How did Spanish ‘strawberry trees’ make their way to Lough Gill?

Late naturalist Dan Cotton chronicled the Sligo coast, from lost whales to alien species

Janthina sea snail. Illustration: Michael Viney

As a beachcomber I was only trudging after him – the diligent, dedicated Dr Don Cotton up there on the Sligo shore, and me, following in the fox's footsteps along the tideline of Thallabawn.

There was the day I was thrilled to pick up two glossy Janthina, the fragile, purple-shelled sea snail that travels the ocean hanging upside down from its raft of self-blown bubbles. Even Rachel Carson, the great biologist of Maine, had to buy herself a specimen. Cotton, head down in the wind, gathered hundreds before he turned for home.

Cotton, who died peacefully at home last week, called himself an ecologist, and in the span of his study of the natural world he was certainly that. But he was also this country’s finest modern naturalist, which is a being all its own.

As ecology breeds more intense specialisms about separate species and their interlinks, the naturalist holds the door wide open, gathering living facts and figures with a passionate appetite for adding to the knowledge now called data.


Cotton came to Ireland from the UK in 1976 to do postdoctoral research at UCD on the impact of new farming practices on the ecology of soil invertebrates. Earthworms held his first concern. Then he moved to Sligo to lecture in ecology and geology at the Regional Technical College.

For him, the counties of Sligo and Leitrim, along with their shores and seas, were endlessly, intensely absorbing. “Anything to do with the environment and wildlife, I threw myself into it,” he said, “and one of those things was the collection of data.”

Alien plants

By the time of his retirement he reckoned he had spent an hour every day since 1994 compiling a database with 150,000 records of woodlice, harvest spiders, butterflies, moths, bumblebees, flowers, birds and mammals. He also analysed the wildlife content of 2,400 publications dating from 1850.

Such assiduous fact-gathering earned a Distinguished Recorder Award from the National Biodiversity Data Centre. It also enriched “a computer book”, a “Natural History of Sligo and Leitrim”, long accessible online through the technical college network. The future of this precious ecological and public resource seems, for the moment, unclear but it must be secured and promoted.

Cotton was part of every survey that came along – winter birds, wetlands, dragonflies, choughs, whooper swans, barnacle geese. He worked for four years to plot the plants of Sligo and Leitrim for the New Atlas of British and Irish Flora, research that raised his concern about the spread of alien plants.

It was the Sligo tideline, however, and its litter of drift that drew his sharpest speculations, from exotic plastic debris to the sad stranding of whales. He helped found the Irish Whale and Dolphin Group and was its onetime chairman.

He documented Sligo’s share of the beaked whales washed ashore in 2018, an exceptional event suggesting naval sonar mayhem far offshore. He compiled records of walruses visiting Ireland, testing each for authenticity.

His study of Atlantic flotsam included some enormous objects, such as a vagrant barge arriving from Newfoundland. Cotton computed its 82-day drift at 35 km a day. A message in a high-riding, windblown plastic bottle took longer in 1987, but set a record for reaching Sligo from St John’s, Newfoundland, in 127 days at an average daily speed of 24.6 km. Such computations mattered to knowing how long a drifting seed may spend in the sea.

Strawberry trees

His papers for learned journals were many and various: a first Irish record of a river snail; two earthworms new to Ireland; an armada of Noctiluca jellyfish; the pied wagtails of O’Connell Street, Dublin; a mass stranding of pram shrimps; a white skate in Sligo Bay; and more .

His last research project, with botanist Micheline Sheehy-Skeffington, was published in the current Sligo Field Club Journal. It explores the history of the last “strawberry trees”, Arbutus unedo, leaning out for light above the lakeshore around Lough Gill.

The beautiful Arbutus is one of the “Lusitanian” species in Ireland, with its nearest native home in northern Spain. Its Irish stronghold is on the shores of Killarney’s lakes, and the trees at Lough Gill have been a mystery. Growing at their climatic limit, had they rooted naturally as “natives” or were they introduced by the local estate family at Hazelwood House?

Cotton spent two days sifting estate records in Sligo Library but found no trace of Arbutus. Ancient pollen suggested a longer-term introduction. Next week’s column describes research at Killarney that hints at the possible, if least guessable, reasons how and why the trees arrived in Ireland.