The Trophic State Index (TSI) can be used to classify lakes, rivers, and reservoirs into different trophic categories as well as to estimate the degree of eutrophication and the corresponding potential fish yield of a water body. Relations between Carlson’s TSI models and culture-based fisheries (CBF) in non-perennial reservoirs are well documented, but their applicability in larger, perennial reservoirs remains less comprehensive. In the present study, 48 reservoirs of varying sizes were examined to investigate the relationships between TSI values derived from Secchi disk depth (SDD) and chlorophyll-a content (Chl-a). Perennial reservoirs varying in size were selected from northern districts: Anuradhapura, Kurunegala, Puttalam and southern districts: Hambanthota and Monaragala. From March 2018 to August 2019, conductivity, pH, water temperature, dissolved oxygen, Secchi disk depth (SDD), chlorophyll-a (Chl-a), and sediment organic matter content (SOM) were measured monthly at five randomly selected sites within each reservoir. Principal Component Analysis (PCA) based on ln(x+1) transformed limnological data, ordinated northern and southern reservoirs separately into two distinct clusters. The first three Principal Components explained 98.9% of the cumulative variance. Conductivity, pH and Chl-a were found to be more important in explaining the variance. When calculated, TSI(SDD) values in each reservoir were well above the TSI(Chl-a) due to the turbidity caused by non-algal particles or colour. When compared with the reservoir size, there were no correlations (p>0.05) between the two TSI types. Log natural converted SDD and Chl-a values showed no significant correlation (p > 0.05) with ln-transformed SOM values across the reservoirs. In conclusion, Chl-a values are more suitable for assessing the trophic state of reservoirs in general since non-algal particulates or colour dominate light attenuation. Further research is needed to find simplified tools such as SDD to relate to the trophic status, thereby improving fisheries management in reservoirs of Sri Lanka.
Consumption of contaminated groundwater is implicated as a risk factor for chronic kidney disease of unknown aetiology (CKDu), which is a public health problem in some tropical countries, including Sri Lanka. However, the application of bioanalytical tools to assess the potential toxicity of groundwater consumed by CKDu-affected communities has received limited attention. This study explored for the first time the potential cytogenotoxic risk of drinking water from selected dug wells in a CKDu endemic area in Sri Lanka using in vivo bioassays (Cyprinus carpio erythrocyte-based and Allium cepa root meristem-based tests), complementary to physicochemical analysis. In dug well water used by households with CKDu, fluoride levels in dry and rainy periods, and electrical conductivity, alkalinity, and total hardness levels in the dry period were significantly higher than the well water used by households with no CKDu cases in the same endemic area. Exposure to water of dug wells used by households with CKDu triggered nuclear buds and fragmented nuclei induction in fish erythrocytes and mitosis suppression and induction of condensed nuclei and binuclei in root meristems in most cases. Kidneys of fish exposed to dug well water exhibited renal tubular degeneration. Bioassays revealed cytogenotoxicity of dug well water, which may be due to interactive toxicity of contaminant mixtures including fluoride and other unknown toxicants. Untreated water from such dug wells may pose cytogenotoxic risks to the consumers, influencing disease progression.
Corbicula sp. is a bivalve species with a widespread global distribution. Originally identified as freshwater cockles, these organisms have since expanded into brackish water environments. In Sri Lanka, Corbicula sp. predominantly inhabits brackish ecosystems, particularly those with dense mangrove coverage. This study was conducted in two distinct locations—Kappungoda in the Negombo Lagoon (NL) and Kattankudy in the Batticaloa Lagoon (BL)—both of which are subject to considerable anthropogenic influence. The primary objective was to assess and compare microplastic (MP) concentrations in water and Corbicula sp. tissue samples from these two lagoon systems. It was hypothesised that MP contamination levels would vary between the lagoons due to differing degrees of human activity. Sampling was carried out in January 2024, with 30 water samples and 30 cockle specimens collected along a 100 m line transect at each site. Standardised protocols were followed for MP extraction and analysis. Results showed that MP concentrations in Corbicula sp. tissues were 1.31 ± 0.23 items g⁻¹ wet weight (WW) in BL and 2.47 ± 0.64 items g⁻¹ WW in NL. Surface water MP concentrations were 3,250 ± 579 items m⁻³ in NL and 4,722 ± 1,448 items m⁻³ in BL. The recovered microplastics were predominantly fibres, fragments, and pellets, with colours including black, blue, red, orange, and white. Fibres were the most common form, and black was the most dominant colour across both sample types and sites. A statistically significant negative correlation was observed between tissue MP concentration and the wet weight of Corbicula sp. across both regions (BL: r = –0.684, p < 0.05; NL: r = –0.717, p < 0.05). We may conclude that there is no significant variation in MP concentration levels between Cobicula sp. and the lagoon waters along the two coastal lines. Furthermore, no correlation was observed between MP contamination in water and in clam tissue at the two sampling locations during the study period. However, smaller clams tended to show higher MP concentrations.
In the deep-sea fishing boats operated from the fishery harbours of southern Sri Lanka, in addition to gillnets and longlines, encircling nets are taken onboard to operate whenever the fishing boat encounters a floating object (flotsam) in the high seas. These flotsam-associated fisheries target shade-loving fish species such as Decapterus russelli (Rüppell) and Elagatis bipinnulata (Quoy & Gaimard), while juvenile tuna species are also caught as bycatch. The present study was an attempt to investigate the status of the fisheries of D. russelli and E bipinnulata using length-based stock assessment and to elucidate the impact of these fishing strategies on three species of small tuna and three species of large tuna. The analysis revealed that D. russelli stock was optimally exploited, while E. bipinnulata showed sub-optimal exploitation, indicating that both stocks remain at safe levels. Length-based indicators (LBIs) showed that the proportion of fish exceeding the mean length at first capture was very low or zero for both small and large pelagic tuna species, while the proportion of immature individuals in the landings was high, suggesting potential adverse impacts of ring netting on these stocks. Although there are claims that catching juvenile tuna around floating objects does not necessarily lead to overfishing, the impact of ring netting on large pelagic tuna fish stocks in the Indian Ocean is a matter of concern, particularly given the substantial increase in ring net effort reported in this study. Therefore, the expansion of this fishery underscores the urgent need for regulatory measures to prevent the risk of future overfishing of tuna stocks.
It is well recognized that the oceans are of utmost importance for the future of humanity. Being one of the largest bays in the world, the Bay of Bengal region (BOBR) has greater potential for harnessing the benefits of the blue economy to humankind. In the present synthesis, it is highlighted that all maritime-related activities including fisheries in the region require proper utilization and management for attaining social, economic and ecological goals. It is a fact that the problems of IUU fishing, marine pollution, ineffective marine regulation and the non-traditional security menace are commonplace in the region. Although there has been a significant increase in both capture fisheries and aquaculture in all BOBR countries, potential multiple blue benefits to the BOBR are likely to be challenged due to geopolitical difficulties, pollution and habitat loss, biodiversity degradation, destructive fishing, and climate change apart from the lack of full implementation of legal instruments. Solid waste pollution due to poor management of abandoned, lost, or otherwise discarded fishing gear and the rapid and unplanned increase in aquaculture, especially shrimp culture is also becoming a great concern for coastal and marine pollution. Moreover, the benefits of blue growth have been unequally distributed and there are several ‘blue injustices’ that have led to the marginalization of small-scale fishers. The inclusion of small-scale fisheries as a core principle in the blue economy agenda and adoption of an interactive governance approach, where participants would deliberate upon their knowledge, experience, and aspirations could serve as an important platform for bringing in concerns of all parties into the blue economy playing field, which will also strengthen the process of knowledge translation between the community and research and facilitate bringing in research outcomes to the decision-making table.
