The “big browns” are spawning in the Owyhee River—brown trout beginning their fall nesting ritual. You can see them excavating their nests in the gravelly shallows.

Wise fishermen know that fish are spawning and try not to disturb them. They avoid walking on gravel bars where they might trample the eggs, or wading upstream from the nests where they might dislodge debris that can smother them. And they don’t fish for these trout, though it’s tempting to do so as they rest near their nests.

These precautions are part of an ethic that governs responsible fishing. But there is a deeper and…