Sampling by a commercial trawler was conducted during February 1984 in the Chilaw Sea, Sri lanka, in order to assess the stock size and to study the depth and substrata related distributions of prawn. The entire extent of the prawn distrib­
ution w as divided into different depth strata and then into a number of rectangles
for trawl sampling. Each trawl tow
was approximately one hour long. Surface salinities and temperatures weft're­corded for each haul. Mud samples were taken from each rectangle to assess' qualitatively their organic content and particle size. Two way analysis of variance
for catch per unit of effort values of major species of prawn indicated a significant variation areawise in the catch rates of Parapenaeopsis stylifera. The same analysis on prawn length data showed a progressive increase in lengths towards the south
from the Dedura river estuary and the Cliilaw lagoon mouth for Penaeus indicia. This area appears to be a source of recruitment. Based on stocks abundance esti­mated by the swept area method, there were substantial reductions in Metopenaeus
dobsoni and Parap. stylifera. This study also indicated that the prawn resources in the Chilaw sea were confined to the 0 • 8 fathom depth range, and were abundant on sand and mud patches with organic material.