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Stigebrandt A.,Gothenburg University | Liljebladh B.,Gothenburg University | de Brabandere L.,Vrije Universiteit Brussel | Forth M.,University of Southern Denmark | And 10 more authors.
Ambio | Year: 2014

In a 2.5-year-long environmental engineering experiment in the By Fjord, surface water was pumped into the deepwater where the frequency of deepwater renewals increased by a factor of 10. During the experiment, the deepwater became long-term oxic, and nitrate became the dominating dissolved inorganic nitrogen component. The amount of phosphate in the water column decreased by a factor of 5 due to the increase in flushing and reduction in the leakage of phosphate from the sediments when the sediment surface became oxidized. Oxygenation of the sediments did not increase the leakage of toxic metals and organic pollutants. The bacterial community was the first to show changes after the oxygenation, with aerobic bacteria also thriving in the deepwater. The earlier azoic deepwater bottom sediments were colonized by animals. No structural difference between the phytoplankton communities in the By Fjord and the adjacent Havsten Fjord, with oxygenated deepwater, could be detected during the experiment. © 2014, The Author(s). Source

Cardinale M.,Swedish University of Agricultural Sciences | Svedang H.,Swedish University of Agricultural Sciences | Svedang H.,Swedish Institute for the Marine Environment | Bartolino V.,Swedish University of Agricultural Sciences | And 4 more authors.
Journal of Applied Ichthyology | Year: 2012

By reconstructing a centennial time-series of stock spatio-temporal dynamics and commercial landings, the long-term erosion is shown of the spatial structure of haddock and pollack in the Skagerrak and Kattegat that resulted in their regional depletion in the area. The erosion occurred in parallel with the development of the industrial fisheries and the peak in landings was followed by a decline in adult biomass and individual size. Also found was that pollack adult biomass was significantly lower for elevated water temperatures, while the response for haddock was less clear. However the main decline of both stocks and the disappearance of their adult aggregations occurred several decades before the unprecedented warming trend, which started in the Skagerrak and Kattegat only in the mid-1980s. These findings also suggest that haddock in the study area is not responding to the scale on which the management of the neighbouring North Sea haddock stock is currently performed. These results illustrate the hazardous consequences of prolonged overfishing on the population structure of commercially exploited stocks and the lack of knowledge which ultimately leads to spurious assumptions on the recovery potential of many fish stocks. Also argued is that the continuation of commercial fishery at 'sustainable' levels adjusted to the present stock productivity might hinder the recovery of these depleted stocks for a long period of time. © 2012 Blackwell Verlag, Berlin. Source

Svedang H.,Institute of Marine Research | Svedang H.,Swedish Institute for the Marine Environment | Andre C.,Gothenburg University | Jonsson P.,Institute of Marine Research | And 2 more authors.
Environmental Biology of Fishes | Year: 2010

The question whether temperate marine fishes typically consist of self-sustaining populations or "open" populations still remains unresolved. At the heart of this population connectivity problem lays the nature of the stock separation mechanisms. Fish populations could be segregated either by environmental forcing, accompanied with opportunistic recruitment of juveniles to spawning areas, or by philopatric behaviours (i. e., inclination of an individual to return to or remain in its natal area). Here we report three, partly independent, studies on Atlantic Cod (Gadus morhua) stock separation in the Kattegat and Öresund (eastern North Sea): characterisation of spawning aggregations with genetic markers, tagging experiments, and analysis of chemical constituents in otolith cores of recaptured fish that could be linked to a specific spawning site. While the genetic investigation showed no population segregation, the observed migratory patterns indicated three separate spawning sites at close distances. The natal dependence on the choice of spawning site was tested by measuring the contents of various trace elements in the otolith core of recaptured tagged fish. Quantification of the trace elements: Ba, Br, Co, Cr, Cu, Fe, Mn, Mo, Ni, Sr, Ti, and Zn expressed as ratios to Ca were obtained using scanning micro PIXE. These results indicated that natal origin could be differentiated between spawning sites, supporting the hypothesis that natal homing is an important stock separating mechanism even over short distances (<100 km). © 2010 Springer Science+Business Media B.V. Source

Cardinale M.,Institute of Marine Research | Svedang H.,Swedish Institute for the Marine Environment
Marine Ecology Progress Series | Year: 2011

The Baltic Sea ecosystem is hypothesized to have undergone a regime shift during the last 3 decades, altering its functioning and the composition of its zooplankton and fish communities. The new stable state has been considered as 'cod hostile' due to reduced spawning success in cod, as well as increased predation on and declining food sources for cod larvae. Nonetheless, the eastern Baltic cod stock has recently recovered after more than 2 decades of low biomass and productivity. The recovery was mainly driven by a sudden reduction in fishing mortality and occurred in the absence of any exceptionally large year classes. The recovery of the cod stock during a 'cod-hostile' ecological regime indicates that fisheries are the main regulator of cod population dynamics in the Baltic Sea. © Inter-Research 2011. Source

Bartolino V.,Swedish University of Agricultural Sciences | Bartolino V.,Gothenburg University | Cardinale M.,Swedish University of Agricultural Sciences | Svedang H.,Swedish University of Agricultural Sciences | And 3 more authors.
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2012

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. Source

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