ECOLOGICAL SYSTEM CHARACTERISTICS AND ECOLOGICAL CAPACITY OF HYPOPHTHALMICHTHYS MOLITRIX AND ARISTICHTHYS NOBILIS IN THE ZHANGZE RESERVOIR BASED ON ECOPATH MODEL

Ecopath is a modeling tool utilized for analyzing the structure and function of marine and freshwater ecosystems, providing an effective means to assess the structure and energy flow within food webs across various ecosystems. Numerous scholars have employed the Ecopath model to establish ecosystem models for oceans, ponds, lakes, estuaries, and reservoirs, aiming to explore ecosystem structure, function and energy flow characteristics, as well as assess the phylogenetic status and maturity. Additionally, the model has been applied to study the ecological capacity of target species in marine ecosystems such as Wangjiadao Islands and Daya Bay, aiding in the evaluation of breeding and releasing activities. However, the use of the Ecopath model to study the ecological capacity of target species in inland lake reservoir ecosystems, particularly during breeding and releasing activities, requires further investigation. To elucidate the fundamental characteristics of the Zhangze Reservoir ecosystem, estimate the ecological capacity of filter-feeding fish species such as silver carp and bighead, and explore the impact of silver carp proliferation and release on the ecosystem, this study employed the Ecopath with Ecosim 6.6.5 (EwE) software package for modeling and analysis. The Ecopath model of Zhangze Reservoir was constructed based on fishery resource survey data from 2022 to 2023, dividing the ecosystem into 16 functional groups based on ecological niches and feeding characteristics of organisms.

The results showed that the trophic level of each functional group ranged from 1 to 3.31. The energy conversion efficiency of primary producers and detritus stood at 9.04% and 9.25%, respectively, with the total energy conversion efficiency of the ecosystem at 9.04%. Moreover, the total flow of each trophic level exhibited an inverse proportion to its trophic level, conforming to the ecological energy pyramid law. The total annual flow of the Zhangze Reservoir ecosystem was measured at 53531.34 t/km², with a system linkage index (CI) of 0.267, system omnivorous index (SOI) of 0.149, Finnish circulation index (FCI) of 11.12%, and the Finnish average track length (FMPL) of 2.881. The degree of connectivity among ecosystem functional groups was relatively close, yet the food web structure lacked complexity, generally indicating an immature stage. The ecological carrying capacities of silver carp and bighead carp were estimated at 161.5 and 70.3 t/km², respectively, representing 3.549 and 1.947 times the current biomass, suggesting significant potential for fishery biomass growth. During the process of silver carp and bighead carp reaching their ecological carrying capacities, the total primary production and total respiration values of the Zhangze Reservoir ecosystem decreased by 0.47 and 0.15, respectively. Additionally, the system connection index (CI) and Finn average path length (FMPL) increased slightly, indicating improved energy use efficiency and a tendency towards increased ecosystem complexity and maturity. Considering adjustments to the biomass of silver carp and bighead carp to reach the maximum sustainable yield of 80.75/km² and 35.15 t/km², respectively, may enhance silver carp production and improve ecosystem maturity. The above results provide insight into the development status of the Zhangze Reservoir ecosystem and offer valuable guidance for fishery enhancement management strategies.