Scaling new depths

Do you know what lurks in our waterways? Peter Marren celebrates the hidden wonders of our rivers, lakes and streams

Our freshwater fishes have not, you might say, had a fair nibble of the worm. For our other backboned animals - the mammals, reptiles and amphibians, and above all the birds - the bookshelves are full. Bird books are a minor growth industry with numerous volumes telling you not only how to tell one bird from another but where to find them and how to watch them. Most of us, probably, know our song thrushes from our mistle thrushes. But how many of us have even heard of a bleak, a bitterling or a Lochmaben vendace? Apart from the famous few, our fishes are nearly as invisible in the media and the bookshop as they are in life.

This is odd in a nation of anglers - and, at the last count, there were about three million of us out there watching the float bob up and down or flinging a dry fly upriver. But angling know-how is all about how to catch a fish. The angler's litany is of spool reels and swimfeeders and snap-trolling; in other words, it's about the how-to business of catching a fish, not the watery world surrounding the fisherman's dangling hook. Freshwater fishes seem to have swum out of our lives. Apart from salmon and trout (and most of those are farmed), only two species still have a commercial fishery: eels and, in a few Scottish rivers, the cucumber-flavoured smelt or sparling - and both are declining.

Not so in times gone by. George Orwell remarked on the solid, Saxon names of our common fishes: chub, pike, tench, rudd. They seemed to him to come from a more peaceful age, when people weren't stressed-out all the time and got outdoors more. Fishes in those days were caught in nets, often from specially made stew-ponds stocked with carp, bream and other fishes. They ate a lot of freshwater fishes back then. Remember King Henry I who died from "a surfeit of lampreys"? Fishes were once even used as currency - the monks of Ramsey Abbey in the Fens were happy to receive their taxes and tithes in the form of wriggling baskets of eels.

This is why the publication of what could be described as an official fish book should be something of a watermark. Freshwater Fishes in Britain - the Species and Their Distribution is the result of a joint project of the Centre for Ecology and Hydrology, the Environment Agency and the Joint Nature Conservation Committee.

It includes the first detailed distribution maps of all of our 43 native fish and 19 introduced ones. It sums up what is known about each one, and includes a lot more about the state of our inland waters and what that means for the fishes that have to live there. More generally, its authors want to "make them more appealing and much better known, and to raise awareness of the vulnerability of our rarer native species".

It will certainly get the cartophiles among us diving into the maps. Here they are for the first time: maps using the familiar 10-kilometre grid showing exactly where our fishes live and how they are distributed about the country. Unlike some other atlases, this one excludes Northern Ireland. This is not apparently for geo-political reasons but because the mapping effort wouldn't stretch that far. Irish fishes must await their own turn.

At first glance, most of our fishes seem to be doing all right. Many are found all over the country, from Cornwall to Aberdeen (the chilly lochs of the Highlands being too much for the insulation of most coarse fish). Roach, rudd, tench and co are probably more widespread today than they would be in a state of nature.

The canal network created fishy motorways across much of lowland England and Scotland, while stocking has meant that the distribution of, say, the roach is roughly the same as that of a dairy cow. It is probably a map of where we have been with the roach, more than a record of the natural distribution of a wild animal.

But the maps of other fishes are much more intriguing. Several species, including the spined loach and the silver bream, are confined to the slow, weedy rivers of eastern England. The reason is not so much ecological as historical, or rather pre-historical. About 8,000 years ago, the ancestors of these fishes were innocently swimming around in the great river system that connected the Thames and the rivers of East Anglia with the Rhine and the Meuse. Then the sea rose over the plains of what is now the Dogger Bank, and the silver breams and spined loaches suddenly found themselves marooned on a large island.

They survived, but, as nobody took enough interest in them to restock them somewhere else, they stayed put. They are now living evidence for the great land bridge with Europe and so useful exhibits for wildlife films.

Another group, comprising the Arctic charr and the whitefish, a bunch of rare herring look-alikes, are confined to their ancestral waters among the lochs and waters of the west. They were apparently once sea-going fish that became land-locked at the end of the Ice Age, and decided to make a go of being freshwater fish.

A quiet life, you might think, alone in a cold lake with plenty to eat and no enemy in sight. But not many British animals enjoy a quiet life. By letting a small fish called the ruffe escape from their tins of live-bait, anglers unwittingly let loose the one species which has a ravenous appetite for whitefish eggs.

What struck me most from this readable and surprisingly entertaining account of our fishes is the repeated mention of the importance of clean water as a habitat for fish. Even bottom-living ones, like roach and tench, like to see where they are going. Fish like to patrol and feed among the submerged jungles of water weeds and lay their eggs on clean gravel beds or the right kind of plant.

Muddy, silt-laden water is not much good for fish. And a lot of rivers and canals are looking pretty muddy at the moment. For example, the other day, when I happened to be collecting water plants from the river Kennet for a natural history display at Marlborough College, it was hard to find any that were not encrusted with silt and slime. And the river Kennet is supposed to be a crystal-clear chalk stream on which the Environment Agency has invested not inconsiderable sums of public money.

Another problem for fishes is that there is no escape. Whatever enters the water is going to enter their body sooner or later. Some years ago, many trout in our river were floating belly-up as the result of a sudden oxygen deficiency.

The culprit turned out to be a mass "bloom" of diatoms originating from the connecting canal, which had effectively sucked the air out of the water. But what caused the diatoms? No one knew, but almost certainly it was muck on the bottom stirred up by motor boats. Our muck. Some pollutants do not kill the fish outright. An increasingly common one, say the authors of Freshwater Fishes, is endocrine drugs from human sewage. The most noticeable effect is to turn the male fish into females.

About half of our fish species are introductions, some of them temporary ones, like the guppies that briefly thrived far from home in the heated waters near a glass factory at St Helens. The zander, or pike-perch, was more successful.

Having been introduced to the River Ouse by a doubtless well-meaning water authority in the 1960s, it is eating its way through the canal network in the Midlands and south.

The zander eats a lot fishes. "The fact that zander take relatively small fishes throughout their life span", says the Environment Agency's Phil Hickley, "means, under some circumstances, the species can almost annihilate the juvenile component of the prey population."

The solution, it seems to me, is to eat the zander. A few years ago, I tried one and it was one of the most delicious fish I have ever eaten, courtesy no doubt of all the native roach it had devoured before ending up on my plate. Eat more zander. It benefits the environment.

One way or another, fishes seem to suffer a great deal from what we do. This timely guide to where fishes live and what they get up to when they are not dangling on a hook deserves to be widely read.

And long live the weeds and the wilderness yet. After all, a fit home for happy fishes would benefit us all in the long run.

'Freshwater Fishes in Britain - the Species and Their Distribution', compiled and edited by Cynthia Davies and others, is published by Harley Books, £25

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