Otter comeback is good news for water voles, bad news for mink.

22/03/2007 00:00:00

Research shows that recent increases in otter numbers in many parts of the UK have led to a decline in mink numbers. American mink and European otters can compete for food or other resources. During the last 20 years or so, the otter has made a dramatic recovery in distributions and numbers after a long decline. Research by WildCRU (Oxford University Wildlife Conservation Research Unit) found a significant link between the increase in otter numbers and the decline in mink.

The evidence

• The decline in mink occurred mostly in the west and north of England, where otter populations have reached considerable densities.
• Mink continue to increase in the east and south of England, where otters are still scarce.
• There is particular potential for competition between otters and mink as they are both semi-aquatic. Furthermore, inter-specific competition among carnivores often involves direct aggression and may have particularly strong effects.
• In 1999, The Otter Trust released seventeen otters into the Upper Thames, where there was already an established population of mink but virtually no otters. Mink declined sharply in the region after the otters were released, while a neighbouring population of mink, free from otter competition, appeared to remain stable.
• There is no evidence that mink have been affected by pollution, disease, trapping or polecat predation.

The reasons for the otter impact on mink are still unknown. However, mink do change their diet in areas where otters are common, eating more terrestrial rather than aquatic prey, possibly to avoid competition. A fall in American mink numbers in the UK would be very welcome amongst those who are concerned with the conservation of native species, especially the highly endangered water vole. Water voles numbers crashed in Britain as a result of habitat loss and mink predation, and they are now threatened with national extinction. Let’s hope that otters will disturb mink sufficiently to allow water vole populations to recover without further human intervention.

Taken from the mammals trust report on the state of 'Britain's mammals 2006'. For further information, to go http://www.mtuk.org/