OTTER - MINK - WATER VOLE RELATIONSHIPS, A SUMMARY J O H N N Y BIRKS Since the American mink (Mustela vison) became firmly established in the wild in the 1950s, changing human perceptions of its impact upon native British f a u n a demonstrate the folly of leaping to conclusions based 011 circumstantial evidence. The decline of the otter (Lutra lutra) coincided closely with the spread of mink along our rivers in the 1960s and 1970s. To many people there was no doubt that the much smaller American invader was the culprit. However, there were other sinister changes taking place in the countryside at the same time which, on closer inspection, were found to be at the heart of the problem. T h e industrialization of agriculture, involving massive habitat loss and the introduction of persistent toxic chemicals had a serious effect upon wetland wildlife. The mink was a mere red herring, and subsequent research has shown that it and the otter can coexist readily. T h e water vole (Arvicola terrestris) has found it harder to survive alongside a vigorous new predator, particularly as the species has endured a long-term decline in Britain due to habitat loss, pollution and disturbance. For many populations the arrival of the mink was like the straw which broke the camel's back. H o w e v e r , that is not to say that the mink is the key agent of the water vole's demise, for the two do coexist in a stable predator - prey relationship in many places. Such places are characterised by the survival of high quality, extensive wetland habitat. Current changes in agricultural policy are providing opportunities to recreate some lost habitats. M a j o r improvements in the quality, extent and integrity of wetlands would, if implemented, help water voles and other wildlife to survive alongside the mink. Furthermore there is growing anecdotal evidence that mink populations are 'settling down' to a lower level as the otter continues its slow recovery following the phasing out of the agricultural chemicals which so nearly exterminated it. Dr. J. D . S. Birks, Conservation Officer, English N a t u r e , Masefield H o u s e , Wells R o a d , Malvern Wells, Worcs. W R 1 4 4PA
Nat. Soc. 29 (1993)
Plate 9: Melanistic W a t e r Vole (Arvicola North-west Suffolk. (p. 113).
this d a r k f o r m is not u n c o m m o n in the Fens of
Plate 10: E u r o p e a n O t t e r (Lutra
able t o co-exist w i t h the M i n k . (p. 113).
Plate 11: American Mink (Mustela of the W a t e r Vole. (p. 113).
vison), now firmly established in the wild and a vigorous p r e d a t o r