Macro-debris and microplastic abundance in the surface soil of mangroves were investigated at the Negombo and Rekawa sites in Sri Lanka. Macro-debris abundance was significantly higher at the Negombo site (664.8 ± 87.47 debris/100 m2) than at the Rekawa site (1.53 ± 1.32 debris/100 m2). At Negombo, plastic was the dominant macro-debris type (56.25%), whereas metal predominated at Rekawa (43.48%). A significant positive relationship between macro-debris abundance and the percentage cover of mangrove aerial roots was observed at Negombo, highlighting the role of these roots as traps for debris. Microplastic abundance in surface soil was also higher at Negombo than at Rekawa (Dunn's test, p < 0.05), with blue microfibres being the dominant type at both sites. Overall, both macro-debris and microplastic pollution were significantly greater at Negombo compared to Rekawa. Consequently, our study highlights the need to implement a robust plan for managing macro-debris pollution, promote environmental education on reducing, reusing, and recycling plastics, and enforcing stricter waste management and plastic production regulations to conserve the mangrove ecosystems at both sites.
High seafood consumption may increase exposure to heavy metals and thereby pose risks to human health. Therefore, twenty five samples of each yellowfin tuna (Thunnus albacares) and skipjack tuna (Katsuwonus pelamis) were collected from major fishery harbours of Sri Lanka between January and August 2024. Fourteen trace metals were investigated using inductively coupled plasma mass spectroscopy (ICP-MS) aiming at updated monitoring of trace metal levels. A risk assessment made on the individual target hazard quotient (THQ) indicated that all concentrations of metals, except for mercury (Hg) in T. albacares, were below 1, revealing negligible non-carcinogenic health concerns. The target cancer risk (TR) values for inorganic arsenic (iAs), and chromium (Cr) were below the 10∁E, showing no carcinogenic risks associated with long-term consumption of tuna. The Se:Hg molar ratios exceeded one for both fish species. Positive selenium health benefit values (HBVSe) were observed in both fish species, indicating their positive contribution to improving the Se status of the consumer while mitigating the toxic effects of Hg. The study emphasizes the dual role of fish as both a nutrient source and a vector for contaminant exposure, emphasizing the need for ongoing monitoring of metal contamination in marine organisms.
The Norwegian research vessel "Dr. Fridtjof Nansen" operating under United Nations flag, conducted four surveys in the waters of Sri Lanka from 1978 - 2018. During the three first surveys carried out annually in 1978 - 1980, a total fish abundance of about 280 000 - 395 000 tons were measured by fisheries acoustics. From the first two surveys signals of potential increases in catches by a factor of two, and use of longlining for catch of deepwater rock fishes were given. In the 2018 survey with the larger and better equipped third "Dr. Fridtjof Nansen", the total fish abundance recorded by fisheries acoustics was just 121-000 tons, and an additional 52 000 tons estimated by the bottom trawl swept area method. These numbers indicated a drastic reduction in the standing biomass of fish species off Sri Lanka during this forty-year period. Total catch per unit effort declined from the 1978-1980 surveys to the 2018 survey, especially for six common fish families. However, for ten other fish families the catch per unit of effort increased. For eight commercially important fish species average length had decreased by about 50% from the 1978-1980 surveys to the 2018 survey. For seven other fish species the average length seems generally to have increased during this forty-year period. Macro-litter as plastic waste and remains of fishing gears were common in the 2018 bottom trawls. Our results support further development of fisheries management plans with harvest control rules as tools to support the sustainability of Sri Lankan fisheries and environmental action plans to reduce macro litter accumulation on the seabed.
This study assessed the technical efficiency (TE), allocative efficiency (AE), and economic efficiency (EE) of 60 intensive shrimp farms in the Puttalam district, Sri Lanka, in 2025, using data envelopment analysis (DEA). DEA was selected because it does not require a pre-specified functional form and accommodates multiple inputs without distributional assumptions, which suits the small, cross-sectional sample used here. The analysis incorporated output quantities, input prices, and input quantities, including labour, feed, post-larvae, dolomite, chlorine, and lime, and key determinants of technical inefficiency were examined using a second-stage Tobit regression. Mean TE, AE, and EE were 80.63%, 79.01%, and 63.76%, respectively, indicating considerable scope for efficiency improvement, particularly in cost management. An increase in total cultured area was the only factor significantly associated with reduced technical inefficiency, suggesting that larger farms benefit from economies of scale. Approximately 70% of sampled farms were profitable, while 30% were non-profitable; all non-profitable farms had experienced disease outbreaks, and over 65% of all farms reported disease occurrence in the preceding year. Feed cost was the dominant input expense, accounting for approximately 55% of total production cost. Based on these findings, the study recommends improving feeding practices and feed conversion ratio (FCR) monitoring to reduce the dominant cost burden, strengthening farm-level disease management and biosecurity to protect profitability, and supporting policies that facilitate production area expansion for smallholder farmers to enhance technical efficiency.
Directly facing the Sumatra and Andaman segments of the Sunda subduction zone, Sri Lanka provides an ideal location to study the large trans-basin tsunamis that occur there. Its location close to the southern boundary of the northern cyclone belt, and the directional advantage of the southern and eastern coastlines makes Sri Lanka one of the best places in the eastern Bay of Bengal region for distinguishing tsunami and cyclone deposits. Although several paleotsunami records have been constructed for the region since the 2004 Indian Ocean Tsunami, most extend only to the last 3000 years, and discrepancies exist among records. Therefore, this study was carried out to construct a longer Holocene tsunami record for the western Bay of Bengal region and to develop a more robust record of large trans-basin tsunamis that occurred at the Sumatra and Andaman trenches, to understand the recurrence interval between events. Thirteen back-barrier environments spanning the southern and eastern coastline of Sri Lanka were selected, and 35 sediment cores (1–5 m long – Total over 100 m length) were extracted along landward transects. Also, one pit was excavated to study abrupt sand layers. After initial logging, 19 sediment cores were selected for further analysis due to visually observed abrupt event layers. Particle size was used as the primary proxy to confirm the observed abrupt sand layers. Sediment texture, sedimentary structures, chemical composition, magnetic susceptibility, and micofossils were used to distinguish marine overwash layers having potential tsunami origin. Stratigraphy and age were used to establish intra- and inter-site, as well as regional, correlations among layers to distinguish regional tsunamis. In addition to five 2004 tsunami sand layers, among the 29 identified ancient abrupt layers with marine origin, 20 were distinguished as high potential paleotsunami (T HP ), and 06 were as medium potential (T MP) tsunami layers deposited during nine events that occurred around 1100, 3000, 4000, 4600, 5700, and 7300 yrs BP (T HP ), and 2000, 5100, 6300 yrs BP (T MP ) based on local and regional-correlation analyses. Abrupt layers deposited during another two low-potential tsunami (T LP ) events and other marine overwash events (OM) were also recognized by this study. In addition, published regional records show widely distributed, chronologically correlating evidence for a paleotsunami that occurred around 600 years BP, which was not observed at our study sites in Sri Lanka. Including the 2004 tsunami, when all 11 trans-basin events (excluding T LP ) reported over the last 7500 yrs are considered, tsunami frequency in the Indian Ocean has increased during the last 1000 yrs and during the interval between 4000–5000 yrs BP. Increased seismicity between 500–1500 yrs BP in the Sunda trench correlates with increased tsunami frequency during the last 1000 yrs.
