Stock assessment of Collichthys lucidus in the 

Pearl River Estuary in data-limited conditions

SHI Dengfu1,3， ZHANG Kui1,2， CAI Yancong1， XU Youwei1， 

SUN Mingshuai1， XU Shannan1， ZHU Jiangfeng1， CHEN Zuozhi1, 2

 (1. Key Laboratory for Sustainable Utilization of Opensea Fishery, Ministry of Agriculture and Rural Affairs, 

South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou510300, China; 

2. Southern Marine Science and Engineering Guangdong Laboratory（Guangzhou）, Guangzhou511458, China; 

3. College of Marine Sciences, Shanghai Ocean University, Shanghai201306, China)

Abstract: Fishery stock assessment is a basic component of modern management to maintain sustainable fisheries exploitation. Traditional assessment methods always require a large amount of statistical data, e.g., catch, abundance index, and even age structure. Due to limited funding and data for such surveys, only 1% of fish stocks around the world have been systematically assessed. Therefore, it is difficult to assess most fishery resources using traditional methods based on the maximum sustainable yield (MSY) principle. In recent years, stock assessment using limited data has become a focus issue in the field of fishery resources. Owing to the ease and objectivity of fish length, the evaluation models based on body length data has gained wide attention for data limited fisheries, including traditional electronic lengthfrequency analysis (ELEFAN) and lengthbased Bayesian biomass estimation (LBB). The big head croaker (Collichthys lucidus) is a commercially important smallsize fish widely distributed in the northwestern Pacific, from southern Japan to the inshore waters of Vietnam, with the majority of its distribution in Chinese waters. This species is smallsized, matures at age 1 yr, and has high fecundity and strong adaptability to salinity. It presents estuarineresident life history and can make a short distance migration from deep to shallow water areas in breeding seasons. Due to overfishing, the stocks in traditionally fished estuaries (e.g., Yangtze River Estuary and Minjiang River Estuary) have dramatically declined. It has important economic value and ecological effect on the ecosystem of Pearl River Estuary. In recent years, with the rapid development of coastal marine development and social economy, the fish resources in the Pearl River Estuary have been severely damaged due to the intensive fishing by human beings and the destruction of habitat by channel dredging. At present, the development and utilization status of  C. lucidus resources in the Pearl River Estuary is not clear. In this study, C. lucidus was sampled from the Pearl River Estuary from 2018 to 2019, and was conducted by bottom trawl fishing boat. The survey was conducted seasonally, namely spring 2018 (March, April), summer (August), autumn (September, October, November) and winter 2019 (December 2018, January and February 2019). The“Yuedongguanyu 92008” bottom trawl fishing boat was used for all surveys, with a length of 21.68 m, a main engine power of 143 kW, and a gross tonnage of 118 t. The bottom trawl nets used in the survey had an upper mesh length of 36 m, a mesh mouth of 5 cm, a cod end mesh size of 3 cm, and a total net length of 50 m. Biological data such as body length, body mass and gonadal maturity were determined from the collected samples. A total of 853 C. lucidus individuals were measured in this study. Based on the length data, we used ELEFAN and LBB methods to study the exploitation status of C. lucidus. Results showed that the body length frequency distribution was obviously unimodal and proportion of individuals in 91110 mm was the highest. The asymptotic lengths based on ELEFAN and LBB method were 160 mm and 156 mm, respectively. The exploitation rates were 0.55 and 0.68, respectively. The estimated total mortality coefficient was 4.81 based on lengthconverted catch curve, and the estimated nature mortality coefficient was 2.16 using Pauly’s empirical equation. Based on the LBB method, the estimated optimal fishing length was 100 mm, and B/BMSY was 0.57. Comparing with the stock in 1980s, although the growth coefficient and the exploitation rate reduced, the biomass level estimated by LBB was below 1, indicating that this stock had been overfished. Although both two methods were based on the assumption that fish growth followed the Von Bertalanffy growth equation, there were completely different computational procedures in the parameter evaluation process. The ELEFAN method obtained the optimal solution of the two parameters L∞ and K by finding the maximum value of the “explained sum of peaks”, and then estimated the values of other parameters through empirical formulas and evaluation curves. Management parameters such as development rate were obtained. The LBB simplified the data requirements, replaced the real values of M, F, and K in the form of M/K and F/K, and determined the L∞, M/K and F/K values through the catch function. Therefore, different evaluation methods resulted in differences in the evaluation results. According to the evaluation results of population parameters of C. lucidus in different sea areas in China, the natural mortality coefficient of C. lucidus in Pearl River Estuary was the highest, which might be caused by the difference of water temperature in different sea areas. According to Pauly’s empirical formula, the higher the water temperature in the habitat area, the higher natural mortality coefficient. The asymptotic body length of Minjiang River Estuary population was the largest, and the growth coefficient of populations in Minjiang River Estuary and Yangtze River Estuary were significantly lower than that of Pearl River Estuary, also due to water temperature. The higher the habitat water temperature was, the faster the metabolism of fish was, the faster the growth rate was, and the larger the growth coefficient was. The difference of asymptotic body length and exploitation rate in different sea areas might be caused by the difference of fishing intensity. Since 1999, the Chinese government has started to control the number of fishing boats and the power of fishing boats in the South China Sea, adjusted the fishery production structure, and vigorously built artificial reefs and implemented enhancement and releasing. This has reduced the intensity of development of fishery resources in the South China Sea. Studies have shown that the fishery policies in the South China Sea in recent years have had a positive impact on the changes in fish biological characteristics, such as the recovery of the average body length and first sexual maturity body length of Evynnis cardinalis in the Beibu Gulf. In this study, the changes in mortality parameters from the 1980s to the present show that the resources of C. lucidus in the Pearl River Estuary have not recovered, and even suffered from high fishing pressure, which indicates that  the current resources have not been recovered. Therefore, in order to conserve and restore Collichthys lucidus resource, it is recommended to implement precautionary fishery management measures such as quota fishing and protected areas on the basis of traditional measures, including strict minimum mesh size, access to gears, and control of fishing effort. 

Keywords: Pearl River Estuary；Collichthys lucidus；resource exploitation status；ELEFAN；LBB method