Abstract
Abstract Large increases in the generation of electricity using marine renewable energy (MRE) are planned, and assessment of the environmental impacts of novel MRE devices, such as kites, are urgently needed. A first step in this assessment is to quantify overlap in space and time between MRE devices and prey species of top predators such as small pelagic fish. Here, we quantify how the distribution of fish schools overlaps with the operational depth (20–60 m) and tidal current speeds (≥1.2–2.4 m/s) used by tidal kites, and the physical processes driving overlap. Fish schools undertake diel vertical migrations driven by the depth of light penetration into the water column, controlled by the supply of solar radiation and water column light absorption and scattering, which in turn depends on the cross‐sectional area of suspended particulate matter (SPM). Fish schools were found shallower in the morning and evening and deeper in the middle of the day when solar radiation is greatest, with the deepest depths reached during predictable bimonthly periods of lower current speeds and lower cross‐sectional area of SPM. Potential kite operations overlap with fish schools for a mean of 5% of the time that schools are present (maximum for a day is 36%). This represents a mean of 6% of the potential kite operating time (maximum for a day is 44%). These were both highest during a new moon spring tide and transitions between neap and spring tides. Synthesis and applications. Overlap of fish school depth distribution with tidal kite operation is reasonably predictable, and so the timing of operations could be adapted to avoid potential negative interactions. If all interaction between fish schools was to be avoided, the loss of operational time for tidal kites would be 6%. This information could also be used in planning the operating depths of marine renewable energy (MRE) devices to avoid or minimize overlap with fish schools and their predators by developers, and for environmental licencing and management authorities to gauge potential ecological impacts of different MRE device designs and operating characteristics.
Highlights
Most current large-scale developments in the marine sector such as oil and gas platforms and offshore wind farms are static and do not have submerged moving parts
Gas-filled scatterer aggregations in the water column detected using the EK60 vessel-based echosounder in October 2016 and January 2017 were mostly juvenile sprat S. sprattus and some whiting Merlangius merlangus according to the trawl samples (Figure 3, see Appendix S2)
We suggest that the depth of light penetration into the water column, calculated using a new method, may predictably determine the depth of diel vertical migrations (DVM) undertaken by sprat schools in the Holyhead Deep
Summary
Most current large-scale developments in the marine sector such as oil and gas platforms and offshore wind farms are static and do not have submerged moving parts. A new aspect of tidal marine renewable energy (MRE) devices is that they have parts, or the entire structure itself, which move through the water and at speeds up to an order of magnitude greater than the prevailing currents. This presents a need to understand the potential spatial and temporal overlap between marine fauna, such as fish (Fraser, Williamson, Nikora, & Scott, 2018; Viehman & Zydlewski, 2015) and top predators such as diving seabirds and marine mammals (Williamson et al, 2017), and mobile MRE devices. Understanding prey distributions of top predators and the processes driving prey presence is required to minimize potential negative interactions of top-predators and associated prey with the tidal kites
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