**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**

Amílcar A. T. Teixeira1 and Rui M. V. Cortes2

*1Polytechnic Institute of Bragança, School of Agriculture, Mountain Research Centre 2University of Trás-os-Montes, Centre for the Research and Technology of Agro-Environmental and Biological Sciences Portugal* 

#### **1. Introduction**

328 Modern Telemetry

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> 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. In fact, a wide variety of techniques, grouped as capture dependent (*e.g.* mark-recapture, telemetry) and independent (*e.g.* visual observation) methods, were used for the investigation of the spatio-

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

*cinerea* L.) were the natural predators found in this stream.

**2.1 Study area** 

Movements of Stocked and Wild Brown Trout (*Salmo trutta* L.) in a Northeastern Stream, Portugal 331

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, PO43- < 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* 

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

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.

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 measures for the Portuguese salmonid streams.

#### **2. Material and methods**

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, northeastern Portugal (Figure 1).
