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Wetlands for Northern Pike Recruitment and Nutrient Reduction
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (Fish migration group)
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (Fish migration group)ORCID iD: 0000-0003-0344-1939
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Wetlands are important ecosystems, harbouring biodiversity, capturing

nutrients, and providing recruitment habitats for several fish species. The Baltic Sea, among the

largest brackish, semi-enclosed seas in the world, is exposed to large amounts of nutrients as well as

the overexploitation of several fish species. One measure to counteract eutrophication is to restore or

build wetlands for nutrient catchment (phosphorus) or removal (nitrogen). To function optimally for

nutrient removal, these wetlands should cover large areas, be shallow, and be covered by vegetation,

creating zones of high microbial denitrification. Wetland environments are also suitable spawning and

nursery areas for several fish species inhabiting the coastal zone of the Baltic Sea. Pike (Esox lucius) a

predatory species that has decreased in abundance in recent decades, use wetlands as recruitment areas

during their anadromous life cycle. After restoring wetlands near the coast and opening the waterways

towards the sea, pike larval emigration increased from a few thousand to over a hundred thousand

individuals. The habitat and food choice, growth and migration of larvae and juveniles were followed

over time, revealing that 80–95% left the wetlands within one month (at a size <6 cm). An optimal

wetland enriches nutrients and creates a high primary production base for zooplankton that are used

as food for pike larvae. Wetlands near the sea can function both as nutrient traps and as recruitment

areas for fish.

Identifiers
URN: urn:nbn:se:lnu:diva-13855OAI: oai:DiVA.org:lnu-13855DiVA: diva2:435951
Available from: 2011-08-22 Created: 2011-08-22 Last updated: 2016-11-09Bibliographically approved
In thesis
1. Anadromous Pike in the Baltic Sea
Open this publication in new window or tab >>Anadromous Pike in the Baltic Sea
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Växjö, Kalmar: Linnaeus University Press, 2011. 110 p.
Series
Linnaeus University Dissertations, 61/2011
National Category
Ecology
Research subject
Natural Science
Identifiers
urn:nbn:se:lnu:diva-13856 (URN)978-91-86491-99-4 (ISBN)
Public defence
2011-09-16, Fullriggaren, Barlastgatan 11, Kalmar, 09:30 (Swedish)
Opponent
Supervisors
Available from: 2011-09-28 Created: 2011-08-22 Last updated: 2016-11-09Bibliographically approved

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