Habitat fragmentation is a major source of biodiversity loss in freshwaters, with rivers around the world fragmented by dams and weirs.

These impoundments restrict connectivity, inhibit diadromous fish migrations across ecosystem boundaries, modify gene-flow and impact population sustainability. However, schemes to restore river connectivity can be achieved through either the installation of ‘fish-passes’ on the structures or through removal of the structure.

There have, however, been few attempts to quantify how threatened species respond to these reconnection schemes, especially in relation to their distributions and genetic structuring. A strong example of a river that has been reconnected using fish passes and weir modifications is the lower River Severn basin in western Britain, where reconnection programmes were completed in 2021.

This PhD will use the lower River Severn basin as its focal study area to assess the spatial and genetic responses of river reconnection to threatened species including European shads Alosa spp., sea lamprey Petromyzon marinus, Atlantic salmon Salmo salar and European eel Anguilla anguilla.

Contemporary environmental DNA methods will be applied to determine spatial distributions of juvenile and adult diadromous species across the basin.

Molecular tools will be applied to samples of these species from eggs to adults to assess the selection pressures at each lifestage and their outcomes for the population, where there will be an initial focus on Alosa spp. and their hybrids.  

Please note: The funding includes waive of tuition fees for 36 months, stipend for 36 months, training costs and research costs for the project.

Key information

Next start date:

21 September 2026

Location:

Talbot Campus, Bournemouth University

Duration:

Expected submission: 36 months Completion: within 48 months

Entry requirements:

BU PhD Studentships are open to UK, EU and International students.

Candidates for a PhD Studentship should demonstrate outstanding qualities and be motivated to complete a PhD in 4 years and must demonstrate:

  • outstanding academic potential as measured normally by either a 1st class honours degree (or equivalent Grade Point Average (GPA) or a Master’s degree with distinction or equivalent
  • an IELTS (Academic) score of 6.5 minimum (with a minimum 6.0 in each component, or equivalent) for candidates for whom English is not their first language and this must be evidenced at point of application.

In addition:

  • Strong candidates are expected to demonstrate strong knowledge and enthusiasm for molecular ecology, as well as a strong aptitude for troubleshooting
  • Candidates are expected to have direct experience of DNA extraction, polymerase chain reaction (PCR), and downstream DNA analyses.
  • Prior experience in constructing DNA libraries, particularly for environmental DNA (eDNA) applications, is desirable but not essential.
  • Strong quantitative skills are also essential, including proficiency in R or Python for data analysis.

Deadline for applications: 30 June 2026

Project details

Aim

The research aim is to use the River Severn catchment as the focal reconnected river, and its diadromous species as the focal populations, to apply a range of genetic and molecular tools to: 

  • Assess the spatial and temporal distributions of diadromous species in the river basin, including across longitudinal gradients and with a focus on the impacts of barriers on these distributions
  • Apply novel eDNA methods to assessing the spatial distributions of sea lamprey juveniles (ammocoetes), with a focus on understanding changes in abundance according to distance from the tidal limit and habitat type
  • Quantify the selection pressures and their actions on different lifestages of the diadromous species, especially how these act on Alosa spp. and their hybrids across egg, larval, juvenile and adult lifestages.

Academic impact

This research will substantially strengthen current knowledge on the genetics of how diadromous fishes respond to river reconnection programmes, including using novel methods to measure the distributions of both juvenile and adult lifestages.

Original data should be able to be generated using both eDNA and population genetic methods for the different species, including the novel application of eDNA sediment sampling for sea lamprey ammocoetes.

These data will be highly publishable in relevant scientific journals as well as for presenting at relevant international symposia.

Societal impact

The regulation of rivers for flood prevention is a major societal issue, especially given changing precipitation patterns through climate change. Despite best-practice and policy guidance from regulators, pressure continues to build for greater regulation of flows through hard-engineering solutions. However, these are likely to have substantial ecological and conservation consequences, with potential for extirpations of migratory species of European importance due to habitat fragmentation.

The opposite approach of allowing rivers to increasingly adopt natural flows and characteristics, with less severe land-use practises in the upper catchment and greater connectivity in the lower reaches, is seen as a viable alternative, with the additional benefit of enabling more sustainability in the populations of threatened migratory species.

This PhD is ideally placed to strongly inform this debate, highlighting the potential conservation and genetic benefits that can accrue from soft-engineering solutions, and so preventing further population declines in threatened species such as diadromous fishes. 

Postgraduate research development opportunities

The PhD provides substantial training opportunities, including:

  • environmental DNA and population genetics: training will be provided in all aspects of these methods, from sample collection through to data analyses
  • research skills: training will be provided via formal and informal approaches on research skills including literature review, writing scientific publications and presentation skills
  • there will also be opportunities for discussing research results and findings with regulators and policy makers, with significant networking opportunities for the successful candidate.