When an old book still rings true today
Forgive me one last look at an old angling classic; one that’s too good to be lost to history, writes Peter Cockwill
IMAKE no apologies for going back to GW Maunsell’s 1933 book, ‘ TheFisherman’sVadeMecum’, which I recently suggested was largely as valid now as it was 84 years ago. What’s changed is that many of today’s anglers are not so observant or in touch with the natural world as their forebears. Harsh? Well, here are some nuggets from the book – see how many sound familiar to you. pH of water is a critical factor for the growth of trout in a natural environment, Maunsell maintained. ‘Acid’ water in the range 4.0 to 6.8 on the pH scale produces small, dark coloured trout – often with large spots, whereas ‘alkaline’ water in the range 7.6 to 8.4 usually produces well-fed trout which often have a silvery appearance. In one chapter, regarding the group of fish we call ‘salmonidae’ there are some fascinating comments, one of which makes a point that I have never heard expressed better: “Underwater food is really the beef and mutton of a trout’s diet while surface food is only the caviar”.
Water temperatures and aerators
We’re well aware nowadays of the problems that arise when water becomes too warm in summer, but there are many who think that the answer begins and ends with aerators; yet this book couches the issue very differently. Did you know that water warms when the sun’s rays warm the lake bed or river bottom, which in turn warms the water? Dark lake or river beds warm faster than light ones and shallow water warms faster than deep. Cold water is denser than warm water but at four degrees Celsius it has its minimum volume and maximum density. Raising or lowering the temperature from this point causes expansion of the volume and explains what happens as temperatures drop in winter. The thin, cold layer formed at the surface sinks, as do successive layers, until the whole body of water is 4 degrees Celsius. Further cooling reduces the density so, being lighter, the colder water now remains at the surface and freezes at 0 degrees Celsius. Shallow water freezes faster than deep water and in fast, running water, there is no appreciable difference from the surface to the bottom. Fascinating, isn’t it? Feeding fish are more affected by the oxygen content and temperature of water than by actual hunger, and oxygen levels are governed by temperature, wind, barometric pressure and plant life. Cold water contains more oxygen than warm water. At 32 degrees Fahrenheit, it holds about 10cc per litre while at 68 degrees it’s only 6cc. Relate this to an individual fish and an eight-inch trout must pass twice as much water through its gills at 60 degrees as it does when the water is 40 degrees. That’s why you see trout ‘panting’ in hot weather, when they sure aren’t interested in feeding. As I often say, you can’t defeat the laws of physics. The warmer the water, the less the oxygen it holds, no matter how much air that aerator pumps in! Wind – warm or cool – produces evaporation and cools the surface of the water, which lets it take up oxygen from the air. Low or falling barometric pressure, on the other hand, cause the surface layers to surrender oxygen to the air, which tends to make the fish go deeper, whereas in high or rising pressure, the surface layers absorb oxygen and the fish move more to the surface. Healthy plant life in strong sunlight consumes carbon and gives off oxygen, whereas decomposing plant life consumes oxygen. The amount of dissolved oxygen in water at about 40 degrees Fahrenheit is around 0.05 per cent by volume whereas in air it is around 21 per cent, which would explain why a fish out of water can seem drunk and disorientated: it suddenly has far too much oxygen to deal with.
Nature’s weather forecasts
I loved the part of the book which relates to Nature. Having spent a larger part of my life outdoors, I realised that I had taken much of it for granted but people whose lives are more detached from it might find the following observations something of a revelation… Frogs and slugs come out at the approach of rain and ducks do lots of quacking and wing flapping as rain comes through. Gulls come inland from the sea as a storm approaches, while swallows and rooks fly higher, as more wind is expected. Goldfish in a bowl will be lively and at the surface in fine weather but rest at the bottom in unsettled conditions. Flowers such as dandelion, anemone and crocus close up as rain is imminent. Now here’s a final selection of similar pointers, even though I could probably get another two columns at least out of this lovely book. Trout take a fly for one of four reasons: hunger, because it looks like something to eat; curiosity, because of its intrigue; tyranny, because it looks like something alive and in distress; and jealousy, because others may get to it before him. Browns in a lake often come at a surface fly from below while rainbows usually come at the fly from a level position. This last point backs up something I have often observed, having watched browns circle underneath a dry fly before creeping upwards to take. Thank you, Mr Maunsell; you have left us with a gem.
“The warmer the water, the less oxygen it holds, no matter how much air that aerator pumps in!”
Aerators are often seen as the answer to warm water temperatures.