The 35-year battle to eradicate 500,000 rats from a Welsh island

A 35-year mission to revive an island's most celebrated residents is at last bearing fruit. More than two centuries after Ynys Seriol's puffin population was decimated by rats from a shipwreck, the seabirds are flourishing once more. The full account of how the Anglesey colony was rescued, along with the obstacles encountered along the way, can now be revealed for the first time. The pivotal moment came with the unexpected arrival of rabbits on the island – a strategy that conservationists had previously dismissed. Nobody has ever taken credit for it. At its peak, an estimated half-a-million rats were wreaking havoc across the rocky island, situated off southeast Anglesey. While professional pest controllers battled the troublesome invaders, just two rats remained until they too were eliminated last year. A central figure in the campaign to rescue the island's puffin population was Jason Zalot. As head skipper at Anglesey Boat Trips, which forms part of the Seawake group, he operates regular boat excursions to the privately-owned island. As a younger man, and with approval from the then Countryside Council of Wales (CCW), he assisted in transporting four tonnes of rat poison to Ynys Seriol (also known as Puffin Island) during the 1990s, reports North Wales Live . "It killed most if not all of the rats," he said. "But by then the grass had grown high, leaving few open spaces for puffins to burrow. "To keep down the grass, and to tackle brambles, it was suggested that goats be imported from the Great Orme at Llandudno . This idea was dropped when CCW realised the goats would need to be vet-checked twice a week and water stations would have to be supplied. It was too expensive. In any case, introducing a non-native species was considered a bad idea." The alternative approach involved rabbits. The island once had substantial rabbit populations grazing the land, but myxomatosis wiped them out during the 1950s. On Ynys Seriol, this led to unchecked vegetation growth, creating even less favourable conditions for puffins. "Long grass isn't ideal for rabbits either," said Jason. "They get cold, wet and eventually die. So we spent two winters cutting back the vegetation. It was hoped rabbits would dig burrows and share them with puffins, as happens on Skomer Island off southwest Wales." In the end, the ambitious rabbit initiative was also shelved: Jason noted they were likewise regarded as an introduced species. Nevertheless, conservationists remained confident they would prove effective. "At the time, someone said to me that, if rabbits were to mysteriously appear on the island, it would be really handy," said Jason. "It just so happened that some rabbits did appear on the island shortly afterwards." With tongue firmly in cheek, he added: "Maybe they swam across." At its height, over 50,000 puffins inhabited the uninhabited island. They coexisted with the monastic remains of St Seiriol and, from 1841 onwards, a semaphore station. In 1816, the puffins' peaceful existence was disrupted by the wreckage of a wooden-hulled sailing vessel from Liverpool. Forced ashore near Penmon Point amid a violent storm, all crew members survived. Other survivors included brown rats. Swept by currents to Puffin Island, 800 metres from Penmon Point, they landed in what amounted to rat heaven, eagerly plundering shallow burrows for puffin eggs and chicks. Even now, shipwrecks remain a serious danger to fragile seabird populations. When a fishing vessel became stranded off Skomer island in December 2022, it prompted a rigorous biosecurity response from the Wildlife Trust to stop rodents reaching the island. A single pregnant rat can generate a colony exceeding 300 in merely eight months. By 1971, Ynys Seriol was overrun by an estimated 500,000 rats. As rat populations grew, the island's puffin colony was devastated. By 1907, numbers had fallen to approximately 2,000 birds. Decades afterwards, when Jason was distributing four tonnes of poison, fewer than 20 puffin pairs were officially remaining. Jason believes the actual figure was nearer "five or six". The poison proved effective. By 1998, the CCW was announcing that the island's rats "appear to have been eradicated". Rabbits possess swimming abilities but typically steer clear of water when possible. Regardless of how they arrived on Ynys Seriol, they became established and began controlling the vegetation. Success for the puffin colony appeared within reach. Unfortunately, it proved short-lived. During 2021, S4C's Cnefin series visited the island. Leading the expedition, Jason, 55, was dismayed to find rodent intruders had returned. "I saw so many rat holes, it looked like someone had gone around with an Uzi submachine gun," he said. "The south east of the island was crawling with them again. They reckon the rats must have swum over from Penmon Point. It was very disappointing." Rats are proficient swimmers - capable of travelling up to 1km in open water and treading water for three days. Nevertheless, Jason was astonished. "It's like us being able to swim the Atlantic," he shuddered. "They probably crossed on a high spring tide when the gap between Penmon and Puffin Island is smaller." Confronted with this renewed danger, a partnership of organisations including North Wales Wildlife Trust and CCW successor Natural Resources Wales launched a fresh eradication campaign. Jason said it was an impressive operation. "They set about a three-year programme of putting rat poison down runs in winter," he said. "They covered every speck of the island. They even has aerial access teams to reach cliff areas. "They deployed motion cameras and even brought in a dog to look for rats. They were that good, they knew only two rats were left - and they knew where they were and what they were up to." Three years ago, a cocker spaniel called Jinx was brought in to prevent invasive species from reaching Welsh islands. His role formed part of a £250,000 project backed by the Welsh Government . Following two years of training with the RSPB to detect rats, the UK's first conservation detection dog was set to work. In March 2025, the final two rats on Ynys Seriol were tracked down and eliminated. The positive effects are already becoming apparent. "We are seeing more and more puffins," said Jason, who makes daily visits to the island. "At one point, only five or six were left, now we're up to 120 and that number is increasing. "Puffins have a four-year cycle. As chicks they leave at the end of July and don't return for four years. When they do, they pair off to breed for the next 30 years, producing one chick per season. "As the island has been rat-free for a little over 12 months, we should see the colony expanding in the coming years. Already this year we've seen record numbers. New areas of the island are coming back to life and young birds are returning for the first time." All of this represents welcome news for Jason and his visitors, who are transported to the island aboard powerful, high-speed boats. Upon arrival, they enjoy a leisurely stroll around the island. "We have all sorts, from Manchester United footballers who like the high-speed thrills and spills, to others who want the David Attenborough stuff," he said. "This morning we had Julia Gillard on board - she was Australia's first female Prime Minister. We had no idea, she gave a different name, but one of the passengers came up and said, you know who that is, don't you? "We can get the boat so close, we have puffins flying in to land just over our heads. And things change every day - today we had fledgling cormorants coming down to the water's edge. It's always interesting." While the island takes its name from its puffins, it is actually cormorants that dominate, with the UK's largest colony residing here. Other residents include grey seals and numerous other seabirds. Anglesey Boat Trips runs two high-speed RIBs from Beaumaris, both equipped with V8 outboards. Further details can be found here.