Sweden

Institute of Freshwater Research

Swedish, Sweden
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Ljunggren L.,Institute of Coastal Research | Sandstrom A.,Institute of Freshwater Research | Bergstrom U.,Institute of Coastal Research | Mattila J.,Åbo Akademi University | And 6 more authors.
ICES Journal of Marine Science | Year: 2010

The dominant coastal predatory fish in the southwestern Baltic Sea, perch and pike, have decreased markedly in abundance during the past decade. An investigation into their recruitment at 135 coastal sites showed that both species suffered from recruitment failures, mainly in open coastal areas. A detailed study of 15 sites showed that areas with recruitment problems were also notable for mortality of early-stage larvae at the onset of exogenous food-intake. At those sites, zooplankton abundance predicted 83 and 34% of the variation in young of the year perch and pike, respectively, suggesting that the declines were caused by recruitment failure attributable to zooplankton food limitation. Incidences of recruitment failure match in time an offshore trophic cascade that generated massive increases in planktivorous sprat and decreases in zooplankton biomass in the early 1990s. Therefore, sprat biomass explained 53% of the variation in perch recruitment from 1994 to 2007 at an open coastal site, where three-spined stickleback also increased exponentially after 2002. The results indicate that the dramatic change in the offshore ecosystem may have propagated to the coast causing declines of the dominating coastal predators perch and pike followed by an increase in the abundance of small-bodied fish. © 2010 International Council for the Exploration of the Sea.


Sundblad G.,Institute of Coastal Research | Sundblad G.,Uppsala University | Bergstrom U.,Institute of Coastal Research | Sandstrom A.,Institute of Freshwater Research
Journal of Applied Ecology | Year: 2011

The juvenile stages of fish are often dependent on specific habitat types for their survival. Protecting these habitats may be crucial for maintaining strong adult stocks. The Natura 2000 network of the European Union offers protection of marine habitats that are essential for the recruitment of many fish species. By protecting these critical habitats the network may be important for maintaining the stocks of these fish species. 2.We present a spatially explicit, GIS-based, assessment of two important components of the ecological coherence of Marine Protected Area (MPA) networks: representativity and connectivity. Representativity can be measured as the proportion of each conservation feature that is protected, whereas connectivity assesses the spatial configuration of the network. We apply these analyses to study the ecological coherence of the Natura 2000 network in a 30 000-km2 archipelago in the Baltic Sea, with respect to a coastal fish assemblage and associated habitats. The analyses are based on fish distribution maps that have been constructed by statistically relating life stage specific occurrence to environmental variables, and thereafter making spatial predictions based on maps of the environmental variables. 3.The map-based analyses show that both the representativity and the connectivity of the network are poor with respect to the studied fish species. In total, 3.5% (11 km2) of the assemblage recruitment habitat was protected and 48% of the potentially connected habitats were included in the MPA network. 4.The assessment explicitly identified geographical areas, visually communicated using maps, where the network should be improved to ensure ecological coherence. 5.Synthesis and applications.Many MPA networks around the world, such as the Natura 2000 network in Europe, have recently come into effect. Establishment of the networks has often been governed by opportunity rather than by strict ecological analyses, primarily because distribution maps of species and habitats have been unavailable. Map-based assessments of the strengths and weaknesses of evolving MPA networks, such as the one presented here, are needed in adaptive management. They can provide an efficient tool for visualising and communicating the results to stakeholders and policy makers in the process of working towards ecological coherence. © 2010 The Authors. Journal of Applied Ecology © 2010 British Ecological Society.


Vladic T.,University of Stockholm | Forsberg L.A.,Södertörn University College | Jarvi T.,University of Stockholm | Jarvi T.,Institute of Freshwater Research
Aquaculture | Year: 2010

The maintenance of brood stock in appropriate conditions is an important requirement for the production of high quality offspring. In this study, we investigated fertility of the two life history forms of Atlantic salmon males, precocious parr, brought up in breeding tanks in the hatchery and anadromous, migratory sea-ranched males, caught when returning to the home river. The sperm quality was assessed by experiments between equal amount of sperm from one adult and one parr male in competition to fertilize eggs of a single female. The paternity was determined by a microsatellite analysis. Parr males achieved greater reproductive success than anadromous males under competition, and anadromous adults had greater fertility in controls as compared to the sperm competition situation. In total, parr males achieved 3.6 times greater fertilization success than anadromous males. Sperm ATP content contributed significantly to male fertility. Our results provide evidence that ejaculates of precociously mature Atlantic salmon parr are of increased quality as an adaptation to high sperm competition intensity due to better maintenance in the fish farm than in the wild. © 2010 Elsevier B.V. All rights reserved.


Wahlberg M.,University of Southern Denmark | Westerberg H.,Institute of Freshwater Research | Aarestrup K.,Technical University of Denmark | Feunteun E.,French National Center for Scientific Research | And 2 more authors.
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2014

Temperature and depth logging tags were implanted into adult eels released on Atlantic west coasts of France and Ireland to study their oceanic migration behavior. For three of the tags, 25 to 256 days after release there was a dramatic rise in temperature from 10. °C to 36. °C and the dive profile changed from depths of 300-1000. m to repeated ascents to the surface. This indicated that the eels carrying the tags had been eaten by a mammalian predator. Two of the tags had sufficient sampling rate to resolve the dives in detail. They recorded a total of 91 dives to maximum depths of 250-860. m lasting 11-12. min and with surface intervals of 5-7. min. More than two thirds of the dives included a rapid descent from approximately 500. m to 600-700. m. From this we infer that the predator was most likely a deep-diving toothed whale. The dives logged while the tags were inside the predator revealed that the temperature usually decreased during dives, and increased again during surface periods. The temperature drops during dives were probably caused by the ingestion of prey or water. These observations provide insights into the behavior of toothed whales foraging in the mesopelagic zone. © 2014 Elsevier Ltd.


Sahlin U.,Lund University | Smith H.G.,Science 37 | Edsman L.,Institute of Freshwater Research | Bengtsson G.,Lund University
Journal of Applied Ecology | Year: 2010

1. The signal crayfish Pacifastacus leniusculus is an invasive species in Sweden, threatening the red-listed nobel crayfish Astacus astacus through spreading the crayfish plague. Time-to-event models can handle censored data on such introduced populations for which the state (successful or not) is only partially known at the last observation, but even though data on introduced populations most often are censored, this type of model is usually not used for likelihood-based inference and predictions of the dynamics of establishing populations.2. We specified and fitted a probabilistic time-to-event model to be used to predict the time to successful establishment of signal crayfish populations introduced into Sweden. Important covariates of establishment success were found by the methods of 'model averaging' and 'hierarchical partitioning', considering model uncertainty and multi-colinearity, respectively.3. The hazard function that received the highest evidence based on the empirical data showed that the chances of establishment were highest in the time periods immediately following the first introduction. The model predicts establishment success to be <50% within 5 years after first introduction over the current distributional range of signal crayfish in Sweden today.4. Among covariates related to temperature, fish species and physical properties of the habitat, the length of the growing season was the most important and consistent covariate of establishment success. We found that establishment success of signal crayfish is expected to increase with the number of days when growth is possible, and decrease with the number of days with extremely high temperatures, which can be seen to approximate conditions of stress.5. Synthesis and applications. The results demonstrate lower establishment success of signal crayfish further north in Sweden, which may decrease the incentives of additional illegal introductions that may threaten the red-listed noble crayfish Astacus astacus. We provide a fully probabilistic statistical evaluation that quantifies uncertainty in the duration of the establishment stage that is useful for management decisions of invasive species. The combination of model averaging and hierarchical partitioning provides a comprehensive method to address multi-colinearity common to retrospective data on establishment success of invasive species. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.


Verspoor E.,Marine Scotland - Marine Laboratory | Knox D.,Marine Scotland - Marine Laboratory | Greer R.,Natural Resources Scotland | Hammar J.,Institute of Freshwater Research
Hydrobiologia | Year: 2010

Three ecologically and morphologically distinct forms of Arctic charr (Salvelinus alpinus L.) have been identified in Loch Rannoch, Scotland, whose evolutionary status and origins are incompletely understood. A study was made of restriction fragment length polymorphism (RFLPs) detected variation in the D-loop, ND1 and cytochrome b regions of the mitochondrial genome, encompassing >3500 bp. Eight RFLP haplotypes were identified that clustered into three distinct clans based on restriction differences and into four clans based on sequence differences. Significant differences in RFLP frequencies were found among all morph groups. The pelagic morph was highly divergent from the two benthic forms, with the benthic forms having variants from only one genetic clan while the pelagic was dominated by a single variant from another clan. The relative divergence observed among benthic and pelagic forms is ~10 fold greater when nucleotide divergence among the haplotypes, as well as haplotype frequency differences, is taken into account. Sequence divergence between haplotypes in the two main clans is of a similar order to that between haplotypes in these clans and a charr from North America. In contrast, divergence among the two benthic morphs relates entirely to differences in haplotype frequencies. The study confirms the genetic distinctiveness of the pelagic and benthic forms as well as of the two benthic forms. It strongly supports previous evidence that the genetic divergence between the pelagic and benthic populations is allopatric in origin. Additionally, the results strongly suggest that the two benthic populations have undergone peripatric divergence through the sequential colonisation of the two basins by one lineage, followed by their spatial separation and reproductive isolation. © 2010 Crown Copyright Marine Scotland.


Bohman P.,Swedish University of Agricultural Sciences | Bohman P.,Institute of Freshwater Research | Edsman L.,Swedish University of Agricultural Sciences | Edsman L.,Institute of Freshwater Research
Freshwater Crayfish | Year: 2011

In Sweden, there are two species of crayfish, the native noble crayfish and the introduced signal crayfish. More than 95% of noble crayfish populations have been lost due to crayfish plague, acidification, pollution and more recently, the accelerated spread of the crayfish plague due to illegal introductions of signal crayfish. An Action Plan for the conservation of noble crayfish has been adopted. This paper describes the current status of noble crayfish in Sweden, and also the process to form management areas with distinctly different basic conditions to conserve noble crayfish. The crayfish situation was monitored with data from the Swedish crayfish database. A questionnaire was also sent to the 21 county administrations' fishery experts. As a result, three management areas were identified. In the northern area, including the island of Gotland, availability of information is regarded as the most important factor for a successful Action Plan, since the most stable noble crayfish populations are situated here. In the southern area, more defensive conservation strategies will focus on remote and isolated populations. In the middle area, the situation is more acute, and there is a need to focus on offensive strategies towards protected areas and education. © 2011 International Association of Astacology.


Clevestam P.D.,Institute of Freshwater Research | Ogonowski M.,University of Stockholm | Sjoberg N.B.,Institute of Freshwater Research | Wickstrom H.,Institute of Freshwater Research
Journal of Fish Biology | Year: 2011

Individual net fat reserves after migration and reproductive investments were calculated for migrating female silver eels Anguilla anguilla (n = 387) collected in the outlet region of the Baltic Sea during the autumn run. It is estimated that 20·4% of the A. anguilla had completely exhausted all initial fat reserves and that 45·0% of A. anguilla were within 90% of complete energy depletion after migration and reproduction. This study concludes that a combination of body size and distance (6900 km) to the spawning area in the Sargasso Sea explains the results. An increase in the costs of migration due to heavy infection with Anguillicoloides crassus was also evaluated in an additional scenario with results showing that 26·4% of the A. anguilla had completely depleted all fat reserves. It is hypothesized that a large proportion of female silver A. anguilla from the Baltic Sea catchment area will have inadequate or suboptimal reserves for successful migration and reproduction. © 2011 The Authors. Journal of Fish Biology © 2011 The Fisheries Society of the British Isles.


Petersson E.,Institute of Freshwater Research | Valencia A.C.,Institute of Freshwater Research | Jarvi T.,Institute of Freshwater Research
Ecology of Freshwater Fish | Year: 2015

Many studies have documented that hatchery-reared salmonids generally have inferior survival after being stocked compared with wild conspecifics, hatchery and wild salmonids have been observed to differ in their antipredator responses. The response of brown trout (Salmo trutta) juveniles (0+) of differing backgrounds to a live predator was compared in two experiments. First, the antipredator behaviour of predator-naïve hatchery-reared brown trout and wild-exposed brown trout were assessed in behavioural trials which lasted for eight days. Second, predator-naïve and predator-conditioned hatchery-reared brown trout were assessed in identical behavioural trials. Brown trout were 'predator-conditioned' by being held in a stream-water aquarium with adult Atlantic salmon (Salmo salar) and adult brown trout for two days prior to behavioural trials. Predator-conditioned hatchery-reared brown trout spent more time in shelters in the trial aquaria than predator-naïve hatchery-reared fish, but did not differ in time spent in the predator-free area. Predator conditioning may account for the increased time spent in the shelter, but does not appear to have affected time spent in the predator-free area. However, even if significant alteration in behaviour can be noted in the laboratory, the response might not be appropriate in the wild. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.


Fjalling A.B.,Institute of Freshwater Research
Knowledge and Management of Aquatic Ecosystems | Year: 2011

When managing crayfish populations, it is important to have access to reliable data on population densities and growth of juveniles. Present sampling methods are mostly active and often labor intensive, do not always yield quantitative data, and may harm the crayfish. A new passive method is described which aims to avoid these disadvantages. It uses a 0.09 m2 trap which is set on the river or lake bottom, well in advance of expected hatching of crayfish eggs. The trap has a substrate which juveniles colonize and a net that fences them in and captures them when the trap is lifted. In field tests, the new trap provided data on mean density (29·m-2) and mean total length (22 mm) of young-of-year signal crayfish which were comparable to data from suction sampling. The enclosure trap may provide data for recruitment studies and become a tool in crayfish research in general. © ONEMA, 2011.

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