Difference between revisions of "Upstream fish migration"

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=Introduction=
 
=Introduction=
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[[File:downstream_migration_mesh_rack.png|thumb|500px|Figure 1: Horizontally inclined mesh rack and guidance of fish through slots in the rack (arrow A) to a tube back to the river to the right (arrow B) in the intake canal of Las Rives HPP in Ariege River, France (Photo: Atle Harby).]]
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[[File:upstream_migration_fishway.png|thumb|500px|Figure 1: Old concrete fishway for brown trout in River Loen, Norway. (Photo: Hans-Petter Fjeldstad).]]
  
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While research and implementation of upstream migration solutions is extensive, and indeed often successful (Scruton et al., 2008), downstream migration of fish remains a major challenge in many river systems. The focus on downstream migration is a result of the increased awareness and knowledge that entrainment in hydroelectric turbines often involves high fish mortality (Larinier and Travade 2002, Fjeldstad et al. 2012, Calles et al. 2013). Safe downstream migration past hydropower structures and intakes is complicated because the fish tend to follow the bulk water flow, which often enters diverting tunnels and turbine intakes. At the same time, downstream migration is crucial for fish to access different habitats for feeding, shelter, spawning and for many fish species, to complete all stages of its life cycle. Hence effective downstream migration passages should be provided, and in particular, if fish can pass upstream a hydropower barrier. The risk of fish injury and mortality from turbine blade strike is particularly harmful for adult fish since the likelihood for blade strike increases with fish length.
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Many fish species migrate in rivers to utilize different habitats at different life stages for spawning, growth and wintering. For many species, migrations are carried out within the same river, while others migrate from their spawning grounds and rearing habitats in rivers to the feeding grounds in the ocean (anadromous behaviour). The European eel displays a catadromous behaviour, with its spawning area located in the Sargasso Sea while they feed along the coasts and in rivers and lakes in Europe. Basically, all fish species show some sort of migratory behaviour or regular movements.  
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In most European rivers and streams there are artificial migratory obstacles and barriers, such as culverts, weirs, dams and power stations. Hydroelectric dams and their tailrace areas represent particular migration challenges. These dams restrict fish migrations and alter the natural habitat for many fish species. This problem is particularly evident for anadromous fishes for which viable populations depend on successful migration from breeding grounds to the ocean and return migrations to spawning grounds. Re-establishment of migration routes is essential to re-introduce or enhance these populations across their distribution areas.
  
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Fish migration delay at power plant reservoirs and forebays is challenging because a rapid and synchronized migration is often essential for the fish to complete the most favourable migration. Such delay can cause increased predation, energy loss and, at worst, fish choose not to migrate, which in turn gives ecological effects.
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Construction of fish passage facilities is widely used to mitigate migration barriers. The first documented fish passes in the 18th century were simple constructions and likely used as a measure to increase population size and fishing opportunities. Since then, anthropogenic impacts and industrial development have fragmented river systems in most large rivers around the world (Nilsson et al. 2005). Accordingly, artificial fishways have been built, including a variety of designs, from minor rip-rap and blasting works to comprehensive combinations of concrete towers and rock tunnels, the tallest nearly 50 meters high. Unfortunately, extensive research over the last decades suggests that many fishways do not have the desired function (Noonan et al. 2011), and that multidisciplinary and site-specific knowledge is required to reach the best solutions (Williams et al. 2011).
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The challenge of safe downstream fish migration is global. Although traditional trash racks or screens themselves are not effective as complete fish barriers, downstream migration past the barrier can be significantly increased if a fish-adapted bypass is designed. Other solutions have also been shown to increase downstream fish survival past hydropower plants, such as guiding screens, louvres, wire screens and partial depth fine screen. Several international studies show that physical structures, such as fine-mesh trash racks with alternative escape routes and bypass arrangements provide very good results for downstream migration, for instance for brown trout and salmon and has in recent years shown good results also for silver eels.
 
  
 
=Upstream fish migration measures=
 
=Upstream fish migration measures=

Revision as of 11:26, 23 June 2019

Introduction

Figure 1: Old concrete fishway for brown trout in River Loen, Norway. (Photo: Hans-Petter Fjeldstad).

Many fish species migrate in rivers to utilize different habitats at different life stages for spawning, growth and wintering. For many species, migrations are carried out within the same river, while others migrate from their spawning grounds and rearing habitats in rivers to the feeding grounds in the ocean (anadromous behaviour). The European eel displays a catadromous behaviour, with its spawning area located in the Sargasso Sea while they feed along the coasts and in rivers and lakes in Europe. Basically, all fish species show some sort of migratory behaviour or regular movements. In most European rivers and streams there are artificial migratory obstacles and barriers, such as culverts, weirs, dams and power stations. Hydroelectric dams and their tailrace areas represent particular migration challenges. These dams restrict fish migrations and alter the natural habitat for many fish species. This problem is particularly evident for anadromous fishes for which viable populations depend on successful migration from breeding grounds to the ocean and return migrations to spawning grounds. Re-establishment of migration routes is essential to re-introduce or enhance these populations across their distribution areas.

Construction of fish passage facilities is widely used to mitigate migration barriers. The first documented fish passes in the 18th century were simple constructions and likely used as a measure to increase population size and fishing opportunities. Since then, anthropogenic impacts and industrial development have fragmented river systems in most large rivers around the world (Nilsson et al. 2005). Accordingly, artificial fishways have been built, including a variety of designs, from minor rip-rap and blasting works to comprehensive combinations of concrete towers and rock tunnels, the tallest nearly 50 meters high. Unfortunately, extensive research over the last decades suggests that many fishways do not have the desired function (Noonan et al. 2011), and that multidisciplinary and site-specific knowledge is required to reach the best solutions (Williams et al. 2011).

Upstream fish migration measures

The various measures to mitigate issues concerning Upstream fish migration are listed below.

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