The responses of rare anadromous fish to river reconnection: using fish movement behaviour to measure population recovery

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

Restoring longitudinal connectivity by weir modification, including the installation of fish passes, is increasingly seen as a solution to the negative consequences for migratory species of river habitat fragmentation. However, there have been few attempts to quantify its ability to restore populations of non-salmonid migratory fishes of high conservation importance, despite many of these species facing unprecedented population declines, such as those detected in the European shads (Alosa spp.) across their range. The River Severn and its tributaries are one of the few remaining British rivers supporting shad populations, but where a series of major impoundments in its lower basin mean these anadromous fish cannot access their historical spawning grounds, resulting in high competition for spawning sites in the lower river, reduced reproduction success and high hybridisation rates between the Alosa spp.

Since 2018, the ‘Unlocking the Severn’ project, a collaborative partnership between the Canal & River Trust, the Severn Rivers Trust, the Environment Agency and Natural England, has been re-connecting shad with over 250-km of lost habitat in the River Severn catchment using weir modifications and engineered fish passes. Consequently, the aim of this interdisciplinary studentship is to quantify the migration response of European shads to river reconnection by measuring and testing their movement behaviour before and after river reconnection. The supervisory team (researchers at the University of Hull (Hull International Fisheries Institute (HIFI), with external supervision provided from Bournemouth University (Professor Rob Britton)), has a strong track record of collaboration with the project partners, with this studentship developed from initial research measuring the upstream migration of shad before reconnection using acoustic telemetry, including long-life transmitters that have enabled the tracking of returning migrators over successive years.

The studentship will test the prediction that the range of migrating shad will expand significantly as catchment-wide human impacts on longitudinal connectivity are remediated. More specifically, how phases of barrier remediation influences movement behaviour over time will be quantified and how particular components of the population (e.g. virgin spawners, returning migrators) are more likely to enter and utilise newly available reaches for spawning. The results will provide powerful insights into how species of high conservation importance respond to anthropogenic river restoration. The research will utilise a combination of field techniques for measuring the temporal and spatial spawning activities of the shad population, but with a strong emphasis on telemetry techniques (e.g. acoustic and passive integrated transponder (PIT) tags). Specifically, acoustic telemetry will assess the upstream migration of shad through the basin and test the influence of obstructions on migration behaviour using strategically located acoustic tracking receivers (including any delays to migration and the relationships with prevailing environmental conditions during passage). A larger sample of shad will be tagged with PIT tags for assessing their movements through the new fish passes. Scales will be removed for identifying fish that have spawned in the river in previous years. There is also potential to expand previous work into population genetics, environmental DNA and the spatio-temporal distribution of spawning. Indeed, the collaborative and interdisciplinary nature of the project means that the student will become experienced in a wide range of field and laboratory skills, while developing strong links to industry.

Entry Requirements:

Candidates are expected to have interests and motivations in aquatic ecology, with a range of field, laboratory and IT skills being essential. Experience using acoustic telemetry and data analysis using R is desirable. You should be interested in both basic and applied science, and keen to work with the CASE partner and to disseminate information to external networks. You must hold an Honours (2.1. or higher) and a Masters degree in a related subject, such as Biology, Ecology or Zoology.