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- Mustamäki, Noora, et al.
(författare)
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Pikeperch (Sander lucioperca (L.)) in Decline: High Mortality of Three Populations in the Northern Baltic Sea
- 2014
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Ingår i: AMBIO: A Journal of the Human Environment. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 43, s. 325-336
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Tidskriftsartikel (refereegranskat)abstract
- The development of three pikeperch (Sander lucioperca (L.)) populations in the northern Baltic Sea was monitored using standardized multimesh gillnets in 1995-2009. Declining trends in the abundances of pikeperch over 40 cm total length, low numbers of individuals older than 6 years, and high mortality rates were observed in all three populations. In the site with the largest commercial catches per unit area and a rapidly increased colony of great cormorants (Phalacrocorax carbo sinensis Blumenbach 1798), also the abundance of pikeperch below 40 cm total length and year-class strength showed declining trends. The adverse population level changes did not correlate with changes in water quality or eutrophication status. Together, the results suggest that in all study sites fisheries are harvesting a large proportion of the pikeperch soon after or even before reaching the maturity, and that predation from great cormorants may increase mortality of juveniles. Pikeperch is important not only for fisheries but also for ecosystem functioning, and our results point at the need for further management measures to ensure viable populations in the areas studied.
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| 2. |
- Olsson, Jens, et al.
(författare)
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Abundance of coastal fish key functional groups
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This core indicator evaluates the abundance of selected functional groups of coastal fish in the Baltic Sea. As a rule,good status is achieved when the abundance of piscivores (i.e. fish that feed on other fish) is above a site-specific threshold value,and the abundance ofcyprinidsor mesopredators(i.e. mid trophic-level fish) is within an acceptable rangefor the specific site. The status of functional groups of coastal fish in the Baltic Sea has been evaluated by assessing the status of piscivores and cyprinids/mesopredatorsduring the period 2011-2015.
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| 3. |
- Olsson, Jens, et al.
(författare)
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Abundance of coastal fish key functional groups. HELCOM core indicator report
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This core indicator evaluates the abundance of selected functional groups of coastal fish in the Baltic Sea. As a rule, good status is achieved when the abundance of piscivores (i.e. fish that feed on other fish) is above a site-specific threshold value, and the abundance of cyprinids or mesopredators (i.e. midtrophic-level fish) is within an acceptable range for the specific site. The status of functional groups of coastal fish in the Baltic Sea has been evaluated by assessing the status of piscivores and cyprinids/mesopredators during the period 2011-2015. For piscivores, good status is achieved in 24 out of a total of 29 monitoring locations, and for 13 coastal HELCOM assessment units out of the 16 that were evaluated. For cyprinids/mesopredators, good status is only achieved in 15 of the 27 monitored locations and thus in seven of the 16 evaluated assessment units. In the locations classified as not good, the abundance of cyprinids was too high in all but one (Hiiumaa, Estonia) of the 12 locations. The environmental status indicated by piscivores is hence slightly better compared to that indicated by cyprinids. Generally, the status of piscivores is better in more northern areas compared to more central areas. For cyprinids/mesopredators, good status is not achieved in the Swedish part of the Quark and Åland Sea, in all Finnish coastal waters except for the Bothnian Bay, and in Estonian and Latvian coastal waters. The level of confidence of the assessment differs across areas and regions as a result of differences in monitoring methodology as well as in some countries poor temporal and spatial coverage of monitoring due to poor financial support for monitoring. The methodological confidence is high in all areas and the confidence in the accuracy of the assessment is high in majority of the assessment units. The confidence in the temporal coverage is high in all areas except for the Latvian and Lithuanian areas, and the confidence in spatial representa bility is the highest in the Finnish areas but poorer in other countries. The indicator is operational in the coastal waters of most countries bordering the Baltic Sea. For the time being, it is not applicable in some areas where coastal fish monitoring data are scarce and further studies as well as time series are needed to yield a reliable as sessment of these areas. In the future, in line with increasing knowledge, the indicator might undergo further development
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| 7. |
- Wennhage, Håkan, et al.
(författare)
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Decline of flounder (Platichthys flesus (L.)) at the margin of the species' distribution range
- 2015
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Ingår i: Journal of Sea Research. - : Elsevier BV. - 1385-1101 .- 1873-1414. ; 105, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- The Baltic Sea is undergoing large-scale environmental change due to eutrophication, climate change, over-exploitation and habitat destruction, with subsequent degradation of living conditions for many fish species. Signs of this unfavorable development are seen as population declines in species affected. We provide the first synthesis and characterization of the recent population decline in European flounder (Platichthys flesus (L.)) in the northern Baltic Sea, using available fishery-independent data from the Finnish coast, which is at the margin of the distribution range of this species. The objective was to document recent changes in the flounder population, identify the onset and quantify the magnitude of the change. The results showed substantial decreases in flounder numbers and biomass across the whole study area during recent decades. Based on the time series data available, flounder abundances declined by 46-97% from the 1990s to the 2000s, with top values in the mid-1990s and current low levels reached in the early 2000s. Additionally, signs of decreasing flounder size and condition were also observed. We discuss potential reasons for the development in terms of environmental change and fishing, and identify potential bottlenecks for population maintenance and mechanisms behind population change, thereby contributing to our general understanding of marginal flounder populations.(c) 2015 Elsevier B.V. All rights reserved.
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