You know its going to be a good talk when extra chairs have to be brought out and that is exactly what happened at the St Magnus Centre Kirkwall on Friday night.
Anne Bignall was presenting her research on Orkney otters to a packed hall at an evening hosted by Orkney Field Club.
Anne has spent thousands of hours observing, photographing, filming and recording otters on the island of Eday .
According to Scottish Natural Heritage (SNH) it is estimated that there are 8,000 otters in Scotland. Visitors and locals alike to Shetland will comment on the frequency of seeing otters there during the day. Orkney seems to be different. Few and far between are daytime sightings of otters and Anne was interested to know why this was. Perhaps we have fewer otters? Perhaps they prefer nocturnal activities?
On Eday Anne had a closed but varied environment on which to carry out her research but even at that she had to restrict her observations to the coastal areas.
One way to look for otters (when they are keeping out of sight) is to find what they leave behind: spraint, otter poo is one sign to find. Anne had recorded where spraint was found round the coastline. But would this be the best way to count otters she pondered? It doesn’t tell you how many otters there are. The National Otter survey would suggest that there are 10 times more otters in Shetland than in Orkney based on this method.
Another method is to find the otter holts (where they live) and use a statistical method to then estimate how many female otters would on average use these holts. Estimates for Shetland using that method resulted in an otter count of between 700 and 800. The problem with using this to estimate numbers in Orkney is that otters must also be observed and a female otter will use several holts. As the otters in Orkney are difficult to see as they prefer to be active at night this means numbers based on this method are compromised.
Anne Bignall searched the coastline of Eday for holts, not an easy task as many are well hidden. Based on her findings she estimated the otter population on Eday to be between 14 and 25 adult animals but felt that this would be more likely to be the lower number.
Ten cameras were placed at holts but with 29 holts to be observed this was less than ideal. The video footage was exceptional and thrilled the audience with otter activity which is so scarce to see in Orkney.
From her extensive observations and research Anne felt that the otters were using the holts when the pups were young but choosing to go elsewhere once they were mature. The otters were also using burrows, places between rocks and sea caves.
The holts tended to be along the coastline but avoiding high cliffs. The free draining sandstone of Orkney results in their being a shortage of fresh water at times. Otters need plenty of fresh water. Pools that they can drink and bathe in. At certain times of year there would be a shortage of this and it may be why otters are limited and go elsewhere. The presence of peat was important in the building of holts. Rabbits also seem to facilitate their construction.
Otters can dive to a depth of 10m but most activity will occur at 2 to 3 meters. They will resort to eating almost anything, however, fish would be their main diet. In winter, with a shortage of food they will take anything they need to – rabbits, birds, etc.
Anne Bignall suggested to the audience that otters may be the only native mammal in Orkney having once swam here thousands of years ago. The number of otters in Orkney appears to be stable but much more research needs to be conducted to find out about these elusive mammals. Road traffic accidents and cub mortality rates are both high so although it is suggested the numbers are stable we don’t really know.
This was a fabulous and informative talk. It was an example of excellent painstaking research which it would be important to build upon and take further.