Behaviour and spatial ecology of resident brown trout in Langsett reservoir and its tributaries with impassable weirs

Owen, Holly

Biological sciences
September 2021

Thesis or dissertation

© 2021 Holly Owen. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

Anthropogenic alterations to river systems, such as the construction of dams and weirs, have significantly impacted fish populations globally by reducing connectivity to key life stage habitats. Langsett Reservoir, situated in south Yorkshire, holds a small population of resident brown trout (Salmo trutta L.), and is fed by two headwater tributaries that have large impassable weirs. Fish passage throughout freshwater systems is one aspect linked to water bodies failing to achieve good ecological potential (GEP), which includes the Little Don and Thickwoods Brook tributaries.
In this study, acoustic telemetry together with Passive Integrated Transponder (PIT) telemetry was used to understand the migratory behaviour and spatial ecology of the resident brown trout in Langsett reservoir. Nine brown trout (fork length 252 – 357mm) were tagged in the reservoir with V9AP accelerometer/ pressure tags and PIT tags to monitor movement around the reservoir and approaches to the weirs, with a focus on spawning behaviours.
The tagged brown trout primarily occupied the littoral zones of the reservoir and demonstrated a diurnal pattern in depth use, occupying depths <1 metre during the night and greater depths during daylight hours (mean daytime depth: 3 metres). Home range sizes differed throughout the study period with the largest recorded in October, November and December, reducing in January – March before increasing again in April and May.
The weirs prevented any upstream movement of brown trout from the reservoir into the tributaries, 100% of the tagged brown trout were detected on one of the two lower PIT antenna (Little Don and Thickwoods Brook) during November and December with no upstream detections. Five (55%) of the tagged brown trout were detected approaching both weirs. The resident population of brown trout in Langsett Reservoir is thus isolated from the available spawning habitat located upstream in the tributaries. It is likely that this has a negative impact on recruitment to the population in both the tributaries and the reservoir.
The results have highlighted that Langsett reservoir may be acting as an ecological trap. Recommendations made relate to mitigating the effects of the weirs present, ideally through the complete removal of the weir structures. Alternatively, the installation of a fish pass is recommended to allow passage between the reservoir and upstream reaches reducing the impact of the barriers and increase recruitment for the Langsett population as a whole.

Department of Biological & Marine Science, The University of Hull
Noble, Richard Arthur Adrian; Bolland, Jonathan D.
Qualification level
Qualification name
3 MB
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