Annual spawning migration of anadromous pike (Esox lucius L.) in streams entering the Baltic Sea

• The movement of pike (n = 3415) was investigated in four streams entering the Baltic Sea in the Kalmar Sound region, Sweden. Migration patterns were monitored during spawning in three of the streams and during the whole year in the forth stream using passive integrated transponders and outer tags. The study was conducted yearly between 2006 and 2010. Mature pike returned (22 – 45%) to the same streams year after year and some fish returned to the same regions of the streams. No incidence of fish visiting another stream than the one where they were marked was recorded and no fish missed the spawning season to return the next year. These results indicated that the reason for fish not returning was due to mortality. The proportions of returning fish indicated homing and the spawning ground fidelity (stream) was high. Return rates were influenced by size of fish, sex and stream identity. We also investigated if sex, size or individual behaviour influenced timing of arrival, departure or duration of stay in freshwater. Diurnal activity was examined in one year in each stream suggesting activity peaks in the morning and evening. The results show that pike in the Baltic Sea are anadromous and that the migration behavior is likely to create barriers for gene flow. The separation in populations by spawning are similar to salmonid species and the management of pike in the Baltic Sea must consider this process in strategies and plans of fishing.

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NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

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