Are growth and recapture of hatchery‐reared and resident brown trout (Salmo truttaL.) density dependent after stocking?

Abstract

Abstract – The population density of brown trout (Salmo trutta) in a small natural system was manipulated in six equal‐length stream sections by stocking hatchery‐reared 1+ brown trout (unstocked, tripled and quintupled) over two consecutive years. The results showed that hatchery‐reared trout grew more slowly and were more mobile than resident trout, and that their growth was inversely density dependent. In contrast, growth of the resident trout was density independent. The recapture of 1+ resident and hatchery‐reared trout was inversely density dependent. This is most likely a consequence of increased competition. However, after a single winter the population density returned to its base level prior stocking and older resident trout showed no density‐dependent recapture. Thus, the advantage of stocking, here higher biomass, may have the detrimental effect of decreasing resident stocks of the same size class during summer.