Effect of Environmental Variables upon Crappie Young, Year-Class Strength, and the Sport Fishery

Abstract

Abundance of juvenile crappies Pomoxis spp. was positively related to floodwater storage in Rathbun Lake, Iowa, from 1972 to 1980. Regression analysis showed that age-0 crappies less than 15 d old increased by 1,330/acre for each million acre-feet–days of water stored above conservation pool from April through August. However, this relationship did not hold for data collected from 1981 to 1989. Abundance of crappies less than 15 d old was also positively related to numerical catch in the sport fishery 2–4 years later. Effects of temperature, wind, substrate, and turbidity on catch of age-0 crappies in townets from 1980 to 1983 were investigated. Once a spawning threshold temperature was attained, turbidity was most influential in determining age-0 crappie densities. About 50% of the variability in larval crappie abundance was explained by turbidity, exclusive of water level. The relationship between substrate firmness and larval crappie abundance was best described by a parabolic function; moderate firmness was associated with highest crappie numbers. Wind was intercorrelated with substrate firmness such that windswept shores provided hostile spawning habitat both in terms of molar action and extremely hard substrate. The 150-mi shoreline at Rathbun Lake was classified to identify prime spawning areas and thereby provide a basis for preserving and enhancing crappie production areas at the lake.