The Biology of River Restoration: Migration and Population Responses of Threatened Migratory Fishes to Restored River Connectivity

Habitat fragmentation is a major source of biodiversity loss in freshwaters, with rivers around the world fragmented by dams and weirs that create impoundments. These impoundments restrict river longitudinal connectivity, inhibit fish migrations across ecosystem boundaries (marine-freshwater), prevent lifecycle completion, modify gene-flow and impact population sustainability. Whilst restoring longitudinal connectivity can be achieved via ‘fish-passes’ on the impoundments, these only favour movements of salmonid fishes. Increasingly, impoundment removal is used as the holistic alternative. There have, however, been few attempts to quantify its conservation and ecological outcomes for non-salmonid migratory fishes, despite these species facing unprecedented European population declines, such as in shads Alosa spp., which are listed on Annex II of the EU Habitats Directive.

Most British rivers suffer substantial longitudinal disconnection, including the River Severn and its tributaries (e.g. River Teme), where major impoundments have been present in their lower reaches for over 150 years. Migratory Alosa fishes thus cannot access their historical spawning grounds and are instead restricted to sharing spawning areas downstream of the final impoundments, resulting in potentially high competition for spawning sites, reduced reproduction success, impacted larval and juvenile dynamics, and long-term population decline. Correspondingly, from 2018, weir removals and new fish-pass engineering in the lower Severn and Teme will re-connect these fishes with over 250 km of lost habitat.

Consequently, the PhD will use the River Severn catchment as the model system, and Alosa spp. as the focal fishes to quantify how their population biology and ecology respond to the longitudinal re-connection. Objectives are to (1) quantify shifts in the spatial utilisation of the rivers by the model fishes pre and post reconnection; (2) assess the temporal changes pre and post reconnection in the spawning stock size and structure of Alosa spp.; and (3) Determine the changes in the larval and juvenile dynamics of Alosa spp. following reconnection, including length of freshwater phase and the transfer of their marine nutrients across the marine-freshwater boundary into the freshwater food-web.

How to apply: Applications are made via our website using the Apply Online button below. If you have an enquiry about this project please contact us via the Email NOW button below, however your application will only be processed once you have submitted an application form as opposed to emailing your CV to us.

Candidates for funded PhD studentship must demonstrate outstanding qualities and be motivated to complete a PhD in 3 years.
Fully-funded studentship candidates must demonstrate outstanding academic potential with preferably a 1st class honours degree and/or a Master’s degree with distinction or equivalent Grade Point Average. An IELTS (Academic) score of 6.5 minimum (with a minimum 5.5 in each component) is essential for candidates for whom English is not their first language.

In addition to satisfying basic entry criteria, BU will look closely at the qualities, skills and background of each candidate and what they can bring to their chosen research project in order to ensure successful completion.