Wintle’s World of Angling – The Otter Part 1

Mark Wintle, an angler for thirty-five years, is on a quest to discover and bring to you the magic of fishing. Previously heavily involved with match fishing he now fishes for the sheer fun of it. With an open and enquiring mind, each week Mark will bring to you articles on fishing different rivers, different methods and what makes rivers, and occasionally stillwaters, tick. Add to this a mixed bag of articles on catching big fish, tackle design, angling politics and a few surprises.

Are you stuck in a rut fishing the same swim every week? Do you dare to try something different and see a whole new world of angling open up? Yes? Then read Mark Wintle’s regular weekly column.

The Otter

There has been much in the angling press over the last year or two about otters, and their impact on our lake (carp) and river (barbel) fisheries. My local Dorset Stour never actually lost all of its otters during the days of serious decline in the sixties and seventies but they were certainly very rare. It is only in the last three years that I have actually made three sightings on the Stour, two at dusk and one in the day. I seized the chance to learn much more about otters when the Dorset Otter Group arranged an open day. Here, I could speak to the experts, and perhaps get nearer some answers to questions like: – How many otters are there now? What is the RSPCA’s role in reintroducing otters? What do otters eat?

In this first article I shall describe how the otter population is re-establishing itself, how the population is estimated, and the perils it faces. I shall also describe the RSPCA’s role in rehabilitating otters.

Next week, in Part Two, I shall report on the findings of a study that is investigating what otters are eating in the Dorset Stour, and discuss how otter predation affects anglers and fisheries including preventative work.

There was a diverse range of speakers during the day, including Professor Paul Chanin (mammal ecologist), Adam Grogan (Wildlife rehabilitation officer for the RSPCA), Clair Rogers (Bournemouth University, studying what otters eat in the Stour), Bronwen Bruce (Dorset Wildlife Trust, who hosted the event), and Peter Irvine (Dorset Otter Group or DOG for short). Wildlife film director Hugh Miles also turned up. When asked why he was there, he said it was to find out how to kill the two otters eating all the carp in his pond that was connected to the Stour by a brook. Hugh was joking though there was an awkward silence for a couple of seconds!

How did the otter become so rare – Causes of the decline
Professor Chanin explained how otter numbers declined catastrophically from the fifties through to the seventies for a variety of reasons. These included otter hunting, loss of habitat mainly through dredging, and poisoning due to the use of first DDT and later the organochlorine pesticides that tend to accumulate in animals at the top of the food chain. With the banning of otter hunting and the pesticides, and a more sympathetic approach to land drainage, otter numbers are recovering well. In the South West of England this is especially true, and there are enough around to start to re-colonise rivers to the east. Some years ago there were some limited re-introductions using captive-bred otters but there was no longer any need to do this as introducing captive-bred otters into existing territories led to conflict. Certainly in my local area, I can remember small areas of riverside being set aside to encourage otters on the Stour, Frome and Piddle as long ago as the late seventies. These were often the inside of horseshoe bends, or old mill leats. On parts of the Dorset Stour, the otter never did totally disappear, and therefore reintroductions have not been needed. The massive dredging programs of the fifties, sixties and early seventies finally ended, giving nature a chance to provide cover on the riverbanks again.

Using DNA to establish numbers of Otters
One of the most difficult problems facing study groups such as the D.O.G. was establishing just how big the otter population actually is. Their territory can span many miles, as much as 25 miles for males, and 12 miles for females. One male might have several females within his territory. These are not always based on a single large river but can encompass several smaller streams and therefore cross watersheds. To try to establish how many individuals there are within a particular catchment Dr Chanin had been using DNA analysis from fresh spraints (droppings). The DNA in these spraints deteriorates quickly due to bacterial and exposure to sunlight so many volunteers have to try and collect it early in the morning (and I thought that it was only anglers that were mad!). These are preserved in ethanol and refrigerated before analysis. The scientists use a number of markers to try to determine unique identities for each otter but because of the close relationships between the otters in any particular catchment, this is not always possible. This technique continues to be refined, and one day may be sufficiently developed to always identify individuals.

As you might expect where there have been very few released initially, eg, just three on the Itchen, this results in inbreeding and genetic defects. But as otter numbers expand in neighbouring catchments, then you start to get a crossover. In time, you get a better mixed population as those that are inbred and weaker are squeezed out by natural selection/survival of the fittest.

Limiting factors on populations
The limiting factor on the population is complex but each clan requires a large area, with an adequate food supply. Food supply is the essential regulating factor on otter density. At present there are few areas with optimum density, most areas are under populated. There are more in the South West, Wye valley, but less in the South East and East Midlands. Otters will fight over territory, even kill each other. The main danger to otters is being killed on roads especially where a busy road divides two river catchments. Similarly, culverts under roads are difficult to swim through when water levels are high. In some areas, there are walkways to enable the otters to travel through the culverts. Fencing is used to prevent otters roaming onto roads in vulnerable places. Other causes include fights with other otters, eel fyke nets, and illegal killing. One of many interesting facts about them is that otters tend to drive out mink from their territories, and will kill them. Although mink (4lbs) are vicious beggars, they stand little chance against a full grown otter (20lbs+). A side effect of this is that as mink are driven out and habitat improved there may be a glimmer of hope for the water vole whose numbers have declined to calamitous levels, but are rising at last in Dorset.

The RSPCA and the rehabilitation of otters
If an adult otter is injured (usually from a road traffic accident) it will only allow itself to be captured if very seriously injured. Its chance of survival is very poor and the otter usually has to be put to sleep.

With cubs, the scenario is different in that the cubs may be orphaned. But before attempting to ‘rescue’ a cub the RSPCA has to be sure that it is genuinely orphaned, and usual practice is to leave it overnight if possible unless it is very distressed or in immediate danger.

The RSPCA keep the cubs for up to twelve months, at one centre in the company of other otters, to allow them to grow to full size. As the otter population has re-established itself, the RSPCA can no longer re-introduce the cubs into uninhabited (from an otter’s point of view) territory. Generally, the cubs are re-introduced into the catchment areas from where they were rescued. They have to take their chance with those already occupying the territory. To find out what happens to them after release, the RSPCA micro chip each cub so that if they turn up dead they can be identified at post mortems. It is important to remember that life in the wild is extremely tough, and the RSPCA have found that only a few of those rehabilitated are still around one year later. Furthermore, the numbers being rescued each year are not that big, around 10 to 20 per year.

In this first article, I have gleaned much from two much longer and detailed articles by those mentioned, as well as the detail given in their respective talks.

In next week’s article, I’m going to tell you much more about what they eat, the potential impact on angling, and how fisheries can protect against them.

Next week: ‘The Otter – Part Two’