Short feeding migration associated with a lower mean size of whitefish in the River Tornionjoki, northern Baltic Sea

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Publikationens författare: Erkki Jokikokko, Henry Hägerstrand, Jan-Olof Lill
Förläggare: WILEY
Publiceringsår: 2018
Tidskrift: Fisheries Management and Ecology
Tidskriftsakronym: FISHERIES MANAG ECOL
Volym: 25
Nummer: 4
Artikelns första sida, sidnummer: 261
Artikelns sista sida, sidnummer: 266
Antal sidor: 6
ISSN: 0969-997X


Abstrakt

The size of anadromous whitefish caught with dip nets in the River Tornionjoki in the northern part of the Gulf of Bothnia has decreased during recent decades. To find an explanation for this trend, ascending whitefish were sampled in the lower part of the river in August 2016, and they were divided into two groups according to fish length. The length of the SMALL group was 32cm (n=32) and that of the LARGE group 33cm (n=65). The elemental analysis of otoliths revealed that the barium concentration was clearly higher in otoliths from the SMALL group compared to the LARGE group. This indicates that the fish in the LARGE grouphad migrated to feed further south in the Gulf of Bothnia, with a higher salinity, than the fish in the SMALL group. Because of this migration difference, and a decline in the gillnet effort, especially in the feeding areas near the river mouth, it is assumed that proportionally more fish in the SMALL group are able to ascend the river to spawn than previously, thus decreasing the mean size. At the same time, the heavy gillnet fishery in the south removes fish from the LARGE group.


Nyckelord

dipnetting, Elemental analysis, gillnet fishing, Gulf of Bothnia, migratory whitefish

Senast uppdaterad 2019-21-11 vid 05:08