Sampling Designs for Monitoring Ichthyoplankton in the Estuary Area: A Case Study on Coilia mystus in the Yangtze Estuary

Abstract

A fishery-independent survey can provide detailed information for fishery assessment and management. However, the sampling design for the survey on ichthyoplankton in the estuary area is still poorly understood. In this study, we developed six stratified schemes with various sample sizes, attempting to find cost-efficient sampling designs for monitoring Coilia mystus ichthyoplankton in the Yangtze Estuary. The generalized additive model (GAM) with the Tweedie distribution was used to quantify the “true” distribution of C. mystus eggs and larvae, based on the data from the fishery-independent survey in 2019–2020. The performances of different sampling designs were evaluated by relative estimation error (REE), relative bias (RB), and coefficient of variation (CV). The results indicated that appropriate stratifications with intra-stratum homogeneity and inter-stratum heterogeneity could improve precision. The stratified schemes should be divided not only between the North Branch and South Branch but between river and sea. No less than two stratifications in the South Branch could also get better performance. The sample sizes of 45–55 were considered as the cost-efficient range. Compared to other monitoring programs, monitoring ichthyoplankton in the estuary area required a more complex stratification and a higher resolution sampling. The design ideology and optimization methodology in our study would provide references to sampling designs for ichthyoplankton in the estuary area.

Effects of Estuarine Environmental Heterogeneity on the Habitat of Gobiidea Species Larvae

“…Using the random stratified sample approach, about 55 stations were established for each survey (Long et al. 2022). A plankton net with an opening width of 80 cm and a mesh size of 505 μm was used to gather all ichthyoplankton.…”

“…The subareas were subdivided further into 159 grids of equal size (3 0 × 3 0 ; 1 0 = 1.85 km) over the entire research region. Using the random stratified sample approach, about 55 stations were established for each survey (Long et al 2022). A plankton net with an opening width of 80 cm and a mesh size of 505 μm was used to gather all ichthyoplankton.…”