Theoretical Study On The Sampling Methods Of Survey For Fishery Stock Estimation

Some preliminary studies on the theory and practice of sampling methods for fishery resources surveys have been done in this study. The study as a whole can be divided into two main areas:one is about the theoretical study of the stations allocation in space for fishery resources survey, including optimized sampling design by special criterion functions and adaptive sampling design based on optimized sampling design at first phase; the other is a comparison of sampling and estimating methods for ma-rine fishing production assessments which is the direct support for the management of governmental fisheries departments. The following three paragraphs presents specific summary of the above studies.We have introduced and evaluated a procedure, the Constrained Spatial Simulated Annealing (CSSA) method, for developing an optimal sampling design for fishery-independent surveys. We used two criterion functions,1) the minimization of the shortest distance (MMSD), and2) the uniform distribution of point pairs for variogram estimation (WM), and three arrangements of the two criteria, all WM, all MMSD, and a combination of MMSD (2/3of samples) and WM (1/3), to construct three optimized sampling designs (denoted as Designs â… , â…¡, and â…¢, respectively). These three de-signs were compared in a simulation study with systematic sampling (Design IV) and stratified random sampling designs (Design â…¤), commonly used in fishery-independent surveys. Three levels of sample size (small, medium, and large) were considered in the developed simulation study using a geostatistical approach. The results showed that for parameter estimation of the spatial covariance function, Design â…¢ was better than the other designs at relatively small sample size, and Design â…¡ performed better than other designs at relatively large sample size. For estimating fish stock abundance, the performance of the designs considered in this study can be ranked as follows:Design â…¡> Design â…£> Design â…¢> Design â…¤> Design â… . It is clearly important to evaluate and improve sampling design based on historical survey data. Such a study allows us to identify an optimal sampling design to balance the quality of the data collected and the costs of the sampling programme, leading to the development and optimization of a sustainable and fishery-independent monitoring programme.The adaptive cluster sampling method is widely applied in terrestrial systems; however it is not suitable for fisheries surveys because of the high costs of uncontrol-lable sampling in practice. An adaptive approach is often used in fisheries surveys to allocate sampling efforts, which usually follows stratified random design. No adap-tive sampling method has been developed based on optimized sampling design which was suggested for fishery independent surveys. An adaptive sampling method based on optimized sampling design by criterion of minimization of the mean of the shortest dis-tance (MMSD) in the first phrase was constructed in this study and compared with five other sampling designs:simple random, stratified random, adaptive based on stratified sampling, systematic, and optimum design based on the MMSD criterion. This design performed neither the best nor the worst among the six sampling designs considered in this study, but its advantages were obvious when the sampling effort saved using this design was considered in the comparison. The method tends to be more flexible and find fish aggregations more precisely. It is based on a more objective sampling design in the first phase compared with other adaptive sampling designs based on stratified sampling. We suggest that this design be considered in developing fishery-independent survey programs.The current approach of fishery statistics collection for Chinese government is to acquire the data bottom-up from several levels of local government departments, which is always with obvious "trimming" signs. Foreign fishery scholars argued that the fish-ing production data from China in international journals, result in a bad international influence; national academics also had similar questions on these data. In the above context, adequate attention has been paid by the relevant government departments, to organize some relevant academic institutions in order to carry out a pilot work on the estimation of marine fishing production by a sampling approach. This study attempts to deal with the problems encountered in the process of the pilot work by computer simulation. Such problems are about estimation methods, and appropriate allocation of sampling size. The results show that the assessment, consistent with the sampling process in layers, tends to be more accurate; the other assessment with the reduced layers tend to be greater than the true values and with larger deviations. The accuracy and precision of assessment with increase of sample size will be improved; and the proportional sampling approach can improve the accuracy and precision of assessment comparing to other methods with same sample size. Accurately grasping the structure of studying object is the premise for stratified sampling to obtain accurate and pre-cise assessment. The results from this study could give a technique reference for the development of the sampling method for the fishing production survey in future.