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

A1 Journal article (refereed)

Internal Authors/Editors

Publication Details

List of Authors: Erkki Jokikokko, Henry Hägerstrand, Jan-Olof Lill
Publisher: WILEY
Publication year: 2018
Journal: Fisheries Management and Ecology
Volume number: 25
Issue number: 4
Start page: 261
End page: 266
Number of pages: 6
ISSN: 0969-997X


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.


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

Last updated on 2019-16-10 at 03:24