Seasonal dynamics in resources of the freshwater shrimps, Macrobrachium nipponense and Exopalaemon modestus in Dianshan Lake

Abstract:

Resources of Macrobrachium nipponense and Exopalaemon modestus are extremely abundant, which occupies a very important position in fisheries of the Dianshan Lake; These species are also the main source of income for local fishermen. This paper focused on studying temporal and spatial changes in resources of the freshwater shrimps, M. nipponense and E. modestus, according to the survey data during the period from August 2010 to August 2011 in the Dianshan Lake. The results showed that the range of carapace length of M. nipponense was 7.05-47.07 mm, averaged(22.192±1.650) mm, dominant carapace length was 15.5-30.5 mm, accounting for 82.98% of the whole carapace length; the range of carapace length of E. modestus was 9.10-38.7 mm, averaged(21.221±1.598) mm, dominant carapace length was 15.5-25.5 mm, accounting for 80.49% of the whole carapace length; Resource density for M. nipponense reached a peak in September and May, while the lowest resource density was in March. Resource density for E. modestus reached a peak in October and April, and the lowest resource density was in June. Spatially, the biomass of M. nipponense and E. modestus witnessed large fluctuations in different areas. The biomass of freshwater shrimp was higher in the open waters than in the coastal zones during winter and spring. However, the biomass of these freshwater shrimps was lower in the open waters than in the coastal zone during summer and autumn. Besides, biomass of the upper half of the Dianshan lake were overall higher than that of the lower half of the lake. This research provides a basis for the rational management and effective exploitation of the shrimp resources in Dianshan Lake, which also provides a reference for the fishery authorities to delimit areas of enhancement and releasing.