Population biology (M2); Peter, Schleiss 53
Longitudinal connectivity of river systems
Armin Peter1 and Anton Schleiss2
1 EAWAG, Seestrasse 79,Kastanienbaum
2 EPFL, 1015 Lausanne
Summary
Effect of river fragmentation in a longitudinal perspective
The collaboration between Eawag and EPFL aimed at documenting how longitudinal connectivity of rivers influences the distribution of fishes in the main stem of the river and its main tributary. Due to the numer- ous artificial barriers the longitudinal connectivity in Swiss streams is heavily affected. We studied the longitudinal distribution of bullhead in the Sense River. Ten microsatellite markers were used to document the small-scale patterns of gene flow of a fish species which is highly isolated in the upstream migration by artificial barriers. High genetic differentiation between sampling sites were found between stream sites separated by only 35 km. A distinct increase of genetic differentiation with geographical distance was observed in the continuous river sections and in the full dataset which included headwater populations which suffer from isolation by man-made barriers. A decrease of genetic variation was observed from the lower reaches towards the headwater reaches. This isolation is pronounced in physically isolated popula- tions. The results show that headwater populations may be vulnerable to extinction, due to their isolation and low genetic variation.
Re-establishing river connectivity
In order to re-establish the connectivity in streams engineers propagated different types of block ramps.
Many of them were constructed in Swiss rivers. In order to facilitate the fish passage in the upstream direction certain hydraulic criteria have to be ensured. Systematic labor experiments were carried out to test different ramp types. Monotonous block ramps hardly fulfill the criteria for successful trout passage.
However structured ramps with slopes between 6–10 % can permit upstream migration of trout.
With extensive field experiments in different streams we studied the upstream migration and ramp pas- sage possibilities for several fish species. The results demonstrate that the following criteria have to be considered: ramp slope – type of ramp – existing and potentially occurring fish species – stability of the ramp during floods – connectivity of ramps for fish species with different swimming capacities. The experiments we carried out made it possible to give the following recommendations to practitioners. – prefer structured ramps – if trout is the only existing fish species the ramps can be constructed quite steep (up to 6 %). In the grayling zone where other fish species and often cyprinid fishes occur the ramp slope should not exceed 3 %. We were also able to detect successful ramp passage for small-sized fish species. However only very limited number of these individuals passed the ramps. In order to answer the question if small-sized fish species could be used as test species for successful ramp passages ad- ditional experiments are needed. We were able to demonstrate that bullhead (Cottus gobio) do not show a homing behavior after translocation and therefore we do not recommend to use bullhead for ramp pas- sage studies.
State of the art (pre-ENHANCE)
Effect of river fragmentation on fishes
A limited knowledge how artificial barriers effect the fish species distribution in the main stem of a river was already available. However it was often neglected how artificial barriers can affect the dispersal rate and therefore lead to isolation and vulnerability of populations.
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Analyses of block ramps concerning hydraulic parameters
Lab experiments with ramps and measurements of water velocities and water depth at block ramps were limited.
Experiments on successful ramp passage for trout
No information was existing on fish passage for different types of ramps. There was no published litera- ture on fish passage experiments with ramps. Statements on ramp passage of fishes were mainly based on assumptions and non scientific experiments.
Ramp passage in consideration of fish length
To our knowledge no information was available about successful ramp passage of different size classes of fish species.
Motivation and research questions
Swiss streams and rivers are highly fragmented. More than 100 000 artificial barriers exist in the 65 000 km of streams and rivers. Therefore the average free-flowing stream reach between artificial barriers is only about 650 m long. The effect of this fragmentation is hardly documented for fishes. Few documenta- tions exist only for species occurrence down- and upstream of the barriers.
River engineers started to construct many ramps in the last years. However, none of these ramps have been studied for successful fish passage. The following research questions were answered:
1. What is the effect of the man-made fragmentation on fish populations?
2. Can fragmentation lead to extinctions of fish species?
3. Is it possible to restore the longitudinal connectivity and the river corridor for fishes in streams?
4. Can lab experiments with ramps deliver informations on ramp passages?
Technical issues
Effects of river fragmentation on bullhead
The Sense River has a very diverse morphology. The middle and upper part of the River have to be considered to be natural (morphology and hydrology). The lower part of the river is channelized and has monotonous habitats. All barriers in the system are artificial. The barriers height is between 0.4 to 2 m.
The two headwaters, the Kalte Sense and the Warme Sense are fragmented by numerous barriers con- structed from 1917 onwards. 15 sites were sampled. The bullhead were caught by electrofishing. We in- cluded also two sites in large tributaries and eight sites in smaller tributaries. For the genetic analyses fin clips were used and stored in 100 % ethanol. Genotyping was carried out using standard methods used in our lab (for details see the paper). Statistical analyses were carried out with GENEALEX,STRUCTURE and COLONY.
Lab experiments of different types of block ramps
A 7.7 m long, 0.5 m wide and 0.5 m deep trough was used in the lab. The morphology of the ramp was made with gravel. The used ramp was 3 m long and had a slope between 6–10 %. Water velocity was measured with a small velocity meter. We used a measuring grid of 12 x 3 cm, respectively 6 x 3 cm for well structured morphology conditions. In order to estimate the fish passage published literature values for trout were used. Four different types of ramps were studied: classical ramp, dissolved structured ramp, meandering ramp with a slope of 10 % and meandering ramp with a slope of 6 %).
Population biology (M2); Peter, Schleiss 55
Fish passage over ramps
14 ramps in 12 different rivers in Switzerland were studied to test the fish passage. For all ramps we sampled the fish by electrofishing upstream of the ramp. The fish were anaesthetized and tagged with a needless injector using alcian blue.
Electronically marked fish were tagged with PIT tags (12 mm and 23 mm) inserted into the body cavity.
The fish were released downstream of the ramp. The successful ramp passage was detected by electro- fishing reaches upstream of the ramp, or by detecting the PIT tags with a mobile or fixed antenna.
For the radio-tagged fish we used nano tags (0.45 g) which were placed into the body cavity.
In order to study the homing behavior of bullhead the caught individuals were translocated and released 50–150 m downstream of the site where they have been caught. More than 4000 fishes were tagged for the ramp experiments.
Innovation
The different studies resulted in novel insights. The effect of river fragmentation could clearly be demon- strated in the isolation and low genetic variation of the headwater populations of bullhead. Isolation and the small population size decrease long-term population viability and adaptive potential and can lead to local extinctions.
In order to estimate the successful ramp passage we established new methods. The PIT tagging is a promising methodology for future ramp experiments and the use of a fixed or mobile antenna allows new kinds of experiments. Our results can be used as specific recommendations for river engineers and future ramp constructions. The gained knowledge will help to re-establish the longitudinal connectivity and stream corridors for upstream migrating fishes. The results also allow an ecological assessment for exist- ing ramps.
We found very clear results for brown trout. Adults can pass steep ramps. However juvenile trout and cyprinid fish species may have passage difficulties at steep ramps because of their limited swimming capabilities.
The collaboration between ENHANCE and joint projects was fruitful. It helped – to stimulate the collaboration between river engineers and biologists
– to document fragmentation effects (isolation and decreased genetic variation) on individuals and popu- lation genetics
– for a general assessment of block ramps by predicting ramp passage on stream reach specific para- meters
Fig. 1. Block ramp Wigger Aarburg, © Armin Peter. Fig. 2. Bullhead: small-sized fish species, © Armin Peter.
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References
Junker, J., A. Peter, C. E. Wagner, S. Mwaiko, B. Germann, O. Seehausen & I. Keller. River fragmentation increases local- ized population genetic structure and enhances asymmetry of dispersal in bullhead (Cottus gobio). Conservation Gene- tics. In press.
Leite Ribero, M., K. Blanckaert, J.-L. Boillat & A. Schleiss. 2011. Elargissement local de l’affluent dans une zone de confluence. Wasser Energie Luft, Heft 3: 235–242.
Schläppi, T. 2011. Does restoration of longitudinal connectivity in rivers using block ramps enhance upstream migration of small fishes ? Master Thesis University of Bern and Eawag: 27 p.
Studer, M. & A. Schleiss. 2011. Analyse von Fliessgeschwindigkeiten und Abflusstiefen auf verschiedenen Typen von Block- rampen. Wasser Wirtschaft,1–2: 67–71.
Weibel, D. & A. Peter. Effectiveness of different types of block ramps for fish upstream movements. Submitted to Aquatic Sciences.
Werth, S., D. Weibel, M. Alp, J. Junker, T. Carpati, A. Peter & C. Scheidegger. 2011. Lebensraumverbund Fliessgewässer:
Die Bedeutung der Vernetzung. Wasser Energie Luft, Heft 3: 224–234.
