Isles of Scilly

The Isles of Scilly is a small Atlantic archipelago of five islands and over 100 islets 45km south-west of Lands End on the British mainland. St Agnes lies to the south, making it Britain's most southerly habitation.

St Agnes has a siamese twin in the small islet of Gugh and the two are joined by a tombolo sandbar that is above water at low tide. Together they cover an area of just 1.5 sq.km, barely reach 20m above sea level and are home to 85 people, including three living on Gugh. 

Best known for cut flowers that have underpinned its agricultural economy, today tourism is also important. Lesser known is that St Agnes and Gugh were probably the first permanently inhabited islands in the world where rodents, in this case brown rats, have been successfully eradicated. This was accomplished in 2013 using ground based poison bait stations.

Predator Eradication Project

Island Size
Small (tiny)
1.5 sq.km
Target Predators
Brown rats
Eradication Methods
​Ground baiting
Project Stage
Post-eradication
​Visited
​September 2018

St Agnes & Gugh Image Gallery

Click on an image to see a larger view with caption.
​Read more about predator eradication on St Agnes & Gugh below.

Brown Rats Eradicated

The Gains

Since the successful 2013 eradication of brown rats, both Manx shearwaters and European storm-petrels have, for the first time in living memory, begun successfully breeding again on St Agnes & Gugh. More than 40 chicks were recorded on the islands in the first two years after the eradication.

Of all the Isles of Scilly, St Agnes & Gugh have sufficient separation from other islands with rats that a rodent recolonisation by natural immigration is unlikely to occur. With rats now eradicated from St Agnes this also reduces the risk of rodents naturally colonising the nearby rat free island of Annet, a nationally important seabird nesting site.
​
The Task

Brown rats colonised St Agnes from shipwrecks in the 1700's. Their ecological impacts included the collapse of breeding populations of seabirds, such as Manx shearwater.

To eradicate them, 1,036 commercial lockable bait stations loaded with poison bait were distributed over both islands. These were set out with an average spacing of about 40 metres.

During 2013, these bait stations were intensively monitored until, in November, no further sign of rodents was present. The islands were declared rat-free after an extensive month-long search in 2016.
The Risks

Now rats have been eradicated from St Agnes & Gugh the key risk is that rodents recolonise the islands by:
​
  • visitors to the island arriving on scheduled ferry services
  • private pleasure craft arriving from anywhere in the world
  • freight arriving from the British mainland
  • rodents not being detected by the surveillance network focused on the coast
  • arriving rodents moving inland away from the coast and escaping detection by the coastal surveillance network 

Preventing Reinvasion

St Agnes is a short boat ride from Hugh Town, the main centre on the largest island of St Mary's. Several scheduled tourist boats bring visitors to the island every day during summer, private pleasure craft also arrive, many resident's have boats and there is also commercial freight to land.

​St Agnes & Gugh are probably far enough offshore to minimise the chance of rodents swimming to the island. The cold water and strong tidal flows further reduce the chances of reinvasion. However, the amount of sea traffic frequently crossing from island to island is a real risk for a rodent recolonisation of the island.

To counter this, the local community have established and maintain a string of rodent surveillance traps and bait stations right around the coast. These are checked by volunteers who maintain a sector each, make checks on a regular schedule and record their results. Wax blocks readily record gnawing, however the resident Scilly Shrew is a source of false alarms. So far this system has worked.

A Kiwi Connection

New Zealanders visiting the Isles of Scilly will quickly recognise a piece of home as native New Zealand coastal plants have been widely planted as shelter to protect flower fields from the strong Atlantic wind. Karo is now widespread but taupata, cabbage trees and pohutukawa can also be seen, some of which are now significant specimen trees.

As with many well intentioned introductions of flora and fauna, some of these species, particularly karo, have become invasive and are causing significant and growing ecological problems. Around one third of St Agnes is a Site of Special Scientific Interest with heath and dune grassland being home to a number of rare plant species.

If invasive karo were to change this open landscape to a treed habitat then significant ecological values would be compromised. Control of karo is being undertaken at a number of sites around the island, however the scale of the problem is daunting.