Hydrobiologia 371/372: 309–319, 1998. 309J. P. Lagardere, M.-L. Begout Anras &G. Claireaux (eds), Advances in Invertebrates and Fish Telemetry.c 1998Kluwer Academic Publishers. Printed in Belgium.

Radio telemetry as a tool to study habitat use of nase(Chondrostoma nasusL.) in medium-sized rivers

Martin Huber & Arthur KirchhoferInstitute of Zoology, University of Berne, Baltzerstr. 3, CH-3012 Berne, SwitzerlandE-mail: martin.huber@zos.unibe.ch

Key words: Chondrostoma nasus, radiotelemetry, habitat use, regulated River, seasonal, home-range

Abstract

Due to a massive population decline of nase (Chondrostoma nasusL.) in the river Aare (Switzerland), a radioteleme-try study was designed to detect the habitat use of this endangered species. Although big individual differencesin behaviour occurred for adult nase, habitat preferences for runs with currents between 0.5 and 1 m s�1, coarsesediments and depths between 1 and 2 m could be shown. The fish used well defined home-ranges for certaintime periods and migrations were mainly found in correlation with spawning or seasonal changes in discharge andtemperature. Seasonal and daily differences in home-range size and habitat preferences were discussed in relationto habitat structure.

Introduction

Knowledge of habitat requirements is of high impor-tance for stock management and conservation ofendangered fish species in medium sized rivers. This isespecially true for rheophilic and lithophilic Cyprinids,a taxon which includes a high proportion of endangeredspecies in central Europe, for which such informationis still scarce (Nelva, 1988; Garner & Clough, 1996;Keckeis et al., 1996; Baras, 1997; Clough & Ladle,1997; Lucas & Frear, 1997). Although habitat protec-tion is the most effective method for species conserva-tion, small scale and simple habitat improvements canbe useful too. However, the needs of the target speciesmust be known (Burgess, 1985; Hermansen & Krog,1985).

Habitat use can substantially vary both at a dai-ly and seasonal time scale, depending on species andenvironment (Baras, 1992; Arnekleiv & Krabol, 1996;Bourke et al., 1996). In addition, the habitat require-ments vary substantially over the live-cycle. Thereforestudies on the larvae, juveniles and adults are need-ed to cover the whole life-cycle of endangered species(Copp, 1992; Bischoff, 1995; Scholten, 1995; Keckeiset al., 1996). Radio telemetry can be a useful tool to

gain such information using only a small number ofindividuals (Priede, 1991) and therefore can be usedon small, threatened populations.

In this contribution the habitat use of adult naseis presented and discussed in relation to habitat struc-ture, daytime and season. The habitat characteristics ofshort segments of a 7th order stream were recorded andcompared with the habitat use. It is assumed that usingthis technique, the small scale distribution of the nasecan be identified and the information used for habitatrestoration.

Study area

The study was performed in the river Aare near Berne(Switzerland), a medium sized 7th order stream. Theflow regime is characterised by the alpine snow meltduring spring and summer and low flow during thecold season, but occasional winter floods occur duringheavy rainfall in the lowlands. The yearly median ofdaily mean discharge (Qm) is 121 m3 s�1. Upstreamlakes and reservoirs reduce the differences in dischargebetween summer and winter (Aschwanden & Wein-

Article: hydr-jl29 Pips nr 165584 BIO2KAP

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Figure 1. Map of the study site, showing the three major sections. Residual discharge section from km 0 to km 9.8, free-flowing reach from km9.8 to 11.05 and reservoir from km 11.05 to km 25.6.

gartner, 1985; Spreaficio et al., 1992; HydrologischesJahrbuch der Schweiz, 1994).

The study site is bordered by two dams and associ-ated hydroelectric power-stations (Figure 1).The upperdam is equipped with a fishpass which is not used bynase (Guthruf, 1996), but the lower dam has no fish-pass. This system with a residual discharge section(mean annual flow reduction 41–60%), a free-flowingreach and an impounded section is typical for mediumsized rivers in Switzerland.

The residual discharge section has a natural mor-phology with a variety of riffles, runs and pools. Thewidth varies between 35 and 70 metres (average 50 m).The free-flowing reach consists only of run sections,its width is about 75 m (from 55 m to 100 m) andthe shore is mostly fixed by rip-rap. The impoundment(width from 75 m to> 500 m) has mainly soft sed-iment and low current. Due to this modifications theriver characteristics have changed in the lower partsfrom the grayling to the barbel and bream region (Huet,1949). In spite of the effluents of two water purifica-tion plants into this section of the river, water qualityis not regarded as problematic for nase (Dedual, 1990;Hydrologisches Jahrbuch der Schweiz, 1994). Howev-er, the impact of medium to high nutrient loads on foodorganisms, especially diatoms, is unknown.

Material and methods

In total 21 adult nase were tagged and tracked betweenOctober 1995 and September 1997 (Table 1). Inautumn 1995 the fish were caught by rod and lineand haul-seine, in spring 1996 by electrofishing onthe spawning site and in winter 1996 by electrofishingfrom a boat at night.

Transmitters (Lotek FRT-3/4, FSM-6) wereimplanted in the body cavity of the anaesthetised (MS222) fish (Hart & Summerfelt, 1975). The incision wasmade ventrally just behind the ventral fins, the externalantennas (40 cm) were trailing outside the body.

The tags weighed between 8.9 to 23.7 g in airand did not exceed 2.8% of body weight; battery lifewas between 295 and 390 days. Frequencies between148.100 and 148.775 MHz and pulse rates between40 and 60 bpm were used. Individual fish could beidentified by frequency and/or pulse rate.

In order to detect differences between habitat avail-ability and habitat use, the study area was divided insegments of 25 m length. Within each segment thehabitat types (riffle, run, pool, reservoir or whirl)and some important habitat parameters (current, sub-strate and depth) were estimated. This was done byvisual observation from the banks during periods of

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Figure 2. Locations of all tracked nase during the whole experimental time in distance (km) from the upper end of the study area. Mean dailydischarge Q (m3 s�1) at the measuring station Schonau just upstream the study area (upper) and in the residual discharge section (lower).Temperature (�C) at measuring station Schonau. Arrows indicate spawning dates (23.4.96 and 5.5.97).

favourable conditions by selecting the best fitting cat-egory of a given set (Table 2). The positions of fishwere assigned to each of these segments and if pos-sible confirmed by visual observation. For segmentsconsisting of more than one morphodynamic unit, themajor habitat type was used for analysis and the varietyrecorded. This was rare for the impoundment (< 1%)and the free-flowing reach (< 7%) compared to theresidual flow section (27%). Habitat mapping was per-formed in winter during low discharge and clear water,in order to be able to estimate coarseness of sedimentand depth. This might lead to an underestimation ofcurrent strength during summer, i.e. segments withlow current will be rarer if discharge is high. Similarlyfor some segments the major habitat type is likely tochange between periods with high and low discharge.Therefore the momentary habitat structure was record-ed during the tracking of the fish. Values of habitatpreference (D) were calculated according to Jacobs(1974)

D = r � p=(r + p) � 2rp;

wherep= proportion of resource available,r = propor-tion of resource used.

Tracking was done manually (Lotek SRX400receiver, three element Yagi antenna), twice a week formost of the time and more frequently during spawn-ing season and at the beginning of the study. At sixoccasions the positions of 18 adult nase were recordedevery two hours in order to study the habitat use on atime scale of 24 hours.

Definitions of the seasons were set after the periodi-city of the tracked nase’s activity pattern, temperatureboundaries and spawning dates.

Autumn: 5.10.95 to 17.11.95 and 16.9.96 to11.11.96 (Start of the study, respectively 16th of Sep-tember until the water temperature dropped below10 �C).

Winter: 20.11.95 to 31.3.96 and 14.11.96 to 31.3.97(Water temperature below 10�C until end of march).

Prespawning: 1.4.96 to 25.4.96and 1.1.97 to 5.5.97(Start of April until peak spawning).

Postspawning: 26.4.96 to 31.5.96 and 6.5.97 to31.5.97 (From peak spawning until end of May).

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Figure 3. Home-ranges for seasons and the whole study time (upper graph); and daily activity areas during the different 24 h cycles (lowergraph). 10%, 25%, median, 75% and 90% intervals; means as symbols;n= number of individual nase included in each season or each 24 hcycle.

Figure 4. Minimal distances swum between two consecutive locations during the 24 h cycles for differnt times of the day.

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Table 1. Length, weight, age and sex of the 21 adult nase tracked during the study. Age was determinedby scale reading, sex by the strength of the first fin ray of the pectoral fin and confirmed by running milkor eggs during spawning season. The presence of the individual fish during the six 24 h cycles and trackingtime are indicated on the right-hand-side (cycle 1: 15./16.11.1995; 2: 28./29.11.1995; 3: 21./22.3.1996; 4:18./19.4.1996; 5: 20./21.6.1996 and 6: 20./21.2.1997)

Fish Length Weight Age Sex Presence in 24 h cycle No. Tracking time

# (cm) (g) (y) 1 2 3 4 5 6

A 46.0 1145 14 – � � 05.10.95–30.11.95

B 45.5 980 11 – � � 13.10.95–18.12.95

C 46.3 1145 15 – � � 19.10.95–22.12.95

D 45.0 840 11 – � � 19.10.95–05.01.96

E 45.8 1115 15 male � � � � 27.10.95–23.04.96

F 48.4 1350 16 – � � � � 20.11.95–16.09.96

G 48.0 1355 12 – � � � 20.11.95–23.04.96

H 47.4 1070 13 – � � � � 27.11.95–17.07.96

I 46.0 – 17 female � 30.04.96–17.07.96

J 52.0 1430 14 female 02.05.96–17.05.96

K 46.3 1230 13 male � � 02.05.96–24.07.97

L 49.8 1265 12 female � 09.05.96–17.07.96

M 52.0 1955 18 female � 20.12.96–04.08.97

N 48.0 1325 15 male � 20.12.96–30.11.97

O 45.0 845 7 male � 20.12.96–07.08.97

P 43.0 895 11 male � 20.12.96–04.09.97

Q 51.0 1520 13 female 20.12.96–17.02.97

R 45.4 1125 13 male � 20.12.96–10.05.97

S 47.1 1190 12 female � 20.12.96–10.05.97

T 46.2 890 12 female 20.12.96–10.01.97

U 41.1 860 7 male � 20.12.96–26.05.97

Mean 46.9 1177 13 5 8 4 4 5 8

Figure 5. Positions of the tracked nase during the first 24 h cycle on the 15./16.11.1995 in distance (km) from the upper end of the study area.The light regime is indicated by the bar at the right-hand side.

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Table 2. Proportions of habitat availability and habitat use of the recorded habitat variables for the wholestudy. Preference index (D) (Jacobs, 1974) for the different seasons and for the whole study

Habitat Habitat Habitat use (D) (D) (D) (D) (D) (D)

variable availability whole study Au- Win- Post- Pre- Sum- Whole

tumn ter spaw- spaw- mer study

ning ning

Habitat typeRiffle 0.07 0.04 0.00 –0.76 0.37 –0.76 –1.00–0.29Run 0.67 0.88 0.60 0.84 0.35 0.38 0.47 0.57Pool 0.03 0.01 –1.00 –0.51 –0.51 0.15 –0.51–0.51Reservoir 0.22 0.02 –1.00 –1.00 –1.00 –0.93 –0.48–0.87Whirl 0.01 0.04 0.68 0.34 0.51 0.87 0.73 0.61

Current0.0–0.1 m s�1 0.05 0.01 –1.00 –0.68 –1.00 –0.68 –0.68–0.680.1–0.5 m s�1 0.42 0.22 –0.51 –0.17 –0.68 –0.53 –0.61–0.440.5–1.0 m s�1 0.22 0.48 0.67 0.67 0.25 0.55 0.35 0.53> 1 m s�1 0.31 0.29 –0.20 –0.75 0.46 0.02 0.33–0.05

SubstrateSilt 0.39 0.03 –1.00 –0.97 –1.00 –0.85 –0.68–0.91Sand 0.03 0.02 –1.00 –0.51 –0.51 –0.20 0.26–0.20Gravel 0.01 0.00 –1.00 –1.00 –1.00 –1.00 0.00–1.00Pebbles 0.23 0.19 0.50 –0.55 –0.37 0.13 0.29–0.12Cobbles 0.31 0.73 0.43 0.89 0.86 0.35 0.29 0.72Boulders 0.03 0.04 –0.51 –0.51 –0.51 0.75 0.150.15

Depth0.0–0.2 m 0.00 0.00 – – – – – –0.2–0.5 m 0.01 0.01 –1.00 –1.00 0.61 0.00 0.000.000.5–1.0 m 0.06 0.06 0.00 –0.52 0.36 0.22 0.08 0.001.0–2.0 m 0.17 0.45 0.60 0.67 0.72 0.53 0.00 0.60> 2:0 m 0.77 0.47 –0.57 –0.58 –0.79 –0.53 –0.05–0.58

Summer: 1.6.96 to 12.9.96 and 1.6.97 to 8.9.97(1st of June until mid-September respectively end ofstudy).

Home-range was estimated as the longitudinal dis-tance between the uppermost and the lowermost loca-tions.

Results

The tagged nase did not use the whole study area,the inhabited part reached from km 3.75 to km 18.4and covered all three major sections (Figure 2). Thesections were not used equally (Chi-square-test,dF = 2,P < 0:001), with 87.88% of all 1229 locations made

in the residual discharge section, 1.71% in the freeflowing part and 10.41% in the reservoir.

For most of the time the specimens did not exhib-it long distance movements. Ninety% of all fish werefound in the same 25 m segment of the river or atmaximum two segments up- or downstream on the fol-lowing tracking. This does not mean that individualfish remained stationary all over the year, they ratheroccupied differentstretches of the river as home-rangesfor certain periods. Migrations were mainly correlat-ed with spawning or seasonal changes of dischargeand temperature (Figure 2). In longitudinal dimension,individual fish used river sections between 625 and11250 m length over the whole observation time (Fig-ure 3).

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Figure 6. Habitat characteristics of all places used during the 24 h cycles for day, dusk, dawn, night and during the whole 24 h surveys(n= number of trackings).

Home-range size was different between the seasons(Kruskal-Wallis-test,n= 58, dF = 4,P = 0:005). Dur-ing winter nase used significant smaller home-rangesthan in summer (Kolmogorov-Smirnov-test,n= 27,P = 0:011), during prespawning (n= 30,P = 0:005)and postspawning (n= 31, P = 0:031). Home-range

size in autumn was smaller than during prespawningtoo (n= 18,P = 0:008). During the 24 hour cycles thespecimens used stretches between 25 and 425 m withan average daily activity area of 120.5 m (Figure 3).Seasonal differences in the size of daily activity areaswere not found.

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Minimal distances swum during 24 hours rangedfrom 50 to 750 m. Movements between segments weremore frequent at twilight, the furthest displacementsalso occurred during dusk and dawn (Figure 4). Sig-nificant differences could be found between night andday (paired t-test, dF = 17,P = 0:049), night and dusk(P = 0:010), night and dawn (P = 0:036) and day anddusk (P = 0:022) in spite of the apparent inactivity ofthe majority of the fish. However, with the transmit-ters used, swimming activity or inactivity could not bedistinguished.

Eight of 34 fish used distinct stretches at day andnight, with movements between stretches taking placeduring twilight (fish A and D, Figure 5). Fish A usedexclusively run segments for the whole 24 h cycle, butpreferred deeper water (> 2 m) and coarser sediment(cobbles of 6.3–20 cm) during the day than during thenight (depth 1–2 m, pebbles of 0.63–2 cm). Currentsstronger than 1 m s�1 were only used once duringdaylight. Fish B also exclusively used run sections anddeeper water during the day. It used segments with cur-rents between 0.1 and 0.5 m s�1 during night and 0.5to 1 m s�1 during the day and a higher proportion offiner sediment during darkness (night: 57 % pebbles,43% cobbles, day: 100% cobbles). However, consid-ering all 24 h cycles only small differences in habitatuse according daytime could be found (Figure 6).

There were obvious differences in the behaviour ofindividual fish even within a single shoal (overlap ofseasonal home ranges and at least once in the same 25 msegment). Some fish showed distinct day and nighthabitats, others did not. Some specimens remained inone stationary shoal, whereas others changed betweensites with stationary shoals.

Compared with the available habitat structures inthe inhabited part of the river (km 3.75–km 18.4, Fig-ure 2), the tagged nase preferred runs and whirls withcurrents between 0.5 and 1 m s�1, hard substratumconsisting mainly of cobbles (6.3 to 20 cm diameter)and depths between 1 and 2 m (Table 2). Soft sub-strates, shallow depths and slow flowing water wereavoided. Pools and the reservoir were rarely used.

As nase did not use their habitat equally all yearround, different seasonal habitat preferences could beexpected. Riffles are important as spawning groundsfor nase (Lelek & Penaz, 1963; Prokes & Penaz, 1978),but were hardly used outside spawning season. Duringthe prespawning period riffles with depths between 0.2and 0.5 m and currents stronger than 1 m s�1 were pre-ferred (Table 2). Pools and whirls were used more oftenafter spawning, probably in search for shelter (high dis-

charge). In summer some fish also used the reservoir,with fine sediment (sand) and deep water (> 2 m). Theapparent preference for strong current (> 1 m s�1) ispresumably due to the high discharge and correspond-ing higher availability during summer compared withwinter, when habitat characteristics were recorded. Nobig differences occurred between general and autum-nal habitat use. During winter most of the tagged fishwere aggregated in a relative short reach at the lowestpart of the residual flow loop. Although shallow areaswere available there, depths less than 1 m were avoid-ed. Currents over 1 m s�1 were rarely used and lowcurrents (0.1–0.5 m s�1) were less avoided than in thewarmer seasons.

Discussion

Adult nase preferred the residual discharge loop, pre-sumably due to its high morphological variability. Thisis in accordance to the findings of other authors (Keck-eis et al., 1996). The free flowing reach and the reser-voir were only used in the warmer seasons during highdischarge when the situation in the residual dischargeloop is dominated by fast runs and only few sites withreduced current velocity are available.

Although nase are known for their spawning andpost-spawning migrations (Penaz, 1996), they remainstationary over longer periods demonstrating pro-nounced home-ranges (Philippart; 1981; Fielenbach,1996). The size of the home-ranges must be largeenough to provide sufficient food for the animals. Dai-ly activity areas of nase in the river Sieg (Germany)(Fielenbach, 1996) were similar in size to that of theAare, in spite of the differences between the two rivers.

Home-range size was larger in the warmer seasonin the river Aare. Fielenbach (1996) also recorded asignificant higher activity with activity-sensitive trans-mitters in the river Sieg. However, the size of dailyhome-ranges was not reduced in both rivers duringwinter. Food availability could force the fish to usean area of similar size, producing enough periphyton.Poikilotherm animals have a reduced metabolism dur-ing winter and therefore need less food, but the naseis known to feed during all seasons except spawningseason (Gyurko, 1959). Feeding with less intensity inwinter but in areas of similar size could be the rea-son for the reduced activity in the same home-rangecompared to the warmer season.

Lusk (1967) described the nase as active, changingits position several times a day. He also described dif-

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ferent feeding and resting habitats in the Rokytna river(Czech Rep.). In the Aare only a part of the fish selectedseparate day and night habitats. Although clear differ-ences in habitat quality between these places couldbe observed for single fish and during some seasons,no such differences could be shown regarding all fishduring the whole study.

Until now no satisfying explanation of the observeddiel activity patterns of nase was described. Gyurko(1959) found full stomachs throughout the day, witha minimum in early morning. For grazers feeding ispossible all day and there is no need for diurnal or noc-turnal activity. On the other hand, Fielenbach (1996)described a clear diurnal activity pattern, and in the riv-er Aare adult nase covered the furthest distances duringdusk and dawn. In case of the barbel (Barbus barbus),Baras (1995) showed that these movements were cor-related with the shift between their resting and feedinghabitats. However, the reasons for the diel activity pat-tern of adult nase are still unclear, because feeding cannot explain these results. If the search for resting placesduring the night is responsible for the habitat shift, thepreference for weaker current, corresponding with fin-er sediment and shallower water, as observed in somefish, makes sense, but there is still a lack of data.

For juvenile nase daily activity with a maximumduring dawn was shown (Bischoff, 1995; Scholten,1995). Changes in the diel activity pattern related toontogenetic changes have been shown for brook char(Bourke et al., 1996) and were related to feeding andsearch for cover. Seasonal variations of the diel activitypattern have been documented in several studies onadult fish of several species, depending on temperatureand day length (Heggenes et al., 1993; Baras, 1995).

Individual differences in behaviour were observed,even within the same shoal, which are difficult toexplain. One explanation could be that shoals areremaining together predominantly by visual orienta-tion (Pitcher, 1979). During twilight fish will lose visu-al contact with each other and start to disperse over awider area.

The nase is known as a shoaling species for juvenileas well as for adult fish; different size and age-classesuse separate river sections in size specific shoals (Lusk,1967; Nelva, 1988; Dedual, 1990). Adult fish arereported to occur in monospecific shoals of a dozento some hundred individuals depending on season andhabitat (Lusk, 1967). Mechanisms of shoaling of naseare unknown so far, except for reproductive behaviour(Prokes & Penaz, 1978; Dedual, 1990). Baras & Cher-ry (1990) proposed individual relations between mem-

bers of a shoal for the barbel, but many authors denysuch relationships for the nase (Lusk, 1967; Fielen-bach, 1996). In the present study shoaling was dynam-ic and individual fish regularly changed shoals. Wesuggest that outside spawning season, nase are non-territorial and aggregate at the most favourable habitatswithin the river. Recent data presented by Baras (1997)demonstrated that, at least for the barbel, the presenceof other individuals of the same species is an importantfactor for habitat selection.

Habitat preferences indicate that optimal sites arerelated to food and cover (Bourke et al., 1996; Per-row et al., 1996). Only coarse substrate can be grazedby nase (Freyhof, 1995). Cobbles as a good sub-strate for periphyton and good to scrape for adult nase,only occur if some minimal current prevents siltation.Strong currents are avoided which reduces the energydemand required to maintain position. Shallow sitesare also avoided due to anglers or predators like largepiscivorous birds (Carss & Marquiss, 1991; Perrow etal., 1996). Deeper water minimises the risk to be seen,but at the same time reduces periphyton growth due tolack of light. Depths between one and two meters, aspreferred in this study, can be seen as trade-off betweenrisk avoidance and food occurrence.

During spawning season habitat use is focused onthe availability of suitable spawning grounds. Otherfactors like food occurrence, cover or energy demandare less relevant then. Shallow riffles with strong cur-rents, clearly avoided during the rest of the year, aresearched for and the fish are taking high risks for repro-duction (Lelek & Penaz, 1963; Prokes & Penaz, 1978).After spawning the fish dispersed over a greater area.Some fish even used the reservoir and the free flowingreach then. It is not known whether they actively select-ed these habitats or were just flushed downstream withthe current. Rising discharge certainly changed thehabitat structures, but at least one fish was found dyingin the reservoir and others were lost at that time. Thenase obviously invested a lot of energy in reproductionand suffered a higher mortality afterwards (Luskova etal., 1995). Tagging at this time of the year proved to beproblematic (Huber & Kirchhofer, 1997). In Winter thenase were often seen in larger aggregations (Ulmann,1997) but concentrated on fewer stretches. During lowdischarge and clear water the fish avoided shallow siteswith less than one meter depth. Strong currents wererarely used and low currents much less avoided thanduring the warmer seasons, presumably to save energyin times of reduced metabolic activity.

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The nase shows high demands on habitat variability,as well regarding different stages in the life cycle, asfor seasonal and to some extent even daily preferences.This might be one reason for the observed populationdecline all over its area of distribution, as a loss inmorphological variability due to channelisation anddamming is observed all over central Europe (Penaz,1996).

Acknowledgements

We thank the Bernese Fisheries Authority, especial-ly M. Fluck, H. Walter and M. Tschan for support;M. Escher for implanting the transmitters and deliveryof fish, T. von Mandach, M. Mezzera, M. Breiten-stein, V. Saladin, H. Malli and M. Gunter for help dur-ing data collection and H. Minder for the haul-seine.The project is supported by the Swiss National Sci-ence Foundation (Project Nr. 31-40885.94) and by theFederal Office of Environment, Forest and Landscape(Project Nr. F-95-5252).

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