For ethical reasons and animal welfare, it is becoming increasingly more important to carry out ecological surveys with a non-invasive approach. Information about fish distribution and abundance in the upper water column is often fundamental. However, this information is extremely hard to obtain using classical hydroacoustic methods. We developed a rigid frame system for pushing upward looking transducers of the scientific echo sounder (38 and 120 kHz) in front of the research vessel. The efficiency of the new approach for monitoring juvenile fish at night was investigated by comparing the results with a quantitative fry trawl in the Římov Reservoir in the Czech Republic. The experimental setup enabled comparisons for the 0–3 m and 3–6 m depth layers, which are utilized by almost all juvenile fish in summer. No statistically significant differences in the estimated abundance of juveniles were found between the two sampling methods. The comparison of abundance estimates gathered by the two frequencies were also not significantly different. The predicted mean lengths from acoustic sampling and the trawl catches differed by less than 10 mm in all comparisons. Results suggest that mobile hydroacoustic upward-looking systems can fill the methodological gap in non-invasive surveying of surface fishes.

This study investigated whether allochthonous inputs generated by cattle and water buffaloes grazing in the catchment or wading in the water in small village reservoirs of Sri Lanka can make a significant effect on yields from culture-based fisheries of those reservoirs. The analysis is based on limnological data of 37 randomly selected reservoirs. As culture-based fish yield data were available over the 2002 - 2003 period only for 23 reservoirs, fish yield data from seven more reservoirs were gleaned for the present analysis. Cattle and water buffalo densities (BD) in 37 reservoirs where limnological data were available, were found to be significantly correlated to the biological productivity-related parameters such as chlorophyll-a content. Culture-based fish yield in the 30 reservoirs varied from 54.6 to 1800.8 kg ha-1 and BD associated with the reservoirs studied varied from 0.90 number ha-1 to 216.25 numbers ha-1. Fish yield (FY) was significantly correlated with BD the relationship being, FY = 4.758 BD + 242.740 (R2 = 0.345; p<0.001). The importance of taking into consideration factors such as grazing cattle and buffalo density in preparing management strategies for culture-based fisheries in small village reservoirs is discussed.

The present study elucidates the socio-ecological status of the marine ornamental reef fish (MORF) fishery in Trincomalee, Sri Lanka, through strategic SWOT analysis. Data were collected through interviews with full-time fishers (n = 49) fishing at Pulmodai, Sampur, and Kuchchaweli reef sites, focus group discussions (n = 3), and participant observations during 2019–2020. Data gathered in-situ were further investigated in detail, analyzed, and grouped into attributes of SWOT analysis. Results revealed higher fishing income (90–900 USD) by 91.84% of respondents as the major strength of the fishery, followed by low production costs (24–240 USD), a low labor force, and others. Seasonality of the fishery, multiple ownership of reefs, and the limited number of fishing hours (4-6 hrs.) were the main weaknesses identified in the system. High global demand, the fish-to-order concept, and the intervention of local buyers were the major opportunities for the fishery. Long market chains, bopyrid isopod infection on Pacific cleaner shrimp, and poor monitoring systems were the major threats to the industry. The MORF fishery in Trincomalee, Sri Lanka, results in higher living standards for fisher communities and empowers them. The present study has policy implications for the MORF fishery and the long-term sustainability of the industry.