When do perch abandon the weeds in fall?
When the weeds stop being worth it. As water falls through the low teens °C (mid-50s °F), shallow vegetation browns and dies, its invertebrate larder thins, and decaying weed actually consumes oxygen instead of making it — so the flats that fed the school all summer go quiet from the inside out. Schools slide down the weedline to the deep edge first, then out onto bare flats and shell beds in 6–12 m (20–40 ft). The tell is green versus brown: the last living green weed patches hold the last shallow fish, and once they brown, the basin has everyone. At Canadian latitudes this runs late September into October; further south it stretches weeks later.
The full story
This answer is one piece of a longer lesson — setups, diagrams and the reasoning behind it.
Same topic, other species
- What happens to crappie as the water starts cooling in early fall? — Crappie
- When do largemouth move shallow in fall? — Largemouth Bass
- Where do muskie go when the weeds start dying in fall? — Muskellunge (Muskie)
- What happens to pike as the water starts cooling in early fall? — Northern Pike
- How should I fish the weeks when summer breaks into fall? — Trout (Rainbow · Brook · Lake)
- What changes for walleye when the water starts cooling in early fall? — Walleye