Together with his research group, Kimmo Kahilainen has studied the changes in fish communities in Finnish Lapland, from the headwaters of Lake Kilpisjärvi (69°N) down to the Arctic Circle. The northern and southern ends of the study area are approximately 300 kilometres apart, and have significantly different climate.
“In the southernmost areas, the average summer temperature is three degrees higher than in Kilpisjärvi, and the amount of rainfall in the south is 30% higher than in the north. These figures correspond with climate change predictions for the end of this century in Lapland, which is to say that the situation in the northernmost lakes will approach the current situation in the southernmost ones,” says Kimmo Kahilainen, who works at the University of Helsinki.
“The headwaters of Kilpisjärvi had lakes with clear water which were dominated by whitefish, but as we moved towards the south, the lake became progressively more turbid and the fish communities were dominated by ruffe and perch. The southernmost lakes were highly turbid, due to intensive forestry practises in catchment, and roach had taken over the lakes from the perch,” Kahilainen explains.
Based on the study it seems that the ranges of ruffe, perch and roach are extending towards the north, and their relative importance in fish communities is growing. Fish that prefer cold and clear waters, such as Arctic char, whitefish, brown trout, grayling and burbot, were completely absent from some of the southernmost lakes in the study, and it is likely that their numbers will decrease in lakes towards the north in future.
Along with the composition of the fish population shifting, the average length of the fish decreased by 50% and the average weight by 90%. However, the relative biomass of fish increased in the lakes.
“For example, the turbid lakes dominated by roach had approximately 50 times the fish biomass of clear water lakes dominated by whitefish. Even though the total biomass of fish community grew significantly, the gradual shift from large salmonid fish towards less valued fish such as ruffe, roach and bleak, has reduced traditional fishing in the southernmost lakes."
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Hayden, B., Myllykangas J-P., Rolls, R.J. & Kahilainen, K.K. 2017: Climate and productivity shape fish and invertebrate community structure in subarctic lakes. Freshwater Biology 62: 990-1003.