Otters and waterways - the health status
of otters (Lutra lutra)
in
southern
and south west England
1988-22005
Summary of a fascinating talk delivered at the October AGM 2005 by V R Simpson of the Wildlife Veterinary Investigation Centre, Chacewater, Truro.
Introduction
Vic had been carrying out post- mortem examinations of otters since 1988 to investigate factors linked to the otter population crash of the 1950s –1970s. Initially this was at the Polwhele Veterinary Investigation Centre (VIC), Truro and since 2001 at his Wildlife VIC, Chacewater. Some 80% of these deaths were road casualties and his detailed reports were sent to the finder, the Cornwall Wildlife Trust and the Environment Agency which has a policy of waterway enhancement for wildlife and was a significant funder of the project. A steady increase in the number of deaths was noticed first in Cornwall and then, as otter colonisation spread eastwards over time, included Devon, Somerset, Dorset and Hampshire.
Good news
Analysis of the livers showed that the concentration of dieldrin and DDT had dropped over time after these pesticides were removed from the market. Alongside a fall in pollutants, the liver vitamin A levels, which had been very low, increased. This was good news as the otter numbers were increasing, and the population spreading.
Otter deaths by month
Road traffic casualties
As the population expanded the number of otters submitted each year increased steadily and 83% were traffic casualties. Total deaths were noted to be strongly linked to the hours of darkness but the highest percentage of road traffic kills occurred in mid/late summer when total submissions were low.
Bite wounds
During the course of examining over 500 dead otters, bite wounds were seen commonly on the face, feet and genitals of both sexes. The spacing of teeth marks gave clues as to the origin and although Vic believed most bites were caused by other otters, a small proportion, spaced at 9-10mm, were associated with mink. Although an otter might win the fight, death could occur later as wounds went septic Cubs and a few immature animals were often killed by domestic dogs Since 1988 Vic had seen a huge increase in the percentage of dead otters with bite wounds which had risen to over half by 2003 which was attributed to increased population pressure.
Otters with bite wounds
The highest percentage of adults appeared to have been bitten in the mid-late summer period whilst the sub-adults 1-1.5 yrs suffered most in the winter.
Dental
lesions
The proportion of otters with teeth missing or fractured increased possibly as a result of fighting. This was not the whole story as damage to premolars due to biting hard objects, possibly from small stones or gravel contaminating food, was also seen. How common was this in living animals? Bacterial infection from damaged teeth was common, and serious, spreading easily from the root to other organs, particularly lungs and heart.
Other observations
There was no immediate explanation for an observed increase in kidney stones since 1996. There was encouraging evidence that some 40% of all the females had bred successfully. A colleague had shown that the most significant part of the otter diet was eels, followed by roach, bream, bullhead, salmonids and amphibians. Catches of loach, pike, birds and mammals had also been found.
Questions
What is the true mortality caused by fighting? Otters dying in road accidents are much more likely to be seen and submitted for examination than otters dying in the countryside and mortality in otters from aggression could be as important as road accidents. Are otters that are in conflict with other otters more likely to be killed by road traffic? In this case, the animals Vic had examined are not truly representative of the population.
Otter deaths per year by county
The Bile Fluke
In 2004, during the course of this work, Vic had discovered a new parasite, Pseudamphistomum truncatum, in the gall bladders of 3 dead otters from Somerset. The first appearance of thickened gall bladders had been noted in Feb. 2000 from an animal in Dorset. By August 2005 the parasite had been identified in a total of 10 otters, mostly in the Somerset Levels. Two mink from Somerset were also shown to be infected although they were not obviously ill. The flukes live in the gall bladder and can cause liver damage and jaundice. Since otters and mink are non-migratory and can only be infected by eating fish, it can be deduced that fish in the area were infected.
Fish hosts
The parasite is well known from fish in Russia and Eastern Europe where it affects otters and their relatives as well as cats, dogs and even humans when raw or Bile flukeslide circa1mm undercooked fish is eaten. In the UK it is thought to have been spread by escaped ornamental fish – the sunbleak and topmouth gudgeon – imported to Romsey, Hampshire in the mid 1980s, although mammals imported from affected regions might be implicated.
The sunbleak has colonised the Somerset Levels, matching the distribution of the fluke in otters. To date, the parasite may be contained within the county but experts are worried that it could spread to other areas and also be passed on when animals, like cats, dogs, otters and foxes eat raw fish which have been infected.
Pseudamphistomum truncatum
This emphasises the importance of continuing this painstaking work in the interests of the wildlife and the adjacent human population. Vic warmly acknowledged the help of volunteers at the Wildlife VIC, staff at the County Wildlife Trusts and the Environment Agency, a major funding body, and last but not least his wife, Jane, who assists with the work in many different ways.