Effect of hydrology on fish catch of trawl-net fishery in the Mekong delta

The Mekong River Commission monitored daily fish catches of five trawl net fishers in the Mekong delta for three years period (2003 to 2005). Hydrological parameters, including water level, discharge, and rainfall were recorded daily in the Chau Doc station. Simple linear regression was used to describe the statistical relationship between catch per unit effort (CPUE) and hydrological parameters, based on method of least squares. Catch per unit effort exhibited a strong seasonal variation, with the highest CPUE in November (wet season), when most fish move from flooded areas back to the mainstream, and lowest catch in the dry season. The peak in mean monthly CPUE lagged behind that of mean monthly hydrological parameters for a period of one to two months. Linear regression analysis showed that the mean monthly CPUE correlated most with mean monthly water level of the previous month (r=0.71; p<0.0001), discharge of two previous months(r=0.72; p<0.0001) and rainfall of one previous month (r=0.56; p=0.002). Lateral and downstream fish migrations were believed to be the main causes affecting those relationships. Fishery regulations should, therefore, be managed in relation to hydrological regime conditions to maintain the fisheries as ecologically sustainable. Moreover, any river flow modification may be detrimental to fish stocks and, therefore, to the fisheries. As a result, any activity that regulates river flow must be taken into account.