Variations in the fish community of the Øra Estuary, SE Norway, with emphasis on the freshwater fishes
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Abstract
The fish fauna in a part of the River Glomma estuary, the Øra estuary, in SE Norway was studied from April to September in 1973 and 1976, and until October in 1975. Analysis of the variations in the fish community by diversity indices showed significant correlation between species diversity H and salinity. A seasonal cycle in the fish community occurred, i.e. a shift from a marine to a freshwater community in spring and the reverse in autumn. Salinity, which in the study area is dependent on river discharge and northern winds, is the main factor acting on the occurrence of the freshwater fishes. The maximum salinity tolerance of the six common freshwater species was 10-12 ‰. Growth features suggest that Leuciscus idus (L.) and Perca fluviatilis L. are semidiadromous. The migration pattern of other freshwater species is briefly discussed.
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