Table 3: Fish species in the River Rhine (Modified after IKSR 2002 a)

Table 4: Fish distribution in the river Rhine 1990-2000 (Modified after IKSR 2002 a)

* The distribution of the for the Alpine lakes indigenous species is restricted to the High Rhine catchment area, e.g. Lake of Constance.

Figure 5. Fish species development in the Lower Rhine (From Wetzel 2002)

Sea trout (Salmo trutta trutta L.) has been always present in catches throughout the Rhine and its tributaries. Several sea trout, captured and marked at the North Sea side of the Haringvliet, were found in the Rhine, thus proving that it migrates from the sea into the river (Bij de Vaate and Breukelaar 1999).

The Salmon 2000 Programme

In the past Atlantic salmon (Salmo salar L.) catches had declined in the Rhine from a total number of more than 200 000 fish in the second part of the nineteenth century to nil (ICPR 1991) (Figure 6). The last salmon was caught in the Rhine in 1957. The decline and disappearance of salmon from the Rhine was due to the following:

• Degradation and reduced number and area of spawning places

• Migration barriers in the main channel and the tributaries

• Closure of the major migration routes to the sea

• Water quality degradation

• Overfishing

The international Rhine Action Programme which started in 1987, one year after the Sandoz pollution disaster, included measures for the reintroduction of the Atlantic salmon. The first salmon migrated from the sea and the Lower Rhine into the Sieg River in 1990 (Steinberg et al. 1991). The return of the Atlantic salmon to the Rhine is seen as the result of the improved water quality, mainly better dissolved oxygen concentrations and of intensive repeated stocking in the upstream regions of the Rhine and its main tributaries.

Stocking activities with salmon of different salmon strains; spawning and nursery areas

Salmon of French origin have been stocked in the Upper Rhine and its tributaries in Switzerland since 1984 (Rey et al. 1996). A private group coordinated stocking until the end of 2002. At present it is paid for from the budget of the Kanton Basel-Stadt. Spawning and nursery areas are in the Rhine tributaries Wiese, Birs and Ergholz.

French salmon strains have been stocked in the French Rhine, the Ill and its tributaries, the Luxemburg river Sauer and the German rivers Ahr and Lahn and tributaries (Vauclin et al. 2000). The first young salmon were stocked in some tributaries of the Sieg in 1988. More than 500 000 salmon fry per year have been released since 1995 (Schmidt and Feldhaus 1999). Stocking takes place with salmon strains of different origins, e.g. from Ireland, Scotland, Norway, Denmark and Sweden. In future a new strategy will be practiced whereby the number of strains will be reduced to three or four and the smolts will be marked to allow better recording of upstream migrating fish (Molls pers. comm.).

Figure. 6. Number of salmon caught in Germany and the Netherlands between 1875 and 1950 (From ICPR 1991)

The first natural reproduction of salmon was proved for the Sieg River system. Living yolksac fry of Salmo salar were found in natural redds in the rivers Sieg, Agger and Bröl in the winter 1993/94. Successful natural reproduction of salmon was also observed in the following years in the Sieg and in other tributaries of the Rhine, e.g. Ahr, Saynbach, Lahn, Ill, Bruche. The present condition of the spawning places and the presence of the migration barriers downstream and in the river, allows a small partial return of self-reproducing populations of salmon in the Rhine.

An assessment of the potential spawning places of the species showed an overall carrying capacity of the French part of the Rhine for Atlantic salmon of 344 100 yearling parr. Roche (1994) estimated a potential yearly return of 900 to 1 700 adults to the area, which requires spawning grounds of approximately 10 ha and nursery grounds of about 150 ha. An assessment of potential spawning and nursery grounds in the Rhine tributaries in Luxembourg (River Our) and in Germany indicates a potential return of a self-sustaining population of about 5 000 adults in the Rhine and its tributaries. The actual registered total spawning surface area for salmon and sea trout in the Rhine and its tributaries is 147.1 ha and 630.9 ha of nursery grounds (IKSR 1999b).

Based on the newer data, the Ill catchment area offers a potential of 49 ha of nursery grounds and 3.5 ha of spawning sites, which would allow the return of about 600 adults. This includes 24.7 ha of nursery areas and 1.8 ha of spawning sites in the Bruche. There are more registered areas in the Kinzig, a tributary of the main and the river systems of the rivers Sieg, Wupper, Dhünn, Eifelruhr, Volme and Weser (ICPR unpublished data).

Fish migration

Most migratory fish stocks declined often to extinction in the River Rhine as a result of poor water quality, combined with the construction of barriers and loss of spawning and nursery grounds (Lelek 1989). The construction of dams and enclosures on the rivers from the North Sea, such as Lake Ijssel and Haringvliet-Hollands Diep that have been transformed from brackish to freshwater bodies, have also had an important impact on the migratory fish species.

The most important impacts of dams are (Raat 2001):

• hampered fish migration through the Afsluitdijk and Haringvliet sluices;

• loss of the nursery function for marine and brackish-water fish species;

• increased danger of passive drift of freshwater fish into the sea at peak discharges;

• loss of the freshwater tidal area in the Biebosch;

• decreased mixing of river and seawater, leading to a concentration of eutrophic freshwater along the Dutch coast and hence to an increased risk of eutrophication.

Fish migration studies within the sea trout migration project

Investigations were started in December 1996 on sea trout and salmon migration routes from the North Sea into the Dutch part of the rivers Rhine and Meuse. These studies have been executed within the framework of the ecological restoration of both rivers. The purpose was to find out what problems these species face during their migration from the sea to the spawning grounds upstream. The fish were caught in the Dutch coastal area and marked with implanted transmitters. Migration was followed by means of fixed detection stations constructed on the banks of the watercourses, which potentially could serve as a migration route (Bij de Vaate and Breukelaar 1999). Two out of 19 detection stations were installed in Germany, one on the Rhine in Xanten and the second on the Sieg. Because of the relatively wide natural variations in conditions under which the migration takes place, fish tagging continued until June 2000. A total of 662 fish (582 sea trout and 80 salmon) were equipped with a transponder. It was concluded that the Nieuwe Waterweg was the most important route for upstream migration in the Lower Rhine. However, only few specimens reached the Lower Rhine and one sea trout returned to the open sea after having been in the Sieg River in August 2000.

Hydropower plants and fish migration

There are 21 hydropower plants on the Rhine mainstem, of which 10 are in Germany-France and 11 in Switzerland. The Mosel, Lahn, Main and Neckar are important tributaries to the Rhine and all of them are equipped with hydropower plants. Fish traps have been installed to check the migrating fish. In the Mosel River the downstream migration of eels is being investigated in a joint venture project of the German Federal Government in Rhine Palatinate and the electricity supply corporation RWE Power AG.

In the River Rhine fish can now migrate up to Iffezheim. With the construction of the fish pass in the next barrier in Gambsheim and the enhancement of the Rest Rhine salmon may reach Basel. The weir of Kembs in the Upper Rhine is provided with a fish pass. A feasibility study on behalf of the ICPR will show the functions of the rest of the Rhine as spawning and nursery areas for salmon and the restoration of the ecological connectivity.

Between April 1995 and March 1996 an in-depth study of upstream migrating fish was carried out on 13 fish passes of 9 hydropower plants of the Upper Rhine and the results were compared with the results of the first surveys of 1985 and 1986. Of 26 fish species barbel and eel dominated in the catches. It can be concluded that the functionality of the fish passes is restricted, mainly because of insufficient supply of attraction flow for the fish (Gerster 1998).

The hydropower plant in Rheinfelden in the Upper Rhine is over one hundred years old. There are plans to construct here a similar fish bypass as that at the hydropower station Ruppoldingen on the Aare River. The fish bypass in the Aare is 1.2 km long, 10 to 20 m wide and has a flow of 2 - 5 m³ s^-1 (Gebler 2002). The fish bypass in Rheinfelden will be approximately 1 km long and 30 - 40 m wide. The discharge will be from 10 m³ s^-1 to 35 m³ s^-1.

There are a number of projects for conversion of riverbanks into shallow gravel banks with bays, such as at the Rhine in Rüdlingen, as an ecological compensation measure when issuing a new licence for the hydro power plant in Eglisau and for the creation of a shallow gravel bank with groynes in the Rhine at Rheinsulz. This project should enhance the environmental conditions for the nose carp (Chondrostoma nasus (L.), barbel and brown trout.

The fish pass in Iffezheim

The Iffezheim dam was built from 1970 to 1975 by France and Germany and equipped with a Borland type fish pass. For many reasons, such as the availability of water supply throughout the year, only a limited fish migration through the pass had been possible. During the International Rhine Rehabilitation Programme an agreement was signed by the French and German parties to construct new fish passes in Iffezheim and Gambsheim. Europe´s largest fish pass on the Upper Rhine was built at Iffezheim Württemberg from 1998 to 2000, financed by the EDF Group - Electricité de France (EDF) and Energie Baden (EnBW), the governments of France and Germany and the EU-LIFE-Programme, at a cost of approximately 7.3 million Euro. The fish pass opened in 2000. One million Euro was paid by the power station owner for additional measures. Over a distance of approximately 300 metres, fish pass through 48 pools and surmount an average elevation of 11 metres depending on the water level, between the downstream and upstream sections. The upper part of the pass consists of 37 individual pools, each with a surface area of 15 m² and a mean water depth of 1.5 m. For the passage of invertebrates (macrozoobenthos) the bottom of each pool is covered with a substrate made of large stones and additional passage holes. The water flows through the fish pass at a steady rate of 1.2 m³ s^-1. An additional flow of 9.8 - 11.8 m³ s^-1 comes from a turbine and feeds the distribution basin to improve the attraction flow for the fish. Heimerl, Ittel and Urban (2001) provide further technical details. The modified vertical slot pass has been designed to fit the needs of the majority of the fish species and allows especially the migration of anadromous fish species such as salmon, sea trout and shad. During the period from June 2000 to December 2002 continuous fish observations and counting stations recorded 33 fish species. For part of the time a video device also recorded fish moving through the fish pass, on some occasions fairly large numbers passing through (Heimerl, Nöthlich and Urban 2002). The main source of information came from a metallic fish-trap run jointly by French and German operators (Degel 2002).

During 2000 and 2001, 75 and 59 salmon and 383 and 216 sea trout were counted in the trap. Sea lampreys were also captured (205 individuals in 2001, none in 2000 because the monitoring started after their migration period), as well as a few shads (5 Alosa alosa and 1 Alosa fallax) (Table 5). 21 fish species were recorded in 2000, but only seven of them in numbers over 100. Two species dominated by number and weight: barbel (n = 3 586, with 3.14 tonnes out of a total of 6.1 tonnes) and bream (n = 1 123; 1.16 tonnes). In 2001, 29 species were recorded, with four main species: barbel (n = 6 593), nose carp, bream and asp, with 12.7 tonnes out of a total of 14.4 tonnes. The results of the first year and a half of monitoring can be summarized as follows:

1. The fish pass is mainly used by large and rheophilic cyprinids, the bream being the only non-rheophilic species of the four major fish species. This is understandable when considering that the length of the pass is over 300 meters. The peak of fish migration takes place in May and June.

2. A significant number of migratory and large salmonids use the fish pass. The age of most of the salmon caught has been determined from scales.

3. Large numbers of asp were recorded for the first time. Such abundance of this species has not been assessed by other means of investigations, including electro-fishing. The observations at Iffezheim are likely to overestimate the proportion of asp in the Rhine fish communities because of the selectivity of the device, that appears to favour the big and fast swimming fish (see point 1.) and possibly due to a specific behaviour of this species.

4. The presence of previously not recorded vimba bream (Vimba vimba L.) and white-eye bream (Abramis sapa (Pallas) has been confirmed. Both cyprinids have colonized the Rhine from their original area of distribution in central Europe, passing through the Rhine-Main-Danube canal.

5. Many species occur in small numbers; a dozen of them appeared in less than 10 individuals in 2001.

6. The monitoring bias should be kept in mind. First, not all species are eager to enter nor able to ascend such a long migrating device. Second, the small species that do reach the upstream part of the fish pass (where the video camera and the trap are situated) have the possibility to bypass these monitoring tools using lateral canals that are closed with bars with interspaces of 3 cm.

Table 5: Number of fish species ascending in the fish pass in Iffezheim in the years 2000 - 2002. (Data from Association Saumon Rhin and Conseil Supérieur de la Pêche)

* Based on trapping
** Based on video counting

(a) only adults ascending (not smolts on downwards migration)

(b) migration monitored in 2000 due to the date of beginning

(c) both species: Alosa alosa and Alosa fallax

(d) counting not efficient due to escape between bars of the trap and passing through the video bypass

(e) Abramis brama

(f) values modified in October 2002 after full scale interpretation by Arnaud RICHARD (Conseil Supérieur de la Péche) and Jean-Luc BAGLINIERE (Institut National de la Recherche Agronomique). The numbers for these species given in previous publications were incorrect

(g) the number of other fish species was 21 in 2000, 29 in 2001 and 27 in 2002

In 2002, the video monitoring has been the main source of data and the trapping only took place at certain periods. Five migratory and 22 non-migratory fish species were recorded. From 4 March to 31 December, 94 salmon and 301 sea trout were counted. As in 2000, sea-winter salmon dominated the sample. Fifty-seven lampreys and about 200 eels have also been recorded. The monitoring has never worked for eels, because they can move through a bypass, thus escaping the video camera (or trap, as during the previous years). Nevertheless, qualitative data on their period of migration are being obtained. As for salmon, their number during the period is in the order of magnitude expected from calculations based on the number of juveniles stocked in the upper part of the basin, but rather on the lower level. The proportion of grilse and the scarcity of 3 winter-salmon (two individuals so far), which is consistent with the current situation and trends observed in salmon stocks worldwide, could be an adverse factor for good colonization of this part of the basin, because these small salmon are less able to pass some of the migratory obstacles not yet equipped with efficient fishways. A stocking strategy (stages of release and genetics) is being discussed in France and the other riparian states and the results will be presented for a wider discussion with the colleagues and biologists who collaborate in the salmon project in the Rhine basin, noticeably those involved within the framework of the International Commission for the Protection of the Rhine (ICPR).

Fish control station on the Sieg River in North Rhine-Westfalia

The Sieg is a typical middle range mountain river that rises in the Rothaar Mountains and flows after 153 km into the Rhine near Bonn. The natural character of the river is the reason for a varied fish population. From the beginning of the 1980s sea trout were observed to be migrating in this river. This led to a pilot project for the reintroduction of salmonids. Modern fish passes were built on all weirs of the lower stretch in North Rhine-Westphalia and upper stretch in Rhineland-Palatinate. This made the migration to important spawning sites and nursery areas possible. In the year 2000 a fish research and catching station, with a fish guidance system leading to a trap, was established downstream in the first weir. The fish caught can be temporarily stored. The trap is checked at least once a day throughout the year. The management and maintenance cost is financed by the federal states of North Rhine-Westphalia and Rhineland-Palatinate.

From June 2000 to December 2002, 468 adult salmon and 184 adult sea trout were captured. When catches at the other weirs are included, 631 salmon and 294 sea trout were captured. When taking into account the catch and recapture results the numbers can be doubled (Nemitz pers. comm.). Eleven other fish species were also recorded by the end of 2002.

COMMERCIAL AND RECREATIONAL FISHERIES

There are only two commercial fishers left on the High Rhine, one in Switzerland and one in Germany. Approximately 80 fishers practice traditionally fisheries on the Upper Rhine stretch downstream to Iffezheim. From Iffezheim downstream to the Dutch border about 48 are engaged in fisheries. Most of them fish in addition to their main business (Dr. Kuhn pers. comm.). About 25 fishers are active in the Rhine-Meuse delta, Lower Rhine-Lek and Ijssel. There are seine fisheries in the Haringvliet-Hollandsch Diep and the cyprinids caught are used for stocking inland waters. Eel is left as the most important commercial species. It is fished with fyke nets and electro-fishing. Eel fishing takes place in the Haringvliet-Hollandsch Diep and in the Ijssel in the Netherlands and in the main channel in Germany. But eel catches are declining because of lower elver recruitment during the last 10 years (Dekker pers. comm.). Pikeperch is fished with gill nets (van Doorn pers. comm.). According to Raat (2001) the commercial fisheries of the Rhine are very restricted at the present.

Recreational fisheries are practiced by several hundred thousand persons and take place in the main river channel and on floodplains. The main species targeted are cyprinids such as roach, bream, ide, pikeperch and northern pike. Fishing requires a licence. Every riparian state and each of the German federal states has its own fisheries legislation and regulations. Only few fisheries statistics are available. In this context the International Fisheries Commission for the Upper Rhine between Switzerland and the German federal state of Baden-Württemberg, which is in charge of the fisheries management, is an exception. The total fish catches in the Upper Rhine are related to a surface area of 2 475 ha (Figure 7).

CONCLUSIONS

With the improvement of water quality in the Rhine the dissolved oxygen concentrations are satisfactory for fish throughout the year. However, the biological quality of the Rhine still needs to be improved. The latest data confirm that both fish and macroinver-tebrate communities contain very few stenotopic species, i.e. those with narrow ecological requirements. Often exotic species, so-called neozoa, dominate the benthic macroinvertebrates. While on a larger scale the number of species has increased, detailed examination of reaches and sections of the Rhine shows that locally the number of species has decreased. This seems to indicate that the variety of habitat structures in the Rhine is still limited. While all the former fish species with the exception of the Atlantic sturgeon have been re-established, the present fish fauna is dominated by eurytopic cyprinids and the number of rheophilous species has declined.

The results of the salmon programme for several tributaries of the Rhine (e.g. Sieg, Ahr, Our, Ill, Bruch) show that there is a good chance that a self-sustaining population of Atlantic salmon will become established. The success of the fish passage in Iffezheim will help to implement the next fish pass at Gambsheim. This will enable anadromous fish, such as salmon and sea trout, to bypass the dams across the Rhine and reach their spawning sites in the Rhine tributaries of the Black Forest and the Vosges Mountains. Still more ecological improvement is necessary for achieving this objective. While ecological restoration and flood protection are the major challenges the present socio-economic functions of the river pose serious constraints on achieving the ecological objectives.

Total fish catches in the Upper Rhine

Figure 7. Total fish catches in the Upper Rhine

Various forms of ecological rehabilitation in the Rhine have been identified: floodplain development for ecological improvement and flood prevention, optimisation of up- and downstream fish migration with an emphasis on the entrance of migrating species from the sea into the Rhine and its tributaries and the restoration of spawning and nursery areas. The success of the restoration projects depends mainly on their acceptance by local stakeholders such as ecologists, communal authorities, tourism, agriculture, forest administration and nature associations. From this socio-economic point of view an inquiry in the German Federal State of Rhineland-Palatinate shows that up to 90 percent of stakeholders support the protection and conservation of the species diversity in floodplain projects and this may be representative also for other regions.

An example of a successful partnership is the environmental non-governmental organizations (NGOs) partnership with the International Commission for the Protection of the Rhine (ICPR) (Buijse et al. 2002). The success of projects also depends on a close cooperation between ecologists and engineers. This is reinforced by the EU Water Framework Directive, which requires of member states a commitment to intensify protection and enhancement of the aquatic environment.

Commercial fisheries have a long tradition in the Rhine system. Today, however, commercial fishing it is practiced only on a small scale by a few fishers, whereas the recreational fisheries are ever increasing in the number of participants and intensity. Both types of fishery play an important role in nature protection and the sustainability of fish stocks.

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