Why do perch lakes run in boom-and-bust year classes?

Because zero parental care hands the whole outcome to spring weather. With no guarding, survival rides on what happens to eggs and fry in their first weeks: a warm, stable spring floods the lake with one enormous cohort; a cold, windy spawn — ribbons stranded, plankton bloom mistimed for the fry — can nearly erase a year class. The lake then spends years showing you that history: "all 15 cm (6 in) fish" one season, jumbos everywhere five years later, is a single strong cohort marching through the population. It also means a slow year on your lake is usually demography, not disappearing fish — and that the boom cohort, competing with itself, may grow slowly until predators and anglers thin it.

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