Bottom trawl survey data analysis based on Delta-distribution model and its application in the estimation of small yellow croak and silver pomfret in the Yellow Sea

There are two groups of methods, namely, the design- based methods and the model-based methods that are commonly used for the analys is of bottom trawl survey data based on swept area method. While the design-bas ed methods enjoy wide application, the model-based methods are seldom used in C hina. The Delta-distribution model-based method is described and then applied for the estimation of small yellow croaker and silver pomfret in the Yellow Sea based on a survey conducted in autumn, 2000. It shows that the stock density of small yellow croaker was 66.3 kg·km-2and its 95% Confidence Interval (CI ) was (23.4，109.2) kg·km-2；the total biomass of small yellow croaker in the survey area was 14 626.9 t and its 95% CI was（5 168.4，24 085.5） t. Stock density of silver pomfret was 19.0 kg·km-2 and its 95% CI was（3.5，34.5 ） kg·km-2, the total biomass of silver pomfret in the survey area was 4 194.3 t and its 95% CI was（773.2, 7 615.4） t. The traditional design-based me thod, however, resulted in much wider confidence intervals with negative low lim its. The above results indicate that the Delta-distribution model-based method may provide estimates with higher precision, and deserve a much wider applicati on in data analysis for the stock assessment using bottom trawl surveys.