Fish–habitat relationships and fish conservation in small coastal streams in southern Spain

MIGUEL CLAVEROa,b,*, FRANCISCO BLANCO-GARRIDOa and JOSE!

PRENDAaa Departamento de Biolog!ıa Ambiental y Salud Pu!blica, Universidad de Huelva, Campus Universitario de El

Carmen,Avda. Andaluc!ıa s/n, 21071 Huelva, Spain

b Departamento de Biolog!ıa Aplicada, Estacio!n Biolo!gica de Don*ana, CSIC, Pabello!n del Peru!, Avda. Mar!ıa Luisa s/n, 41013 Seville, Spain

ABSTRACT1. Studies dealing with the fish fauna of coastal streams are scarce in the

scientific literature, particularly those from Mediterranean climates. Owing to their small size, these systems suffer extreme seasonal fluctuations, following the typical Mediterranean flood–drought cycle and leading to a high risk of extinction to freshwater fish.

2. This work analyses fish distribution in 14 stream stretches belonging to eight basins in the northern sector of the Strait of Gibraltar (southern Spain). Fish–habitat relationships were studied through multivariate ordination techniques at two scales: basin and stretch.

3. A principal components analysis clearly discriminated larger and more sinuous basins from smaller and steeper ones. This ordination was related to the non-migratory freshwater fish species richness and to the total number of fish species present in the middle reaches of each basin.

4. The main sources of variation in community composition and habitat characteristics in the different stretches were related to a clear upstream–downstream gradient, along which total species richness increased.

5. These small coastal basins are inhabited by two highly endangered species, Andalusian toothcarp (Aphanius baeticus) and Iberian chub (Squalius pyrenaicus), and have similar or higher overall freshwater species richness than larger adjacent basins. The near absences of flow regulation and introduced species make these streams one of the few types of Iberian aquatic system where unaltered fish–habitat relationships can be studied.

KEY WORDS: Mediterranean streams; local extinctions; freshwater fish; longitudinal gradients; small river basins

INTRODUCTION

The characteristics of stream fish assemblages are determined by abiotic and biotic processes operating at multiple spatial and temporal scales (Matthews, 1998). In streams

with marked environmental variation,

*Correspondence to: Miguel Clavaro, Departmento de Biolog!ıa Ambiental y Salud Publica, Universidad de Huelva, CampusUniversitario de El Carmen, Avd/Andaluc!ıa s/n, 21071 Huelva, Spain. E-mail: miguel.clav e ro@dbasp. u hu.es

.

local habitat features may be less important in structuring fish communities than large-scale factors (Angermeier and Schlosser, 1989). This seems to be the case for streams in Mediterranean climates, which suffer predictable seasonal drought events of greatly variable intensity from year to year (Gasith and Resh,1999). The harsh conditions imposed by summer droughts in Mediterranean streams may act as a critical filter for their inhabitance by freshwater fish species (Poff, 1997; Magalha* es et al., 2002b). In fact, it has been suggested that the variation in fish assemblages in Mediterranean streams can be explained by large- scale factors, particularly the position of a river stretch within a catchment (Filipe et al., 2002, Magalha* es et al., 2002a).

Most studies on stream fish undertaken in the Iberian Peninsula have focused on low-order streams in large basins (Rinco! n et al., 1990; Pires et al., 1999; Godinho et al., 2000; Bravo et al., 2001). Though there is a high probability of extinction of fish populations occupying these streams, it can be compensated by recolonization from larger watercourses downstream (Osborne and Wiley, 1992; Gotelli and Taylor, 1999a). In contrast, small coastal streams may contain impoverished freshwater fish communities owing to the impossibility of recolonization after local extinctions, and the frequent domination of fish assemblages by diadromous species (McDowall, 1998). As in other areas (Martin-Smith and Laird, 1998), these species-poor systems have rarely been studied, mainly because of a generalized ‘more is better’ syndrome (Matthews, 1998).

Mediterranean rivers and streams have long suffered intense alterations due to the high water demand in

these densely populated areas and to the unpredictable availability of this resource (Hamdy et al., 1995). Inaddition, many Mediterranean Iberian rivers and streams are now heavily polluted by undiluted urban andagricultural effluents (Prenda and Gallardo, 1996; Prat and Munne!, 2000). Impoundment is also awidespread phenomenon, and most large- and medium-sized watercourses have regulated flows and arefragmented by large dams (Prenda et al., 2002). This structural, physical and chemical deterioration offluvial ecosystems is one of the main threats to Iberian freshwater fish fauna (Doadrio, 2001), commonlyacting synergistically with introduced species (Ross, 1991; Corbacho and Sa! nchez, 2001). Coastal streamsin some southern and western areas are amongst the few Iberian Mediterranean watercourses that maintainrelatively unpolluted waters, unaltered flow and pristine fish communities. The conservation value of thesestreams has rarely been stressed (Clavero et al., 2002) although they provide habitat for endangered speciesand are one of the few systems where unaltered fish–habitat relationships can be studied (Doadrio, 2001).However, these streams are strongly threatened by increasing population density in coastal areas, and thedevelopment of tourism.

This study analyses fish distribution and assemblage structure in eight coastal basins in southern Spain.

These streams are very small (in general shorter than 10 km), thus suffering extreme flow fluctuationsfollowing the characteristic Mediterranean flood–drought cycle. In most summers even larger streamsbecome reduced to a few isolated freshwater pools (Clavero et al., 2002). The specific objectives of thisstudy were:1. To describe the distribution of fish in the area, with special emphasis on freshwater

species, and to assess their conservation value.2. To link freshwater fish species distribution and richness to the characteristics of different basins.3. To analyse changes in fish assemblages along an abrupt upstream–downstream gradient in the short

length (55 km) from headwater conditions to estuarine and tidal-influenced areas.

METHODS

Study area

The study area is located in the southern tip of the Iberian Peninsula, comprising a coastal area of about30 x 6 km2 (Figure 1). The area is characterized by a steep relief, reaching more than 800 m a.s.l. in less than

Jara

1 **

Ib erian Peninsula

Algeciras

Miel 14 N

138

123

2 9

4 11

57 10 *

6

Western b asins Eastern b asinsTarifa

10 km

Figure 1. Location of the stretches used for fish sampling. Black circles denote upper stretches and white circles denote lower stretches. Stretches marked with an asterisk were sampled on only a single occasion and were used in

the basin analysis, but not in the stretch analysis (see Methods).

a 6 km straight line from the coast. Elevated areas are mainly composed of sandstone, producing acidic, nutrient-poor soils, and the lowlands are characterized by loamy or marly non-acidic substrata (Ibarra,1993; Ojeda et al., 2000). The average annual rainfall is highly variable (1396, 1019, 737 and 616 mm at the four meteorological stations included in the study area) owing to the abrupt relief, though the lack of precipitation during summer is a common feature (Ibarra, 1993). However, the interception of moist south- easterly winds, which are dominant during summer, can reduce to some extent the impact of summer drought in some zones (Ojeda et al., 2000).

Fish sampling

Fish were surveyed in 13 stretches of eight basins within the study area (Figure 1). Stretches were classified as ‘lower’ or ‘upper’ by their minimum distance to the tidal influenced area (less than or greater than

500 m). Extensive surveys were performed in March, June and October 2001 and May 2002, each one of them covering most of the study stretches. An additional limited survey was performed in January 2002. Fish were captured using electrofishing, fyke nets or both

techniques (Table 1). Electrofishing was carried out whenever water conductivity allowed it, using backpack (230 V, 1 A) or standard (230 V,

1–2 A) electrofishing gear. Fyke nets were used overnight (set around 9 p.m. and lifted around 9 a.m.) and always in pairs with different mesh sizes (15 mm and 7 mm). Between 5 and 10 pairs of nets were placed in each of the stretches in the different surveys. Owing to the heterogeneity of sampling methods and effort used, only presence–absence data were considered in analysing the structure of fish assemblages (Belliard et al., 1997; Pires et al., 1999).

Captured fish were identified and then released, though some fish samples were

eventually frozen and taken to the laboratory to allow further measurements and identification. Identified species were classified

Table 1. List of the stretches studied, grouped by basin. The fishing effort employed during electrofishing (length) or net sampling (number of pairs of nets) in each stretch is also shown, together with the total number of fish

captured by the two methods. Stretch codes are the same as those in Figure 1

Stretch Basin Code Electrofishing Fyke netsUpper Valle Valle 1 333 m 23 pairs

Lower Valle Valle 2 – 24 pairsUpper Jara Jara 3 692 m 28 pairsLower Jara Jara 4 – 23 pairsLos Lances Beach – 5 – 26 pairsLower Vega Vega 6 824 m 30 pairsUpper Vega Vega 7 574 m –Upper Guadalmes!ı (I) Guadalmes!ı 8 100 m –Upper Guadalmes!ı (II) Guadalmes!ı 9 220 m –Lower Guadalmes!ı Guadalmes!ı 10 479 m 28 pairsMaraber Maraber 11 150 m –Lobo Lobo 12 100 m –P!ıcaro P!ıcaro 13 460 m –Miel Miel 14 150 m –

Total 3982 m 182 pairs

Captures (individuals) 3048 3220

as ‘freshwater’ or ‘estuarine-diadromous’ species. The number of non-migratory freshwater species and the total number of fish species present in middle reaches (including both freshwater and diadromous species) were recorded in the different basins. Total, freshwater and estuarine-diadromous species richness were also calculated in each stretch and survey. This number was a minimum estimate, since different species of the genus Liza (Mugilidae) were treated as a single species, owing to difficult field identification.

Habitat characterization

Two different approaches were used to describe fish habitat. First, a physiographical description of each of the studied basins (macrohabitat) was made using data provided by Ibarra (1993) (Table 2). Second,13 habitat variables were measured in each of the stretches (mesohabitat) surveyed; these were recorded at5–10 points per survey separated by 20 m within the area where electrofishing or net sampling wasperformed (Table 2). These mesohabitat variables included physical and chemical parameters (temperature,conductivity, pH, dissolved oxygen and turbidity), stream-bed and flow descriptors (substrate coarseness,width, depth and water velocity) and riparian vegetation cover (herbaceous, shrubs and trees). Theavailability of a refuge for fish was also estimated as the area (in metres squared) that could offer effectivecover (Prenda et al., 1996) in a 4 m wide band perpendicular to the stream channel.

Statistical analysis

Two different analyses of fish distribution were performed. The first one was made at the level of the river basin. Physiographical descriptor variables of the different basins were summarized by means of principal components analysis (PCA). The resulting principal components (PCbasin) were related to primary freshwater fish richness and number of fish species occupying middle stretches of each basin.

The second analysis included all stretches sampled, except those sampled on a single occasion (see Figure 1). This analysis was based on a presence–absence matrix, which summarized data from electrofishing and net sampling. To extract the main sources of variation in the composition of fish

Table 2. Environmental variables used to characterize the basins and the stretches where fish sampling was undertaken

Stretchb

Basin variablea Variable MethodBasin area A (km2) Temperature (8C) YSI model 55Main channel (MC) length L (km) Conductivity (mS cm–1) Crison CM 35MC sinuosity A/L Turbidity (FTU) Hanna Instruments HI 93703Elongation factor (Schumm, 1956) Dissolved oxygen (mg L–1 and %)

YSI model 55Drainage density (km km–2) (Horton, 1945)

pH Crison pH-metre 507

MC slope (m/1000L) Water velocity (m s–1) Floating object, three replicatesOrder at mouth (Strahler, 1964) Depth (cm) Rigid meter, six measurementsN order-1 watercourses Width (m) Flexible meter

Substrate coarseness (1–9) Wentworth scale, six measurementsHerbaceous cover (%) Visual estimate, two or three observationsShrub cover (%) Visual estimate, two or three observationsTree cover (%) Visual estimate, two or three observationsFish refuge (m2 in a 4 m band) Visual estimate, two or three observations

a Variables recorded for eight basins.b Measures taken every 20 m, 5–10 times per stretch and survey.

Table 3. Distribution of fish species or families in the study area. The stretch numbers are the same as in Figure 1. Species marked with an asterisk were not included in the DCA of fish assemblages

Stretch

Western basins Eastern basinsFish species/family 1 2 3 4 5 6 7 8 9 10 11 12 13 14

FreshwaterChub Squalius pyrenaicus + + + + + +LoachBarbelAndalousian toothcarp*Mosquitofish*

Cobitis paludicaBarbus sclateri Apahnius baeticus Gambusia holbrooki

+ + +

+

++

+

+

Estuarine diadromousEel Anguilla anguilla + + + + + + + + + + + + + +Sandsmelt Atherina boyeri + + + + + + + +Grey mullets Fam. Mugilidae + + + + + + +Sea bass Dicentrarchus spp. + + + +Common goby Pomatoschistus spp. + + + +FlatfishPipefish*White bream*

Fam. SoleidaeSyngnathus abasterDiplodus sargus

+++

++

+ +++

communities, a detrended correspondence analysis (DCA) was performed. This unconstrained multivariate technique produces a simultaneous ordination of rows and columns (plots and species) and performs better than PCA when data have unimodal distributions (McGarigal et al., 2000). Only species occurring in at least five transects were included in the DCA (see Table 3). At the same time, a PCA was carried out using a mesohabitat variable matrix. The principal components extracted are hereafter referred to as PCstretch.

The relationships between descriptor variables of fish communities and macro- and meso-habitat characteristics were studied through correlation analysis and two-sample tests. Variables departing strongly from an expected normal distribution were log (base e; continuous variables) or arcsine (percentages) transformed. However, non-parametric tests were occasionally used when assumptions for parametric analysis were not met.

RESULTS

Summary of captures

During the surveys, 3982 m of watercourses were electrofished and 182 pairs of fyke nets were set, resulting in the capture of 6268 fish (Table 1). These belonged to a minimum of 16 species, though some of them were grouped into families for further analyses (e.g. grey mullets, Mugilidae, including Liza, Chelon and Mugil ) (Table 3).

Eel (Anguilla anguilla) and sandsmelt (Atherina boyeri) were the most widespread species, occupying both lower and some upper stretches. In fact, eels were detected in all stretches studied, being present in the study area at altitudes higher than 500 m. Grey mullets were also present in most basins, but were never located in middle stretches. Other estuarine species were found only in western basins (Table 3).

Among strictly freshwater fish (referred to simply as ‘freshwater fish’ hereafter) chub (Squalius pyrenaicus) was the most widely distributed species, being present both in western and eastern basins. Barbel (Barbus sclateri) and loach (Cobitis paludica) were only found in the western (loach) or the eastern (barbel) sectors. Both Andalusian toothcarp (Aphanius baeticus; referred to simply as ‘toothcarp’ hereafter) and mosquitofish (Gambusia holbrooki) were located in only one stretch in a single survey (Table 3).

Analysis of river basins

The PCA involving the physiographical descriptors of each basin produced a single component (PC1basin) that accounted for more than 72% of the original interbasin variance (eigenvalue: 5.82). The gradient defined by PC1basin had larger and more sinuous basins towards its positive extreme, with longer and higher order main channels and more order 1 watercourses. Basins had higher drainage densities and channel slopes towards the negative extreme of PC1basin. There were significant differences between the characteristics of basins in the western and eastern sectors of the study area (see Figure 1), as shown by their PC1basin scores (Mann–Whitney U test; Z=2.2; p50.05). The ordination of basins made by PC1basin was strongly and positively correlated with their freshwater species (r=0.73; p50.05) and with the species richness in their middle reaches (r=0.94; p50.001) (Figure 2).

Analysis of river stretches

The presence or absence of nine fish species or families (Table 3) was recorded in 36 stretches/surveys. The DCA performed produced only one significant axis (axis 1; eigenvalue: 0.51), accounting for 65% of the distances in the original multidimensional space (Figure 3(a)). Axis 1 clearly discriminated stretches and surveys dominated by primary freshwater fish (chub, loach and barbel) from those dominated by estuarine fish. There was a strong positive correlation between axis 1 scores and the number of freshwater fish species in each stretch and survey (r=0.87; p50.001), whereas the contrary pattern was observed in the case of estuarine-diadromous species (r=—0.82; p50.001). Axis 2 did not add any explanatory power to the ordination produced by axis 1 (in fact it diminished it).

The PCAstretch produced two components that accounted for more than 50% of the original variance

(Figure 3(b)). PC1stretch (eigenvalue: 4.79; 34.2% explained variance) could clearly be interpreted as a

N fr

eshw

ater

sp

ecie

s

PC2

stre

tch

Axi

s 2

N sp

ecie

s in

mid

dle

stre

tche

s

3 4

2 3

1 2

0 1

Drainage densityMain channel slope

PC1basin Ar eaN order 1 watercourses

Main channel lengthMain channel order

Sinuosity

Figure 2. Relationship between the main variation gradient of the basins studied (PC1basin) and the number of primary freshwater and total fish species found in the middle reaches of each.

Bsc

(a)

Sol Dic

Pom

Mug

AboAan

Cpa

Spy

Axis 1

Summer- Autumn

Spring

(b)

Upper stretches PC1stretch

Lower stretches

Figure 3. Ordinations produced by: (a) the first two axes of the DCA of fish distribution in the different stretches and surveys; (b) the first two principal components of the PCA of the environmental characteristics of the stretches studied in the different surveys. As in Figure 1, black circles denote upper stretches and white circles denote lower stretches. Aan: Anguilla anguilla; Abo: Atherina boyeri; Bsc: Barbus sclateri; Cpa: Cobitis paludica; Dic: Dicentrarchus spp.;

Mug: Mugilidae; Pom: Pomatoschistus spp.; Sol: Soleidae; Spy: Squalius pyrenaicus.

gradient running from upper to lower stretches (t=5.2; p50.001). It was positively influenced by the width, depth, conductivity and pH of river stretches and negatively influenced by their substrate coarseness, water velocity and tree cover. Eastern stretches scored significantly lower PC1stretch than western stretches (t=3.4; p50.01). PC2stretch (eigenvalue: 2.43; 17.4% explained variance) represented the seasonal change in the habitat characteristics, being positively correlated with water temperature and negatively correlated with water velocity, dissolved oxygen and herbaceous cover. PC2stretch scores were significantly different

Axi

s 1

Spec

ies

richn

ess

Freshwater fish

Estuarine fish

(a)

9

7

5

3

(b)

1

Upper stretches

PC1stretchLower

stretches

Figure 4. Relationship between the main source of variation in the environmental characteristics of the stretches studied (PC1stretch)

and: (a) the main source of variation of fish assemblages (DCA axis 1); (b) fish species richness.

depending on the month when each survey was performed (one-way analysis of variance F=9.75; p50.001). Post-hoc tests (Tukey HSD) showed that significant differences (p50.05) occurred between spring (March and May) and summer–autumn (June and October) surveys.

There was a very high concordance between the main gradient of variance of habitat characteristics (PC1stretch) and fish community composition (axis 1), as shown by the strong correlation of the two variables (r=—0.86; p50.001) (Figure 4(a)). At the same time, there was a significant increase in the species richness along the gradient running from upper to lower stretches (r=0.47; p50.01) (Figure 4(b)), though freshwater species richness showed a clear decrease along this gradient (r=—0.72; p50.001). Total species richness also showed a negative correlation with PC2stretch (r= —0.31; p= 0.06), though only of marginal significance, denoting a seasonal reduction in the number of species from spring to summer–autumn.

DISCUSSION

Analysis of river basins

These results show that freshwater fish richness is tightly linked to basin size and

associated variables, which is a commonly observed pattern in different biogeographic areas (Hugueny, 1989; Oberdoff et al.,1995; Me!rigoux et al., 1998; Clavero et al., 2004). In the small basins studied, differences in richness can be attributed to variations in extinction risk. Larger drainage areas have a buffer effect on environmental

variation that is characteristic of lotic ecosystems, which is accentuated in Mediterranean areas, promoting the persistence of fish species (Angermeier and Schlosser, 1989; Taylor and Warren, 2001). In small and isolated systems, such as those in the study area, the loss of species due to extinction cannot be compensated by immigration, resulting in species-poor assemblages (Martin-Smith and Laird, 1998).

The differences in the physiographical characteristics of basins in the western and eastern sectors of the study area could be used in broad outline to explain the distribution patterns of the three most widespread freshwater species. Loach usually occupies middle or lower river reaches, with low current and sandy or gravel substrata (Perdices and Doadrio, 1997). These environmental conditions occur rarely in the eastern sector of the study area, where streams have steeper slopes, and where the characteristic features of lower reaches rarely occur (Ibarra, 1993). Suitable habitat for loach is only found in western basins within the study area. Barbel may have a higher extinction risk than other fish species in the area, owing to their larger body size (Gotelli and Taylor, 1999b). In fact, barbel species have been shown to be more abundant in high- order watercourses within Mediterranean basins (Pires et al., 1999). Barbel inhabited La Jara River at least during the 19th century (Madoz, 1845–1850) and is known to have become extinct in two streams in the area (Valle and Guadalmes!ı) in the 1990s (Clavero et al., 2002). It can be assumed that barbel originally occurred in all basins in the study area, though the species may always have been rare. The species has survived in the Rivers Miel and P!ıcaro probably because of the higher influence of orogenic fogs in their basins, which attenuate to some extent the effects of summer droughts (Ojeda et al., 2000). Chub is a ubiquitous species (Doadrio, 2001) that is often dominant in intermittent and/or small Iberian streams (S. pyrenaicus or ecologically equivalent congeneric species; Pires et al., 1999; Magalha* es et al., 2002a). The distribution of this species in the area, occupying basins in western and eastern sectors, fits well with those previous observations.

Analysis of river stretches

The upstream–downstream river gradient in the composition of fish assemblages has been studied extensively (e.g. Schlosser, 1982; Moyle and Vonderacek, 1985; Belliard et

al., 1997). Features such as species composition and richness, fish density and dominant fish size or ecological types are known to change along lotic longitudinal gradients

(Angermeier and Karr, 1983; Balon et al., 1986; Schlosser, 1990; Pires et al., 1999; Filipe et al., 2002; Magalha* es et al., 2002a). These changes have been linked to gradual

variation in water depth, current velocity, substratum and habitat complexity (Gorman and Karr, 1978). In the study area there were clear longitudinal changes both in habitat

features and fish assemblages, though variation in the latter was caused by the presence of estuarine species, especially grey mullets. Owing to their small size, these basins have a

very poor freshwater fish fauna, usually with one or two species present in each. In these conditions a longitudinal zonation of freshwater fish assemblages (e.g. Doadrio et al., 1991;

Cowx and Welcomme, 1998) is unlikely to occur, since each species would tend to occupy all available habitats within the catchment. Thus, only freshwater and estuarine areas

can be defined in relation to fish communities, with a clear increase in species richness from the impoverished upper stretches

to tidally influenced stretches.

Conservation value

Though the basins studied are small, the freshwater fish fauna of the area is important for conservation. Four freshwater fish species occur in a total drainage area of only 192 km2, which is the same richness as the adjacent Guadalete River (3360 km2) and Barbate River (1290 km2), and higher than in the Guadiaro River (1505 km2), which is inhabited by three

freshwater fish species (Doadrio, 2001). Moreover, toothcarp, which is not found in any of those larger basins, is a critically endangered species, with only nine known populations, some of which have suffered sharp declines (Doadrio et al., 2002; Clavero et al., in press). According to the IUCN criteria applied to Spain (Doadrio, 2001), some southern chub populations,

including those in the study area, are listed as endangered and loach is listed as vulnerable. In this area, eel occurs at one of its maximum altitudes in the Iberian Peninsula, owing to the widespread fragmentation of rivers elsewhere by damming.

The conservation value of the fish fauna is enhanced by the almost complete lack of introduced species. The establishment and expansion of non-native fish populations is probably the main threat facing indigenous Iberian fish species (Elvira, 1995; Doadrio, 2001). The presence of alien species is usually linked to degraded or altered environments, such as those created by river impound- ment or channelization (Herbold and Moyle, 1986; Ross, 1991; Corbacho and Sa! nchez, 2001). There are no such modifications in the basins studied, with the exception of a small dam that is closed only during summer months, deterring the establishment of alien species. In fact, the only non-native species captured in the area, mosquitofish, was recorded in a single survey at the end of the dry season. The species was not found in two subsequent surveys in the same stretch after autumn–winter floods, having apparently disappeared.

Since unaltered rivers and streams are one of the most scarce and endangered types of aquatic ecosystem in the Iberian Peninsula, those still remaining should be given high priority for conservation (Clavero et al.,2004). The recent freshwater fish extinctions recorded in the area (Clavero et al., 2002) strongly justify control of human impacts in these stream systems. Statutory protection is now well developed in the study area, which lies almost completely within two Natural Parks and Sites of Community Importance (SCIs) (Parque Natural Los Alcornocales and Parque Natural del Estrecho). Three additional small SCIs have been proposed in the area, one of them with the specific aim of protecting the Iberian loach population of La Jara River (CMA, 2004). However, some of the most important stretches for fish conservation, such as the one including the Andalusian toothcarp population in La Vega River, are still unprotected and threatened by tourism and industrial development (Clavero et al., in press). Moreover, territorial protection may not be a sufficient conservation tool for fish in streams, because water management in Spain is almost independent from the management of protected areas. In fact, the recent barbel extinctions in the Guadalmes!ı River occurred within the limits of a Natural Park (Clavero et al., 2002). Effective conservation action for freshwater fish should, therefore, involve co-ordination between territorial protection and water management.

ACKNOWLEDGEMENTS

We thank L. Barrios, M. Narva! ez, A. Rebollo and J. Valle for their help during the field work. Dr I. J. Winfield and an anonymous referee made valuable comments that greatly improved the manuscript. The work was supported financially through the projects ‘Medidas compesatorias de la Autov!ıa a-381 Jerez de la Frontera-Los Barrios’ and ‘Biotic integrity and environmental factors in watersheds in south-western Spain. Application to the management and conservation of Mediterranean streams’ (Ministerio de Ciencia y Tecnolog!ıa, REN2002-03513/HID).

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