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Elemental fingerprinting in otoliths reveals natal homing of anadromous Baltic Sea pike (Esox lucius L.)
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.
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]

Northern pike (Esox lucius) inhabit the coastal areas of the Baltic Sea. A large part of the fishes show anadromous

behaviour and spawn in streams and rivers but spend most of the time foraging in the sea. We examined

spawning migration in four streams in the southwest part of the Baltic, situated within a radius of 50 km. Using

juvenile pike in the streams as references, otolith analysis by microPIXE revealed unique elemental patterns (Sr,

Zn, Br, Co and Mn) for the juveniles in each of the four different streams. The strontium signal in the otolith

of the juveniles was used as an indicator of freshwater origin and the time spent in the stream (size of juveniles).

Adult marked pike in their migrating spawning phase were caught in each of the streams and otoliths were

analysed. Defining earlier freshwater origin by the Sr signal from the otolith core to the increase in Sr when the

fish as juvenile pike migrated to the sea, element composition was determined. A principal component analysis

showed that the elemental fingerprint during the freshwater phase several years back was similar for adult fish

and juveniles inhabiting the stream today. The results indicated native homing of the adults to a specific stream,

a process further corroborated by results from electronic marking (Pit-tags) with the return of adult individuals

over several consecutive years. We interpret the results as evidence that pike in the Baltic Sea consists of several

sub-populations and are developed by homing to specific spawning streams. The results of the study may have

implications for fishery management as pike in the Baltic Sea cannot be seen as homogenous “stock“, but instead

consists of different, unique populations similar to the pattern demonstrated in salmon (Salmo salar).

National Category
Biological Sciences
Research subject
Natural Science, Aquatic Ecology
Identifiers
URN: urn:nbn:se:lnu:diva-13854OAI: oai:DiVA.org:lnu-13854DiVA, id: diva2:435950
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. p. 110
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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Engstedt, OlofLarsson, Per

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