Annuli in transverse thin sections of otoliths from largemouth bass Micropterus salmoides were verified by four methods. First, the number of daily rings between successive annuli was similar to the potential number of growing days in each of the first 3 years of life. Second, all of the annuli were formed between the last of April and the first part of July. Third, the lengths of age‐I‐VI largemouth bass back‐calculated from otoliths were very similar to those determined from a mark‐recapture study. Fourth, the number of otolith annuli agreed with the known ages (II+ and V+) of largemouth bass in samples from a hatchery and a lake.
The growth and survival of 50 largemouth bass (Micropterus salmoides) tagged with Floy anchor tags (FD‐68B) and marked with a pectoral fin clip were compared to a control group of 50 untagged and unmarked bass during a 191‐day study period in a 0.08 hectare pond. Survival of the experimental and control groups was 100 and 98%, respectively. There was no significant difference (P = 0.05) between the total lengths, weights, or condition values of fish in the experimental or control groups at either the start or end of the experiment. These results indicated that the use of Floy anchor tags in conjunction with an accessory mark had no significant effect on survival or growth of largemouth bass under the controlled conditions of this study and suggested that this tagging and marking combination could be used to provide reliable estimates of vital fishery statistics for this species.
Comparative growth rates of largemouth bass (Micropterus salmoides) from heated and ambient areas of Coffeen Lake, Illinois, were estimated by back calculation of lengths at annuli using transverse sections of otoliths and by recovery of marked fish after one growing season. Calculated lengths at otolith annuli were judged to be representative of the population growth, indicating that this technique was a reliable approach to obtaining growth information on largemouth bass from thermally affected environments. Growth of the Coffeen Lake population was more rapid than most other midwest populations. Fish recaptured in heated areas generally exhibited greater annual growth increments than those recaptured in ambient areas. Young largemouth bass (ages 1‐4) from heated areas had significantly greater (P < 0.05) mean lengths than those from ambient areas according to back‐calculated estimates. This was attributed to a longer growing season and earlier hatching time in thermally affected areas.
Under contract with Commonwealth Edison Company, the Illinois Natural History Survey studied this cooling lake ecosystem intensively from August 1973 through August 1977 to determine the effect of the thermal discharge and combustion byproducts on the local environment. Investigations included detailed studies of water quality, plankton, aquatic macrophytes, clams, benthos, fish, fish harvest or creel, waterfowl, trace metals, and pesticides. Some studies (water quality, benthos, clams, and aquatic macrophytes) were terminated in 1976, and others were initiated to consider the distribution of larval fishes in the cooling loop and the effect of the impingement and entrainment of fish by the power plant. In June 1975 , the Illinois Natural History Survey received additional support from the Electric Power Research Institute (EPRI) of Palo Alto, California, to expand investigations at Lake Sangchris. The expanded work consisted of three parts: (1) a study of the relationship between the fisheries and the physicochemical conditions associated with power production, including fish temperature preferences, potential dangers to the biological system, benefits to plant and animal communities, and causes of environmental degradation associated with power production; (2) construction of a fish production model from the large accumulation of physical-chemical-biological data; and (3) a comparison of fish production in Lake Sangchris with that of Lake Shelbyville, a nearby flood control reservoir. This work has been completed, and a four-volume final report: Evaluation of a Cooling Lake Fishery, has been published by EPRI (1979-1980). However, those investigations cannot be completely separated from the work supported by Commonwealth Edison and reported here. The investigative work was carried out by an interdisciplinary team of specialists. Administration and overall coordination of the project were handled at the Illinois Natural History Survey headquarters in Urbana, while field activities were coordinated through a field station at Kincaid, a few miles from the lake. Most of the fishery biologists were based at the field station; other team members were based in Urbana where more extensive laboratory and analytical facilities were available.
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