Migration of rheophilic fish in the large lowland rivers Meuse and Rhine, the Netherlands

Transcription

1 Fisheries Management and Ecology Fisheries Management and Ecology, 2008, 15, Migration of rheophilic fish in the large lowland rivers Meuse and Rhine, the Netherlands Institute for Marine Resources and Ecosystem Studies, IJmuiden, The Netherlands Abstract Large-scale migratory patterns of adult rheophilic fish [barbel, Barbus barbus (L.), chub, Leuciscus cephalus (L.), ide, Leuciscus idus (L.), nase, Chondrostoma nasus (L.)] were studied in relation to habitat quality and possible migration barriers in the lower rivers Meuse and Rhine, the Netherlands, using a telemetry system with transponders and detection stations based on inductive coupling. Most fish moved over short distances (<10 km), especially those residing in river stretches with high habitat diversity year-round. About 16% of fish used river stretches over 50 km and two ide moved more than 200 km along free-flowing river stretches. One-third of barbel, chub and nase from a Weir-regulated river stretch moved upstream during the spawning season to spawning habitats. Some fish resided in the areas immediately downstream of s and fishways during the spawning season, although it was unclear to what extent these observations reflected habitat choice or barriers to migration. KEYWORDS: barrier, cyprinid, fishway, habitat, migration, telemetry. Introduction Many riverine fish species make longitudinal movements between habitats, e.g. moving from over-wintering habitat to spawning habitat (Northcote 1984; Lucas & Baras 2001). The extent of such movements depends on local habitat availability to complete different phases of the annual cycle. River regulation is one of the main causes for strong declines in river fish populations (Dynesius & Nilsson 1994; Peter 1998; Aarts, Van den Brink & Nienhuis 2004) caused by habitat loss and strong reductions in migration opportunities resulting from construction of barriers (e.g. dams, s, sluices and hydropower plants). Telemetry studies on the migration of rheophilic cyprinids in rivers have become popular for evaluating short-range movements and habitat use (Lucas & Baras 2001). Individual migratory movements of adult cyprinids may vary from less than 100 m to more than 100 km, depending on habitat diversity and migration possibilities (e.g. Waidbacher & Haidvogl 1998; Lucas & Baras 2001; Winter & Fredrich 2003; De Vocht & Baras 2005). A telemetry system with transponders and detection stations based on inductive coupling (Breukelaar, Bij de Vaate & Fockens 1998) was used to compare largescale migration patterns of four rheophilic cyprinid species and possible effects of barriers in three river sections of the River Meuse, the Netherlands, differing in habitat suitability and occurrence of possible migration barriers (s with fishways). Barbel, Barbus barbus (L.), chub, Leuciscus cephalus (L.) and nase, Chondrostoma nasus (L.), are lithophilic spawners and typical inhabitants of small rivers and the mid-range of large rivers. Ide, Leuciscus idus (L.), is a phytolithophilic spawner and more typical for lower reaches of large rivers. It was hypothesised that rheophilic fish in -regulated river stretches with limited suitable spawning habitats would be more vagile than their congeners in free-flowing river stretches with greater habitat diversity. Furthermore, upstream movement past potential barriers (e.g. s with fishways) would vary seasonally, with a tendency towards greater passage prior to spawning. Material and methods Study area The River Meuse (mean annual discharge 230 m 3 s )1 ) and River Rhine (2200 m 3 s )1 ) share the Dutch delta Correspondence: Joep de Leeuw, Institute for Marine Resources and Ecosystem Studies (Wageningen IMARES), PO Box 68, 1970 AB IJmuiden, The Netherlands ( joep.deleeuw@wur.nl) doi: /j x

2 410 Wadden Sea Afsluitdijk North Sea IJsselmeer Vecht 2 Amsterdam IJssel Haring vliet Nederrijn 9 29 Rotterdam Rhine 7 Waal K Sambeek 25 Keizersveer 26 Lower Meuse Weir-regulated Meuse 13 Germany 50 km Kessel Weir Weir with fishway release Release site 16 detection Detection station Belgium Border Meuse K4 15 Roer 27 Borgharen 28 K2 hydropower Hydropower station Figure 1. Nedap Trail detection stations (encircled numbers) and release stations (arrows at Borgharen, Kessel, Sambeek and Keizersveer) of fish with transponders in the lower Rhine and Meuse. Bars indicate s, bars with T bars indicate s with fishways. Detection stations K2 and K4 are located upstream of hydropower station entrances, detection station 25 upstream a fishway, and stations 18, 19 (Afsluitdijk), 21 and 22 (Haringvliet) upstream of discharge sluices to the sea. with connected river branches (Fig. 1). The mid-reach part of the Dutch/Belgium Meuse (Border Meuse 70 river km between stations 28 and 33/K4 in Fig. 1) is free flowing and has extensive gravel beds, shallow banks and deeper pools with a high diversity of water flow habitats suitable for spawning and wintering rheophilic fish species. Further downstream (between stations 24 and 33), the -regulated section of the Meuse (96 river km) has sandy bottoms and consists of impounded river stretches with rip-rap shores and s with V-stepped fishways (Boiten 1990), which were built between 1991 and At the downstream end is a without a fishway (Fig. 1). A tributary, the River Roer, discharges into the upstream part of the Weir-regulated Meuse section, and has many suitable spawning areas related to natural river meanders, gravel substratum and natural shore lines. It has one with a fishway close to the mouth of the tributary (Fig. 1). The lower section of the River Meuse (downstream stations at the discharge sluices to the North Sea, 112 river km) has a sandy substratum and is free flowing, but regulated with levees, and extensive river stretches have groynes; rip-rap shores alternating with more natural shorelines. The Lower Meuse has several open connections to the lower mostly free-flowing branches of the River Rhine (except for three s in the northern Nederrijn branch). The main Rhine branch, the Waal, has sandy substratum and shores, groyne fields and a few side-channels providing suitable spawning and nursery habitats for rheophilic fish (Grift 2001).

3 MIGRATION OF RHEOPHILIC FISH 411 Hydropower stations cover part of two s with fishways (K2 at the upstream end of the Lower Meuse section and K4 demarcating the Weir-regulated Meuse and Border Meuse sections, respectively; Fig. 1). The main branches of the rivers Rhine and Meuse are cut off from the North Sea: the Afsluitdijk (stations 18 and 19) has closed the IJssel estuary since 1932 and the Haringvliet dam (stations 21 and 22) has closed the main branch in the western delta since An artificial outlet gives free access between the Rhine, Meuse and the sea via the seaport of Rotterdam. Telemetry system Fish movements were studied using the Nedap Trail system (Breukelaar et al. 1998) based on inductive coupling of surgically implanted, individual-specific transponders (battery life expectancy about 2 years) and a network of 29 detection stations in the lower River Rhine and Meuse (Fig. 1). Detection stations consisted of double loop across the river bed or fishway. The stations sent interrogation signals every 4 s. When a transponder was activated by a station, it sent back a unique code and was automatically switched off for the following 2 min to prolong battery life. Barbel (n = 76), chub (n = 51), ide (n = 110) and nase (n = 8) were caught using commercial eel fyke nets and electric fishing at four locations in the River Meuse (Fig. 1, Table 1). Fish were anaesthesised with 2-phenoxyethanol (0.9 ml L )1 ). A transponder (Nedap Trail Ltd, glass cylinder, mm, 9.5 cm 3, 26.5 g in air, 16.0 g in water) was placed in the abdominal cavity via a 2- to 3-cm ventral incision behind the base of the left pectoral fin. The wound was closed by three independent stitches of dissolvable vicryl. The fish recovered in a 100- L overflow tank with running water pumped up from the adjacent river. When the fish were actively swimming and had regained stability, they were released at their capture location. Most fish were caught and released between February and May Six additional barbel were released in December 2003 and 1 chub and 21 ide were released in March All fish were of adult size (36 70 cm total length) and, if possible, their sex was determined based on external features. Recordings until 30 June 2006 were assembled in this study, a period of over 3 years exceeding the battery life of all individuals. Migration behaviour Migration behaviour was derived from recorded passages over detection stations. The network of fixed stations (distance between adjacent stations typically tens of kilometres) does often not allow for the Table 1. Number of fish released and number observed within river stretch only or observed also upstream or downstream the river stretch Released Not observed Within stretch Upstream Downstream Border Meuse Barbel * (2) 0 (0) Chub * (4) 0 (0) Nase (0) 0 (0) Weir-regulated Meuse Barbel (1) 0 (0) Chub (0) 0 (0) Nase (0) 0 (0) Ide (1) 1 (0) Lower Meuse Ide M: 0 (0) R: 16 (14) M: 1 (0) R: 7 (4) Number of fish that returned to a river stretch after upstream or downstream movement is given between brackets. In the Lower Meuse, ide could either move upstream and downstream across the Meuse (M:) or via open connections to the free-flowing Rhine branches (R:). *Fish observed in ship sluice, but occurrence of upstream movement unknown. y All upstream movements occurred via free-flowing Rhine branch Waal (station 10 in Fig. 1). detection of short-range movements. Any (long distance) movement across a detection station, however, will be picked up from the monitoring network. The occurrence of failed detections was 8% in a study of downstream migrating silver eel during high river discharges (Winter, Jansen & Bruijs 2006), but was considered much lower at lower discharges and upstream migration via fishways. Compared with hand-held tracking systems, the Nedap trail system has a limited spatial coverage, but a high temporal coverage for identifying long-range fish movements. Upstream migration over barriers (s, shiplocks, sluices and fishways) was deteremined from subsequent passage of the nearest downstream and nearest upstream detection station, respectively. Passage behaviour around the and fishway at Sambeek (stations 24, 25 and 26) could be studied in more detail. Stations 24 and 26 covered the entire width of the River Meuse just downstream and upstream the, respectively, while station 25 covered the upper compartment of the fishway. At the hydropower stations K2 and K4, detection stations were positioned in front of the entrance (i.e. upstream) of the turbines where trashracks with 10-cm spaces between bars were present (see Winter et al for further details). Station 28 at Borgharen was positioned in a small

4 412 sluice at the (no fishway). Stations 18, 19, 21 and 22 were positioned in front of discharge sluices to the Wadden Sea and North Sea, respectively. Results Migration patterns Over the study period (February 2003 to June 2006), most fish movements were detected in summer or around the spawning period (February to March in ide, April to May in barbel, chub and nase; Fig. 2). The number of observations decreased over the years (last observation July 2005) mainly because of a combination of battery expiration and mortality. Barbel, chub and nase from the habitat-rich Border Meuse remained in the river stretch throughout the study period, undertaking only local movements (33% were not observed at either of the stations, Table 1). Four barbel and two chub visited the upstream (a) 200 Number of individuals days (b) 10 Number of individuals Chub Nase Barbel Ide Month Month Figure 2. (a) Seasonal activity pattern (number of individual days per month, one individual day refers to one day one individual has been detected by one or more detection stations) of barbel, chub, nase and ide during the entire study period. Arrows indicate dates of batches of released fish with transponders. Decay over the years reflects end of battery life (>1000 detections or >2 yr) and/or mortality. (b) Seasonal pattern of number of detected upstream passages of s with fishways for barbel, chub, nase and ide (summed over the entire study period). shiplock sluice but it was impossible to identify if they moved (temporarily) further upstream. Two barbel, three chub and one nase from the Weirregulated Meuse moved >25 km upstream to the Border Meuse and one chub moved >20 km upstream to the tributary river Roer (in total 32% of released fish) in late March or April, just before the spawning season. After the spawning season, only one barbel returned from the Border Meuse to the Weir-regulated Meuse (Table 1). The fraction of lithophilic spawners (i.e. barbel, chub and nase; grouped because of low numbers engaged in large-distance movements) moving upstream from the Weir-regulated Meuse river stretch, relative to the number of fish residing within the river stretch, was significantly larger than the fraction of (possibly) upstream moving fish from the Border Meuse observed at the shiplock sluice [2 2 table: within vs upstream and Border Meuse vs Weir-regulated Meuse; WilliamÕs correction (G adj) = 16.9, d.f. = 1, P < 0.001; assuming that all fish not observed also resided within the river stretch: G adj = 10.3, P < 0.005]. Most ide remained in the Weir-regulated Meuse and 70% were not observed (note the large river stretch without detection stations at the release site Kessel, Fig. 1). Two ide moved upstream to the Border Meuse without returning and one ide migrated to the Roer and returned after the spawning period. Ide from the free-flowing Lower Meuse showed the most frequent and largest migration movements. Nine individuals moved >38 km upstream in the Meuse until the with a fishway and hydropower station (station 32 and K2 in Fig. 1), but none migrated further upstream (Table 1). Many ide (40%) migrated upstream (>45 km) via the Waal, the free-flowing branch of the Rhine, during the spawning season; most of them returning to the lower Meuse and Rhine branches after spawning. Two ide made excursions exceeding 200 river km via the Waal and IJssel to IJsselmeer; one returning along the same route, the other migrating upstream via the river branches IJssel and Rhine to Germany (station 13, no further records). The fraction of ide moving upstream from the Lower Meuse via free-flowing Rhine branches was significantly larger than the number of ide moving upstream from the Weir-regulated Meuse (2 2 table, within vs upstream: G adj = 19.6, P < , within + not observed vs upstream: G adj = 24.0, P < ). Passage of potential migration barriers Less than 10% of fish passed one or more s with fishways in an upstream direction and only 2.5% in a

5 MIGRATION OF RHEOPHILIC FISH 413 downstream direction (Table 2). By contrast to frequent movements observed in river stretches between s in spring, summer and autumn, all (except one) upstream passages of s occurred just before or during the spawning season in spring (Fig. 2). At s with detection stations immediately upstream and downstream the, it was possible to observe fish that approached a in an upstream direction without subsequent passage and fish that actually passed the via the fishway and were observed further upstream (Table 3). Ide frequently remained downstream during the spawning season and only 20% passed the to the upstream river stretch. By contrast, 80% of barbel, chub and nase (grouped because of small numbers) approaching a in upstream direction subsequently passed the (2 2 table, G adj = 7.8, P < 0.005). In the downstream direction, only 26% of all fish approaching a subsequently passed the (Table 3), with no significant difference between ide and the other species (2 2 table, G adj = 0.01, P >> 0.05). Two barbel and one ide moving in the downstream direction were observed at the upstream entrance of the turbines of the hydropower station at Linne (station 12), all returning upstream afterwards, but one barbel was Table 2. Number of individuals observed passing a potential migration barrier and number of passages (between brackets) n individuals (n barrier passages) Released Passage upstream Passage downstream Barbel 76 2 (4) 1 (1) Chub 51 5 (9) 0 (0) Nase 8 2 (3) 1 (2) Ide (17) 8 (12) Passages in upstream direction include only s with fishways; passages in downstream direction include s (with or without fishways or hydropower plants) and discharge sluices to sea. Table 3. Number of individuals observed in front of at station 12/33/K4, station 24/25/26, station 23/32 or station 9/29 and number that passed the in upstream or downstream direction Upstream direction Downstream Passed Downstream direction Upstream Passed Barbel Chub Nase Ide detected later again at the entrance of the turbine without further detections thereafter. Two downstream passages of barriers with very limited facilities for upstream migration were recorded, one ide at a without a fishway (between stations 23 and 24), and one ide at the discharge sluice of Haringvliet (station 22) into the North Sea; both did not return. Discussion Most fish moved over rather short longitudinal distances (<10 km) within the rivers throughout the year. Many fish (30%) were only observed close to the release site and a large fraction (43%) were never recorded at the nearest detection stations (well over 10 km from the release site at Kessel and Keizersveer, leaving short-range movements unnoticed). Relatively short-range movements (0 15 km) in the adult life stage of rheophilic species have also been observed in other telemetric studies on chub (Lucas 2000; Fredrich, Ohmann, Curio & Kirschbaum 2003), barbel (Lucas & Batley 1996; Lucas 2000; Ovidio & Philippart 2002; De Vocht & Baras 2005), nase (Ovidio & Philippart 2002) and ide (Winter & Fredrich 2003). This study focused on the less-frequent and less-studied large-scale movements, which typically occurred before or during the spawning season, suggesting that these movements were primarily motivated by searching for suitable spawning habitats. Barbel, chub and nase from the Weir-regulated Meuse tended to migrate to upstream river stretches with higher habitat diversity including suitable spawning habitats, than those residing in the more natural and habitat-rich Border Meuse. It is unknown to what extent the shiplock sluices upstream of the Border Meuse prevented passage to river stretches in Belgium. De Vocht & Baras (2005) found a tendency for shorter movements of adult barbel in river stretches of the Border Meuse with high habitat diversity where suitable habitats for spawning, wintering and feeding are available nearby (few hundred metres to few kilometres). Nursery habitats such as slow-flowing, shallow side-channels of the lowland river stretches of the Rhine can sometimes be found more than 100 km downstream of spawning sites of barbel and reached by larval drift (Grift 2001). Spawning migration patterns of individual fish were sometimes repeated across years, but some fish (especially from the Weir-regulated Meuse) permanently moved to river stretches with apparently more suitable conditions (Border Meuse and Roer). Winter & Fredrich (2003) also found that individual ide often showed similar spawning migration patterns in subsequent years, but that migration patterns appeared

6 414 more flexible in the free-flowing Elbe (Germany) than in the -regulated Vecht (the Netherlands; Fig. 1). They hypothesised a trade-off between spawning habitat availability and costs of migration, which would determine the spawning site fidelity. Only few fish, relative to the high number of fish with implanted transponders, approached or passed barriers, both in upstream and downstream directions, despite the availability of fishways. This was partly because of the relatively short river stretches (<10 km) that most fish used, and partly because long-range migrations (especially in ide at the Lower Meuse/ Rhine), if they took place, were over barrier-free river stretches. The extent to which the barrier function of s, despite fishways, is maintained depends both on the motivation and capacity of fish to move upstream or downstream and on the possibilities to cross the barriers. The type of V-stepped fishways used at the s in the Meuse and Rhine proved to be suitable for many fish species and sizes of fish (Winter 2007). The suitability is therefore considered sufficient for upstream migration of adult fish in this study, although the probability of detecting the attraction flow of the fishway might reduce the frequency of successful passages (e.g. Bunt 2001; Scruton, Booth, Pennell, Cubitt, McKinley & Clarke 2007a; Scruton, Pennell, Bourgeois, Goosney, Porter & Clarke 2007b; Winter 2007). More detailed observations around barriers showed that some fish spent time in front of barriers, either downstream or upstream, before they either crossed the barrier or remained in the river stretch. Ide regularly approached a upstream during the spawning season, but 80% did not pass the fishway and spent several days to weeks in the area downstream the. Two possible explanations for this are proposed: (1) ide considered the area immediately downstream of s as suitable spawning habitat with well-oxygenated water and presence of suitable spawning substrate (coarse sand or gravel) (Ovidio & Philippart 2002; Winter 2007) or (2) the attraction flow of the fishway was insufficient relative to the tailrace of the s to detect the entrance of the fishway preventing further upstream migration. Delays or migration failures at barriers with fishways have also been observed in upstream migrating salmon, Salmo salar L., and sea trout, Salmo trutta L., on their way to spawning areas (e.g. Thorstad, Økland & Finstad 2000; Bij de Vaate, Breukelaar, Vriese, De Laak & Dijkers 2003; Scruton et al. 2007a), barbel (Baras, Lambert & Philippart 1994), ide (Winter 2007) and downstream migrating kelts and smolts (Kemp, Gessel & Williams 2005; Arnekleiv, Kraabøl & Museth 2007; Scruton et al. 2007b) and silver eels, Anguilla anguilla (L.) (Winter et al. 2006). River regulation often affects both habitat quality and migration opportunities, such as in the Weirregulated Meuse. As in other studies, rheophilic fish in this study adopted highly variable migratory behaviour and probably adapted to some extent to unnatural habitats. As a result of this behavioural plasticity and multiple impacts of river regulation, it remains unclear as to the extent to which trade-offs between habitat quality and migration opportunities affect habitat choice and ultimately population sizes of rheophilic fish. Aarts et al. (2004) concluded from comparisons with historical references that limited habitat diversity caused by river regulation was the main cause for the greatly diminished riverine fish populations in the Rhine and Meuse. However, rheophilic fish populations of the Meuse and Rhine have recently shown some recovery in response to locally (re)constructed spawning and nursery habitats (side channels) and the construction of by-pass fishways along s and shiplock sluices since the 1990s (De Leeuw, Buijse, Grift & Winter 2005). Acknowledgments André Breukelaar (Rijkswaterstaat RIZA), Gerben Slob and Koos Fockens (NEDAP) provided logistics with respect to the Nedap trail system. Fishermen Nelissen, Klop & Zn, and Hanz Wiegerinck, Hendrik Westerink, Jan van Willigen and Henrice Jansen (IMARES) helped to catch fish and assisted with transponder implantations. Ulrika Beier and three anonymous referees made helpful comments on the manuscript. This study was funded by the Ministry of Agriculture, Nature and Food quality, the Netherlands. References Aarts B.G.W., Van den Brink F.W.B. & Nienhuis P.H. (2004) Habitat loss as the main cause of the slow recovery of fish faunas of regulated large rivers in Europe: the transversal floodplain gradient. River Research and Applications 20, Arnekleiv J.V., Kraabøl M. & Museth J. (2007) Efforts to aid downstream migrating brown trout (Salmo trutta L.) kelts and smolts passing a hydroelectric dam and a spillway. Hydrobiologia 582, Baras E., Lambert H. & Philippart J.C. (1994) A comprehensive assessment of the failure of Barbus barbus (L.) migrations through a fish pass in the canalized River Meuse (Belgium). Aquatic Living Resources 7,

7 MIGRATION OF RHEOPHILIC FISH 415 Bij de Vaate A.B., Breukelaar A.W., Vriese T., De Laak G. & Dijkers C. (2003) Sea trout migration in the Rhine delta. Journal of Fish Biology 63, Boiten W. (1990) Hydraulic design of the pool-type fishway with V-shaped overfalls. Proceedings of the International Symposium on Fishways. Gifu, Japan: Publications Committee, pp Breukelaar A.W., Bij de Vaate A. & Fockens K.T.W. (1998) Inland migration study of sea trout (Salmo trutta) into the rivers Rhine and Meuse (the Netherlands), based on inductive coupling radio telemetry. Hydrobiologia 371/372, Bunt C.M. (2001) Fishway entrance modifications enhance fish attraction. Fisheries Management and Ecology 8, De Leeuw J.J., Buijse A.D., Grift R.E. & Winter H.V. (2005) Management and monitoring of the return of riverine fish species in the Netherlands. Archiv fu r Hydrobiologie 155(Suppl.), De Vocht A. & Baras E. (2005) Effect of hydropeaking on migrations and home range of adult barbel (Barbus barbus) in the River Meuse. In: M.T. Spedicato, G. Lembo & G. Marmulla (eds) Aquatic Telemetry: Advances and Applications. Proceedings of the Fifth Conference on Fish Telemetry held in Europe. Ustica, Italy, 9 13 June Rome: FAO/COISPA, pp Dynesius M. & Nilsson C. (1994) Fragmentation and flow regulation of river systems in the northern third of the world. Science 266, Fredrich F., Ohmann S., Curio B. & Kirschbaum F. (2003) Spawning migrations of the chub in the River Spree, Germany. Journal of Fish Biology 63, Grift G.E. (2001) How Fish Benefit from Floodplain Restoration Along the Lower River Rhine. Thesis, Wageningen, the Netherlands: University of Wageningen, pp Kemp P.S., Gessel M.H. & Williams J.G. (2005) Finescale behavioural responses of pacific salmonid smolts as they encounter divergence and acceleration of flow. Transactions of the American Fisheries Society 134, Lucas M.C. (2000) The influence of environmental factors on movements of lowland-river fish in the Yorkshire Ouse system. The Science of the Total Environment 251/252, Lucas M.C. & Baras E. (2001) Migration of Freshwater Fishes. Oxford: Blackwell Science, pp Lucas M.C. & Batley E. (1996) Seasonal movements and behaviour of adult barbel Barbus barbus, a riverine cyprinid fish: implications for river management. Journal of Applied Ecology 33, Northcote T.G. (1984) Mechanisms of fish migration in rivers. In: J.D. McCleave, G.P. Arnold, J.J. Dodson & W.H. Neil (eds) Mechanisms of Migration in Fishes. New York: Plenum Press, pp Ovidio M. & Philippart J.-C. (2002) The impact of small physical obstacles on upstream movements of six species of fish. Synthesis of a 5-year telemetry study in the River Meuse basin. Hydrobiologia 483, Peter A. (1998) Interruption of the river continuum by barriers and the consequences for migratory fish. In: S. Jungwirth, S. Schmutz & S. Weiss (eds) Fish Migration and Fish Bypasses. Oxford: Fishing News Books, Blackwell Science, pp Scruton D.A., Booth R.K., Pennell C.J., Cubitt F., McKinley R.S. & Clarke K.D. (2007a) Conventional and EMG telemetry studies of upstream migration and tailrace attraction of adult Atlantic salmon at a hydroelectric installation on the Exploits River, Newfoundland, Canada. Hydrobiologia 582, Scruton D.A., Pennell C.J., Bourgeois C.E., Goosney R.F., Porter T.R. & Clarke K.D. (2007b) Assessment of a retrofitted downstream fish bypass system for wild Atlantic salmon (Salmo salar) smolts and kelts at a hydroelectric facility on the Exploits River, Newfoundland, Canada. Hydrobiologia 582, Thorstad E.B., Økland F. & Finstad B. (2000) Effects of telemetry transmitters on swimming performance of adult Atlantic salmon. Journal of Fish Biology 57, Waidbacher H.G. & Haidvogl G. (1998) Fish migration and fish passage facilities in the Danube: past and present. In: S. Jungwirth, S. Schmutz & S. Weiss (eds) Fish Migration and Fish Bypasses. Oxford: Fishing News Books, Blackwell Science, pp Winter H.V. (2007) A Fisheye View on Fishways. Thesis, Wageningen: University of Wageningen, pp Winter H.V. & Fredrich F. (2003) Migratory behaviour of ide Leuciscus idus: a comparison between lowland rivers Elbe, Germany, and Vecht, the Netherlands. Journal of Fish Biology 63, Winter H.V., Jansen H.M. & Bruijs M.C.M. (2006) Assessing the impact of hydropower and fisheries on downstream migrating silver eel, Anguilla anguilla, by telemetry in the River Meuse. Ecology of Freshwater Fish 15,