Time filter

Source Type

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. Source

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. Source

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. Source

Vladic T.,University of Stockholm | Forsberg L.A.,Sodertorn 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. Source

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. Source

Discover hidden collaborations