Impact of Bottom Trawling on Sediment Texture and Organic Matter Along Inshore Waters of Kerala (South India)

Abstract

Sediment texture and organic matter were analysed before and after trawling in samples collected from 0-50 m depth zone during December 2000-November 2001, along Kerala coast (Long. 75° 56/00 to 76o10' and Lat. 9058' to 10010'). Up to 40 m depth the composition of sand, silt and clay were 0.19 - 15.8%, 35.33 -60.53% and 29.9 - 53.12% respectively. Beyond ' this, sand was dominant (sand 32.6 - 96.15, silt 1.8 - 33.8, clay 2.45- 26.48%). In samples collected before trawling, sand, silt and clay ranged from 4.76 - 87, 45.85-55.71 and 43.18 - 47.38% respectively. In the samples collected after trawling the corresponding values for sand, silt and clay were 21.25 - 35.7, 51.28 -63.92 and 13.03 - 21.6% respectively. Organic carbon in 0-30 m depth zone ranged from 0.229 - 7.68% and it showed highest variations in July especially at depths 0-10 m and 10-20 m with respective values of 4.45 and 4.75% before trawling; while in the after trawling samples it was reduced to 2.21 % and 1.90% respectively. The sand and silt fractions showed a significant increase whereas a drastic reduction in clay fraction was observed especially in 0- 40 m depth zone due to bottom trawling.