Seasonality, abundance and biology of tawilis (Sardinella tawilis) in Taal Lake, Batangas

Abstract

A landed fish catch survey was conducted in ten landing centers around Taal Lake from June 2008 to May 2009. Fish catch and unit effort were recorded at 2 days interval for 10 days a month in the established sampling stations. Inventory of fisherfolk, boats, and gear was also conducted. A total of 300 'tawilis' samples per month were measured and dissected to determine the biological and population parameters. Results showed that there were 2,488 fisherfolk, 2,250 fishing boats, and 15,947 units of fishing gear recorded in Taal Lake. Tawilis production in the lake has declined. In 2009, tawilis production was 132 mt, a reduction of 82 % from the average production from 1996 to 2000. However, tawilis remained to be the most dominant fish in the open waters with about 36% of the total fish catch. The major gear used to catch tawilis were gill net and beach seine with catch per unit effort (CPUE) of 6 kg/day and 35 kg/day, respectively. There were 4,646 fish samples analyzed with an average fork length of 9.8 cm, average total length of 11.1 cm and an average weight of 13.2 g. The sex ratio obtained was 1 male to 0.85 female. Spawning of tawilis is all year round with highest gravid samples from March to May and November to December. Tawilis with an average fork length (FL) of 9.9 cm and weighs about 13.9 g has an estimated 4,848 eggs. The analysis of length frequency data has an estimated L8 of 16.8; K value of 0.59; total mortality (Z), 3.46; fishing mortality (F), 1.93; natural mortality (M), 1.54; and exploitation rate (E), 0.56. The fishing mortality was higher than the natural mortality and the exploitation rate exceeded the optimum 0.3-0.5 which implies that there is overfishing of tawilis in the lake.