Where the River meets the Sea: The Shannon Estuary
River estuaries have always had a special allure for me. These wide expanses that are neither river nor ocean, neither land nor sea, are being shaped by the endless rhythm of the tides on one side and the flow of the river on the other. At high tide, there is just a wide swathe of water; only low tide reveals the intricate pattern of channels and runnels that have been carved into the vast areas of sand and mud by the flowing waters, and this strange landscape is teeming with life.
The Shannon, together with the Fergus River, which joins the Shannon near Ennis, form Ireland’s largest estuary complex, and the vastness of these mudflats is enthralling. I remember a New Year’s morning waiting for the sunrise at Drumquin Point, south of Clarecastle, close to where the Fergus meets the Shannon. Here, the mudflats extend to the horizon. It is a vast world of waterlogged sand and mud, understated but dwarfing everything in its vicinity. Its smooth, reflective surface is only disrupted by the network of channels that grow tree-like through the dense substrate. As light levels rose on this cold and overcast winter morning, the damp surface of the mud started to glow in the colours of dawn: bluish at first, then slowly turning into shades of purple and magenta. Just before sunrise, the expanse glared in rich red and orange tones, then the sun rose over the horizon, quickly disappearing behind the clouds and the estuary returned to muddled shades of brown.
In the dull winter twilight that followed, the sounds of the estuary echoed eerily across the wide open landscape. The oystercatchers announced themselves with a high-pitched, sharp call, and seconds later a group of birds zipped by, flying close to the surface to find a quiet place for breakfast. The striking colours of the birds, the black and white body and the bright-red beak, were, however, muted under the dark sky. Further out on the mudflats, dark shapes moved here and there in search of food. Some strode gracefully, others scuttled randomly, and yet others stood motionless. The air was filled with chittering, whistling, bubbling and chirping, one of the most beautiful soundscapes I can imagine. The sound of the estuary.
The Shannon Estuary stretches for some one hundred kilometres between Limerick and the Atlantic Ocean, which it meets between Kilcredaun Point on its County Clare side and Kilconley Point in County Kerry. Here, the wide waterway opens even further into the mouth of the Shannon. This expanse of water is enclosed by sheer cliffs, and its entrance is marked by the headlands of Loop Head to the north and Kerry Head to the south. Beyond those headlands lies the open Atlantic.
The Shannon Estuary is a bit of a paradox. For centuries, this waterway has been one of the main routes into Ireland for both passengers and goods, as well as an important fishing ground. While local fishery has been in decline for a while, goods are still being brought into Ireland via the Shannon Estuary and unloaded at the deep-water port at Foynes, which is one of the biggest in Ireland and handles cargo from all over the world. Not too far away from Foynes sits Shannon Airport, one of the major airports of the country, on the banks of the estuary. There is also the controversial Aughinish Alumina plant and two coal, oil and gas fired power stations, one at Moneypoint on the Clare side and one in Tarbert on the Kerry side. Those not only add to the shipping traffic but also pose a constant threat to the fragile habitats of the estuary.
Despite this human presence, the Shannon Estuary is one of Ireland’s most intriguing and important sites for wildlife. The sheer cliffs around the mouth of the Shannon are breeding sites for fulmars, kittiwakes, guillemots and razorbills that arrive in their hundreds in early spring, turning the coast into a cacophony of cackling, growling, whistling and twittering. One reason for these birds to choose the mouth of the Shannon as their nesting site is the rich food supply. Herring and sprat are abundant, and these not only attract the local nesting population but also animals from further afield. Gannets have their nesting site on the Skellig Islands, some one hundred kilometres south, but are a common sight at the lower estuary during the summer.
The shores of the estuary are also home to some permanent residents. Cormorants and shags, along with herring gulls, lesser black-backed gulls and greater black-backed gulls still appear in high numbers, while rarer species like the chough, unmistakable with its red beak and legs, and the raven, with its wonderfully eerie croak, have established a stronghold here.
After the summer visitors have reared their offspring and left the cliffs in a sprinkled black and white pattern – a painting of guano on rock – they return to the open ocean to make space for the winter visitors. The Shannon Estuary features a good number of small islands and sheltered creeks, inlets and bays, most of which reveal wide sandy beaches and vast mudflats once the tide is out. These places are the perfect wintering grounds for waders and waterfowl, providing not only a rich food supply but also protection from the worst of the winter weather. Brent goose, whooper swan, lapwing, curlew, greenshank, redshank, golden plover, knot, dunlin, wigeon and others join resident birds like the grey heron, little egret, oystercatcher, ringed plover, snipe, shelduck and mallard from October onwards.
From a distance, the mudflat, this expanse of glorious mud and sand, appears dull and lifeless. A closer look, however, reveals an abundance of life . Mudflats consist of very small sand particles, smaller than the grains found on a sandy beach, that have been moulded together by tidal currents. The electrical charge that causes repulsion between the grains is very much reduced in the tiny particles that form the mudflat. This makes them stick together more easily, and the inhabitants do the rest by adding mucus and faeces to the mix. The result is a very stable habitat that can resist the action of the tides much better than a sandy beach.
Most of the mudflat community lives underground. Apart from single-celled organisms like diatoms (a type of algae), cyanobacteria and flagellates, worms – including the lugworm and the sand mason – and bivalves – among them the cockle, razor shell and scallops – are the main inhabitants. Both worms and bivalves are an important food source for crustaceans like crabs and lobsters, the various fish species of the estuary, and the waders, who are uniquely adapted to search for this kind of food. Birds with long beaks like the oystercatcher are tactile foragers and actively probe the ground for prey. Birds with shorter beaks like the plover are visual foragers. They wait for signs of activity, and only go in when they notice movement under the surface. These different feeding methods become obvious in the behaviour and movement of the birds. While the oystercatcher roams in a rather calm and organised way, probing the ground with every step, plovers are all over the place, running, stopping, looking and running again, without showing any discernible pattern in their movements.
Adjoining the mudflat in many places is a saltmarsh. These areas are often dominated by the common cord grass. This invasive species is a hybrid between the native small cord grass and the smooth cord grass, which was introduced from North America. Initially this hybrid grass, with its dense rooting system and thick growth on the surface, was very welcome and used to stabilise the coastline. Soon, however, the common cord grass took matters into its own hands and spread aggressively all along the Irish coast. Today, it is not only a threat to the native flora, but the common cord grass also takes over feeding and roosting sites for waders and wildfowl. Where the common cord grass hasn’t invaded yet, the native saltmarsh flora, which includes a number of salt-tolerating wildflowers, still thrives. Throughout spring and summer, a trio of purple flowering plants add a splash of colour to the landscape of the saltmarsh. It starts in April with thrift, also known as sea pink, which often grows side by side with scurvy grass, a small white flowering plant . In summer, sea lavender appears, with its delicate, tiny flowers, followed by the striking sea aster, whose yellow and purple flowers turn into fluffy seed heads towards the end of the season.
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Away from the shore lives a somewhat unexpected group of animals that are locally known as the Shannon Dolphins. They are bottlenose dolphins and form one of only a few resident groups in the whole of Europe. The Shannon Estuary has been their home for hundreds, if not thousands, of years. One of the earliest accounts of the Shannon Dolphins might be found in the local legend of the Cataigh (or Catach), a sea monster that claimed Scattery Island, one of the small islands of the estuary. It was described as an enormous eel with a line of sharp barbs along its back and dagger-like teeth that were long enough to curl around the island. Because there is some truth in every legend, it is likely that there really was a sea monster – or in this case, probably many of them. Witnessing a group of dolphins travelling with their fins cutting through the water, one could indeed imagine an eel-like creature swimming along, and a close look at a dolphin’s teeth indeed reveal dagger-like shapes.
Today, over one hundred dolphins are present at the estuary at any given time. Of those, around forty are permanent residents, while the others come and go throughout the year. The Shannon Dolphins travel in groups which can consist of up to twenty individuals but are on average considerably smaller. While these groups are very fluid, known as ‘fission-fusion’ society, it is generally individuals of the same sex and age that travel together. Groups of mothers with calves, for example, can regularly be seen in the Shannon Estuary.
The reason the estuary is so popular among dolphins is the same as it is for birds: the rich food supply that is being brought in by the strong tidal currents. Bottlenose dolphins in general live on a diet of fish, squid, and sometimes small crustaceans. The Shannon Dolphins are most likely mainly fish eaters, feeding on resident fish like bass and various species of flatfish as well as pelagic species like herring or sprat that venture into the estuary. In late summer and autumn, salmon becomes a major part of their diet and the animals can be seen tossing salmon in the air, a behaviour that is probably associated with both playing and learning.
Bottlenose dolphins travel and hunt in small groups and find their way – as well as their prey – through echo location. While a dolphin’s eyesight is similar to our own, it is of little use in the often murky waters of the estuary, so echo location is a much more reliable method to get around safely. The dolphins emit a series of pulses and clicks from an area near their blowhole known as the melon. When these sounds hit a solid object like a fish or a boat, they bounce back and the dolphin picks up those echoes through its lower jaw, from where they are transmitted to its inner ear. Because sound travels five time faster in water than in air, this way of experiencing the world is very effective. It is also thought that certain variations of those clicks and pulses, along with whistles, are a form of communication between the animals. Tailslapping can also be a kind of communication. Depending on the strength of the slap, this behaviour could be a warning to other animals or an attempt to make contact. Tailslapping has also been observed as part of hunting techniques to stun the prey. Another popular hunting technique that can be observed on the Shannon is a group of dolphins circling a school of fish to keep them together, while individuals repeatedly dash into the tightly packed ball of fish to feed.
Dolphins are not the only marine mammals in the Shannon Estuary. Other cetaceans, especially minke whales, regularly find their way into the area, and bigger whales like humpbacks and orcas can be seen passing or feeding off the headland of Loop Head. Common seals are regular visitors, while grey seals are known to rear their young in the small storm beaches at the mouth of the Shannon and the lower estuary. Unlike common seal pups, who can swim within hours of birth, the offspring of the grey seal is born with a white fluffy coat that needs to be shed before the youngsters can enter the water. This takes up to six weeks, and during this time both mother and pup are stationary, the pup hauled up on the beach while the mother patrols the waters around the cove. Seals are the source of another legendary figure, the selkie, which appears not only in local tales but legends all over Ireland and Scotland. Usually the selkie, like a mermaid , is trying to seduce and then cause harm to a fisherman that has done her wrong. Other stories tell of fishermen trying to trick the selkie into a life on land, where she will spend her days in human form as the mother of the fisherman’s children. Otters are also common, but their secretive lifestyle makes them a most elusive animal. They feed mainly on fish, and the size of their territories can range from two to twenty kilometres. The territories of coastal otters are usually smaller due to a better and more varied food supply, while river otters often occupy very long stretches of their chosen waterway. Spread throughout their territory, otters have a number of holts, or underground dens, that they use to rest and rear their young. Despite being seen very rarely, the Irish otter population is one of the most stable in Europe, and the Shannon Estuary is one of their strongholds.
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Human life and wildlife have so far been coexisting in a delicate balance at the Shannon Estuary. While the estuary itself is a busy shipping lane and the shoreline has been fortified and built up for industrial use in many places, there is sufficient room left for fauna and flora to thrive. This, however, doesn’t mean that all is perfect. The constant and ever-increasing shipping traffic causes significant noise pollution, which can especially affect the bottlenose dolphins. Industrial waste, untreated sewage and run-off from pastures that can contain chemical elements from pesticides and fertilisers all find their way into the Shannon Estuary, either directly or via its tributaries. Another growing concern is the sheer amount of plastic that is being brought into the estuary through the tidal currents. The upper reach of the tide that was once marked by colourful seaweed accumulations is today a mix of seaweed, plastic bottles and other containers, fishing nets, cans and other flotsam and jetsam of human origin. One of the biggest environmental threats in the area, and a long-running and controversial topic of discussion, is the Aughinish Alumina refinery. Red mud, also known as red sludge or bauxite tailings, is a waste product of the refining process that turns bauxite ore into aluminium. This red mud is highly toxic because of its alkalinity, and at Aughinish it is being stored in large reservoirs close to the estuary. Any leakage could have a devastating effect on all wildlife in the Shannon Estuary, and rumours about leakages, coverups and health problems of local residents have been around for many years. The other two major industrial buildings, the power stations at Killimer and Tarbert, had their own share of problems over the years but are now in the process of being shut down as part of the climate action plan. All in all, the future of the Shannon Estuary hangs in an uncertain balance, now more than ever.
Carsten Krieger, from "Wild Ireland"