Abstract
Freshwater fisheries are central to food security in China and this remains one of the most important priorities for the growing human population. Thus, combining ecosystem restoration with economics is pivotal in setting successful conservation in China. Here, we have developed a practical management model that combines fishery improvement with conservation. For six years, a ban on fertilizer and a reduction of planktivorous fish stocking along with the introduction of both mandarin fish Siniperca chuatsi and Chinese mitten crab Eriocheir sinensis was apparent in Wuhu Lake, a highly eutrophic lake located in the middle reaches of the Yangtze River. Annual fish yield decreased slightly after the change in management, whereas fisheries income increased 2.6 times. Mandarin fish and Chinese mitten crab accounted for only 16% of total fisheries production but for 48% of total fisheries income. During this six year period, water clarity increased significantly from 61 cm to 111 cm. Total nitrogen, total phosphorus and chlorophyll decreased significantly from 1.14 to 0.84 mg/L, 0.077 to 0.045 mg/L, and 21.45 to 11.59 μg/L respectively, and macrophyte coverage increased by about 30%. Our results showed that the ecological status of shallow lakes could be rapidly reversed from eutrophic to oligotrophic using simple biomanipulation, whilst maintaining fisheries economic value. It also offers a better approach to shallow fisheries lake management in Asia where traditionally the stocking of Chinese carp and use of fertilizers is still popular.
Highlights
China has become the most significant contributor to world aquaculture with an annual production of 41 million tonnes (i.e. 62 percent of global aquaculture production in 2012) [1]
The added challenge within an East Asian context is to maintain the economic value of the fisheries in addition to the lake restoration, as this aspect is central to the local population endorsing any new management options
Within four years following the start of the management change, the overall annual fish yield decreased by 3% from pre biomanpulation mean ± s.e. = 785000 ± 5000 kg to post biomanpulation 763000 ± 30000 kg; the Chinese carp, including H. molitrix, A. nobilis C. idellus and Cyprinus carpio decreased from mean ± s.e. = 630400 ± 67000 kg to 477625 ± 161640 kg
Summary
China has become the most significant contributor to world aquaculture with an annual production of 41 million tonnes (i.e. 62 percent of global aquaculture production in 2012) [1] This rapid economic development has led to a range of environmental changes directly impacting fisheries [2]. The current use of fertilizers in these shallow lakes lead to a bottom up eutrophication of these ecosystem via an increase of nutriment load alongside a bottom up impact on macrophytes and plankton via the choice of fish species stocked [10,11]. Changing community structure through the introduction of top predators with less impact on nutrient load coupled with a reduction in fertilizer and carp species could lead to a whole food web trophic cascade and result in improved water quality and increased macrophyte abundance [12]. Previous research in shallow lakes of the Yangtze floodplain only focused on estimating the stocking capacity of piscivorous fish, the biomass and production of small fish as well as bioenergetics of mandarin [18,19,20,21,22,23,24]
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