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Dissanayake D.C.T.,National Aquatic Resources Research and Development Agency NARA | Stefansson G.,University of Iceland
Invertebrate Reproduction and Development | Year: 2010

Sea cucumbers are a conspicuous component of the macrobenthos in the tropical marine environment and support numerous artisanal fishing activities throughout the Indo-Pacific. Although sea cucumbers have been subjected to various investigations by many authors, little attention has been given to species in the coastal waters of Sri Lanka. The reproductive biology of Holothuria atra, the most abundant and widely distributed commercial species was investigated in the northwestern coastal waters of Sri Lanka from July 2008 to 2009. When the reproductive biology of H. atra was evaluated using gonadal indices and histology of gonads, it was found that synchronous seasonal gametogenesis with some asynchrony among individuals during the prolonged spawning season and individuals with mature gonads were dominant throughout the year, reaching a peak in March and September. In addition, population structure was assessed based on sex ratio, minimum reproductive size and the relationship between the reproductive pattern and environmental parameters. The sex ratio of H. atra was found to be close to 1:1. Spawning began in April and October when temperature was at a maximum. Length at first sexual maturity was 16.0 cm (total length). Fecundity of H. atra was in the range of 430× 103 to 5,993 × 103 oocytes per individual. © 2010 Balaban.

Jinadasa B.K.K.K.,National Aquatic Resources Research and Development Agency NARA | Edirisinghe E.M.R.K.B.,Rajarata University | Wickramasinghe I.,University of Sri Jayewardenepura
Food Additives and Contaminants: Part B Surveillance | Year: 2013

Mercury (Hg) is a global environmental pollutant that has been the cause of many public health concerns. It is transferred through trophic level and bio magnification in the food chain. Total Hg level was measured by cold vapour atomic absorption spectrometry in muscle tissue of 176 Swordfish (Xiphiasgladius) samples ranging from 11.8-112.0 kg total weight and 45-278 cm total length, collected from major fish landing sites in Sri Lanka during July 2009 to March 2010. Total Hg concentration varied between 0.18-2.58 mg/kg wet weight (ww), with a mean value ± standard deviation of 0.90 ± 0.52 mg/kg ww. Of the investigated samples 32% exceeded Hg limits as set by the European Union and Sri Lankan legislation (1 mg/kg, ww). Hg concentration of swordfish showed a significant positive relationship (P value < 0.05) with the fish length and weight. Consequently, consumption of larger fish leads to an increase in the exposure level for consumers. © 2013 © NARA.

Dissanayake D.C.T.,National Aquatic Resources Research and Development Agency NARA | Dissanayake D.C.T.,University of Iceland | Stefansson G.,University of Iceland
Aquatic Living Resources | Year: 2010

The sea cucumber stocks off the east and northwest coasts of Sri Lanka were estimated by surveying 1307 km2 and 1779 km2 by an underwater visual census (UVC) in June and October 2008 respectively. The presence of twenty-five sea cucumber species belonging to seven genera; Actinopyga, Bohadschia, Holothuria, Pearsonothuria, Stichopus, Thelenota and Acaudina was identified in five hundred sampling sites randomly selected in each area. The overall average density (± SD) of sea cucumbers was higher in the northwest (350 ± 648 ind ha-1) than in the east (90 ± 130 ind ha-1) and low-value species were predominant in both survey areas (79 ± 125 ind ha-1 in the east, 244 ± 488 in the northwest) when compared with medium (10 ± 34 ind ha -1, 105 ± 175 ind ha-1, respectively) and high-value category (<2 ind ha-1). The estimated total biomass in the northwest (13 024 t) was roughly four times greater than the east (3027 t). Holothuria edulis was the most abundant species in numbers while Holothuria atra had the highest stock biomass in both areas. Sea cucumber densities were significantly different among the habitat (p < 0.001) and depth categories. The highest density was reported in rocky habitat associated with seagrass and / or macroalgae. The density of low-value species was significantly high in 1-10 m depth category (p < 0.001) in the northwest while other commercial groups were dominant in 20-30 m depth range in both areas. Temporal banning of the fishery for high and medium-value species would be a better management option to avoid further stock depletion. © 2010 EDP Sciences, IFREMER, IRD.

Dissanayake D.C.T.,National Aquatic Resources Research and Development Agency NARA | Dissanayake D.C.T.,University of Iceland | Stefansson G.,University of Iceland
Journal of the Marine Biological Association of the United Kingdom | Year: 2012

The sea cucumber fishery has been providing an important means of livelihood to the coastal fishing communities in Sri Lanka for centuries. Stock status, level of exploitation and mortality parameters of eleven commercial sea cucumber species were studied off the north-west and the east coasts of Sri Lanka using data collected from an underwater visual census and fishery-dependent surveys carried out in 2008 and 2009. The total abundance of sea cucumbers was higher in the north-west than the east (P < 0.01). However, the total abundance of all the species declined between 2008 and 2009. The commercial fishery predominantly relies on two nocturnal species: Holothuria spinifera and Thelenota anax. Holothuria spinifera had the highest contribution (73.2%) to the total landings in the north-west while this was provided by T. anax (93%) in the east. Both catch per unit effort and total landings declined in 2009 compared to 2008 having three exceptions (H. spinifera, Holothuria atra and Stichopus chloronotus) in the north-west. Further, the collection of immature individuals, reduced landings of high-value species and temporal shifting of fishing activities were observed in both areas. Two approaches (simple linear regression and random effects models) were used to estimate the natural mortality of sea cucumbers and the estimated values were 0.50 yr -1 and 0.45 yr-1, respectively. Apart from the management of local sea cucumber resources, this information is important to update the regional and global sea cucumber statistics as well as for launching regional management programmes. Copyright © Marine Biological Association of the United Kingdom 2011.

Dissanayake D.C.T.,National Aquatic Resources Research and Development Agency NARA | Dissanayake D.C.T.,University of Iceland | Stefansson G.,University of Iceland
Journal of the Marine Biological Association of the United Kingdom | Year: 2012

Despite their economic importance, the ecology of many sea cucumber species is poorly understood and factors influencing their habitat preferences remain largely unexplained. The distribution and habitat preference of two sea cucumber species; Holothuria atra and Holothuria edulis were studied off the north-west coast of Sri Lanka by underwater visual census in October 2008. The relationships between the density of each species and the habitat variables, such as mean grain size, organic content (% of dry weight), gravel (%), silt-mud (%), and depth, were examined using a generalized additive model. All these variables except silt-mud have significant influence (P < 0.05) on the habitat association of H. atra. The shallow water (<10 m) seagrass habitat with sediments characterized by 2-3.5% organic content, 15-25% of gravel and coarse sand (0.7-1.2 mm) were the most preferred conditions by H. atra. High densities of H. edulis were found in the shallow (<10 m) depths of rocky areas with algae and seagrass. Favoured bottom sediment conditions of H. edulis were mainly similar to the conditions preferred by H. atra, except organic content which did not significantly influence the habitat preference of this species. The preference towards the specific habitat characteristics seems to be associated with their feeding and protection. An understanding of habitat preference would be useful to improve the management of these sea cucumber populations and enable more precise stock assessment. © 2011 Marine Biological Association of the United Kingdom.

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