CR2025_37 Assessing production, residence and nursery values for finfish in saltmarsh habitats in South Wales to inform management strategies for conservation and restoration

Lead Supervisor: Nicole Esteban, Department of Biosciences, Swansea University

Email: n.esteban@swansea.ac.uk

Co-supervisors: Richard Unsworth, Department of Biosciences, Swansea University; Angus Garbutt, UK Centre for Ecology and Hydrology; Ida Algren Nielsen, Natural Resources Wales 

This PhD explores the pivotal factors influencing finfish productivity within saltmarsh habitats, aiming to optimise restoration initiatives and sustain finfish productivity in these ecosystems. Saltmarshes and saltmarsh restoration are renowned for the numerous ecosystem services they offer, including coastal defence, carbon sequestration, nutrient cycling, and water filtration (McKinley et al., 2018). However, despite the recognition of these benefits, the role of saltmarshes as fish nursery grounds is overlooked in the management of these habitats. Furthermore, the existing literature on the benefits of saltmarshes for fish populations is limited. Much of the research of fish in saltmarsh habitats in both the UK and continental Europe has focused primarily on diet (e.g., Joyeux et al., 2017; Stamp et al., 2023), and only a few studies address saltmarsh fish assemblages in Europe (Laffaille et al., 2000; Veiga et al., 2006; Ribeiro et al., 2012). Moreover, our understanding of fish assemblages in UK saltmarshes is spatially limited to southeast England (Colclough et al., 2002; Pickett et al., 2004; Green et al., 2009). This gap indicates a need for more rigorous, data-driven studies to fully document the ecological and economic value of saltmarshes in supporting fish communities. Addressing this gap will inform  conservation and restoration policies that recognize and maximize the nursery habitat service provided by saltmarshes.

The overall aims of this PhD are to explore the factors influencing finfish productivity within saltmarsh habitats to address the underlying question: “Which variables lead to productive saltmarshes (in terms of finfish) in South Wales?”, with the goal of informing optimal management strategies for restoration projects aimed at enhancing finfish productivity. A range of techniques will be used to collect data including year-round monthly fish surveys using seine and fyke nets, interannual fish surveys for indicative months, acoustic fish tagging to assess residence in saltmarsh, vegetation composition assessments, and monitoring of grazing intensity. Outputs will include estimations of nursery value of saltmarsh for finfish, finfish production values, economic value of the habitat and improved understanding of the influence of biotic and abiotic factors on saltmarsh production (e.g. how does vegetation composition, grazing intensity and topography affect overall assemblage), addressing three evidence gaps for saltmarsh (NRW, 2022). By identifying and understanding the key drivers of high productivity in natural saltmarshes, we can apply these insights to enhance the effectiveness of restoration projects for finfish production.

It is envisaged that PhD chapters will address the underlying question and there is scope for the student to develop the specific objectives. Likely chapters include:

1. What is the current understanding of saltmarsh habitat value for finfish production? Conduct a metadata analysis from the existing literature for UK saltmarshes to estimate value in terms of finfish.
2. Estimation of nursery value of saltmarsh habitat for finfish. Combine assessments of finfish nursery value with evidence of repeated use of saltmarshes by finfish using acoustic tracking of selected species to address the NRW evidence need of how fish use saltmarshes as nursery habitats.
3. Estimate finfish productivity in terms of biomass from saltmarsh habitats. Assess how biomass production vary in saltmarshes (and managed realignment) across South Wales via monthly finfish surveys with seine and fyke netting over a year to address the NRW evidence need for increased understanding of how saltmarshes act as supporting habitats for commercial and non-commercial fish species.
4. Assess the economic value of saltmarsh habitat for commercial finfish species to understand how valuable are saltmarsh habitats to the commercial fishing industry addressing the NRW evidence need for an economic evaluation of commercial fish species.
5. Investigating the influence of abiotic and biotic factors within saltmarsh habitats on finfish assemblages, to inform management planning with a focus on spatial orientation of saltmarsh effects on finfish assemblage (e.g. proximity to freshwater input); grazing and vegetation composition effects on finfish assemblage; topographic effects on finfish assemblages.

Training opportunities: 

Data collection will involve a range of techniques including fish identification, biometrics, acoustic tagging of fish, UAV surveys. The student will be trained in all techniques to gain relevant qualifications (e.g., Home Office personal licence).

The CASE partner of this PhD (Natural Resources Wales (NRW)) will provide a placement for the student to work on a range of projects within the organisation. 

Student profile: 

Candidates must have either a first class or 2i honours degree and/or a distinction at Masters’ level in marine biology. The candidate should have skills to develop the proposed PhD chapters. Experience with fieldwork and a postgraduate degree (MRes or MSc) based around fieldwork surveys of finfish would be desirable. Skills should include being accomplished in data analysis with the ability to manipulate large data sets using R, ArcGIS or other software. 

Co-Sponsorship details: 

This project will receive a CASE award from Natural Resources Wales