Illinois Natural History Survey - University of Illinois

INHS Reports Summer 2001

Largemouth Bass Recruitment and Stocking Strategies

Although largemouth bass are frequently stocked in many Illinois impoundments to compensate for variable recruitment, the long-term contribution of stocked fish to recruitment and harvest of natural bass populations is unknown. Because stocking is only one of several management options for this species, it is critical that additional information on factors limiting recruitment processes be identified. The ultimate goal is to develop management strategies that maximize growth, recruitment, angling opportunities, and harvest of largemouth bass in Illinois impoundments. Our ongoing research in cooperation with the Division of Fisheries, Illinois Department of Natural Resources should enable us to achieve these goals.

Largemouth bass recruitment depends on a variety of biotic and abiotic factors such as prey availability, predator abundance, population structure, vegetation, water level, temperature, spawning habitat, and angling. Our objective is to determine important mechanisms affecting largemouth bass recruitment in Illinois impoundments to help improve bass fisheries and optimize management efforts. Thus far we have sampled 10 lakes to assess the influence of these factors on largemouth bass recruitment. The lakes chosen for this study varied in surface area, latitude, and productivity. In addition, we chose lakes with poor, medium, and good largemouth bass recruitment.

Densities of young-of-year (YOY) largemouth bass are different across lakes and years, suggesting recruitment is lake dependent as well as dependent on large-scale environmental events. Environmental events such as below-normal temperatures or below-average rainfall will also likely influence recruitment across years. The importance of these variables can be assessed only through multiyear evaluations. Our preliminary results suggest it is likely that the number of successful spawners, predation, and available prey have a large influence on growth and survival of juvenile largemouth bass. We found that peak YOY largemouth bass abundance occurred in lakes with high juvenile bluegill densities. It is unclear whether the abundance of juvenile bluegill directly affects bass recruitment or whether similar factors are affecting both species. Growth of largemouth bass also differs across lakes and becomes more pronounced through fall. Additional study years will help us to identify factors controlling largemouth bass growth and survival and will increase our ability to effectively manage largemouth bass populations.

Removal of spawning males by angling in the spring may or may not affect largemouth bass recruitment. Another objective is to assess the level of angling for nesting bass in Illinois and to determine its impact on reproductive success and annual recruitment. We are currently monitoring the amount of angling for nesting bass through bass tournaments and creel surveys. To examine the relationship between reproductive success and recruitment in largemouth bass, we are monitoring nesting success in Lincoln Trail Lake and ponds at the Sam Parr Biological Station. By draining these ponds in the fall, we will be able to assess the number of juveniles produced and determine the relationship between reproductive success and fall recruitment. This information will help us identify the critical period of recruitment for YOY largemouth bass.

Stocking of largemouth bass is often used to compensate for poor recruitment in an already existing bass population. Surprisingly, few studies have looked at the effectiveness of different largemouth bass stocking strategies. We are evaluating the success of four size groups (2", 4", 6", and 8") of stocked largemouth bass in several lakes across Illinois. Preliminary results from Lake Charleston in Coles County, Woods Lake in Moultrie County, Homer Lake in Champaign County, and Lake Mingo in Vermilion County indicate that larger fingerlings (6" and 8") have higher survival rates than small and medium fingerlings. Mortality related to stocking stress was not evident in any size class of stocked bass. Size of largemouth bass collected in the fall and spring was related to the initial size at stocking. Cost-benefit analyses will be conducted to determine the most appropriate stocking options for use in Illinois under various conditions. We also are evaluating rearing techniques by stocking both hatchery-reared and pond-reared largemouth bass fingerlings in Lake Shelbyville in Moultrie and Shelby counties, Lake Jacksonville in Morgan County, and Walton Lake in Montgomery County. Fingerlings from rearing ponds contributed more than those from hatchery raceways in all three lakes. Higher survival of the rearing pond bass may be the result of these bass being stocked at a larger size.

We are also evaluating the long-term contribution of stocked largemouth bass to the numbers of harvestable and reproducing adults. Largemouth bass are being stocked into selected study lakes with a genetic tag (fixed for the MDH-B2B2 genotype). Background allele frequencies were collected on each study lake before largemouth bass were stocked. Following introductions, the relative increase in the frequency of individuals in that year class with that rare MDH-B2B2 genotype will be used to determine the relative success of the stocking. Once those year classes reach maturation, the contribution of the stocked individuals relative to resident, native individuals in number of young produced will be determined for several successive year classes. In addition, information on the importance of rearing technique, size of stocked fish, forage base, cover, resident predators, physical-chemical conditions, and stocking stress in determining largemouth bass stocking success will allow optimal use of hatchery- produced fish.

John H. Hoxmeier, Joe J. Parkos, Ken G. Ostrand, David P. Philipp, and David H. Wahl, Center for Aquatic Ecology

Charlie Warwick, editor