Comparative Studies on Effects of Predation by Fish on Daphnia in Lake Donghu (China) and Loch Leven (Scotland)

Comparative Studies on Effects of Predation by Fish on Daphnia in Lake Donghu (China) and Loch Leven (Scotland)

Yufeng Yang, Linda May, Iain Gunn, Xiangfei Huang, and Jiankang Liu

Comparative Studies on Effects of Predation by Fish on Daphnia in Lake Donghu (China) and Loch Leven (Scotland)This is part of Ecosystem Approaches for Fisheries Management
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From the data of Daphnia surveys made in 1979-1996 in Lake Donghu (China) and in 1978-1982 and 1992-1995 in Loch Leven (Scotland), two shallow eutrophic lakes near Wuhan and Edinburgh, respectively, the authors analyzed the long-term changes in densities and size frequency of Daphnia. The results showed annual average densities of Daphnia (station I + station II) in Lake Donghu were negatively correlated with fish yield. Daphnia densities tended to decrease after the introduction of rainbow trout to Loch Leven from 1993 on. The size-frequency distributions of Daphnia showed that small-sized Daphnia were dominant in Lake Donghu, but the distributions in Loch Leven changed little.

The comparative studies showed that the Daphnia population was determined largely by fish in Lake Donghu, with a high stocking rate of planktivorous fish, and also by predatory copepods. In Loch Leven, food resources, water temperature, etc., were key factors causing a stable Daphnia population, the introduction of rainbow trout having little effect on Daphnia, but analysis of gut contents of rainbow trout demonstrated an apparent size-selective predation for Daphnia larger than 1.4 mm in length. A low fish stocking rate may be one of the important reasons for the stable Daphnia population in Loch Leven.

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