**2.1 Study area**

330 Modern Telemetry

temporal behaviour of freshwater fish (Lucas & Baras, 2000), although the comparisons and the validity of some results have been questioned (Gowan & Fausch, 1996). Recent technology and the development of a set of techniques (e.g. passive integrated- PIT, acoustic, radio and electromyogram- EMG transmitters), broadly referred as biotelemetry, enabled new information for researchers in basic and applied ecology, namely related with a better understanding of the physiology, behaviour and energetic status of free-living animals (Cooke et al., 2004). Radiotelemetry has been widely used, providing a highresolution, in temporal and spatial scale, of information at individual level. Despite of the high costs of individual radio-tags and the detection equipment that restrict the number of tagged fishes, different studies were made to evaluate the home range of target species, like diel (Belanger & Rodriguez, 2001) and seasonal movements (Burrell et al., 2000), the influence of environmental factors (Ovidio et al., 1998) and the efficacy of fishways (Scruton et al., 2002). On the other hand, passive integrated transponder (PIT) technology has been developed for monitoring the individual movements of free-ranging fish for tracking (Prentice et al., 1990a; Armstrong et al., 1996; Greenberg & Giller, 2000), even small aquatic animals in shallow waters, involving low equipment costs and the possibility of addressing numerous questions in fields of animal behaviour, habitat use and population dynamics not covered by radiotelemetry (Roussel et al., 2000, Quintella et al., 2005). The indefinite life span and high tag retention with no apparent effects on growth and survival of tagged animals are other advantages mentioned to the PIT telemetry (Ombredane et al., 1998; Bubb et al., 2002). Several improvements occurred in the PIT technology throughout the last decades. Initially, stationary systems were used to evaluate the migration and survival of fish passing through fishway orifices (Prentice et al., 1990b; Castro-Santos et al., 1996) or streamwide antennae (Barbin-Zydlewski et al., 2001). In recent years, different types of portable equipments, like the flat-bed antenna design (Armstrong et al., 1996), the multipoint decoders connected to several flat-bed antennae (Riley et al., 2003) and the portable antenna (Roussel et al., 2000; Coucherousset et al., 2010), were developed and adapted to assess the behaviour of local populations in shallow streams. However, there is a lack of studies combining both radio and PIT telemetry technologies to study the behaviour

of trout populations and this possibility is important to enhance the data quality.

measures for the Portuguese salmonid streams.

**2. Material and methods** 

northeastern Portugal (Figure 1).

The objective of the present study was to evaluate the spatial and temporal behaviour of wild and hatchery-reared brown trout populations in a stream of northeastern Portugal after stocking. Radio and PIT telemetry technologies were combined in order to study the movements of these sympatric populations. Radiotelemetry was used for large-scale continuous monitoring of individual fish and detailed information on movements was obtained at two distinct temporal scales: day-by-day and hourly diel cycles. Complementarily, PIT telemetry allowed a fine-scale approach considering the microhabitat use and activity pattern of each tagged fish in a confined area. This information was relevant to analyse the efficiency of stocking, the evolution of stocked fish condition and the potential impacts on the wild populations in order to define the most appropriate management

The study was carried out in summer and autumn of 2002 and 2005 in a salmonid stream, the Baceiro River, tributary of the Douro River, located in the Montesinho Natural Park, The Baceiro River is a third-order stream, approximately 25 km long, mean annual discharge of 1.93 m3.s-1 and mean gradient of 4%, subjected to a reduced human pressure and a land use cover dominated by oak (*Quercus pyrenaica* Willd.) forests and also some meadows and planted chestnut (*Castanea sativa* Mill.) and *Pinus* spp., which contributes to the low impact on water composition (conductivity < 70 μS.cm-1, dissolved oxygen > 9 mg.l-1, alkalinity < 25 mg HCO3-.l-1, hardness < 15 mg CaCO3.l-1, NO3- < 0.5 mg.l-1, PO4 3- < 0.1 mg.l-1). This stream is characterized by a constrained channel, gravel-pebble over sand streambed and riparian vegetation is well developed and dominated by alder (*Alnus glutinosa* (L.) Gaertn.), although willow (*Salix salvifolia* Brot. and *S. atrocinerea* Brot.), poplar (*Populus nigra L.*) and ash (*Fraxinus angustifolia* Vahl) trees are also present. The stream width ranged between 5 m in the riffle to 12 m in the pool habitats, with maximum depth of 3 m. During summer (late) and autumn (early), the water temperature ranged from 5.0 to 19.0 ºC and discharge from 0.05 to 2.1 m3.s-1 (the last after a storm event). It is important to mention that, during 2005, an extremely dry period was observed in the region and the stream became intermittent during a part of the summer. In the stream segment, the fish community consisted almost exclusively of wild brown trout populations and few numbers of nase (*Pseudochondrostoma duriense* Coelho) and Iberian chub (*Squalius carolitertii* Doadrio). Otter (*Lutra lutra* L.), water snakes (*Natrix maura* L. and *Natrix natrix* L.) and heron (*Ardea cinerea* L.) were the natural predators found in this stream.

Fig. 1. Map of study area in the Baceiro River, a salmonid stream located in the Douro basin.

Combining Radio and PIT-Telemetry to Study the Large and Fine-Scale

located near of Baceiro River.

(summer 2005).

readings were averaged at 0.2 and 0.8 of total depth.

Movements of Stocked and Wild Brown Trout (*Salmo trutta* L.) in a Northeastern Stream, Portugal 333

Fig. 3. Trout radio-tagging procedures and recover period of stocked trout in fishfarms,

The habitat unit selected for the release of stocked trout was 210 m long by 9.0 m mean width by 2.5 m of maximum depth, comprising all representative microhabitats of stream segment. Temperature (thermometer, accuracy of 0.1 ºC) and water column velocity (Valeport flowmeter, accuracy of 0.01 m.s-1) were daily measured (Figure 4) and stream discharge determined near the stocking site. Velocity at 0.6 of total depth was considered as the mean water column velocity when the depth was less than 0.75 m. At deeper points the

Fig. 4. Measuring temperature (oC) and water column velocity (m.s-1) in the Baceiro River

The fish were monitored and located at least once a day until the end of their transmitter's battery life during the whole study period (14 days in 2002 and 64 days in 2005). Net daily journeys were registered, which were defined as the distance between locations at two consecutive days. During 2005, the fish were also monitored hourly for a partial diel cycle (from 06.00 a.m. to 24.00 p.m.) for eight days (week periodicity). Such registrations took place on 23 and 30 September, on 7, 14, 21 and 28 October and on 4 and 12 November. All tracks were conducted along the stream banks and the potential disturbance of fish activity minimized. To measure the trout movements, yellow fluorescent marks were sprayed on the
