Relationship between water mass and distribution of plankton and relative abundance of pelagic fish in the gulf of Thailand and east coast of peninsular Malaysia

Abstract

Oceanographic data of 81 stations in the Gulf of Thailand and EastCoast of Peninsular Malaysia from two survey cruises of MV.SEAFDEC of theSoutheast Asian Fishery Development Center were used in the study. Thefirst cruise was during 3 September to 3 October 1995 and the second cruisewas during 23 April to 23 May 1996. It is the first systematic andintensive field observation, after the Joint Thailand-Vietnam-US NAGAExpedition in 1959-1961. Water masses in the Gulf of Thailand and East Coast of PeninsularMalaysia were classified by Temperature-Salinity diagram,Temperature-Salinity-Time diagram and Optimum Multi-parameter Analysis.Their relationships with available biological data were determined. Five water mass; Gulf of Thailand water mass (GOT), Mekong water mass(MK), Surface of the South China Sea water mass (SSCS), Mixed of Gulf ofThailand and Surface of South China Sea water mass and subsurface SouthChina Sea water mass (SuSCS) were found in the study area. Thedistributions of each water mass varied seasonally. Relationship between water mass and biological distribution indicatedthat SSCS water mass was the indicator of low total abundance ofzooplankton with high proportion of chaetognatha. The result also showedpositive relationship between lower layer of GOT water mass and abundanceof phytoplankton but negative relationship with abundance of pelagic fish