Population Dynamics of Black Crappie in Lake Okeechobee, Florida, following Suspension of Commercial Harvest

Population dynamics of black crappies Pomoxis nigromaculatus in Lake Okeechobee, Florida, were monitored from 1981 to 1987 to document changes that occurred following suspension of commercial harvest for this species in 1981. Black crappie abundance increased substantially. Mean annual catch per unit effort (CPUE) of otter trawls increased from 1.9 fish/min in 1981 to 22.4 fish/min in 1987. In addition, the estimated winter-spring angling harvest of black crappies on the north end of the lake increased from 34,000 fish in 1980-1981 to over 700,000 fish in 1986-1987. Increased abundance of black crappies resulted from a reduction in annual mortality from 65 to 39% due to suspension of commercial harvest and recruitment of strong yearclasses spawned in 1980, 1983, 1984, and 1985. Multiple linear regression revealed that year-class strength of black crappies was positively related to water levels during the spring spawning season and to CPUE of January trawls for individuals at least 178 mm in length (total-length basis); water level was the more important of the two variables. As black crappie density increased from 1981 to 1987, mean lengths in January of age-2 and age-3 fish declined by 24 and 38 mm, respectively. Nonetheless, growth did not cease after age 3, and preferred lengths (≥ 250 mm) were attained by age-4 and older fish. Because black crappie density in 1987 was at its highest level since population monitoring began, commercial harvest could probably be reinstated with little anticipated effect on angler catch rates. However, low to intermediate harvest quotas must be set to avoid the boomor-bust dynamics created by the original commercial harvest program. Increased mortality due to commercial harvest would also be expected to increase the sizes of black crappie available to anglers.