Dartmoor rivers and the effect of climate change

By Ken Spalding

“It’s no use you two walking up there” said the farmer, clad in green overalls and wellington boots, as he strode down the field towards us.

“That river dried up in the summer, so there won’t be any fish.” My colleague and I were on the River Wolf at Broadwoodwidger in the autumn of 1976, about to check the river for signs of salmon spawning, in particular, redds dug by the female in which eggs are laid as the male fertilises them.

We had parked in Broadwoodwidger and walked down to the river as part of the yearly task of counting salmon redds on all river systems, collating the information to be put on spawning maps. By this means, carried out by river wardens all over Devon and Cornwall, a picture could be built up over the years, showing where this activity took place. The point about this particular year of 1976 was that it was one of the driest on record, with water shortages in the West Country necessitating drought orders, hose pipe bans, standpipes in some areas and a devastating effect on wildlife.

We had a Minister of Drought to try and ensure that supplies of water were adequate to keep life going! The River Wolf is now the main supply river to the large storage reservoir Roadford Lake, not yet constructed in 1976, so drying up of this river supply would have very serious consequences for the South West population if repeated over a number of years. The year 1976 is likely to be a good indicator for future summers. Meteorological experts tell us that climate change will mean hot dry summers, with increased rainfall in the winter period.

Changes are already becoming apparent – earlier springs, hot summers like 2006 and a later autumn running into what used to be winter. So we are likely to see repeats of 1976 as a much more frequent occurrence, with some devastating effects for wildlife. Low summer flows then, even on rivers larger than the Wolf, caused the flows to drop to a trickle, forcing fish populations into some larger pools, where they were easy prey to mink, otter, heron, cormorant, kingfisher, goosander and man. Higher temperatures also had a detrimental effect, causing fish to die due to water temperatures. So predators had a field day, although even these would suffer if this warmth was a feature of every summer, simply because there would be less of a fish population to feed on.

The underwater food chain generally, from the smallest creatures such as nymphs, including those of damsel flies and dragonflies, upon which fish feed, would be less prolific. Indeed, in 2007, anglers, particularly fly-fishermen in the south and east of the country, were complaining of the lessening amounts of nymphs and flies that they imitate to catch trout and salmon. This is an effect of the warm summer of 2006 particularly, but likely to be repeated in future years. What of salmon returning on migration in our West Country rivers?

After some years at sea, these fish return to their home river to spawn in the higher reaches to lay or fertilise their eggs. There are many rivers flowing from Dartmoor that hold such migratory fish.
Before they enter the river they stay in the estuaries to await the first increased autumn flow and to adjust their body system to live in fresh instead of salt water, a process known as osmosis.

In 1976 many salmon died in estuaries, awaiting flows that did not come until too late, where again they were predated upon. This in turn meant that spawning rates were low. If the forecast increased winter flows in rivers follow the summer droughts with higher winter rainfall, this will also affect the fish population. Spawning redds can be washed out by floods and there are no places for small immature fish to shelter. Underwater life will be much reduced. Extremes of water levels and fluctuations of current are generally bad news for a consistent population of rivers. Wildlife dependent on underwater creatures, whether it be minute daphnia or a small fish, will of necessity suffer and become less.

I for one would not like never again to see a fish dimpling the surface of a river to take a fly, or a kingfisher flashing up a river to perch and plunge after fry, or marvel at damsel or dragonflies hunting for food or mating in the summer. The English riverside will change and it will deplete us all unless we do something about it.

Rich people and politicians cannot escape from the planet. We look to the latter to effect changes that might halt the march towards habitat destruction for all. As far as Dartmoor rivers are concerned, I feel we must find some way to hold water in the summer in the upper reaches, to be released slowly to keep rivers in a constant state and alive.

This need not necessarily mean the construction of large dams, rather smaller constructions, maybe not even permanent from year to year, as well as a series of small holding lagoons dug out on river systems in the higher reaches to keep water there in the summer. Thus water could be released slowly as well as providing some small habitats for wildlife.

Perhaps existing water supply dams could be raised to retain more water. Hydro-electric schemes should be constructed on all streams if possible to generate clean electricity. With all the flowing Dartmoor water these would not be as visually polluting as wind farms. Whatever we do, we certainly have to rethink how we live if we wish to keep our rivers and countryside as they are.

Ken Spalding was a Countryside Ranger for 20 years, is a phenologist and author from Chagford.

Stuart Clarke

Author: Stuart Clarke

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