Changes in the distribution of marine top predators in the North Sea associated with future offshore wind farm developments

Abstract

Shelf sea ecosystems are facing rapid environmental change, as urgent demands for renewable energy sources drive large-scale expansion of offshore wind farm (OWF) infrastructure and subsequent reshaping of marine habitats in these regions. As the size and number of OWF structures increase, hydrological conditions in both near-field and far-field habitats are expected to change. With both structures themselves inducing additional mixing, and energy extraction resulting in impacts to atmospheric and hydrodynamic processes, large-scale developments have the potential to alter the drivers of trophic levels processes, including primary productivity and resultant impacts to prey distribution and behaviour. These changes may, in turn, affect the suitability of habitats and foraging sites for marine top predators, who often rely on areas that provide predictable and persistent foraging opportunities. As recent decades have also witnessed changes in the distribution and abundance of top predators in shelf sea regions, understanding links between oceanographic processes, prey availability, and marine top predators is key to understanding and predicting potential changes to their distributions. In this thesis, a novel mechanistic modelling approach is employed to understand the impact of physics on prey availability, and subsequently the impact of prey availability on marine top predators. By integrating long-term marine top predator datasets (POSEIDON) and prey surveys (ICES DATRAS) with 3D hydrodynamic model simulations (Delft3D-FM DCSM), these relationships are examined at the scale of the North Sea, with respect to the future upscaling of offshore wind in the region.

In the first research chapter, the potential impacts of future OWF scenarios on shelf sea hydrodynamics and lower trophic level processes are investigated using a fully coupled three-dimensional hydrodynamic and water quality model. Simulations of future OWF scenarios reveal potential changes in mixing processes, which disrupt seasonal stratification and primary productivity, with impacts intensifying under more extreme future OWF scenarios. In the second research chapter, drivers of prey species presence and aggregation are investigated through the development of a species distribution model. Based on simulated environmental changes from the first research chapter, relative shifts in habitat suitability under future OWF scenarios are quantified. Simulated impacts to prey species habitat are diverging, spatially heterogenous, and dependent on species existing distributions, with species predominantly in the central and southern North Sea identified as the most affected. In the final research chapter, marine top predator habitat use and distributions are investigated based on the physics-to-prey-to-predator pathways identified in the previous chapters. Subsequent impacts under OWF scenarios are applied, identifying areas most at risk from altering predator habitat use at this scale. Following results from the first two chapters, identified impacts are not limited to OWF boundaries, and may have subregional effects in the far-field. The combination of the densely planned OWFs with the intermittent seasonal stratification processes result in areas of the southern North Sea, such as the German Bight, being areas of greatest impact to bottom-up ecosystem drivers of higher trophic level distributions. Potential implications to marine top predators may be most relevant for species with constrained movement during seasons of breeding or moulting (seabirds). On-going monitoring of species responses at these scales will be necessary to fully assess realised impact.

By incorporating both hydrodynamics and prey availability, this study provides deeper insights into the processes driving marine top predator habitat use, improving predictive capabilities for changing ecosystems and supporting directed monitoring and management in the region.

Date of Award	12 Dec 2025
Original language	English
Awarding Institution	Bangor University
Sponsors	INSITE
Supervisor	Simon Neill (Supervisor) & James Waggitt (Supervisor)