Combining Radio and PIT-Telemetry to Study the Large and Fine-Scale Movements of Stocked and Wild Brown Trout (Salmo trutta L.) in a Northeastern Stream, Portugal
Chapter
Stream-resident salmonid movements have been the subject of numerous studies and their
behaviour is relatively well-known (Harcup et al., 1984; Heggenes, 1988). For example,
brown trout (Salmo trutta) is described as a sedentary species based on the behaviour
displayed, often associated to the strong site attachment to a territory or home range
(Bridcut & Giller, 1993; Armstrong & Herbert, 1997). Other salmonids like brook (Salvelinus
fontinalis) (Roghair & Dolloff, 2005) and cutthroat trout (Oncorhynchus clarki) (Hegennes et
al., 1991) showed similar behaviour. However, there are studies reporting a wide range of
movements for brown (Meyers et al., 1992; Young, 1994), cutthroat (Hilderbrand &
Kershner, 2000) and brook (Gowan & Fausch, 1996) trout populations. Trout behaviour can
be modified by natural (e.g. fish density, food availability) and especially by man induced
factors (e.g. environmental degradation, harvest and stocking) responsible for major threats
of wild populations (Laikre et al., 2000). Indeed, stocking of hatchery-reared brown trout is a
management tool commonly used to improve the recreational fishing (Cowx, 1999). This
activity is responsible for a sudden artificial increase of fish density in a particular area.
Negative impacts on wild populations, such as genetic contamination, competition, predator
attraction and disease transmission were often referred (White et al., 1995; Einum &
Fleming, 2001; Weber & Fausch, 2003) and are potentially amplified with the dispersal
failure, since many hatchery-reared trout tend to remain near of the stocking site (Cresswell,
1981; Aarestrup et al., 2005). There are also contradictory results, as reported by Bettinger &
Bettoli (2002) where stocked trout dispersal reached over 12 km in the downstream
direction, just 24 hours after their release. Cortes et al. (1996) found for Portuguese salmonid
streams that, during three successive years (2000 to 2003), less than 20% of stocked brown
trout remained in the stream segment, one month after the release. However, in this study a
mark-recapture method was used that did not allow to assess the main causes of the fish
depletion and was not appropriate for the observation of fish behaviour.
