Why do perch schools sort themselves by size?
Three mechanical reasons. Same-sized fish cruise at the same speed, so a mixed school would constantly tear itself apart; same-sized fish eat the same menu, so a size-sorted school grazes one habitat efficiently instead of arguing over two; and perch eat perch — a 10 cm (4 in) fish swimming beside a 30 cm (12 in) one is swimming beside a predator, so the small have every reason to keep their own company. The angler-facing consequence is the most useful rule in the sport: the first fish tells you what the next fifty look like, and changing your catch means changing schools, not changing lures.
The full story
This answer is one piece of a longer lesson — setups, diagrams and the reasoning behind it.
More questions about Territory & aggression
Same topic, other species
- Do male crappie actually defend their nests? — Crappie
- Why do repeated casts to the same spot finally draw a strike? — Largemouth Bass
- Can muskie and pike coexist in the same lake? — Muskellunge (Muskie)
- How much do pike really eat other pike? — Northern Pike
- Why do smallmouth attack lures far bigger than what they eat? — Smallmouth Bass
- Do trout defend their spawning areas? — Trout (Rainbow · Brook · Lake)
- Why does hooking one walleye seem to switch the whole school on? — Walleye