Movements of 60 stream-dwelling wild Atlantic salmon Salmo salar (97-118 mm
), each tagged with a passive integrated transponder, were monitored during
Four trials in an enclosed section (24 m long, 45.1 m(2) total area) of a
stream at a range of densities (four, eight, 16 and 32 fish per enclosure).
patterns of space use differed markedly between individuals, with 80% of f
ish establishing home ranges within 8 days of introduction to the enclosure
(settlers) and the remainder continuing to move throughout the length of t
he enclosure (non-settlers). Although aggressive interactions were quite fr
equent and dominant fish were observed chasing subordinates, there was cons
iderable overlap of home ranges of settlers at all densities; this was the
case even at lower densities at which only a fraction of the enclosure was
used by the fish. Thus, rather than adopting fixed territories, the salmon
showed a high Level of space sharing. Individual fish used the same local a
rea in different ways, ranging from highly localized Feeding on drifting fo
od items to a wider-ranging strategy of specialising on benthic food. Among
the fish that settled absolute growth rates were inversely related to body
size, and at high densities fish lost weight. These results suggest that s
pace use in wild juvenile salmon is more complex than a mosaic of territori
es, that salmon demonstrate significant variability in individual space use
patterns, and that large fish may suffer disproportionately when populatio
ns are at the carrying capacity of their environment.