Life of a Chalkstream. Simon Cooper

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СКАЧАТЬ the head. It is violent and fast. From the other side of the river I can hear the flesh being torn apart. Strangely they are not competitive about the catch; they wait their turn. When one has had enough he or she will lay what is left down for another to pick it up.

      I have never yet seen the otters catch a salmon; maybe they are too big or simply swim away fast rather than hide. Trout are the most common, eels not far behind, and grayling the most prized – in winter they devour every last morsel of the latter. In the summer part-eaten fish or eels, too big for the otter pups to finish, are common. With the eels the head seems to be the only bit they like to eat; decapitated eels are a common sight in the morning dew. I usually kick them back into the river for the crayfish. I used to throw the part-eaten fish into the field – dead fish on the riverbed can look alarming to visitors – but since I have discovered that otters are partial to a five-day-old, decomposed trout I also kick them back in on the grounds that it might save the life of another fish.

      It is something of a fallacy that trout love the fastest water in a section of a river to live out their lives; in fact almost the reverse is true. The older and bigger a trout becomes, the more he or she gravitates to the deeper, slower parts, so autumn is the only time we get to have a good look at the long-term residents who are the brood stock for the next generation. If you are a tiny little juvenile trout the fast, shallow water is a great place to grow up because you have the place to yourself. For the bigger trout the effort of holding station in the riffles, the fast-flowing shallow water that separates the pools, is too much for any possible rewards and the risk from predators like herons very high. But for the little, tiny trout even a good-sized pebble will provide shelter from the flow whilst waiting for a tasty nymph to come tumbling by. Predators? Well, when you are small it is all about the lesser of evils. Yes, you could be plucked from the stream by a kingfisher, but in truth your greatest danger lies from the very adult trout that probably spawned you. The one thing all fish love to eat is other fish.

      The trout I hoped would gather on the gravel beds in North Stream would be fast developers to do so at three years; four is more common and it is the females who first seek out the ideal patch to set up the nursery. It is true that fish often head upstream to spawn to seek out the purest water and best laying gravel, but unlike say Pacific salmon that congregate in the uppermost point of a river in a giant, swirling pink mass, brown trout are smarter than that. Quite frankly they travel only as far as they need to travel, be it a metre or a mile, which is why I had high hopes for our newly restored stream. Brown trout are eminently practical when it comes to spawning; if they have to travel 20 miles upstream to find the perfect place and mate they will do it, but if both are within a few yards, why bother? I was hoping North Stream would be that place, the breeding ground for the trout that inhabited Gavelwood already. The main river was fine, but the stream would be better with more places for redds and a better nursery for the eggs once hatched. From my point of view, it was all about making it easy for the female, because creating a redd is tough work. She positions herself over the chosen spot and then with flicks of the tail or a sideways movement of the body gradually dislodges a few pieces of gravel at a time. With thousands of movements, executed thousands of times over a period of days, gradually an indentation is cut in the gravel of the riverbed. Some of the stones get carried away on the current, but others gradually pile up in a mound at the downstream end of the cut. This mound, seemingly an unimportant by-product of the excavation, will in fact be vitally important when the females come to lay their eggs. But for now our female has to seek out the right location for her redd. The main river is just too fast in most places, as no sooner will she start to dig a hole than the rapid flow will scour it flat again, and even if she succeeded, when it comes to mating the eggs would be whipped away in the current before fertilization had had a chance to take place. So in the search for the ideal spot I am hoping that the trout moving upstream will turn right into the relative calm of North Stream to check it out.

      Every action in a river causes some sort of reaction, so digging up the riverbed, however well intentioned, causes all sorts of commotion for other river creatures, and in this particular case the tiny ones. The gravel riverbed is home to millions of invertebrates, animals like snails, bloodworms, nymphs and shrimps, which thrive in the constant temperature of the chalkstream water. While 10ºC might be a very cold bath for humans, for this group it is perfect. And if they thrive, so do the creatures that eat them, namely the fish. Fish are opportunists. Unlike people they don’t have a routine that tells them it will be lunch at such and such a time. If food comes along they eat it and the moment that the redd cutting begins I will see the yearlings – fish under twelve months old – gathering below the cutting area to start hoovering up the unfortunate invertebrates, who can only drift helpless on the current until they either get caught in some weed, float down to the bottom or get swallowed. It must also be said that the yearlings, or parr, are not just there for the food; as eager adolescents they are standing by to add their bit to the spawning process. These ‘sneakers’ as they are called will slip between the adults at the crucial moment. Whether they contribute much in a normal year is debatable, but nature brings them to sexual maturity early as a back-up plan. In a bad year, maybe caused by low water or some other natural disaster that prevents enough males making it to the redds, there will at least be someone there to complete the job.

      Fish are not beyond digging into the gravel themselves to find food. Watch a grayling in a river and you will see him go tail up, push his snout down into the gravel and with a puff of silt around his head suck up a shrimp. But why go to all that effort when a redd-making trout does the work for you? This is a winter feast that will only be bettered by the trout eggs themselves. And in the hot summer days, when anglers start to feel the heat and the fish get lazy, there are opportunities for both to capitalize on the dislodged food sites. At four or five spots across Gavelwood water meadows I have places where the cattle can either wade across the river or get into it to drink. As your average bovine drinks around seven gallons a day, maybe twice as much in hot weather, that is a lot of getting in and out of the river. And every time they do it stirs up the riverbed, uprooting the inhabitants. Trout get to know this, so they wait downstream, only moving out from the shade when the muddied water gives them notice of food to come. I do the same, and a well-cast shrimp imitation as the clouded water starts to clear will often turn a dead afternoon into a successful one.

      The gravel of North Stream was abundant, but the decades of neglect had left it rock-hard, without the winter floods to break up the surface and sweep away the silt that had formed a crust. Within a week of reopening the Stream the worst of the silt and mud had been washed away to reveal plenty of potential spawning grounds, but when I tested them out the reality was depressing. Jabbing a garden fork into random sections of the riverbed I was mostly rewarded with a bruised hand. The tines would barely penetrate more than an inch or two. This was bad news. If I could not break through with a steel fork then the trout would find the same and keep moving on upstream to abandon North Stream. There were two options – do nothing or intervene.

      Do nothing is not so bad if you don’t mind waiting for years. Gradually, nature, in the form of exceptionally heavy winter flows, would break up the surface into the loose gravel that a trout might easily dislodge. But I didn’t feel inclined to wait for years, so intervention, in the form of gravel-blasting, was the remedy. Gravel-blasting is not the nuclear solution it might at first sound. You take a high-pressure water pump with a steel probe on the end, stand yourself in the river, press the probe down into the gravel to a depth of about 6 inches and then wait while the water from the pump does the work, washing away the decades of silt that was binding together the gravel stones. When the water starts to run clear, you pull the probe out and push it back into the gravel a foot or so away. For the first ten minutes this is a fun job, but after a while the novelty palls. It is effective, however, and when you stand on the bank to admire your handiwork there is always a certain amount of satisfaction – the riverbed looks like a freshly plumped pillow and the gravel will positively glisten.

      While the trout are starting to weigh up the options of North Stream, our salmon pick up the pace as the scent of the home river gets stronger. Past Land’s End they start to hug the coastline, the beaches of Cornwall then Devon almost in sight. Gradually the pack thins out as one by one they peel СКАЧАТЬ