Exploring mechanisms underlying recruitment of white crappie in Ohio reservoirs

Organisms that produce many, small offspring generally exhibit variable population size, owing to variation in production and survival of offspring. Using a life-history approach, we focused on ecological mechanisms underlying the production and survival of white crappie Pomoxis annularis, a popular North American sport fish exhibiting high variability in recruitment to maturity (i.e., age-2).; Offspring production begins with adult energy allocation to reproduction. Female white crappies initiate ovary development during autumn, 6 months before spring spawning. To understand why females develop ovaries “early”, we used optimality and simulation models. Results revealed that early ovary development is an adaptation to uncertainty in spring feeding conditions.; To investigate how mean condition and egg production of the adult population influence larval density and age-2 catch per effort (CPE), we sampled white crappie from 14 reservoirs. Although mean condition influenced ovary characteristics, only population egg production influenced larval density and age-2 CPE. Thus, population egg production can limit recruitment success.; After larvae hatch, numerous mortality events occur before recruitment to age-2. We focused on two periods: between the larval and juvenile stage and during the first winter of life. In reservoirs, we evaluated how zooplankton density, water temperature, and larval density influenced larval growth and survival. Growth increased with zooplankton density, whereas survival was unrelated to any measured variable. We then evaluated how food, fish size, and winter severity influenced winter survival in the lab. Winter severity regulated survival with only 47% of the juveniles surviving the severe winter, and 97% surviving the mild winter. Although temperatures <4°C caused mortality in the lab, fish may occupy ≥4°C habitat during Ohio winters in the field.; Overall, white crappie recruitment is likely set by the egg or larval stage, though considerable winter mortality remains a possibility. With this caveat, we recommend that managers use catch restrictions to increase adult biomass and subsequent egg production to improve poor recruitment. Higher egg production should increase larval density and ultimately the number of fish recruiting to both maturity and the sport fishery.