EVALUATION OF FISHING BAN EFFECT IN THE POYANG LAKE BASED ON FISH BODY LENGTH STRUCTURE ANALYSIS

Poyang Lake has been under a comprehensive ten-year fishing moratorium since 2020. This study analyzed the changes in three indicators—average body length, Proportional Size Distribution (PSD), and the proportion of sexually mature individuals—among 25 major fish species in Poyang Lake before the ban (2017—2019) and after the ban (2021—2022). The objective was to evaluate the effects of the fishing ban on population structure of these species. The results showed that after two years of continuous fishing prohibition, the phenomenon of individual dwarfism in major fish species was effectively alleviated, resulting in an increase in the proportion of larger and sexually mature individuals, thus optimizing the population structure. Among the 25 assessed fish species, 24showed an increase in average body length ranging from 2.3% to 115.0% (P<0.05), with corresponding increases in their PSD values by 3 to 71 (P<0.05). Additionally, the proportion of sexually mature individuals increased by 23.2% to 10712.8% for 20species. However, one species, Pseudolaubuca sinensis, exhibited a decrease in average body length of 5.0% (P<0.05) and a decline in PSD value of 21 (P<0.05). For eight fish species (Cyprinus carpio, Xenocypris argentea, Saurogobio dabryi, Coilia brachygnathus, Hemiculter lucidus, Culter alburnu, Acheilognathus macropterus, and Pseudolaubuca sinensis), no significant changes in the Fulton's condition factor were observed. Furthermore, five species (Cyprinus carpio, Parabramis pekinensis, Hemiculter leucisculus, Pseudolaubuca sinensis, and Acheilognathus macropterus) showed a decrease in the proportion of sexually mature individuals, ranging from 23.5% to 79.8%. In the assessment of population stability status, prior to the fishing ban, 21species were categorized as unstable (PSD<50 and PSD>80), while only 4species were deemed stable (50≤PSD≤80). Following the implementation of the fishing ban, the number of unstable species decreased to 15, whereas the number of stable species increased to 10. In summary, the population structure of the majority of major species in Poyang Lake improved following the fishing ban, although some species showed different changes. It is recommended that the comprehensive fishing ban in Poyang Lake should be sustained, along with continuous and comprehensive monitoring of fish populations, to achieve effective recovery of fishery resources and enhancement of overall ecosystem service functions in Poyang Lake.