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A strategic programme for NERC Lowland catchment research
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Off-river fish habitats : influence of flow regimes & management implications: summary

A fuller description of this project is also available.

Overview of the project

Many freshwater fishes utilise different habitats during their lifecycles and in response to changes in environmental conditions. Maintenance of habitat diversity and access to habitats is strongly influenced by the degree of connectivity within lowland river catchments. Lateral connectivity to floodplain habitats is increasingly at risk from changes in land management and hydrology.


This project had three main aims, to:

  • test the hypothesis that switching between main channel and off-river habitats is a fundamental ecological characteristic for many lowland river fishes;
  • elucidate, by experimental means, the influence of key environmental factors such as discharge and turbidity on lowland river fish behaviour and habitat use; and to
  • collect data and develop models of how fish use lateral habitats in relation to habitat characteristics, including those associated with changes to the hydraulic regime and land-use in lowland catchments, in order to inform the sensitive management of floodplain systems for fish communities.

Main findings

Flow, and associated variables such as aquatic vegetation and substrate, was found to be the main factor distinguishing side channel habitats and their fish communities. However, each side channel type (ditches, natural streams, millstream) has specific ecological functions for the fish community of the river Frome.

The results highlight the ecological variability of off-river side channel habitats, their utilisation for a variety of fish species and age groups and a high degree of flux of the fish populations between the main river and side channel habitats, including ditches. This supports the hypothesis that switching between main channel and off-river habitats is a fundamental ecological characteristic for many lowland river fishes.

Three side channel types were distinguished:

  1. Floodplain ditches fed by groundwater and influenced by backwater ponding due to downstream connectivity with the main channel at high flows.
  2. Side channels containing substantial flow due to upstream connections with the main channel.
  3. Tributary streams that receive substantial runoff during peak flow events, but which are dominated by backwater effects at other times due to connectivity with the main channel at their downstream ends.

Researchers observed a variation in strategies for using habitats amongst individuals. For example, small, mature male pike entered spawning ditches earlier and spent more time there than larger males and females.

Factors responsible for sub-population structuring of habitat use have been identified for the first time. Although the adaptive significance is not yet fully understood, its existence should be appreciated in the context of lowland river mangement. More about the main findings of this project

Description of activities

  • Quarterly sampling of seven side channels over a three year period, including drainage ditches, natural streams and a millstream, together with repeated habitat measurements.
  • Water levels within each side channel were continuously monitored.
  • Passive Integrated Transponder (PIT) telemetry was used at entrances of side channels to determine fish activity.
  • Environmental properties, eg water temperature, were quantified using a combination of field monitoring and numerical modelling.
  • Radiotelemetry of fishes, especially of pike, was used to gather home range and habitat use data.

Areas of application

The outcomes of this research will mainly be used by policy-makers and regulators, especially the Environment Agency and Defra in the context of ecologically sensitive management of river catchments.

Related and future work

Aspects of the work are relevant to work being undertaken by Durham University as part of the new Rural Economy and Land Use Programme (RELU) project "Angling in the Rural Environment".

Researchers' details

Principal Investigator:


More researchers who worked on this project More researchers who worked on this project


All publications from LOCAR projects are listed in the publications database.

Several papers describing the results of this project have been submitted to journals and are under review.

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