**3. Results**

336 Modern Telemetry

Type I PIT tag 25 22.3 ± 1.6 126.7 ± 28.2 1.12 ± 0.08 0.08 ± 0.02 Type II PIT tag 25 23.2 ± 1.3 146.2 ± 24.9 1.16 ± 0.07 0.85 ± 0.17

A) < 15.0 8 13.3 ± 1.2 23.5 ± 6.7 1.00 ± 0.07 0.10 ± 0.03 B) 15.0-20.0 8 17.0 ± 1.2 48.6 ± 9.8 0.98 ± 0.08 0.22 ± 0.04 C) > 20.0 9 22.0 ± 1.9 108.9 ± 30.3 0.97 ± 0.04 0.46 ± 0.15

Table 1. Mean ± standard deviation (S.D.) of total length (*L*T), mass (*M*), Fulton's condition factor (*K*) and tag ratio of the pit-tagged brown trout in the Baceiro stream, during summer

Fig. 6. PIT-tagged trout passing over an antenna, during field experiment in the Baceiro

The analyses of movement and activity patterns of stocked and native trout populations were based on the non-repeated data (the continuous repeated records of each fish in the same antenna were not considered) recorded by the MPD unit during the five weeks of

*\* K = 100(M. LT-b), where M*- trout mass (g); *LT*- total lenght (cm); *b-* alometric coefficient

*M*  (g) *K*\* Tag ratio \*\* (%)

Trout Group Fish

\*\* 100.(tag mass).(trout mass)-1

River (summer 2005).

**1) Stocked** 

**2) Native** 

2005.

Number

*L*T (cm)

### **3.1 Radio-telemetry analysis**

A distinct movement pattern was detected comparing stocked and native brown trout (Mann-Withney *U*-test, P< 0.001), from the radiotelemetry survey carried out in autumn 2002 (Figure 7). An initial stationary behaviour of stocked trout (for five days remaining in the stocking site) was replaced by their migration in a downstream direction, and at the end of 14 days (transmitter battery life) the fish were located in a small pool, 1,500 m from the stocking site. The magnitude of the displacement was correlated with the increase of stream discharge (Spearman correlation *r*S> 0.85, P< 0.01). Conversely, wild trout remained near the stocking site hiding under a fallen tree, in spite of the non-residency status. It was only detected a downstream movement of 200 m coinciding with a sudden rainstorm, which raised the water level by 1 m. Nevertheless, after this period, the wild trout followed the upstream migration and travelled to feeding zones (90 m from stocking site) near a riffle/run habitat.

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 339

Fig. 8. Dispersal of six stocked brown trout (T1 to T6) after being released in the Baceiro stream, on 16 September 2005. Symbols are daily positions of radio-tagged trout for 64 days

A common feature observed was the progressive downstream migration of the fish that displayed movement. The longest movement was reported for T3, which travelled over 4,500 m within 64 days, and for T5 and T6 located over 1,100 m from the stocking site, corresponding, respectively, to mean downstream progression velocities of 66.2 m.d-1 and 16.5 m.d-1. This downstream movement was not detected continuously over every diel cycle and the interruptions in the migratory behaviour were more prolonged in the artificial pools. Indeed, during the study, 95% of fish locations were recorded in pool instead of run/riffle habitats. In opposition, T1 remained in the same pool habitat. Consequently, significant differences (*U*-tests, P< 0.001) were found for dispersal between fish showing stationary (T1) and a higher mobility behaviour (T3, T5, T6) and for the T.D.M. (*U*-test, P< 0.05) between T3 and the remaining fish, based on the sixty-eight diel tracks (trout were located once per day). The environmental conditions influenced the stocked trout behaviour. In fact, fish showed distinct movement patterns depending on two distinct periods identified during this study: 1) from 16 September to 9 October, characterized by dry and hot conditions (mean water temperature 12 ºC and discharge < 0.05 m3.s-1) stocked fish exhibited restricted movements, confined to the stocking site; 2) from 10 October to 18

(transmitter battery life).

Fig. 7. Dispersal of one stocked and one native brown trout after being released in the Baceiro stream, on 15 October 2002. Symbols are daily positions of radio-tagged trout for 14 days (transmitter battery life).

Of the experiment conducted during summer/autumn of 2005 with six radio-tagged stocked trout, four individuals (T1, T3, T5 and T6) were tracked during the entire study period (64 days) and trout T2 and T4 signals were missed early, respectively on the 27th of October (after 42 days) and on the 31st of October (after 46 days) (Figure 8). Individual movements of stocked radio-tagged trout released in the Baceiro stream exhibited different patterns: a wide-range of displacements was recorded, and at the end of the registration period, the displacement of fish from the stocking site (dispersal) varied from 0 to 4,500 meters (Table 2).


Table 2. Characteristics of stocked radio-tagged trout in the Baceiro stream (September to November 2005).

Fig. 7. Dispersal of one stocked and one native brown trout after being released in the Baceiro stream, on 15 October 2002. Symbols are daily positions of radio-tagged trout for 14

> Mass (g)

Table 2. Characteristics of stocked radio-tagged trout in the Baceiro stream (September to

T1 26.8 223.5 64 0 T2 26.5 193.5 42 -350 T3 26.5 228.5 64 -4500 T4 25.5 178.4 46 -200 T5 27.7 209.6 64 -1025 T6 26.0 171.3 64 -1125

Days tracked Total

Dispersal (m)

Of the experiment conducted during summer/autumn of 2005 with six radio-tagged stocked trout, four individuals (T1, T3, T5 and T6) were tracked during the entire study period (64 days) and trout T2 and T4 signals were missed early, respectively on the 27th of October (after 42 days) and on the 31st of October (after 46 days) (Figure 8). Individual movements of stocked radio-tagged trout released in the Baceiro stream exhibited different patterns: a wide-range of displacements was recorded, and at the end of the registration period, the displacement of fish from the stocking site (dispersal) varied from 0 to 4,500

days (transmitter battery life).

Total Length *L*T (cm)

meters (Table 2).

November 2005).

Trout code

Fig. 8. Dispersal of six stocked brown trout (T1 to T6) after being released in the Baceiro stream, on 16 September 2005. Symbols are daily positions of radio-tagged trout for 64 days (transmitter battery life).

A common feature observed was the progressive downstream migration of the fish that displayed movement. The longest movement was reported for T3, which travelled over 4,500 m within 64 days, and for T5 and T6 located over 1,100 m from the stocking site, corresponding, respectively, to mean downstream progression velocities of 66.2 m.d-1 and 16.5 m.d-1. This downstream movement was not detected continuously over every diel cycle and the interruptions in the migratory behaviour were more prolonged in the artificial pools. Indeed, during the study, 95% of fish locations were recorded in pool instead of run/riffle habitats. In opposition, T1 remained in the same pool habitat. Consequently, significant differences (*U*-tests, P< 0.001) were found for dispersal between fish showing stationary (T1) and a higher mobility behaviour (T3, T5, T6) and for the T.D.M. (*U*-test, P< 0.05) between T3 and the remaining fish, based on the sixty-eight diel tracks (trout were located once per day). The environmental conditions influenced the stocked trout behaviour. In fact, fish showed distinct movement patterns depending on two distinct periods identified during this study: 1) from 16 September to 9 October, characterized by dry and hot conditions (mean water temperature 12 ºC and discharge < 0.05 m3.s-1) stocked fish exhibited restricted movements, confined to the stocking site; 2) from 10 October to 18

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

and the remaining weeks.

trout; = stocked trout.

Movements of Stocked and Wild Brown Trout (*Salmo trutta* L.) in a Northeastern Stream, Portugal 341

showed the incisions to be healed up and only two stocked trout had signs of tag expulsion. At the same time, only 28% (Type I tags) and 32% (Type II) of stocked fish survived, reaching a minimum of 4% at the end of the study (7th week). On the other hand, 92% of native tagged fish remained alive in the study area. Furthermore, the variables *K* and *M* (only for Type II- PIT tagged fish) displayed a significant decrease (Mann-Whitney *U*-tests, P< 0.05) for the stocked fish and smaller size classes (A and B) of native trout. The CCA's ordinations (Figure 10 and 11) showed a similar relationship between the microhabitat variables and stocked and native trout for the two defined periods (eigenvalues of 0.472 and 0.177 for the 1st period and 0.228 and 0.124 for the 2nd one), and the first two axes explained, respectively, 63.8% and 65.0% of the variation relating to trout populations and the environmental variables. The Monte Carlo randomization test detected for both CCA's showed significant results for the sum of all eigenvalues (199 permutations, P< 0.05). For both CCA's a set of variables (*e.g.* total depth, dominant and subdominant substrate, aquatic cover, overhanging vegetation, distance to riffle and the distance to the nearest streambank) presented a similar importance that contributed to the distribution of stocked and native trout along the sympatric period and no substantial differences were detected between the initial adaptation period (1st week)

Fig. 9. NMDS ordination of stocked and native brown trout in the Baceiro stream (summer 2005). Ordination was based on a matrix of pair-wise Bray-Curtis similarities coefficients constructed from non-repeated records, log transformed (Log[*x*+1]). Symbols: = native

2D Stress: 0,24

November, coinciding with successive precipitation events (discharge > 0.40 m3.s-1) and the lowering of water temperature (mean= 8.4 ºC), the stocked trout displayed an obvious dispersal. Most of stocked trout (83%) began the displacement, towards downstream almost immediately after the flow increase. These movements were significant and positively correlated with stream discharge (*r*S> 0.54, P< 0.05), except for T1 (*r*S= 0.22, P> 0.05) and T4 (*r*S= 0.26, P> 0.05), and negatively correlated with water temperature (*r*S> 0.54, P< 0.05). D.H.R. was calculated for tagged fish, based on the hourly monitoring movements (partial diel cycle from 06.00 a.m. to 24.00 p.m.), and ranged from 0 to 475 m (mean= 82 m). Significant differences were only detected for D.H.R. between T1 vs. T3 and T3 vs. T4 (*U*tests, P< 0.01; Table 3).


Table 3. Variations of daily home range, mobility and exploitation (mean ± standard deviation, S.D.) of habitat by stocked trout in the Baceiro stream (based on eight partial diel cycles).

T.D.M. for the same period, showed values varying from 0 to 950 m and trout that displayed a superior migratory behaviour, like T3, T5 and T6, exhibited also greater daily movements and differed significantly from T1, T2 and T4, suggesting that fish showing higher mobility exploited more intensively their D.H.R. (*U*-tests, P< 0.01; Table 3). During the eight partial diel tracks, stocked fish was more active during day and twilight periods, and their mobility decrease at night (*U*-tests, day vs. night and twilight vs. night, P< 0.05). However, these results are limited to a short night period (21.00 to 24.00 hours).

#### **3.2 PIT-telemetry analysis**

A total of 44,934 fish records (identified tag codes) were successfully registered by the MPD unit for both populations, during five consecutive weeks after stocking release, with 80.3 % corresponding to stocked fish and 19.7% to native trout.

The NMDS ordination showed, in a two-dimensional space, the separation between native and stocked trout (Figure 9). The ANOSIM one-way analysis demonstrated significant differences between stocked and native trout (P< 0.001).

With regard to non-repeated data, a similar proportion was obtained for both populations (83.2% for stocked and 16.8% for native trout) considering the total of 14,369 registrations. However, stocked tagged trout density was double that of the native trout. During the study period, a small number of tag codes were not identified (0.02 %). Three stocked and two native trout (both from B class) were not identified by any antenna during the study period, suggesting that mortality (one native fish was captured dead) or/and tag expulsion can occur after the surgical implantation of the transmitters. Nevertheless, all tagged fish that survived and were captured by electrofishing, five weeks after stocking,

November, coinciding with successive precipitation events (discharge > 0.40 m3.s-1) and the lowering of water temperature (mean= 8.4 ºC), the stocked trout displayed an obvious dispersal. Most of stocked trout (83%) began the displacement, towards downstream almost immediately after the flow increase. These movements were significant and positively correlated with stream discharge (*r*S> 0.54, P< 0.05), except for T1 (*r*S= 0.22, P> 0.05) and T4 (*r*S= 0.26, P> 0.05), and negatively correlated with water temperature (*r*S> 0.54, P< 0.05). D.H.R. was calculated for tagged fish, based on the hourly monitoring movements (partial diel cycle from 06.00 a.m. to 24.00 p.m.), and ranged from 0 to 475 m (mean= 82 m). Significant differences were only detected for D.H.R. between T1 vs. T3 and T3 vs. T4 (*U*-

Total Distance Moved

Exploitation (T.D.M./D.H.R.)

(T.D.M., m)

Table 3. Variations of daily home range, mobility and exploitation (mean ± standard deviation, S.D.) of habitat by stocked trout in the Baceiro stream (based on eight partial diel

T.D.M. for the same period, showed values varying from 0 to 950 m and trout that displayed a superior migratory behaviour, like T3, T5 and T6, exhibited also greater daily movements and differed significantly from T1, T2 and T4, suggesting that fish showing higher mobility exploited more intensively their D.H.R. (*U*-tests, P< 0.01; Table 3). During the eight partial diel tracks, stocked fish was more active during day and twilight periods, and their mobility decrease at night (*U*-tests, day vs. night and twilight vs. night, P< 0.05). However, these

A total of 44,934 fish records (identified tag codes) were successfully registered by the MPD unit for both populations, during five consecutive weeks after stocking release, with 80.3 %

The NMDS ordination showed, in a two-dimensional space, the separation between native and stocked trout (Figure 9). The ANOSIM one-way analysis demonstrated significant

With regard to non-repeated data, a similar proportion was obtained for both populations (83.2% for stocked and 16.8% for native trout) considering the total of 14,369 registrations. However, stocked tagged trout density was double that of the native trout. During the study period, a small number of tag codes were not identified (0.02 %). Three stocked and two native trout (both from B class) were not identified by any antenna during the study period, suggesting that mortality (one native fish was captured dead) or/and tag expulsion can occur after the surgical implantation of the transmitters. Nevertheless, all tagged fish that survived and were captured by electrofishing, five weeks after stocking,

T1 54 ± 20 95 ± 73 1.77 ± 0.96 T2 88 ± 35 194 ± 52 2.45 ± 1.01 T3 118 ± 64 255 ± 77 2.54 ± 1.14 T4 40 ± 21 87 ± 73 2.08 ± 1.20 T5 74 ± 26 272 ± 277 3.29 ± 1.04 T6 117 ± 148 266 ± 188 2.98 ± 1.16

results are limited to a short night period (21.00 to 24.00 hours).

corresponding to stocked fish and 19.7% to native trout.

differences between stocked and native trout (P< 0.001).

tests, P< 0.01; Table 3).

**3.2 PIT-telemetry analysis** 

Daily Home Range

(D.H.R., m)

Trout code

cycles).

showed the incisions to be healed up and only two stocked trout had signs of tag expulsion. At the same time, only 28% (Type I tags) and 32% (Type II) of stocked fish survived, reaching a minimum of 4% at the end of the study (7th week). On the other hand, 92% of native tagged fish remained alive in the study area. Furthermore, the variables *K* and *M* (only for Type II- PIT tagged fish) displayed a significant decrease (Mann-Whitney *U*-tests, P< 0.05) for the stocked fish and smaller size classes (A and B) of native trout. The CCA's ordinations (Figure 10 and 11) showed a similar relationship between the microhabitat variables and stocked and native trout for the two defined periods (eigenvalues of 0.472 and 0.177 for the 1st period and 0.228 and 0.124 for the 2nd one), and the first two axes explained, respectively, 63.8% and 65.0% of the variation relating to trout populations and the environmental variables. The Monte Carlo randomization test detected for both CCA's showed significant results for the sum of all eigenvalues (199 permutations, P< 0.05). For both CCA's a set of variables (*e.g.* total depth, dominant and subdominant substrate, aquatic cover, overhanging vegetation, distance to riffle and the distance to the nearest streambank) presented a similar importance that contributed to the distribution of stocked and native trout along the sympatric period and no substantial differences were detected between the initial adaptation period (1st week) and the remaining weeks.

Fig. 9. NMDS ordination of stocked and native brown trout in the Baceiro stream (summer 2005). Ordination was based on a matrix of pair-wise Bray-Curtis similarities coefficients constructed from non-repeated records, log transformed (Log[*x*+1]). Symbols: = native trout; = stocked trout.

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

experiment established.

1.0


influence.

**Subdom. substrate**

**Distance to Riffle**

Movements of Stocked and Wild Brown Trout (*Salmo trutta* L.) in a Northeastern Stream, Portugal 343

all native trout classes, except for adult native fish during the dawn period (*U*-tests, P< 0.05). The activity rhythm pattern of both stocked fish groups took place mainly at dawn and day and to a lesser extent at night periods. This activity pattern was roughly adopted by adult native trout, which differed significantly compared with the smaller size classes, precisely for dusk and night periods (*U*-tests, P< 0.05). Complementary analyses, based on the polynomial regressions (Figure 12), confirmed the distinct behaviour displayed by dominant trout (C Class > 20.0 cm), more active during the daylight period, related to the smaller native classes (A and B classes ≤ 20.0 cm), showing higher mobility during dusk and night periods. In fact, a temporal segregation was observed and probably dependent on the high density (three times more) promoted in the confined area as a result of the stocking

**Total Depth**

**Aquatic Cover**

**Dominant Substrate**


Fig. 11. CCA ordination diagrams of the 2nd to 5th week for the Baceiro stream: distribution of native and stocked trout according to the selected microhabitat variables for the two first

axes. The arrows represent the microhabitat variables and the symbols are the trout identification: *A)* arrows- total depth ; aquatic cover; overhanging vegetation; distance to riffle; distance to the stream bank; dominant and subdominant substrate; *B)* Symbols: = native trout; = stocked trout. The length of the arrow is a measure of the importance of

the environmental variable and the arrowhead points at the direction of increasing

**Distance to Stream Bank**

Fig. 10. CCA ordination diagrams of the 1st week for the Baceiro stream: distribution of native and stocked trout according to the selected microhabitat variables for the two first axes. The arrows represent the microhabitat variables and the symbols are the trout identification: *A)* arrows- total depth ; aquatic cover; overhanging vegetation; distance to riffle; distance to the stream bank; dominant and subdominant substrate; *B)* Symbols: = native trout; = stocked trout. The length of the arrow is a measure of the importance of the environmental variable and the arrowhead points at the direction of increasing influence.

Comparatively, a greater proportion of the overall movements recorded for the dominant native trout occurred during the day period but no obvious activity pattern was detected among fish of same class. The diel activity pattern of trout varied substantially between both populations and with the type of PIT tags used. A significantly higher number of movements (62% of total non-repeated records) was detected by the MPD unit between Type II PIT tagged stocked trout and the remained groups for every diel period (dawn, day, dusk and night) defined (*U*-tests, P< 0.05). Despite of the distinct detection range of the PIT tags, the Type I- PIT tagged stocked trout movements were also significantly different from

**Subdominant Substrate**

**Distance to Riffle**

**Distance to Stream Bank**

**Total Depth**

**Aquatic Cover**

**Dominant Substrate**

**Overhanging Vegetation**

**-1.0 1.0**

Comparatively, a greater proportion of the overall movements recorded for the dominant native trout occurred during the day period but no obvious activity pattern was detected among fish of same class. The diel activity pattern of trout varied substantially between both populations and with the type of PIT tags used. A significantly higher number of movements (62% of total non-repeated records) was detected by the MPD unit between Type II PIT tagged stocked trout and the remained groups for every diel period (dawn, day, dusk and night) defined (*U*-tests, P< 0.05). Despite of the distinct detection range of the PIT tags, the Type I- PIT tagged stocked trout movements were also significantly different from

Fig. 10. CCA ordination diagrams of the 1st week for the Baceiro stream: distribution of native and stocked trout according to the selected microhabitat variables for the two first axes. The arrows represent the microhabitat variables and the symbols are the trout identification: *A)* arrows- total depth ; aquatic cover; overhanging vegetation; distance to riffle; distance to the stream bank; dominant and subdominant substrate; *B)* Symbols: = native trout; = stocked trout. The length of the arrow is a measure of the importance of the environmental variable and the arrowhead points at the direction of increasing

**-1.0**

influence.

**1.0**

all native trout classes, except for adult native fish during the dawn period (*U*-tests, P< 0.05). The activity rhythm pattern of both stocked fish groups took place mainly at dawn and day and to a lesser extent at night periods. This activity pattern was roughly adopted by adult native trout, which differed significantly compared with the smaller size classes, precisely for dusk and night periods (*U*-tests, P< 0.05). Complementary analyses, based on the polynomial regressions (Figure 12), confirmed the distinct behaviour displayed by dominant trout (C Class > 20.0 cm), more active during the daylight period, related to the smaller native classes (A and B classes ≤ 20.0 cm), showing higher mobility during dusk and night periods. In fact, a temporal segregation was observed and probably dependent on the high density (three times more) promoted in the confined area as a result of the stocking experiment established.

Fig. 11. CCA ordination diagrams of the 2nd to 5th week for the Baceiro stream: distribution of native and stocked trout according to the selected microhabitat variables for the two first axes. The arrows represent the microhabitat variables and the symbols are the trout identification: *A)* arrows- total depth ; aquatic cover; overhanging vegetation; distance to riffle; distance to the stream bank; dominant and subdominant substrate; *B)* Symbols: = native trout; = stocked trout. The length of the arrow is a measure of the importance of the environmental variable and the arrowhead points at the direction of increasing influence.

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

**0.0**

**4. Discussion** 

**0.2**

**0.4**

**Relative Probability of Use**

**0.6**

**0.8**

**1.0**

 **Small stocked Big stocked**

**Small stocked = 1.1\*10<sup>6</sup>**

**Big stocked = 2.8\*105-10843.0\*x+157.3\*x<sup>2</sup>**

Movements of Stocked and Wild Brown Trout (*Salmo trutta* L.) in a Northeastern Stream, Portugal 345

**-41534.5\*x+596.4\*x<sup>2</sup>**

**0.01-3.00h 3.01-6.00h 6.01-9.00h 9.01-12.00h 12.01-15.00h 15.01-18.00h 18.01-21.00h 21.00-24.00h Period (hours)**

Fig. 13. Activity pattern based on polynomial regressions, performed for stocked trout: small- Type I PIT-tags; big- Type II PIT tags) using PIT Telemetry technology relative to eight diel periods and three hours classes in the Baceiro stream, during summer 2005. The dependent variable represents the relative probability of use (standardized to a 0-1 scale).

Native brown trout showed a significantly less dispersal behaviour than stocked trout. However, caution should therefore be taken in the interpretation of this result since only two fish were considered in the exploratory experiment. Nevertheless, the limited movement exhibited by native fish was also identified in several studies (Knouft & Jutila, 2002; Maia, 2003), although, as referred by Bunnel et al. (1998), it may be function of the size of the habitat that provides adequate feeding and resting zones. These authors mentioned that brown trout movement varied among individuals of a same population, but most fish moved within a single continuous riffle/run-pool sequence in a diel cycle. In opposition to the resident trout movement, strictly related with the energetic cost/benefit ratio, Bachman (1984) found an erratic behaviour for the recently stocked trout. According to this study, confirmed by personal observations, hatchery-reared brown trout displayed a typical behaviour acquired in raceway tanks and moved constantly, leading to an excessive expenditure of energy in the swimming activity and agonistic encounters, which contributed to poor growth and survival rates in the wild environment. Stocked radiotagged trout in the Baceiro stream showed a clear tendency to dispersal in downstream

**-3.8\*x<sup>3</sup>**

**-1.0\*x<sup>3</sup>**

**+0.009\*x<sup>4</sup>**

**+0.002\*x<sup>4</sup>**

Fig. 12. Activity pattern based on polynomial regressions, performed for native trout, considering the different size classes: A) small < 15.0 cm; B) median 15.0-20.0 cm; C) big > 20.0 cm) using PIT Telemetry technology relative to eight diel periods and three hours classes in the Baceiro stream, during summer 2005. The dependent variable represents the relative probability of use (standardized to a 0-1 scale).

**Period (hours)**

The comparisons between polynomial regressions calculated for the native size classes and stocked brown trout (Figures 12 and 13), showed similar behaviour only for the bigger individuals (dominant native and stocked trout) in spite of the increased probability of spatial competition and agonistic events. However, the morphological (fin deformities, hyperbuoyancy), physiological (stress response) and behavioural (lack of social hierarchy, weak territorial behaviour) characteristics presented by many stocked trout could explain their potentially disadvantageous performance in relation to dominant wild fish. The higher density referred for the PIT experiment established, did not affect the body condition of dominant native trout and contribute to explain the superior capacity to explore the available resources, namely in terms of feeding and resting activities. This pattern was not observed for smaller native trout and for stocked trout populations that showed a significant decrease in the body condition during the five weeks experiment.

Fig. 13. Activity pattern based on polynomial regressions, performed for stocked trout: small- Type I PIT-tags; big- Type II PIT tags) using PIT Telemetry technology relative to eight diel periods and three hours classes in the Baceiro stream, during summer 2005. The dependent variable represents the relative probability of use (standardized to a 0-1 scale).

**Period (hours)**
