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Long term changes in spawning volume for Baltic Sea cod (Gadus morhua)
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
Dept. of Systems Ecology, Stockholm University, Sweden.
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In the brackish Baltic Sea, cod (Gadus morhua) can reproduce only in a few deep areas, of which the Eastern Gotland basin and the Bornholm basin are the most important ones. Successful spawning requires oxygen concentrations larger than 2 ml r-1 and salinity larger than 11. The water domain that meets these requirements is referred to as the cod spawning volume. Salinity and oxygen data were collected during the period 1905-1997 and 1923-1997 from the Eastern Gotland basin and the Bornholm basin respectively. They have been analysed for changes in spawning volume over time. For each sampling occasion the spawning volume was calculated based on depth specific vertical distribution of salinity and oxygen concentration, combined with bathymetric data. The Bornholm basin constitutes a stable but limited spawning area for cod, contrary to the Eastern Gotland basin where the spawning volume is more uncertain but can be much larger. The estimated spawning volume decreased over time in the Eastern Gotland basin. This change is probably caused by increased deepwater oxygen demand due to increased organic material load from primary production. The latter is an effect of the ongoing eutrophication.

Keyword [en]
cod, spawning volume, Baltic Sea
National Category
Social Sciences Interdisciplinary
URN: urn:nbn:se:liu:diva-79296OAI: diva2:540284
Available from: 2012-07-09 Created: 2012-07-09 Last updated: 2012-07-09Bibliographically approved
In thesis
1. Modelling organic matter dynamics in aquatic systems
Open this publication in new window or tab >>Modelling organic matter dynamics in aquatic systems
2000 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Organic matter is a small but active part of the global carbon cycle. About one third is stored in the oceans where it has a relatively short residence time. The rest is found in the terrestrial biomass and in the soil. Aquatic systems exchange C02 with the atmosphere. Autotrophic organisms fix C02 into their biomass, while heterotrophic organisms respire C02 when utilising organic matter. Systems with large supply of organic matter by inflow can be net heterotrophic, which thus release more C02 than what they fix.

Two systems are studied, the Lake Ortrasket in northern Sweden and the Baltic Sea. In the Baltic primary production is the main source of organic matter, while in the lake dissolved organic matter from inflow dominates. Other characteristics of the Baltic Sea are that it is brackish and has a long residence time compared to the freshwater lake. These systems are studied with different types of models.

For the Baltic proper deep water, an inverse model of the water, salt and heat fluxes was used to estimate an oxygen budget including oxygen consumption. The oxygen levels in the Baltic proper deep water are critical due to the low supply and large consumption. The oxygen consumption is mainly due to organic matter degradation. The low oxygen and salinity levels in the Baltic have consequences for, among other things, the cod spawning success.

The lake model is a mechanistic model of dissolved organic carbon based on a Lagrangian fluid particle model and a one-dimensional physical model. The results show that Lake Ortrasket is a net heterotrophic system. In spite of the differences between the systems, both seems to have similar organic matter degradation rates, ~50 g C m-2 yr-1.

To supplement, time series of phosphate concentration were studied in the Baltic proper surface layer. These show seasonal variations coupled to the primary production, and this time dependence was modelled. The main purpose of the model is to complete corrupt observation time series, which is useful for environmental model studies.

Place, publisher, year, edition, pages
Motala: Kanaltryckeriet, 2000. 77 p.
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 214
Vatten, Kol, Oceanografi, Hydrologi
National Category
Social Sciences Interdisciplinary
urn:nbn:se:liu:diva-32133 (URN)17993 (Local ID)91-7219-825-7 (ISBN)17993 (Archive number)17993 (OAI)
Public defence
2000-09-22, Hörsal Planck, Fysikhuset, Universitetsområdet Valla, Linköping, 10:00 (Swedish)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2014-08-27Bibliographically approved

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Rahm, Lars
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Department of Water and Environmental StudiesFaculty of Arts and Sciences
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