Bluegills: Biology and Behavior

6: Reproduction


The age at which bluegills mature varies depending on latitude, food resources, predation pressure (including angling), and competition. The optimal reproductive age of any teleost depends only on natural mortality and growth rate.617 Bluegills start to breed at age-4 (females) and 7 (males), or longer than 160 mm TL, in Lake Opinicon,618 but commonly at age-1 and 75–125 mm TL for both sexes in the southeastern United States,619 although breeding occurs at larger size and greater age in unfished waters (see Chapter 8). Bluegills at Par Pond, South Carolina, for example, mature at 75–215 mm TL (ages 3–4), or 1–2 years later and ~80 mm TL larger than those at comparable latitude where angling is permitted.620 Alabama bluegills can spawn at 4 months and 28–56 g, although most activity is seen at 1 year.621 Michigan bluegills spawned at age-1 in ponds with sufficient food and little competition.622 Utah bluegills mature at about age-4 under conditions of low predation.623

Maturity can also be delayed until ages 3–4 and 180–200 mm TL in southern populations experiencing a history of intensive predation.624 Delayed maturation is thought to enhance fitness by increasing mating success of males and the fecundity of females.625 Fishes demonstrate indeterminate growth, and fecundity is related to body size.626 Female bluegills in South Carolina can be 40 × more fecund at age-3 than at age-1.627 A territorial male that is 6% larger than its cohorts can produce 50% more fry.628 Stunting is common in the absence of effective predators (Chapter 8), and there would be little to gain from delaying reproduction.629 Mortality rates might remain the same, and the increased fecundity that comes with large size would not alleviate growth suppression.