Event Title

Session D2: Direct and Indirect Consequences of River Fragmentation for Spring and Autumn Spawning Fish

Location

Groningen, The Netherlands

Event Website

http://fishpassage.umass.edu/

Start Date

22-6-2015 3:00 PM

End Date

22-6-2015 3:15 PM

Description

Abstract:

Fish passages are thought to mitigate negative effects of river fragmentation on migratory fish, however, their effectiveness is still debated. We here aimed to determine how dams, despite being equipped with fishways, affect the movement of the two common salmonid species European grayling (Thymallus thymallus) and brown trout (Salmo trutta). We analysed 28 years of upstream fishway passage data in combination with radio telemetry data in two high gradient, low-temperature Norwegian rivers.

Dams with fishways delayed the upstream spawning migration of European grayling in spring by one to two months. Radiotelemetry indicated structural upward movements of European grayling in March and April, while fishways typically opened late May or early June. This delay in upstream migration shifted their migration into periods of peak spring flood. Spawning migration of brown trout in the autumn was not fully completed when the fishways already closed for the winter, thus not all individuals could complete their migration.

Both brown trout and European grayling are partial migrants within the freshwater of the studied river systems, i.e. only part of the individuals in the population migrate. We show in a conceptual framework how increased costs of migration can reduce the proportion of migrants in these populations, and therewith lead to increased density dependent effects among the enlarged number of resident individuals. Fragmentation can therefore, indirectly, also affect the fitness of resident individuals in populations far downstream barriers. Given the increased number of barriers currently being built worldwide, it is important to realize that only proper management of fishways can avoid unexpected effects of habitat fragmentation on both the migratory and resident individuals in fish populations.

Comments

Presenting Author Bio: Casper van Leeuwen is a postdoctoral researcher in ecology and evolution with an interest in biological dispersal, animal behaviour, plant and animal physiology, and in particular the interaction between these components in an evolutionary context. Experienced in ecological fieldwork, laboratory experiments, population genetics, phylogenetics and statistical analyses. Currently her is working on the effects of river fragmentation for migrating salmonids in Norway.

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Jun 22nd, 3:00 PM Jun 22nd, 3:15 PM

Session D2: Direct and Indirect Consequences of River Fragmentation for Spring and Autumn Spawning Fish

Groningen, The Netherlands

Abstract:

Fish passages are thought to mitigate negative effects of river fragmentation on migratory fish, however, their effectiveness is still debated. We here aimed to determine how dams, despite being equipped with fishways, affect the movement of the two common salmonid species European grayling (Thymallus thymallus) and brown trout (Salmo trutta). We analysed 28 years of upstream fishway passage data in combination with radio telemetry data in two high gradient, low-temperature Norwegian rivers.

Dams with fishways delayed the upstream spawning migration of European grayling in spring by one to two months. Radiotelemetry indicated structural upward movements of European grayling in March and April, while fishways typically opened late May or early June. This delay in upstream migration shifted their migration into periods of peak spring flood. Spawning migration of brown trout in the autumn was not fully completed when the fishways already closed for the winter, thus not all individuals could complete their migration.

Both brown trout and European grayling are partial migrants within the freshwater of the studied river systems, i.e. only part of the individuals in the population migrate. We show in a conceptual framework how increased costs of migration can reduce the proportion of migrants in these populations, and therewith lead to increased density dependent effects among the enlarged number of resident individuals. Fragmentation can therefore, indirectly, also affect the fitness of resident individuals in populations far downstream barriers. Given the increased number of barriers currently being built worldwide, it is important to realize that only proper management of fishways can avoid unexpected effects of habitat fragmentation on both the migratory and resident individuals in fish populations.

https://scholarworks.umass.edu/fishpassage_conference/2015/June22/86