Fish stocks in the Âncora River, north Portugal: Food consumption estimated with a bioenergetics model

Abstract

In the 19 km long Âncora River, divided by 20 waterfalls and dams and emptying to the Atlantic Ocean in north Portugal, fish were sampled for the bioenergetics study. Average monthly water temperature during the year at sites along the river course was in the range 8.5–21°C. The four fish populations’ consumption, both in energy and mass units, was lower at sites in the middle course of the river, which was isolated from upstream sites by numerous waterfalls and dams. The gross ( K 1) and net ( K 2) ecological efficiencies of brown trout, roach and nase were very low, but detritus was their dominant food item. Eel, which ate animal food only had two to three times higher growth efficiencies than other fish. High mean monthly water temperatures from May to August and the isolation effect were probably the causes of a low utilisation of consumed food for growth in the populations investigated.