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.
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.
Regional fisheries management organizations are mandated to reduce impacts of commercial fishing activities on non-target species. This is particularly important because fishing associated with natural drifting objects and artificial fish-aggregating devices across the oceans poses adverse impacts on non-target species, including juveniles of tuna species. In the Indian Ocean off Sri Lanka, deep-sea fishing boats are engaged in fishing with gillnets, longlines, and encircling nets associated with natural floating objects. The present study aimed at investigating whether target species and bycatch species in the catches of fishing methods can be differentiated to introduce effective management to the fisheries and to perceive driving forces in terms of the nature of fishing strategies with a view to recognizing appropriate management measures. From the boats operated from four fishery harbors of southern Sri Lanka from February 2018 to December 2020, species compositions of landings of 1915 fishing operations consisting of gillnetting, longlining, flotsam-associated ring netting, and a combination of ring netting with gillnetting and longlining were analyzed separately for each fishing method. Also, cost components of individual fishing operations and corresponding net revenues, gleaned from logbook records of boats, were scrutinized. This analysis underscored that there was a noticeable difference in species caught in the five types of fishing boats, consisting of large tuna and tuna-like species in the landings of longlines and drift gillnets. Landings of flotsam-associated ring netting were dominated by shade-loving species and juvenile tunas. As fuel cost is considerably lower in ring net fisheries than in gillnet and longline fisheries due to shorter trip duration and as there is higher net revenue from the fishing operations, there is an increasing trend of ring netting associated with floating objects. Under the existing legal framework, this fishery can be restricted by introducing high seas licenses.
