Otters on the move

Over the past 5 years or so myself as well as many other people have noticed the gradual increase in range and density of Otters across Britain. In North Yorkshire I am fortunate enough to live less than 2 miles from an active territory. This has been occupied as long as I have been interested enough to look. Now it is pleasing to see other areas being occupied by otters. Much of East Yorkshires riparian habitats are unlike North Yorkshires. East Yorkshire is more intensively farmed and has less wild retreats. However the species is doing very well there, especially around the River Hull catchments. A sure sign that issues arising from agricultural intensification and river quality are changing for the better.

It is amazing what small ditches and tributaries otters can be found on. The site where the photo was taken below is a commercial fishery, which the otters access using a series of ditches which run through adjacent open arable land. Otters are strongly territorial mammals and often occupy large linear territories, which contain numerous holts or couches (resting places). Generally the animals in Yorkshire occupy territories between 5 and 10km, with a male territory often overlapping a number of smaller female ones. Otters are more than capable of ranging 10km in a night on hunting trips. The fact otters occupy such large linear territories means that they are extremely active when it comes to sprainting (marking the territory with spraints (droppings)), unlike foxes and badgers they are often far away from parts of the territory at any one time, making it essential to remind intruders that the area is taken.

This increase in numbers is not popular with everyone including fishery and fish farm owners. Where otters can cause financial damage to fish stocks. This is a subject for another post entirely. Otters largely declined across Britain during the 19th century, where otter hunting was a common practice. A small increase in numbers between the early 1900s and 1950s was soon cut short by the introduction of the cyclodiene organochlorine insecticides, with which we usually associate with declines in raptors. This was applied in an agricultural sense as seed dressings and in sheep dip. Like in the peregrine (and other predators), otters store these chemicals in their fat reserves, in which it slowly builds up with each poisoned meal the otter eats, eventually leading to secondary poisoning. In addition DDT (dichlorodiphenyltrichloroethane) is thought to increase blindness in otters. Modern causes of otter mortality are largely linked to road casualties and drowning  in eel fyke nets, lobster creels and fish traps.   

Above is the rather characteristic image showing where an otter (most likely a bitch or youngster) has left the water and moved up the bank. Otter prints show a characteristic set of 5 toes (sometimes the 5th does not register), these are rounded with a small nail. These sit in front of a large pad and are quite different to the star shaped slender toes of a mink. This photo was taken in East Yorkshire.