PART TWO - WHAT THEY EAT, AND THEIR IMPACT ON FISHERIES
Otters
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What Do Otters Eat On The Dorset Stour?
The big question that every angler asks is, “what do otters eat?” Clair Rogers, a third year student at Bournemouth University, with lots of help from many volunteers that collect spraints for analysis, has been painstakingly analysing what they eat in the Stour. She doesn't have much to go on for there are often few clues in the spraints. It has been a case of carefully separating the remains to see if anything identifiable can be found. Not every spraint contains bones, scales or other remains. For fish, she can identify the species from scales, jawbones and vertebrae. Sometimes, bird remains are found, like the foot, believed to be a moorhen's, shown at the open day. Other foods may leave no evidence at all in the spraint though it may be found on the riverbank. A good example of this is river mussels. These are bitten open and the soft parts eaten leaving the shells with distinctive signs of the otter's teeth. As you can imagine, the vertebrae of many of the fish are very small though different types of fish have different vertebrae. In some cases the identification is only generic, ie, roach and dace vertebrae are sufficiently similar that they are counted the same but a perch vertebra is identifiably different.
Much of the fish diet is what one would expect; eels, perch (I've seen the otter-eaten remains of perch on the Stour), roach and dace. But other fish surprised me; such tiddlers as sticklebacks and minnows. I've already mentioned river mussels; they also eat small mammals, crayfish, birds, and in the sea, crabs. Like most animals, the otter takes advantage of suitable and abundant food supplies. A typical food intake for an adult otter is about 2lbs per day.
Otters and Eels
At the open day, Hugh Miles asked what the effect of the eel decline is on otters. This decline is thought to be as much as 99% over the last twenty years. The simple answer is that they will rely on other food. As eels are one of their favourite foods l wonder if the rapid decline of the eel population is at least partly contributed to by the gradual re-establishment of otters on many rivers. This must be only a minor factor compared to the major ones such as over-fishing of both elvers and adult eels, possible changes in the Gulf Stream currents, pollution and parasitic infestation. As the otter is protected and being actively encouraged, and the eel is a favourite food for otters, there must be a strong case for stopping all commercial fishing of eels, including elvers, something that will be unpopular with those commercially involved.
The fishing of adult eels includes the use of fyke nets. A fyke net is a fixed net that is supposed to be marked. Each net has a fixed wall type net that leads into the main part that is like a keepnet but with sections, except that as an eel enters each section, there is an inward pointing funnel that makes it difficult for them to escape. All nets must by law be fitted with an otter guard (a plastic grill) on the mouth of the net but many don't and you can hardly blame the otter for investigating a fyke net that contains eels or other fish. But once the otter is inside, its chances of escape are remote and it drowns. What worsens the situation is that more fyke nets are unlicensed than licensed, and if you're working an illegal net you hardly care about otter guards, or any fish that get trapped accidentally.
Otters and Big Carp
Over the last few decades, many gravel pits, lakes and ponds have been dug, some for the prime purpose of fisheries. As the fundamental requirement for a fishery is water to fill it, many are situated near streams and rivers. Furthermore, many gravel deposits occur in river valleys such as the Avon, Colne and Frome valleys. I'm sure you can think of many more; the Trent, the Darent, the Lea, the Thames valleys. Today, there are hundreds and hundreds of fisheries that are close to rivers and streams, and there are still more being dug. As anglers, we know that many have been developed as carp fisheries. Modern strains of carp grow quickly; fish of five pounds can reach more than thirty pounds in five or six years in the right environment. Stock fish like this might typically cost £25 to £30 each, yet be worth in excess of £2000 once they reach 30lbs or more several years later. We need to be aware of one more characteristic of carp; carp are a warm water fish. In cold weather, with water temperatures of 4°C or less, they are comatose. If a hungry otter finds these virtually static carp in winter then it will have little difficulty in catching and killing one. The otter eats what it can, and may return to eat more. Remember that eels are not only becoming scarce but also much harder to find in winter. The result is that a number of vulnerable waters have lost large, irreplaceable carp.
There is only one practical way to protect an enclosed stillwater fishery from otter predation, and that is to fence it off with suitable fencing. This can be very expensive, and to this end, the NAA, spearheaded by the SAA, continues to campaign for part funding to the tune of £250,000 per annum for a ten-year programme to protect vulnerable waters.
NAA Press Release 17/4/04.
It's time for DEFRA to take anglers' concerns seriously.
As you can see, anglers need to work closely with the various conservation bodies such as English Nature, The Wildlife Trusts, and the EA on this rather than making ill informed, politically naïve and insensitive statements calling for the removal of otters. Such options will not happen.
A similar situation has occurred with barbel on several rivers including the Hampshire Avon and some Yorkshire rivers. As these cannot be fenced off, it is hard to see how the situation can be managed at all. Substantially increasing pressure on the EA and DEFRA is probably the only option to improve fish stocks where it can be shown that the overall fish stocks are very low due to pollution, cormorant/goosander predation, eel decline, or other environmental factors such as habitat loss. The other alternative is clean but lifeless rivers, something that is useless to otters and much other wildlife, as well as anglers. There is a gradual awakening, triggered by bodies such as the SAA, Trout and Salmon Association and ACA, that the current situation regarding sewage pollution, cormorant predation, and continuing urbanisation of our waters is having a catastrophic effect on the whole eco-system.
As responsible anglers, we have got to re-examine our approach to our sport. In managing our waters, restocking with comparatively cheap and modestly sized fish to replace the occasional losses is going to have to be the acceptable way forward for waters of this nature, and occasional losses on this type of venue must perhaps be accepted. It is certainly far too expensive and largely impractical to restock with 30lb carp, however, and ways must be found to protect large, specimen fish. There is no doubt that DEFRA are going to have to meet us halfway with funding to protect some fisheries, as well as finally realise that without action on cormorants there will be increasing numbers of catchments that simply don't have enough fish to support otters.
Finally, On a Much Lighter Note, Looking out for Otters
There were two more talks during the day; one was about otters in Poole Harbour and its hinterland. Much of the harbour is wild and surprisingly there is less evidence of otters around the Harbour than one might expect. On the nearby rivers, the Stour, Avon, Frome and Piddle there are established populations. One of my questions was whether the urbanised stretches of river would have any otters on them, given the amount of disturbance and dog walking along their banks. The answer is yes, the disturbance appear to make little difference.
The other talk was about changing historical attitudes to otters, and described the many historical references to otters. During the open day, I also got a chance to learn a little about the signs that show otters are active. There are at least three clues to look out for; the droppings, footprints (much bigger than mink's at about 2” across), and areas where the otter enters the water. It seems that I have been spotting some of the spraints for years but not realised what I was seeing! I shall have to keep my eyes peeled.
I'd like to thank all those that made me welcome at the Dorset Otter Group open day, and Paul Klinkenborg and Chris Burt of the SAA for their assistance.
Next week: 'Aquarium Gazing'
