| 1. |
- Ahlbeck, Ida, et al.
(författare)
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Evaluating fish diet analysis methods by individual-based modelling
- 2012
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 0706-652X .- 1205-7533. ; 69:7, s. 1184-1201
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of diet compositions is important in ecological research. There are many methods available and numerous aspects of diet composition. Here we used modelling to evaluate how well different diet analysis methods describe the true diet of fish, expressed in mass percentages. The methods studied were both basic methods (frequency of occurrence, dominance, numeric, mass, points) and composite indices (Index of Relative Importance, Comparative Feeding Index). Analyses were based on both averaged stomach content of individual fish and on pooled content from several fish. Prey preference, prey size, and evacuation rate influenced the performance of the diet analysis methods. The basic methods performed better than composite indices. Mass and points methods produced diet compositions most similar to the true diet and were also most robust, indicating that these methods should be used to describe energetic-nutritional sources of fish.
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| 4. |
- Bartolino, Valerio, 1979, et al.
(författare)
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Historical spatiotemporal dynamics of eastern North Sea cod
- 2012
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - : Canadian Science Publishing. - 0706-652X .- 1205-7533. ; 69:5, s. 833-841
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Tidskriftsartikel (refereegranskat)abstract
- Recent analyses of historical data of fish abundance and distribution have shown the importance of a long temporal perspective in the evaluation of the current status of fish populations, but pose numerous difficulties such as fragmentation and inhomogeneities in the amount of available information in space and time. Using mixed-effects models in a multiscale analysis, we identified an appropriate spatiotemporal scale of investigation of a high-quality, spatially explicit historical data set, and we reconstructed the long-term spatial dynamics of Atlantic cod (Gadus morhua) in the Kattegat– Skagerrak along the 20th century. We identified a northern and southern main aggregation of adult cod in the study area, corresponding to the Skagerrak portion of the North Sea and the Kattegat cod stocks, respectively. The stocks showed specificities in their spatial dynamics, but common extensive loss of coastal aggregations during the last decades when only 13% (Kattegat) and 35% (Skagerrak) of the estimated early century cod biomass was left. Our reconstruction showed that the collapse of the cod stocks in the area followed the peak in landings in the 1960s–1970s, suggesting that the postwar development of the industrial fisheries played a major role in the decrease of local abundances and disappearance of local adult cod aggregations.
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| 5. |
- Berggren, Terese, et al.
(författare)
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Warmer water increases early body growth of northern pike (Esox lucius), but mortality has larger impact on decreasing body sizes
- 2021
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - : Canadian Science Publishing. - 0706-652X .- 1205-7533. ; 79, s. 771-781
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Tidskriftsartikel (refereegranskat)abstract
- Large fish species often display truncated size distributions related to harvest. In addition, temperature, food availability and density dependence affect body growth and together with natural mortality influence population size structure. Here we study changes in body growth, size distributions and mortality in both harvested and nonharvested populations of northern pike (Esox Lucius) over 50 years along the Baltic Sea coast and in Lake Malaren, Sweden. For coastal pike, body growth has increased coincidentally with increasing water temperatures, yet in the last two decades there has been a decrease of larger individuals. In Lake Malaren, in contrast, size distributions and body growth were stationary despite similar increases in water temperature. A dominance of slow-growing individuals in older age classes was evident in all studied populations, also in the no-take zone, suggesting other factors than fishing contribute to the mortality pattern. We propose that increasing temperatures have favoured body growth in coastal areas, but this has been counteracted by increased mortality, causing pike sizes to decline. To regain larger coastal pike, managers need to consider multiple measures that reduce mortality.
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| 6. |
- Bohman, Patrik, et al.
(författare)
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Predicting harvest of non-native signal crayfish in lakes —a role for changing climate?
- 2016
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - : Canadian Science Publishing. - 0706-652X .- 1205-7533. ; 73:5, s. 785-792
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Tidskriftsartikel (refereegranskat)abstract
- The signal crayfish (Pacifastacus leniusculus) was introduced to Sweden in 1960, and it has a high commercial and recreational value, but it may also have negative effects on native ecosystems. To better predict how climate warming will affect population dynamics of this cool-water crayfish, we explored the role of temperature and density dependence as explanatory factors of the subsequent years’ catch rates of commercially sized signal crayfish in four Swedish lakes. We found air temperatures to be good proxies for water temperatures in all lakes, except during winter. We could only obtain water temperature data for Lake Vättern, and winter temperature data were therefore only included in the analysis of catch-per-unit-effort patterns in this lake. Our results indicate that increasing mean air temperatures will potentially affect the population dynamics of coolwater freshwater crayfish species such as the signal crayfish. Based on data from four lakes, it seems that the population dynamics of signal crayfish are lake-specific and could be affected by either recruitment during the juvenile stage, the survival and growth of adults, or both. Increased fluctuations in water temperature during winter may potentially influence adult survival. To better predict the effects of global warming on the dynamics of cool-water crayfish populations, we suggest that future studies should investigate recruitment in crayfish along temperature gradients and the influence of variations in water temperature on winter mortality.
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| 7. |
- Brodin, Tomas, et al.
(författare)
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Electronic tagging and tracking aquatic animals to understand a world increasingly shaped by a changing climate and extreme weather events
- 2024
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 0706-652X .- 1205-7533. ; 81, s. 326–339-
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Forskningsöversikt (refereegranskat)abstract
- Despite great promise for understanding the impacts and extent of climate change and extreme weather events on aquatic animals, their species, and ecological communities, it is surprising that electronic tagging and tracking tools, like biotelemetry and biologging, have not been extensively used to understand climate change or develop and evaluate potential interventions that may help adapt to its impacts. In this review, we provide an overview of methodologies and study designs that leverage available electronic tracking tools to investigate aspects of climate change and extreme weather events in aquatic ecosystems. Key interventions to protect aquatic life from the impacts of climate change, including habitat restoration, protected areas, conservation translocations, mitigations against interactive effects of climate change, and simulation of future scenarios, can all be greatly facilitated by using electronic tagging and tracking. We anticipate that adopting animal tracking to identify phenotypes, species, or ecosystems that are vulnerable or resilient to climate change will help in applying management interventions such as fisheries management, habitat restoration, invasive species control, or enhancement measures that prevent extinction and strengthen the resilience of communities against the most damaging effects of climate change. Given the scalability and increasing accessibility of animal tracking tools for researchers, tracking individual organisms will hopefully also facilitate research into effective solutions and interventions against the most extreme and acute impacts on species, populations, and ecosystems.
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| 8. |
- Carlström, Julia, et al.
(författare)
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Spatial and temporal impact of pingers on porpoises
- 2009
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 0706-652X .- 1205-7533. ; 66:1, s. 72-82
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Tidskriftsartikel (refereegranskat)abstract
- Bycatches are considered the most serious threat to harbour porpoises (Phocoena phocoena) and other small cetaceans worldwide. Pingers are used to reduce bycatch levels, but may also deter porpoises from critical habitats. We investigated the spatial and temporal responses of porpoises to simulated bottom-set nets equipped with periodically operating Dukane NetMark 1000 pingers. Echolocation rates were monitored by porpoise click train detectors (PODs) placed at and around the nets, and a shore-based observation team recorded surfacing positions and movements. Pinger sound significantly reduced the median echolocation encounter rate by 50%–100% at PODs placed up to 500 m and reduced the sighting rate up to 375 m from the simulated net. The average distance of approach increased by 300 m. When pingers were silent after being active for 24 h 50 min, the return time of porpoises was 6 h, in comparison with 2.5 h after pingers had been silent. During the study period of approximately 50 days, habituation was detectable at two of nine PODs. The results indicate that pingers affect porpoises at greater distances than previously observed. This confirms that pingers are an effective bycatch mitigation measure, but alternative solutions should be applied in ecologically important habitats and migration routes. An example is given from the Baltic region. Bycatches are considered the most serious threat to harbour porpoises and other small cetaceans worldwide. Pingers are used to reduce bycatch levels, but may also deter porpoises from critical habitats. We investigated the spatial and temporal responses of porpoises to simulated bottom set nets equipped with periodically operating Dukane NetMark 1000 pingers. Echolocation rates were monitored by porpoise click train detectors (PODs) placed at and around the nets, and a shore-based observation team recorded surfacing positions and movements. Pinger sound significantly reduced the median echolocation encounter rate by 50-100% at PODs placed up to 500m, and the sighting rate up to 375m from the simulated net. The average distance of approach increased by 300m. When pingers were silent after being active for 24h 50min, the return time of porpoises was 6h, in comparison to 2.5h after pingers had been silent. During the study period of approximately 50 days, habituation was detectable at two of nine PODs. The results indicate that pingers affect porpoises at greater distances than previously observed. This confirms that pingers are an effective bycatch mitigation measure, but alternative solutions should be applied in ecologically important habitats and migration routes. An example is given from the Baltic region.
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| 9. |
- Dekker, Willem, et al.
(författare)
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Assessment of the fishing impact on the silver eel stock in the Baltic using survival analysis
- 2013
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - : Canadian Science Publishing. - 0706-652X .- 1205-7533. ; 70:12, s. 1673-1684
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Tidskriftsartikel (refereegranskat)abstract
- Restoration of the depleted stock of the European eel (Anguilla anguilla (L.)) requires anthropogenic impacts to bequantified, reduced, and controlled. In this article, we assess the impact of the silver eel fishery on the Baltic Coast in Sweden, applying survival analysis to 60 years of mark–recapture experiments, involving 8000 recaptures out of 18 000 releases. Thehazard of being recaptured (overall 46%) varies along the coast and declined substantially over the decades. But, most notably,the hazard for the individual diminishes strongly after the first kilometres en route. This individualized hazard disqualifies themore traditional mark–recapture methodology, which assumes random recaptures. We advocate the general use of survivalanalysis for conventional mark–recapture data. The result of our analysis indicates that the impact of the fishery just prior the2009 fishing restrictions was in the order of 10%—in itself well within sustainability limits, though only but one of the factors contributing to the mortality in the Baltic Sea.
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| 10. |
- Ek, A S, et al.
(författare)
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A paleolimnological assessment of the effects of post-1970 reductions of sulfur deposition in Sweden
- 2001
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 0706-652X .- 1205-7533. ; 58:8, s. 1692-1700
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of diatoms in sediment cores from 10 acidic (pH < 6) lakes in southern Sweden shows that eight of the lakes have acidified after 1950, while two lakes have not significantly acidified. However, since the 1970s, sulfur deposition has decreased by 50%, and lake water chemistry monitored since 1983 shows an initial reversal of acidification. However, the diatom data do not indicate that a general recovery in pH has occurred yet. The diatoms show that a small recovery has occurred in only one lake (pH increase from 4.7 to 4.9). The 10 lakes vary in total organic carbon content from 2 to 17 mg.L-1. According to the diatoms, the lakes with high total organic carbon (>9 mg.L-1) have not acidified as much as the lakes with lower total organic carbon (<7 mg.L-1). We ascribe this difference in response to acid deposition to the buffering capacity of organic acids. Knowledge of the role of organic acids when combined with anthropogenic acid deposition is important in predicting responses to decreasing acid deposition and the time scales required for recovery. Paleolimnological methods are shown here to provide valuable information for these purposes as well as to provide a long-term perspective on lake acidity changes needed for the evaluation of recovery.
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