Climate Change and Monitoring of Temperate Lakes

Provided the predicted 2°C temperature increase during this century, lake ecology will go through dramatic changes, and this must be addressed in fish management in purpose of exploitation as well as in species preservation. In temperate lakes with fish communities dominated by cold-water and cool water fish, temperature increase will affect the species dominance. Extended growth season will benefit recruitment of less cool adapted species, total fish density may increase and growth will decrease of some species. Lakes dominated by salmonid fish may become dominated by cyprinids and percids. Primary production will increase due to extended growth season and increased precipitation. This can reduce the oxygen level in the deep layer of lakes when the organic matter decomposes, whereas the upper layer is too warm for cold-water species. In addition, increased density of small plankton feeding fish will reduce the algae feeding zooplankton. Lakes should be monitored by means of modern and sophisticated methods, monitoring lakes from satellites and in situ loggers, and pelagic fish may be counted by echosound-ing. To counteract increasing density of plankton feeding fish, fish biomass removal is a possible measure, though the effect is limited in time.