Use of Nutrients and Chlorophyll-a for Fish Catch Estimation in Srinakarin Reservoir, Kanchanaburi Province

Abstract

               The study aimed to: 1) formulate a fish catch estimation model for Srinakarin Reservoir in Kanchanaburi Province, using nutrients and chlorophyll-a as indicators for fish catch estimation; and 2) develop a sustainable management policy for the reservoir area and its fisheries resources. From April 2008 to March 2009, water samples were collected every two months at 15 selected sampling stations representing upstream, midstream and downstream areas that included point sources and non-point sources, and for the same period, samples of fish species were collected from six private fish landing ports every month.

                The results showed that the Srinakarin Reservoir was oligotrophic, containing an average of 4.099 mg/m3 of chlorophyll-a and its water quality was appropriate for aquatic animal life. The distribution of nutrients and chlorophyll-a varied, depending on the period and collection area. Nutrient and chlorophyll-a concentrations upstream were higher than those in the middle and downstream sections. The average concentrations of nutrients were highest in the rainy season (June to September), average in summer (February to May) and lowest in winter (October to January), whereas the average chlorophylla concentrations were highest in summer (5.307 mg/m3) and average in the rainy season and winter (4.591 and 2.399 mg/m3, respectively). The ratio of forage to carnivorous fish was estimated as 1.813:1. All parameters used to estimate the fish catch (FC) showed that the catch had a low positive relationship to chlorophyll-a, whereas nutrients could be used to estimate the fish catch, especially, ammonia nitrogen (NH3-N), which was suitable for fish catch estimation throughout the year. A suitable linear regression model was FC = 29,892 - 90,509 (NH3-N); (R2 = 0.44). Ammonia nitrogen had a moderately negative relationship to the fish catch and could explain up to 44% of the fish catch. 

                   Based on the equation developed in the study, the results could be used to estimate the fish catch satisfactorily and also the resultant environmental changes in the Srinakarin Reservoir. This model could be applied to predict the fish catch in other reservoirs in Thailand with the same topographical features.