Frontiers in Marine Science (Dec 2015)
Unexpected dominance of 1 year old parr among migrating salmon and sea trout individuals in the River Siesartis, Lithuania
Abstract
Among longest freely flowing salmon and sea trout migration routes in Europe, few remains in Lithuania. Data collected from Lithuanian rivers during 1999-2010 showed that catadromous smolt migration usually takes place from end of March to mid of May. Intensity of migration mostly depends on water level and temperature. In general, catadromous migration can last from 2 to 6 weeks, but in rivers of the Baltic Sea region the main run takes only 1-3 weeks starting with water temperature +4,8 and ends at 12,8oC. Mean smolt lenght typically varies from 100 to 240 mm, majority of them being 2-3 years old. However, 1 year age parr unexpectedly dominated among salmon juveniles descending towards the Sea in the restocked Siesartis River, which is situated 400 km to the Baltic Sea. The same phenomenon has been observed among migrating sea trout individuals, too. Mass migration of 1 year age salmon and sea trout parr with mean body length ranging from 69 to 150 mm can hardly be explained by density-dependant regulatory mechanisms alone. Possible impact of particularly long distance migration route is also discussed.
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