Homing behaviour of displaced stream-dwelling brown trout

Behavior and growth of juvenile brown trout (Salmo trutta) following upstream and downstream displacement

“…In contrast to the findings by Halvorsen and Stabell (1990) as well as Armstrong and Herbert (1997), our study did not detect a large degree of homing behavior because no trout returned home and only eight trout were recaptured within 200 m of the point of first capture. Instead, our study suggests that brown trout generally are sedentary with a relative average movement of 34.2 m ( §10.3 m) which is similar to the reported home ranges (15À50 m) from Hesthagen (1988) and Harcup et al (1984).…”

“…However, after being displaced for four days, the previous territory owner only managed to outcompete the new intruder in 25% of the cases. In the present study, fish were moved approximately two times the distance used by Halvorsen and Stabell (1990) and perhaps we have passed the threshold distance above which it is too costly in terms of energy and time expenditure, and/or predator exposure to return. Alternatively, fish might not be able to regain previous holding places from other residents or newly introduced fish.…”

“…It can be argued that experimentally displaced fish may not behave naturally and a lack of homing, therefore, may be due to the experimental design. However, several previous studies have used displacement designs and demonstrated effects on homing (Armstrong & Herbert 1997;Halvorsen & Stabell 1990). Thus, differences between studies with similar design would still be valid.…”

“…Olfactory cue is believed to be the key mechanism for homing. Halvorsen and Stabell (1990) neatly demonstrated that with the olfactory organ destroyed only a small fraction of displaced brown trout returned home whereas more than 40% of both upstream-and downstream-displaced control groups returned home. Generally, homing should be less beneficial if the fish is transferred to an environment with lower densities of competitors and/or higher prey densities and fish displaced downstream ought to be able to home to a larger extent due to the presence of chemical cues from upstream habitats.…”

“…The mark-recapture technique does not give us detailed information on diel movement and overlapping territories, but because fish are displaced out of their territory, we can estimate whether they return to their territory. Our hypotheses were (1) that brown trout displaced downstream could identify the olfactory cues of their home site and, therefore, would be better at returning home compared to fish being displaced upstream (Halvorsen & Stabell 1990), and (2) that fish released at the same spot as they were caught would grow faster than removed individuals due to the benefits of the prior residence effect (Huntingford & Turner 1987).…”