salmon fishing

is an excellent book by Hugh Falkus (isbn 0-85493-114-9 ). Unusually I'm going to quote from one page - the preface:
No creature on earth treats the dogmatist more sternly than Salmo salar.
Contradictory in everything he does, Salmo cannot be tied down by dogma.
In addition to providing days of rare enchantment, it taught me that much of what of what I had read about Salmo's behaviour was pretty dubious. Often, the fish I was watching seemed a different creature from the one encountered in print. And over the years it began to dawn on me that far from being fact, a lot of what I had hitherto taken for granted was indeed fallacy; that most authors had written about what they thought salmon did, not what they had seen them do.
Since then I have tested certain of their statements, some of which will be found amongst these pages: assertions by acknowledged experts and regarded as Gospel - but unsound. Most of the accepted tenets of salmon fishing started as conjecture; but gradually, parroted by writer after writer, part of this conjecture became "fact".
In salmon fishing there is no magic substitute for water-sense, skilful presentation, and persistence.
We are wise to move with the deliberation of the heron, that most stealthy of waders.
I think small hooks are preferable to big hooks - they usually get a better hold.
I remain convinced that black is the most attractive colour for a salmon fly.
I suggest that the nearest we can come to a definitive statement is to say that salmon tend to react to large flies sunk deep at temperatures below 45°, and to small flies near the surface at temperatures above 50°.