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Author:
Engstedt, Olof (Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences) (Fish migration group)
Title:
Anadromous Pike in the Baltic Sea
Department:
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences
Publication type:
Doctoral thesis, comprehensive summary (Other academic)
Language:
English
Place of publ.: Växjö, Kalmar Publisher: Linnaeus University Press
Pages:
110
Series:
Linnaeus University Dissertations; 61/2011
Year of publ.:
2011
URI:
urn:nbn:se:lnu:diva-13856
Permanent link:
http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-13856
ISBN:
978-91-86491-99-4
Subject category:
Ecology
SVEP category:
Marine ecology
Research subject:
Natural Science
Abstract(en) :

The pike (Esox lucius) is a major predator and top-down regulator in the Baltic Sea where it exists in two sympatric forms. One spawn in streams and rivers and the other one spawn in the sea. During the last decades, the habitats for both of these forms have developed in a negative way. In some freshwater systems, up to 90 % of the water areas have disappeared, mainly through drainage and straightening of watercourses for agricultural purposes. In the sea, reproduction habitats decrease due to construction of harbours and human activities that create disturbances. The perhaps largest single factor negatively affecting recruitment of pike in the sea is the eutrophication. Bottoms are overgrown with filamentous algae and shallow bays are covered with dense Phragmites belts decreasing the habitats suitable for spawning. Further on, a predator on egg and fish larvae, the three-spined stickleback (Gasterosteus aculeatus) has increased in abundance. It is difficult to restore and enhance pike production in the sea and probably the only economically viable alternative is to make restorations in freshwater. However, there is a limited knowledge about the freshwater spawning pike in the Baltic Sea. Thus in this thesis I, together with my coauthors, set out with an aim to increase the knowledge base regarding anadromous pike behaviour.

We found that pike of natal freshwater origin were common in the Baltic Sea. Through Sr:Ca studies in otoliths, about 45 % of the pike were interpreted to be of freshwater origin. The majority of the pike had emigrated out of freshwater at a length below 6 cm. These results indicate that freshwater recruitment is successful, contrasting the vast areas available for spawning in the sea. This creates incitements that restoration measures in these watercourses could have a significant effect on the pike population in the Baltic Sea.

Further, in four streams running out in the Baltic Sea, more than three thousand pike were marked to study spawning migration. About 30-40 % returned to the same river the subsequent year. Most of the pike used the lower parts of the stream for spawning. The homing of pike to a watercourse indicate that freshwater pike in the Baltic Sea consist of specific populations and this is crucial information when taking decisions on fish restoration measures.

Three wetlands adjacent to streams were restored for pike production. The most successful restoration involved minimal digging, with flooded grasslands providing optimal conditions for spawning. The first spawning season after restoration increased the pike production hundredfold.

In conclusion, the anadromous pike are numerous in the Baltic Sea. To compensate for the decline in pike populations in the sea, “pike-factories” created along the coastline are probably the most justifiable option.

Public defence:
2011-09-16, Fullriggaren, Barlastgatan 11, Kalmar, 09:30 (Swedish)
Degree:
Doctor of Philosophy (PhD)
Supervisor:
Larsson, Per (Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences)
Opponent:
Svedäng, Henrik, Docent (Havsmiljöinstitutet, Göteborg)
Available from:
2011-09-28
Created:
2011-08-22
Last updated:
2011-09-28
Statistics:
183 hits
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