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Characterization of bio-physical features in Thalawila fishing ground, North-western coast of Sri Lanka

Authors:

HB Jayasiri ,

LK
About HB

National Aquatic Resources Research and Development Agency (NARA), Crow Island, Colombo 15.

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K Arulananthan,

LK
About K

National Aquatic Resources Research and Development Agency (NARA), Crow Island, Colombo 15.

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SUP Jinadasa

LK
About SUP

National Aquatic Resources Research and Development Agency (NARA), Crow Island, Colombo 15.

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Abstract

Fish aggregation is area specific and strongly links with oceanographic processes and parameters. The sea off Thalawila in the North-western region of Sri Lanka is a major fishing ground particularly for the tuna longline fishery. To study the monsoon response on fishing, environmental data on temperature, conductivity, depth and chlorophyll profiles along with plankton sampling were collected at seven selected locations during the first inter-monsoon and the Northeast monsoon in 2007. The depth of the thermocline was 80 − 90 m during the inter-monsoon, and 40 − 60 m during the Northeast monsoon. The observations indicated that the depth of the chlorophyll-a maximum varied from 20 − 80 m. The deepest depth of chlorophyll maxima was found in April. However, there was a broader peak of chlorophyll varying within the depth range of 20 − 80 m in January and March. The values of mean phytoplankton and zooplankton abundances of the area were 3273 ± 771 and 55.36 ± 9.82 indi. L-1, respectively. The chlorophyll-a concentration and the zooplankton density varied as a function of time, but the spatial variability was less significant. The relative compositions of phytoplankton revealed that diatoms dominated with 91 % of the total population followed by 8 % dinoflagellate contribution. The zooplankton analysis indicated the dominance of crustacean larvae comprising about 48.4 % with copepods of about 37.04 %. The present analysis indicated that chlorophyll significantly correlated with the phytoplankton and zooplankton density (p < 0.01). The findings suggest that thermal structure of the water column and food availability are likely to determine the aggregation of fish off the North-western coast of Sri Lanka.

DOI: http://dx.doi.org/10.4038/jnsfsr.v42i3.7399

J.Natn.Sci.Foundation Sri Lanka 2014 42 (3): 255-264

How to Cite: Jayasiri, H., Arulananthan, K. & Jinadasa, S., (2014). Characterization of bio-physical features in Thalawila fishing ground, North-western coast of Sri Lanka. Journal of the National Science Foundation of Sri Lanka. 42(3), pp.255–264. DOI: http://doi.org/10.4038/jnsfsr.v42i3.7399
Published on 10 Sep 2014.
Peer Reviewed

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