Optimization of Sampling Effort for Different Fishery Groups in the Yangtze River Estuary, China

The Yangtze River Estuary (YRE) plays an important role in the conservation of fishery resources in the Yangtze River basin, and the Chinese government has established a special fishing ban management area at the YRE. To assess effects of the fishing ban, survey design and appropriate effort need to be determined and implemented. This study used long-term trawl survey data of the YRE (2004–2017) to explore the effects of survey effort (8–30 continuous survey stations selected by systematic and stratified sampling) on precision and accuracy of estimates of abundance of different fishery groups in the YRE. Estimated precision for a given number of survey stations varied by season and fishery group. Precision of systematic sampling fluctuated with the number of stations. Precision of stratified sampling with a proportional allocation scheme gradually increased with the number of survey stations. We suggest including 15–20 survey stations for all fishery groups sampled using the examined sampling methods.This study provides a research reference for selecting the survey effort (number of survey stations) for a fishery-independent survey in the YRE under the backgroud of conservation.