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Acoustic telemetry was used to track salmon smolts during river migration and into the open marine coastal zone. We compared migration direction and speed with particle tracking simulations to test the hypothesis that marine migration pathways are defined by active swimming current following behaviour. Habitat-specific survival rates, movement speeds, depths and directions in riverine, estuarine, and coastal habitats were also quantified. Salmon post-smolts did not disperse at random as they entered the unrestricted, coastal zone of the North sea; rather they chose a common migration pathway. This was not the most direct route to marine feeding grounds (ca. 44° N); north in the direction of the prevailing currents. Particle modelling showed that the actual post-smolt migration route was best predicted by active swimming at 1.2 body length.sec.−1 at a bearing of 70° from north but not by current following behaviour. Fish migrating in larger groups and earlier in the migration period had increased migration success. We conclude that: post-smolts have preferred migration routes that are not predicted by the shortest direction to their ultimate destination; they do not simply use the current advantage to migrate; and that they actively swim, occasionally directly against the current prevailing at the time.

The Orkney Islands and surrounding waters (known as the Pentland Firth and Orkney Waters Strategic Area, PFOW) contain a significant portion of Scotland's tidal and wave energy resource. This paper forms part of a wider study modelling tidal and wave processes, and planned renewable energy extraction, in PFOW using 3D hydrodynamic and spectral wave numerical models. Such hydrodynamic models require a number of spatial data, i.e. high resolution bathymetry, model boundary conditions and measurements for model validation, which are hard to obtain in extreme environments such as PFOW. This paper examines the characteristics and selection criteria of the data used for the development of the models. Most of these data are freely available, and could form part of an open source marine renewable energy hydrodynamic modelling toolbox. In order to include the planned tidal and wave energy developments in the hydrodynamic models of the wider study, realistic tidal and wave device array scenarios are required. However, there is still considerable uncertainty regarding the type of devices that will be deployed and device array layouts. Here, we describe the process undertaken, in consultation with industry, to develop a small number of generic device types and array scenarios for the PFOW, based on insight provided by documentation submitted by developers as part of the Scottish marine licensing process. For tidal developments, an algorithm was developed to determine the site specific array configuration, taking into account the number of turbines, water depth, tidal current direction and the spatial distribution of mean kinetic energy. The wave development sites did not require such detailed site specific placement of devices, and the generic layouts could simply be constructed in most cases without the need for detailed site specific resource characterisation. It is anticipated that the renewable energy industry will be able to adopt our data selection criteria to ensure models developed for environmental impact assessments satisfy the quality requirements of the regulator. Similarly, the methodologies developed for characterising generic device types and array layouts will be useful to academia and government researchers, who do not necessarily have access to detailed device and site specific information.

Seawater turbidity due to suspended particulate material (SPM) is an important property of a marine ecosystem, determining the underwater light environment and many aspects of biological production and ecology. SPM concentrations are largely determined by patterns of sediment resuspension from the seabed due to shear stress caused by waves and currents. Hence planning for the construction of large scale offshore structures which will alter regional hydrodynamics needs to consider the consequences for SPM concentrations. Here we develop a one-dimensional (vertical) model of SPM dynamics which can be used to scope the effects of changes in wave and tidal current properties at a site. We implement the model for a number of sites off the east coast of Scotland where we have extensive data sets to enable numerical parameter optimisation. The model performs well at simulating fluctuations in turbidity varying from flood-ebb tidal cycles, spring-neap cycles, storm wave events, and an annual cycle of SPM concentration which is attributed to seasonal consolidation of seabed sediments. Sensitivity analysis shows that, for the range of seabed sediment types in the study (water depth 16–50 m; mud content 0.006–0.380 proportion by weight), relatively large (50%) attenuations of tidal current speed are required to produce changes in water column turbidity which would be detectable by observations given the variability in measurements. The model has potential for application to map the large scale sensitivity of turbidity distributions to the installation of wave and tidal energy extraction arrays.

Storm surges are an abnormal enhancement of the water level in response to weather perturbations. They have the capacity to cause damaging flooding of coastal regions, especially when they coincide with astronomical high spring tides. Some areas of the UK have suffered particularly damaging surge events, and the Firth of Clyde is a region with high risk due to its location and morphology. Here, we use a three-dimensional high spatial resolution hydrodynamic model to simulate the local bathymetric and morphological enhancement of surge in the Clyde, and disaggregate the effects of far-field atmospheric pressure distribution and local scale wind forcing of surges. A climatological analysis, based on 30 years of data from Millport tide gauges, is also discussed. The results suggest that floods are not only caused by extreme surge events, but also by the coupling of spring high tides with moderate surges. Water level is also enhanced by a funnelling effect due to the bathymetry and the morphology of fjordic sealochs and the River Clyde Estuary. In a world of rising sea level, studying the propagation and the climatology of surges and high water events is fundamental. In addition, high-resolution hydrodynamic models are essential to forecast extreme events and to prevent the loss of lives, or to plan coastal defences solutions.

Densely populated coastal areas of the North Sea are particularly vulnerable to severe wave conditions, which overtop or damage sea-defences leading to dangerous flooding. Around the shallow southern North Sea, where the coastal margin is low-lying and population density is high, oceanographic modelling has helped to develop forecasting systems to predict flood risk. However coastal areas of the deeper northern North Sea are also subject to regular storm damage but there has been little or no effort to develop coastal wave models for these waters. Here we present a high spatial resolution model of northeast Scottish coastal waters, simulating waves and the effect of tidal currents on wave propagation, driven by global ocean tides, far-field wave conditions, and local air pressure and wind stress. We show that the wave–current interactions and wave–wave interactions are particularly important for simulating the wave conditions close to the coast at various locations. The model can simulate the extreme conditions experienced when high (spring) tides are combined with sea-level surges and large Atlantic swell. Such a combination of extremes represents a high risk for damaging conditions along the Scottish coast.

Due to the importance of parasite and disease controls for animal welfare, environmental sustainability and the economic viability of the finfish aquaculture industry in coastal waters, spatial management measures need to take into account the degree of connectivity between management areas. This paper describes the model integration (one-way nesting) of local high-resolution and wider domain hydrodynamic models around Scotland and the combination of their outputs to force a bio-physical modelling application to support marine spatial management. We used climatological flow fields from a hydrodynamic modelling framework (the “Scottish Shelf Model”) to estimate the degree of connectivity between Scottish finfish aquaculture Farm Management Areas (FMA) using bio-physical simulations of virtual organisms representing the planktonic phase of parasitic sea lice, an important problem for the aquaculture industry. Three types of analysis are carried out: presence/absence of connections between FMAs as the most extreme case, connection probabilities above a defined biologically-meaningful threshold, and above-threshold connection probabilities with a weighting associated with farmed fish within-area biomass (as a proxy for sea lice production) as a more realistic scenario. We find a general northward flow of particles from mainland farms aligned with the prevailing circulation and high connection probability towards the north. Some regions (Loch Linnhe/Sound of Mull) can be classified as net exporters and some (east coast of the Western Isles, the north-west coast) as net receivers of particles. A few selected regions show far reaching connections above the biologically-meaningful probability threshold, for example across the Minch between the Scottish mainland and the Western Isles. Other areas such as Shetland appear to be self-contained and internally well inter-connected. Our results are relevant to the marine aquaculture industry and regulators as they can provide useful information that can be used to develop effective strategies for parasite control.

As oil reserves in established basins become depleted, exploration and production moves towards relatively unexploited areas, such as deep waters off the continental shelf. The Faroe-Shetland Channel (FSC, NE Atlantic) and adjacent areas have been subject to increased focus by the oil industry. In addition to extreme depths, metocean conditions in this region characterise an environment with high waves and strong winds, strong currents, complex circulation patterns, sharp density gradients, and large small- and mesoscale variability. These conditions pose operational challenges to oil spill response and question the suitability of current oil spill modelling frameworks (oil spill models and their forcing data) to adequately simulate the behaviour of a potential oil spill in the area. This article reviews the state of knowledge relevant to deepwater oil spill modelling for the FSC area and identifies knowledge gaps and research priorities. Our analysis should be relevant to other areas of complex oceanography.