Factors affecting Atlantic salmon (Salmo salar L.) in the Mersey catchment, North West England, and the potential for a recolonisation

Billington, Sam

Biological sciences
October 2015

Thesis or dissertation

© 2015 Sam Billington. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

Salmon became locally extinct from the River Mersey, northwest England, during the 1950s – 1970s due to deterioration in water quality and man-made barriers. Stray salmon began entering the River Mersey in the 1990s but a self sustaining population has yet to become established. The aim of the study was to review and investigate the recent history of the Mersey catchment, the current status of and factors effecting the salmon population and the potential for a natural recolonisation of River Mersey.

The requirements of adult and juvenile salmon and homing and staying in salmon were reviewed. The physiochemical requirements of salmon are highly specific with connectivity of fundamental importance to upstream migration. In reviewing the status of the Mersey catchment flow manipulation, obstructions to migration, poor water quality and river modifications were common in all rivers. Adult and juvenile salmon have been captured in the Mersey catchment since 2000 but have consistently been caught in low numbers and smolts have not been captured.

Genetic analysis was used to assign salmon entering the Mersey to their region of origin. The Mersey is dependent on stray salmon with the majority from rivers in the Solway and Northwest England areas. A tracking study was used to determine salmon behaviour and route choice in the Mersey catchment and salmon were found to be prevented from moving freely within or upstream of the lower Mersey catchment. Habitat surveys undertaken throughout the catchment revealed a general trend of key habitats existing upstream of barriers and inaccessible to adult salmon. Salmon are unable to recolonise the Mersey catchment in its current state. There are a range of management and restoration options available to restore salmon to the Mersey catchment but a coordinated and concerted effort is required to be successful.

School of Biological, Biomedical and Environmental Sciences, The University of Hull
Cowx, I. G. (Ian G.); Harvey, Jon P.
Qualification level
Qualification name
6 MB
QR Code