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Quantitative indices of herring infestation in Sakhalin waters reveal a high infection rate of fish in the basin of the Sea of Okhotsk, off the east coast of the island. Moreover, in certain years almost 100% of herring were infested. The so-called local populations as well as widely migrating Sakhalin Hokkaido herring are confined to the area of this waterbody. In the basin of the Sea of Japan, off the west coast of Sakhalin, the indicator values of herring infestation are much lower. The local population as well as widely migrating herring of Sakhalin Hokkaido population are confined to this marine area. The causality analysis of herring infestation in these areas allows to confirm our earlier conclusions about population structure of herring inhabiting the waters around Sakhalin Island.
Fish are heavily influenced by the nature of the flood regimes of the rivers in which they live. These fluctuate naturally from year to year but recently increasing pressure on water for a wide range of uses other than fisheries has led to human activities that have substantially altered the flood regimes of many rivers throughout the world. This has resulted in the loss of fish production and biodiversity. There are now efforts to mitigate for these changes that include release of artificial floods from dams or polder sluices. The typical flood curve contains several characteristics that may influence the survival and growth of the individual fish species. Understanding of these characteristics will help design appropriate flood curves and maximize benefits from the water available.
The last free stretch of the River Paraná inside of Brazilian territory, about 230 km of the former 810 km, runs in a wide floodplain, which flood regime is controlled in part by upstream dams. Aim to evaluate the impacts of different levels of hydrological control on the regional fish diversity, nutritional condition, trophic categories proportion, reproduction and young abundance monthly sampling were carried, between 1986 and 1993, during three annual periods with different flood duration and intensity. Lagoons, secondary channels and river channel was sampled with gillnet of different mesh size and standardized effort. Diversity, evenness indexes and number of species increased with the occurrence of floods. The trophic category proportions varied among the periods considered, with a decrease in piscivores participation and an increase of iliophages, herbivores and insectivores (terrestrial) participation in big flood years. The tendencies for piscivores guild were not uniform to every pecies. The variations on the nutritional condition reveal that the absence of flooding has a negative effect on greater migratory species and positive on sedentary ones. The young abundance shows, however, that fail in the flooding has a strong negative impact on de recruitment of all the reproductive strategies. It’s stressed the operational procedures in the upstream dams and the maintenance of the floodplain integrity is essential to preserve the regional biodiversity, fisheries and particularly the greater migratory fishes population.
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