Title: Assessment of demersal fishery resources of the southeast and southwest waters of Vietnam, based on bottom trawl surveys 2000-2005

This study is a preliminary analysis on abundance indices, fish assemblages and assessments of the biodiversity of the demersal fish resources of the Southeast and Southwest waters, Vietnam, based on bottom trawl surveys conducted during the years 2000 - 2005. The survey program was implemented under the project of “Assessment of the Living Marine Resources of Vietnam - ALMRV” which was supported by DANIDA (Danish International Development Agency) and Vietnamese government. A commercial fishing boat equipped with 500 HP engine was used. The sampling gear used was a bottom trawl with an opening width of 11.6 m and the stretched mesh size of the cod-end of 35 mm. The surveys were designed based on a “fixed station system”, stationary grid with an average distance of 30 nautical miles between hauls. All tows were conducted during the daytime. The average towing speed was 3.5 and towing duration of 1.0 hour. CPUA (catch per unit area) is used to standardize the abundance index. Catchability (q) is assumed to be constant for all fish species. Kriging technique is applied to map the distribution of the demersal fish stock of the Southern water of Vietnam. The evenness, richness and biodiversity of the demersal fish communities distributed in these areas are evaluated by estimating the values of various indices including Shannon-Weinner index (H’) and Pielou’s index. Ward Hierarchical Cluster analysis is applied to analyze the biological assemblage of the fish stocks. The study shows a considerable decrease in fish abundance of the area during the period from 2000 to 2005 and a high variance in the relative abundance as well as the structure of fish community by seasonal monsoons. Different patterns of fish assemblages of the demersal fish in the Southeast and the Southwest waters were observed.