Man-made structures set in tidal streams can be a feeding hotspot for seabirds, according to new research involving the University of Plymouth.
Strong currents interacting with hard structures – including boulders, piers or floating buoys – can generate turbulent wakes which, at times, make prey available to surface foraging seabirds, such as terns.
For this research, marine scientists from Queen’s University Belfast, Plymouth and Bangor University focused on a tidal channel linking Strangford Lough, in Northern Ireland, with the Irish Sea.
The researchers investigated the number of terns feeding at two natural wake sites, a rock island and a whirlpool, and a man-made site – the SeaGen tidal energy structure.
While terns searched for food at all three features, tern numbers on average were highest at the man-make wake, which also experiences the highest currents.
Dr Lilian Lieber, Bryden Centre Research Fellow from the School of Chemistry and Chemical Engineering at Queen’s, led the research. She explains:
“The aim of our study was to understand predator responses to environmental change; such as how man-made structures cause changes to local flow dynamics and how this may affect seabird foraging. We found that SeaGen’s wake has the power to mix up the entire water column, making potential prey items more accessible to foraging terns, similar to a prey conveyer belt. We used a combination of vantage point counts, drone flights, hydrodynamic modelling and hydroacoustics (using sound to measure underwater characteristics) and found that SeaGen’s wake generated the most intense foraging hotspot for terns, coupled to the flood tide.”
Co-investigator Dr Alex Nimmo-Smith, Associate Professor in Marine Physics at the University of Plymouth, used UAVs (drones) to record video from above the wake features to observe the exact seabird foraging regions in relation to the turbulence in the water.