Strategy of Stock Enhancement Using EnhanceFish Model: A Case of Acanthopagrus latus Enhancement in Nanlang Water Area, Zhongshan City

Abstract

In recent years, the fishery resources in China's coastal and inland waters have declined seriously, along with a significant decrease in the number of economic fish stocks in many natural waters. Enhancement and release are important measures to conserve fishery resources, protect biodiversity and replenish the fishery environment. Since the 1980s, enhancement and release have gradually become an important way to increase fishery resources in China. With the yearly increase in variety, quantity, and scale of enhancement and release, the problem with the low efficiency of enhancement and release has become increasingly prominent. Therefore, a scientific and reasonable variant of the enhancement and release technique is the key to ensure its successful role in resource proliferation, including prior scientific planning as well as an accurate evaluation post release. At present, there are many studies on release assessment methods. Ecopath model method and empirical assessment method are often used to carry out pre-release planning research. Ecopath model method determines the release quantity in the water area by calculating the ecological capacity of the release water area. However, this method, like the empirical assessment method has the disadvantage of an extensive assessment of the capacity limiting its accuracy in planning the release quantity. The commonly used methods for evaluating the effect of post-release include external tagging method and statistical evaluation method. The external tagging method causes certain damage to fish and has poor stability, making it unsuitable for large-scale enhancement and releasing. The statistical evaluation method needs regular follow-up post release, making it manpower-, resources- as well as cost-intensive. In order to formulate scientific enhancement and release strategies and improve the effect of breed enhancement and release, the EnhanceFish model was introduced in this study using Acanthopagrus latus as the research object, Nanlang water area as the research area, and considering the life cycle, growth rate, mortality, sexual maturity, heritability, recruitment, economic cost and effort as the study parameters. The enhancement and release model of A. latus in Nanlang water was constructed, and the optimal release size, ecological capacity, population structure, and economic benefits of A. latus were scientifically evaluated in order to provide scientific guidance for the rational and standardized formulation of enhancement and release strategies.In this study, the effects of spawning stock biomass, profit, and fishing effort on the ecological structure of A. latus were comprehensively considered, and an intuitive data model was constructed to determine the range of release quantity and fishing effort. The results showed that the natural recruitment amount increased with the increase in releasing quantity. When the release quantity was 2 million, the natural recruitment amount reached the progressive value of 1.6 million. Therefore, the number of A. latus released in Nanlang water area was 0-1.6 million. While evaluating the relationship between fishing effort and economic benefit before release, the profit was 1 000 CNY assuming the current fishing effort E=1. When the fishing effort was E 1, the profit decreased with the increase in fishing effort. When it was E > 2, the profit was 2 000 CNY, which has no research value. Therefore, the limit of fishing effort E is 0-2.

Keywords

• enhancefish model
• ecological capacity assessment
• stock structure
• economic benefit