Event Title

Session E3: Future Challenges

Location

Groningen, The Netherlands

Event Website

http://fishpassage.umass.edu/

Start Date

22-6-2015 5:15 PM

End Date

22-6-2015 5:40 PM

Description

Abstract:

As explained in the previous presentations, since the late 80s of the last century a lot of effort has been spent into building up new salmon populations in the Rhine by stocking juveniles, restoring spawning places and building fish passages. After more than 25 years we have to conclude that a selfsustaining population is not yet realised. In fact since 2007 there is a declining trend of returning salmons, while the reason for this decline remains unknown. In the life-cycle of salmon there are several bottlenecks to pass and in the coming years we plan to analyse the most critical ones. Some examples of possible increased mortality in some of these phases of the lifecycle: - During the phase of downward migration of smolts there is evidence of high and possible increased mortality by predators and hydropower stations. The evidence is given by telemetry research presented by Breukelaar. Future research has to be focussed on this kind of mortality. - At the end of the period at sea an important bottleneck (literally) occurs at the river-mouth at Haringvliet, when the adult salmon return to the river and are gathered at the Haringvliet weirs. There is still fishery allowed outside a 250 m zone from the weirs. There are signals that the fishery increases and we will give more attention to this in the next years. - When entering the river a large part of the incoming salmon makes a turn and goes back to sea. We plan to analyse and explain this behaviour by giving attention to the genetic composition of these individuals and by comparison with the introduced individuals. - In addition to that we have to investigate the functioning of the fish passages, which may lose their efficiency in the course of time. - Apart from the salmon eel, allis shad and houting profit from these measures as well. In particular the latter two are good examples of gradually restoring populations in some parts of the Rhine river basin.

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Jun 22nd, 5:15 PM Jun 22nd, 5:40 PM

Session E3: Future Challenges

Groningen, The Netherlands

Abstract:

As explained in the previous presentations, since the late 80s of the last century a lot of effort has been spent into building up new salmon populations in the Rhine by stocking juveniles, restoring spawning places and building fish passages. After more than 25 years we have to conclude that a selfsustaining population is not yet realised. In fact since 2007 there is a declining trend of returning salmons, while the reason for this decline remains unknown. In the life-cycle of salmon there are several bottlenecks to pass and in the coming years we plan to analyse the most critical ones. Some examples of possible increased mortality in some of these phases of the lifecycle: - During the phase of downward migration of smolts there is evidence of high and possible increased mortality by predators and hydropower stations. The evidence is given by telemetry research presented by Breukelaar. Future research has to be focussed on this kind of mortality. - At the end of the period at sea an important bottleneck (literally) occurs at the river-mouth at Haringvliet, when the adult salmon return to the river and are gathered at the Haringvliet weirs. There is still fishery allowed outside a 250 m zone from the weirs. There are signals that the fishery increases and we will give more attention to this in the next years. - When entering the river a large part of the incoming salmon makes a turn and goes back to sea. We plan to analyse and explain this behaviour by giving attention to the genetic composition of these individuals and by comparison with the introduced individuals. - In addition to that we have to investigate the functioning of the fish passages, which may lose their efficiency in the course of time. - Apart from the salmon eel, allis shad and houting profit from these measures as well. In particular the latter two are good examples of gradually restoring populations in some parts of the Rhine river basin.

https://scholarworks.umass.edu/fishpassage_conference/2015/June22/59