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

Trout Fisherman (UK) - - Contents -


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.

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