Mouse fishing is a calculated obsession. You're chasing one fish — the biggest brown in the run — and almost everything about it is backwards from regular fly fishing. Daylight is bad. Bright moon is bad. A "perfect cast" is irrelevant. What matters is the wake the fly leaves behind it on the surface.
The window is the darkest two hours of the night, in summer when water is warm enough that big trout are nocturnal hunters. New moon or heavy overcast is ideal. The middle of a hot, still afternoon is the wrong time — go home and sleep.
The setup:
- 7-8 weight rod. You're throwing a wet, water-logged fly and need backbone to land a 20+ inch brown in the dark.
- Short, heavy leader. 6-8 feet of 0X-2X. No need for delicacy. The fly is the size of a dock rat.
- A deer-hair or foam mouse pattern. Morrish Mouse and Mr. Hanky are workhorses. Buy them with rabbit-strip tails for extra wiggle.
Cast across-stream toward the bank. Strip slowly — one short pull every 2-3 seconds. The fly leaves a V-shaped wake. Big browns watch the wake before they commit; the take is often a heavy boil or an audible slurp, sometimes followed by 5 seconds of nothing before the line goes tight.
Set hard, on a long delay if you can manage it. The take feels nothing like a normal trout eat. Listen more than you watch.