**5. Conclusion**

The combination of the different methodologies used, *i.e.* radio and PIT-telemetry, allowed a better understanding of the movement patterns and spatial distribution of stocked and native trout through intensive tracking of a small number of radio-tagged fish over a short time scale and continuous monitoring of movements and microhabitat use by PIT-telemetry. As pointed out by Ovidio et al. (2009) gaps in the fish behaviour can be closed using complementary methodologies. This study also confirmed previous observations following distinct methodologies (*e.g.* snorkelling, electrofishing), which detected, just one month after, a low proportion of stocked brown trout in the stream segment where they had been released (Cortes et al., 1996; Teixeira et al., 2006). The potential negative impacts of stocking on wild population seemed to be limited in time and space and were demonstrated by the monitoring of fish movement (*e.g.* radiotelemetry), since a high dispersion was registered, mainly in downstream direction, of the majority of stocked fish. The rapid decrease of stocked fish condition, the variation of hydrological parameters and the vulnerability to predation were factors that contributed to the low efficiency of the stocking programs. For these reasons, stocking of brown trout as a management tool for supplementing the recreational fisheries in rivers must be questioned based on the reduced adaptation of stocked trout to wild environment. However, in specific conditions it could be a costeffective option, namely if catchable-size trout were used and applied to selected areas where angling pressure is intense. It is possible that a greater proportion of stocked trout never adopt the adequate behaviour that normally is displayed by native trout. Probably the minor adaptation of hatchery-reared fish to the wild environment is more visible when stocking is made recurring to fish of superior size/age (> 1+). Although Pedersen et al. (2003) had found a higher survival and adaptation of smaller brown trout (0+) over a period of 11 months, a longer time is needed to fish reach the legal catch size for anglers and, as referred by Aarestrup et al. (2005), stocking with trout over the legal size limit could be the correct management tool for supplementing the recreational fisheries. Finally, it is important to consider alternative management techniques with low ecological risks like the improvement of the fish habitat and protective measures (*e.g.* catch-and-release, better management and angling regulations), to promote a superior biogenic capacity of the aquatic system and assure the conservation and/or exploitation of self-sustainability of wild trout populations.

### **6. Aknowledgments**

We wish to thank Ângelo Saraiva, Tiago Martins and Paula Escalda for their field assistance. Thanks also to Rogério Rodrigues, Graça Barreira, Julieta Sampaio and Augusto Maia from Forestry Governmental Services and the hatchery personnel at Marão and Castrelos Trout Hatchery.
