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Post‐stocking behaviour of hatchery‐reared European grayling , Thymallus thymallus (L.), and brown trout, Salmo trutta L., in a semi‐natural stream
Author(s) -
Thorfve,
Carlstein
Publication year - 1998
Publication title -
fisheries management and ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.693
H-Index - 55
eISSN - 1365-2400
pISSN - 0969-997X
DOI - 10.1046/j.1365-2400.1998.00087.x
Subject(s) - brown trout , grayling , stocking , salmo , fishery , biology , trout , electrofishing , ecology , fish <actinopterygii>
Hatchery‐reared, juvenile European grayling, Thymallus thymallus (L.), and brown trout, Salmo trutta L., were each stocked six times into an area of a semi‐natural stream. The order in which the two species were released was switched after every second experimental stocking. Temporal and spatial post‐stocking dispersal, effects of previously stocked species, feeding behaviour and the influences of sex and size were studied. During each 48‐h experimental release period, some fish were recaptured in a trap situated 200 m downstream from the stocking site, and fish remaining in the stream after each experimental release were caught by electric fishing. Significantly more grayling than trout moved downstream and left the semi‐natural stream. Proportions of stocked grayling recaptured in the trap within 2 h and from 2 to 48 h post stocking in the stream were 36.4% and 10.0%, respectively. Corresponding recapture rates for brown trout were both 1.5%. Most of the grayling and brown trout that did not leave the stream early were recaptured in deep, slow‐moving water at low velocities in the release area. The presence of grayling at the time that the brown trout were stocked resulted in significantly fewer brown trout staying in the upper part of the stream. Within 48 h of their release, 33.3% and 22.8% of the grayling and brown trout, respectively, had eaten natural food items. The mean length of brown trout recaptured in the upper part of the stocking area was significantly lower than that of fish recaptured in the lower part and in the trap. Among brown trout, males showed a significantly greater propensity to eat and to stay in the upper part of the stream near the stocking site compared with females . Brown trout with natural food items in their stomachs had significantly lower mean length than trout without such items. No sex‐ or size‐related differences were found in the spatial distribution or feeding activity of grayling.