Optimization of sample size for lake fish resources survey

Abstract:

Fishery-independent surveys are essential for collecting high quality data to support fisheries stock assessment and management. Sample size (number of sites) plays a significant role in determining the quality of survey data. A fishery survey in Dianshan Lake was conducted as a case study to analyze the effect of sample size on accuracy and precision for estimates of fish abundance or fish species diversity using resampling techniques. Results showed sample size can be reduced while still achieving relatively high precision and accuracy for most indices measuring abundance and biodiversity. The relative estimated error(REE) for all the indices increased when the sample size decreased in four sampling seasons. For most indices in the four sampling seasons, the REE was stable or slightly increased when the sample size decreased from 24 to 8. The REE had a significant and positive relationship with the CVs of the corresponding indices for the four sampling seasons and had different levels of values for each index in the four seasons.For the sake of the same precision for different indices in one season, the sample size needed for analyzing fish diversity indices was smaller than the one required while analyzing species abundances indices.To maintain the same precision for one index in different seasons, the sample size needed for analyzing abundance indices and fish diversity indices were the largest in winter and summer respectively.The study suggests that the optimal sample size identified in a lake fishery survey design may be different with respect to different goals. Sample size could be reduced to some extent in the subsequent surveys to reduce the negative effect of the survey on fish species with low abundance in the study area.