Evaluation of Agricultural Contamination Level by Heavy Metals and Pesticides in Sediments of Rivers and Water Bodies for Shrimp Fishing in the Lower Ouémé: Case of the Aguigadji, Ahlan and Sele Stations in Benin

This study assessed sediment contamination by heavy metals and pesticide active ingredients linked to chemical inputs used in agricultural activities in the lower Ouémé. Pesticide residues from the organochlorine, pyrethroid and organophosphorus families were investigated by gas chromatography, and heavy metals (Cd, Pb, As, Ni, Zn, Fe, Mg, Cr and Hg) by atomic absorption spectrophotometry. The metallic pollution indices, the contamination factor (CF) and the ecological risk index were calculated. The results revealed 8 active ingredients in the rainy season and 9 in the dry season. Glyphosate was the active ingredient with the highest concentration at all stations, 9.65 ± 0.84 mg/kg recorded in the dry season at the Aguigadji station. All glyphosate values were above the EQS. DDT, Atrazine and Endosulfan also showed high concentrations in the dry and rainy seasons. Emamectin, Abamectin and Lambda Cyhalothrin also showed high concentrations in the dry season at Aguigadji, Ahlan and Sele. Only glyphosate was recorded at the control station (Toho), but in very low concentrations. Lead showed the highest concentrations at all the stations, 265.96 ± 21.02 mg/Kg in the rainy season and 255.38 ± 79.09 mg/Kg in the dry season, all detected at the Aguigadji station and above the EQS. Zn, Ni, Fe, Cu and Cr were all representative in both the dry and rainy seasons at the contaminated stations. Manganese showed high concentrations in the rainy season. Pb showed very high contamination (FC ≥ 6) at the Aguigadji and Ahlan stations and significant contamination (3 ≤ FC 6) at the Sele station in both the rainy and dry seasons. Ni, Hg and Cd, showed either moderate or significant contamination at the contaminated stations. The risk values showed a considerable ecological Ri (190 ≤ Ri < 380) in the rainy season and a moderate ecological Ri (95 ≤ Ri < 190) in the dry season at these contaminated stations.

Design and Realization of Cold Disaster Early Warning System for Subtropics Aquaculture

By analyzing the subtropics aquaculture present situation,the necessity of the construction of cold disaster early warning system for subtropics aquaculture,the research goal and the duty were expounded. The system structure and the frame were introduced in detail. Several key questions and their solutions of the cold disaster early warning system for subtropics aquaculture were put forward.

A review on fishing gear in China: Selectivity and application

In the 1980s,China’s offshore marine fishery resources declined,thus fishing gear selectivity gradually became a focus of scientific fishery research.Studies of fishing gear selectivity mainly focus on five kinds of fishing gear:trawls,shrimp beam trawls,stow nets,gillnets,and pots.Cover net method is the main method used in the comparative study of codend selectivity of both trawls and stow nets.These results showed that(1)Bottom trawls,targeting Larimichthys polyactis(the Little yellow croaker)and Trichiurus haumela(the Hairtail),should have a minimum mesh size of the codend no less than 60 mm in the Yellow and East China Seas.While the codend should use a square mesh with a minimum mesh size of 40 mm due to the variety of targeted species in the South China Sea.(2)Pair pelagic trawls,targeting pelagic species such as Engraulis japonicus(the Japanese anchovy),Pampus argenteus(the Silvery pomfret),Scomberomorus niphonius(the Spanish mackerel),as well as bottom species such as L.polyactis and T.haumela,should have a minimum mesh size of the codend no less than 56 mm in the Yellow Sea.(3)Shrimp beam trawls should use shrimp/fish separator devices(e.g.,separator panels,vertical separator panels,and sorting grids)to improve intra-species selectivity and reduce by-catch of non-target fish.(4)Canvas stow nets,targeting L.polyactis and T.haumela,should have a minimum mesh size of the codend no less than 55 mm.(5)Gillnets,the minimum mesh size should be determined for catching traditional economic species,but also the optimal mesh size for newly developed species.Such as,gillnets with mesh size of 35-38.71 mm targeting Harpodon nehereus(the Bombay duck),55 mm targeting L.polyactis and Nemipterus virgatus(the Golden threadfin bream),72 mm targeting Dentex tumifrons(the yellow sea breams)or Scomberomorus commersoni with body length of 280 mm,100 mm targeting P.argenteus,104 mm or 146 mm targeting 2-3 year or 6-7 year S.niphonius,120 mm targeting S.commersoni with body length of 380 mm,and 144 mm targeting Pampus chinensis(the Chinese pomfret).(6)Pots,the steel-framed round pots targeting Portunus trituberculatus(the swimming crab)should have a 33 mm height of escape vent or an 8 cm diameter escape hole,and the steel-framed round pots or accordion-shaped trap targeting Charybdis japonica(the Asian paddle crabs)should have a 30 mm height of escape vent installed on the side of pots.These results of fishing gear selectivity from the scientific basis for the implementation of fishing gear access systems,especially for identifying the minimum mesh size of fishing gear.In the future,the Fisheries Research Institute of China should conduct long-term investigations of selectivity in trans areas.Developing fishing gear access systems that are in line with a sustainable development is of great significance for the conservation and restoration of offshore fishery resources in China.