Coastal areas are diverse habitats. This interface between marine and terrestrial habitats supports groups of animals happiest in water and land, respectively. It also represents home for a few specialised and robust species that choose to have the best of both worlds by living in the extreme intertidal habitats. This aggregation of marine, terrestrial and intertidal species presumably explains the high diversity of life in coastal areas. However, for marine mammals and seabirds, there may be other reasons why coastal areas are so appealing. Currents are highest alongside coastlines, due to the energy of the oceans being squeezed into shallower areas, causing water to accelerate. Topography is also most complex at coastlines, with features such as headlands and islands dominating certain areas. As these fast currents interact with complex topography, water starts to spin and swirl, and turbulent structures characterised by unpredictable and unstable movements emerge. Such flows are not favourable for controlled swimming, and the shoals of small fish that feed predators are unable to escape or react to predators easily. Therefore, where you see boils or standing waves on the water, you often see a marine mammal or seabird.
Harbour Porpoise are frequently observed using turbulent structures emerging from
headlands and islands. Here an individual use seen breaching within a boil at Bull Bay.
This is particularly true in north Anglesey. If walking along the cliff-path, many people’s attention is drawn to the marine mammals and seabirds using the narrow strip of water along the coastline, in particular the incredibly high numbers of harbour porpoise. If you looked a bit closer, you would also see the turbulent structures that these animals are exploiting. You may notice that those emerging from headlands or islands bear a resemblance to those behind piers, breakwaters and tidal stream turbines. This is an example of how coastal developments not only change the aesthetics of the landscape, but also processes associated with the habitat they occupy. As we know that the behaviour of marine mammals and seabirds is strongly influenced these processes, an understanding how animals use currents and topography can help mitigate impacts on populations.
At the School Of Ocean Sciences, we have been studying marine mammals and seabirds across North Anglesey since January 2017. We have selected seven locations that are characterised by a wide variety of physical conditions – from sheltered and placid bays to exposed and dynamic headlands. In surveys lasting upto 2 hours, an observer records the total number of animals using each site every 5 minutes. These are then linked to detailed information on the current and turbulence properties at that location. We are now starting to analyse our results in detail. However, early outputs suggest that areas characterised with intense turbulence are consistently used by a wide variety of species across all seasons. Interesting, the introduction of human structures in coastal regions increases turbulence by increasing topographical complexity. Therefore, our results suggest some possible benefits of coastal developments for our populations of marine mammals and seabirds. Despite this, we must ensure that the structures themselves do not harm animals. For instance, collisions between diving animals and tidal stream turbines remains a concern – as do strikes between slow-moving marine mammals and ships using breakwaters and piers, for instance. We need to consider all these possibilities when deciding whether to install structures.