Papers by M.J.S. Wijeyaratne
International Journal of Aquatic Biology, 2020
The present study was carried out to determine the distribution of Najas marina , an invasive flo... more The present study was carried out to determine the distribution of Najas marina , an invasive floral species in the Ramsar site of Madu Ganga Estuary in Sri Lanka using ASTER satellite data. Cloud free ASTER imageries of Madu Ganga Estuary with 15 m resolution were atmospherically corrected using the FLAASH in ENVI software. The NDVI was calculated and unsupervised classification was applied for the study site for each image and the distribution maps of N. marina were developed from 2007 to 2014. Methodology was validated using in situ data, which were collected in 2014 with monthly intervals parallel to ASTER overpass. The derived distribution maps indicated that N. marina was distributed in about 31% of the estuary in April 2014. The highest densities were mostly found in bay areas and peripheral areas. Maps developed for December 2007, December 2009 and December 2013 indicated that there is a temporal variation in the distribution of N. marina over the years. The overall distribu...
Turkish Journal of Fisheries and Aquatic Sciences, 2016
This study was aimed to determine the present level and past trends of eutrophication of the Bolg... more This study was aimed to determine the present level and past trends of eutrophication of the Bolgoda North lake, Sri Lanka using in situ Chlorophyll-a (Chl-a) measurements and remote sensing data obtained from Advanced Space-borne Thermal Emission and Reflectance Radiometer (ASTER) satellite data. From March to October 2013, Chl-a, nitrate and phosphate contents of the lake were measured once a month on the days of ASTER overpass and using standard laboratory methods. Cloud-free ASTER images of the lake for the 2000-2013 period were atmospherically corrected using Fast Line-ofsight Atmospheric Analysis of Hypercubes (FLAASH) and in-situ Chl-a data were regressed with atmospherically corrected three ASTER Visible and Near Infrared band ratios of the same date. The green/red band ratio, which had the highest coefficient of determination, was used to develop algorithm for generation of 15-m resolution Chl-a distribution maps. Results indicated that eutrophication of this lake has incre...
International Journal of Aquatic Biology, Jun 19, 2015
Wetland Zooplankton Index (WZI) was developed for the low country intermediate zone of Sri Lanka ... more Wetland Zooplankton Index (WZI) was developed for the low country intermediate zone of Sri Lanka using 20 reservoirs located between latitudes 7°20'22.081"N-7°48'33.558"N and longitudes 80°1'44.55"E-80°9'51.509"E. WZI ranged from 1.56 in Anukkane reservoir which is located in a low flat terrain in the midst of agricultural lands to 3.69 in Tampana reservoir which is located in a hilly area with a watershed mainly covered with forests. WZI showed a significant negative correlation with the Nitrate-N content (r =-0.797) and cumulative content of Nitrate-N and total phosphorus (r =-0.795) indicating that it can be used as an indicator of the degree of eutrophication of inland reservoirs in the low country intermediate zone of Sri Lanka.
Sri Lanka Journal of Aquatic Sciences, 2020
Ocean & Coastal Management, 2019
Importance of participatory approaches in the management of small-scale fisheries is being increa... more Importance of participatory approaches in the management of small-scale fisheries is being increasingly highlighted today throughout the world. Brush park fishery in Negombo estuary, Sri Lanka is a small-scale fishery where traditional ecological knowledge (TEK) accumulated over generations is utilized to optimize the harvests. In the present study, the institutional robustness of the community-based management system of this fishery, which is based on TEK was assessed using Ostrom's modified design principles. Results showed that the degree of community-based management is not effective in successful management of this fishery due to common pool nature. Nevertheless, there is potential for integrating some institutional design principles through intervention of centralized management authorities. As such, co-management regimes that empower local communities are needed for the sustainability this fishery.
Environmental Biology of Fishes, 2017
Brush park fishery in Negombo estuary, Sri Lanka is a traditional fishing practice which relies o... more Brush park fishery in Negombo estuary, Sri Lanka is a traditional fishing practice which relies on fishes attracted to artificial woody fish aggregation devices. This study investigates whether constituent species in these brush parks exhibit morphological variations in relation to their dietary habits. Fishes caught in brush parks were sampled from April 2014 to April 2016 covering rainy, intermediate and dry seasons. There were 817 specimens of 46 species belonging to 24 families. From each specimen, 17 morphological attributes were determined and diet composition of each species was analyzed in terms of relative biovolume. Trophic index of each species estimated from the proportions of dietary items and their possible trophic level in the community was significantly related to two body proportions (Maximum body height/Maximum body width and Total length/ Maximum body height) which described shape of fish. Principal component analysis of morphometric attributes and dietary habits indicated that the species in the higher trophic levels are characterized by slender, long-body shapes and those occupy lower trophic levels are predominantly laterally compressed with deep body shapes. As such, structure of coexisting species in brush parks of Negombo estuary is predominantly along the trophic dimension and is related to morphological traits of constituent species. The predictive power of ecomorphological correlates with diets of fish species other than mugilids which are attracted to brush parks, can therefore be considered as a useful tool for conducting rapid ecological assessment.
Sri Lanka Journal of Aquatic Sciences, 2016
The grey mullets (Family: Mugilidae) have been described as plankton feeders, herbivores, omnivor... more The grey mullets (Family: Mugilidae) have been described as plankton feeders, herbivores, omnivores, slime feeders, foul feeders, bottom feeders, etc. In general, grey mullets are known to be benthic feeders. During a comprehensive trophic ecological study of fish assemblages in brush-parks in the Negombo estuary, Sri Lanka, carried out from 2014 to 2016, a food item that was not found in the aquatic environment, such as zooplankton, phytoplankton, macrophyte or detritus, was observed in the gut contents of mugilids. In this communication, the authors report that the frequency of occurrence of these peculiar items in the gut contents were shedded gill epithelia. Even though shedded gill epithelia were not considered as a food item, they were the most common item in the stomach contents contributing to 49.9% of the mean volume of stomach contents.
Sri Lanka Journal of Aquatic Sciences, 2018
Life history information on six endemic fish species namely Belontia signata, Pethiya cumingii, P... more Life history information on six endemic fish species namely Belontia signata, Pethiya cumingii, P. nigrofasciata, Puntius titteya, Rasboroides vaterifloris and Garra ceylonensis inhabiting the Kalu Ganga and Kelani Ganga river basins in Sri Lanka was evaluated. The growth constant of the fish species showed a positive relationship with the river order where they inhabited. The length at 50% maturity (Lm) significantly correlated with the asymptotic length and growth constant indicating that fishes with slow growth become sexually mature late in their life cycles. The optimal lengths for sustainable exploitation of the fish species studied were significantly (p<0.01) correlated with asymptotic lengths and lengths at 50% maturity whereas negatively correlated with natural mortality. This analysis indicated that Lm was a foremost function of size of fish apart from maximum length observed (Lmax,) and that Lm and Lmax can be used as deterministic variables for quantifying optimal siz...
Asian Fisheries Science, 2012
Sri Lanka Journal of Aquatic Sciences, 2017
Journal of Applied Ichthyology
ABSTRACT
Abstract is available at: http://repository.kln.ac.lk/handle/123456789/4322
Abstract: The suitability of a handheld spectrometer and ASTER satellite data for monitoring Chlo... more Abstract: The suitability of a handheld spectrometer and ASTER satellite data for monitoring Chlorophyll-a (Chl-a) in Lake Kasumigaura, Japan was tested in July 2010 to December 2013. ASTER based Chl-a retrieval algorithms were developed support with in-situ Chl-a, MODIS OC3 Chl-a and Kakemaoki and Koshin automated water quality monitoring stations Chl-a. ASTER VNIR band ratio were regressively analyzed with the corrected MODIS Chl-a and automated station values obtained for each ASTER date on a day by day basis. The regression equation of the ASTER band ratio (B1/B2), with highest correlation was used to generate high-resolution Chl-a distribution maps. Significant correlation between the ratio of the reflectance peak at 705 nm and the Chl-a absorption at 678 nm and the in-situ Chl-a content was observed and these reflectance ratios were used to establish spectrometric Chl-a estimation algorithms. Proposed algorithms can be successfully adopted to determine localized environmental ...
Sri Lanka Journal of Aquatic Sciences, 2010
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Papers by M.J.S. Wijeyaratne