Progress in Fishery Sciences (Feb 2024)
Construction and Application of the Habitat Quality Index of Eriocheir sinensis Spawning Grounds
Abstract
Eriocheir sinensis is an important fishery resource in the Yangtze River basin, which has brought about huge socio-economic benefits. The estuarine spawning grounds of E. sinensis, however, has experienced negative effects, such as habitat alteration and degradation of the water environment, in the mid- to late 1980s as a result of the construction of water conservation projects, land reclamation along the estuary, and pollution input. In addition, the overexploitation of E. sinensis resources has contributed to a sharp decline in its resources. To develop rational and scientific habitat management plans, the estuarine spawning habitats of E. sinensis have received attention in recent years. Currently, the distribution pattern and habitat characteristics of E. sinensis spawning grounds in the Yangtze River estuary have been explored from the perspective of resource distribution; however, habitat quality has not been further investigated. Studies on habitat quality can more effectively support the development of fishery habitat management strategies by serving as a tool to objectively assess the functional status of aquatic habitats. The habitat quality of the Yangtze River estuary has a substantial impact on the resources of E. sinensis as it is the only spawning ground for this species in the Yangtze River basin and is also the largest in China. Therefore, the behavior of E. sinensis during reproduction and spawning, which reflects the habitat quality of the spawning grounds, served as the foundation for this study. The evaluation of the habitat quality of E. sinensis spawning grounds was based on the parameters of reproductive performance and quantitative distribution. The habitat quality index (HQI) of E. sinensis spawning grounds was built by screening evaluation indices, weight analysis of evaluation indices, and construction of evaluation criteria. To provide the necessary scientific tools for examining E. sinensis spawning grounds in the Yangtze River estuary and to establish a solid scientific foundation for managing estuarine spawning grounds for this species. The spawning grounds of the Yangtze River estuary were monitored using egg-holding crabs of E. sinensis, and sampling was performed using gillnets positioned at certain locations. Key environmental parameters influencing the spawning activity of E. sinensis, such as water depth, turbidity, dissolved oxygen (DO) in bottom water, salinity (SAL), and temperature (T) were gathered during the sampling process. Through anatomical measurements of collected egg-holding crabs, physiological characteristics including carapace width, absolute fecundity, relative fecundity, condition factor, hepatopancreas index, and reproductive effort were gathered and collected. The characteristics of egg-holding crab population distribution and reproductive success were key factors considered when choosing the evaluation indices. The catch per unit effort of egg-holding crabs is a quantitative distribution characteristic, and the reproductive performance characteristics primarily rely on correlation analysis to determine the traits that can objectively respond to the reproductive performance of egg-holding crab, which are RF and HSI. Subsequently, a hierarchical evaluation system is created based on the characteristics of the evaluation indices. The response relationship between the environmental elements and each evaluation index serves as the foundation for the weight analysis of the evaluation indices. The environmental factors were analyzed separately with each evaluation index for redundancy analysis (RDA), and the results of the RDA were used to understand the degree of influence of each evaluation index on environmental characteristics. It is also used as the basis for the weight value of the evaluation indices, and the weight value of each evaluation index is determined by combining the hierarchical analysis method. Finally, a multi-index comprehensive scoring technique was used to determine the HQI of the E. sinensis spawning grounds, and guidelines for evaluating habitat quality were developed. The findings revealed a strong response relationship between egg-holding crab reproductive performance characteristic indicators and environmental factors (91.9%, F=9.0, P=0.042), which has significant application value when assessing the habitat quality of their spawning grounds. The evaluation revealed that the survey sites´ HQIs ranged from 0.33 to 0.84, and 47% of the survey sites assigned a "medium" or higher rating to the habitat quality level. Overall, the northern bank of Hengsha had a greater habitat quality than the deepwater canal. The HQI developed in this study has obvious advantages in quantitatively assessing the habitat quality of E. sinensis spawning grounds because it has a greater interpretation rate of environmental elements (94.9%, F=12.0, P=0.038) than quantitative distribution characteristics. The maximum percentage of HQI was explained by DO, SAL, and T when each environmental factor was used as an independent explanatory variable, accounting for 74.0% (F=22.7, P=0.004), 44.0% (F=6.3, P=0.044), and 33.0% (F=3.9, P=0.076), respectively. DO, SAL, and T were the key environmental factors influencing the habitat quality of E. sinensis spawning grounds. In this study, the Yangtze River estuary was chosen as the spawning ground for E. sinensis, and the quantitative distribution and reproductive performance characteristics of this species were employed as the foundation for evaluating habitat quality. The spawning grounds of the Yangtze River estuary for E. sinensis were further investigated in terms of habitat function using the HQI, which was built based on the characteristics of the evaluation indices. This study identified the major habitat factors that influence the habitat quality of these spawning grounds.
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