The 35-year campaign to eradicate half a million rats from North Wales island
A 35-year quest to restore the fortunes of an island’s most famous inhabitants is finally paying dividends. More than 200 years after Ynys Seriol’s puffin colony was ravaged by shipwrecked rats, the birds are once again thriving. The inside story of how the Anglesey colony was saved, and the setbacks it suffered, can now be told for the first time. The turning point was the mysterious appearance of rabbits on the island – a move ruled out by conservationists at the time. No one has ever claimed responsibility.
At one point, an estimated half-a-million rats were running riot of the rocky island, which lies southeast of Anglesey. As professional exterminators waged war against the pesky invaders, just two rats held out until, last year, they too were dispatched. A key protagonist in the fight to save the island’s puffin colony was Jason Zalot. As chief skipper at Anglesey Boat Trips, part of the Seawake group, he runs regular boat tours out to the privately-owned island.
As a young man, and with the blessing of the then Countryside Council of Wales (CCW), he helped shift four tonnes of rat poison to Ynys Seriol (aka Puffin Island) in the 1990s. “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 next solution was rabbits. At one time the island was heavily grazed by rabbits but they were wiped out by the myxomatosis virus in the 1950s. On Ynys Seriol, this had caused vegetation to increase, making it even more hostile 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.” Ultimately, the great rabbit experiment was also abandoned: according to Jason, they too were considered an introduced species. Yet conservationists were convinced they would do the trick. “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.” 'Rat paradise'
At their peak, more than 50,000 puffins lived on the uninhabited island. They shared it with the monastic ruins of St Seiriol and, from 1841, a semaphore station. In 1816 the puffin’s idyll was shattered by the loss of a wooden-hulled sailing vessel from Liverpool. Driven ashore near Penmon Point during a severe storm, all crew members were rescued. Other survivors included brown rats. Carried by currents to Puffin Island, 800 metres from Penmon Point, they washed up in rat paradise, greedily raiding shallow burrows for puffin eggs and chicks.
Even today, shipwrecks continue to pose significant threats to vulnerable seabird populations. When a fishing boat ran aground off Skomer island in December 2022, it triggered a strict biosecurity response from the Wildlife Trust to prevent rodents reaching the island. A single pregnant rat can produce a colony of over 300 in just eight months. By 1971, Ynys Seriol was infested by an estimated 500,000 rats. At rat numbers expanded, the island’s puffin colony was decimated. By 1907, it was down to around 2,000 birds. Two decades later, when Jason was deploying four tonnes of poison, fewer than 20 puffin pairs were officially left. Jason understands the number was closer to “five or six”.
The poison worked. By 1998, the CCW was declaring that the island’s rats “appear to have been eradicated”. Rats return
Rabbits can swim but most will avoid water if they can. However they managed to reach Ynys Seriol, they became established and set about keeping vegetation in check. Success for the puffin colony beckoned. It was only fleeting. In 2021, S4C’s Cnefin series paid a visit to the island. Guiding the trip, Jason, 55, was horrified to discover rodent invaders were back. “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 excellent swimmers - they can cover up to 1km in open water and tread water for three days. Even so, Jason was staggered. “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.” Faced with this renewed threat, a coalition of groups including North Wales Wildlife Trust and CCW successor Natural Resources Wales, mounted a fresh extermination offensive. 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 employed to stop invasive species reaching Wales’ islands. His appointment was part of a £250,000 project funded by the Welsh Government. After training for two years with the RSPB sniffing out rats, the UK’s first conservation detection dog was launched into action.
Record puffin numbers
In March 2025, Ynys Seriol’s last two rats were finally cornered and killed. The benefits are being felt already. “We are seeing more and more puffins,” said Jason, who visits daily. “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 which is good news for Jason and his customers, who are conveyed to the island on bone-rattling, high-speed power boats. Once there, they have a slow meander 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.”
Although the island is named for its puffins, it is cormorants who rule the roost, being the UK’s largest colony. Other inhabitants include grey seals and myriad other seabirds. Anglesey Boat Trips operates two high-speed RIBs from Beaumaris, both with V8 outboards. Excursions are 100% recommended by Facebook reviewers. Details on can be found here. The North Wales Live Whatsapp community for top stories and breaking news is live now - here’s how to sign up.
