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We evaluated 24-h poststocking survival of fingerling black crappies Pomoxis nigromaculatus(mean total length 117 mm) that were cheek-tagged with binary-coded microwire (CW) tags and estimated the percent contribution of stocked fish to a naturally occurring year-class in a Florida lake. Retention of CW tags at 15 d was high (96%), but posttagging survival of CW-tagged fish was low compared with reports for other CW-tagged species and for untagged fingerling black crappies. Survival at 24-h averaged 26% (SD = 11) for CW-tagged fish held in a cage in Lake Jeffords, Florida. Ten months after stocking 294 fingerling black crappies/ha in Lake Jeffords, only 4.8% of the age-1 fish sampled from the lake with otter trawls had CW tags. Low posttagging survival probably contributed to the low percent contribution of stocked fish to the naturally occurring year-class.

Distribution of 16 Florida largemouth bass Micropterus salmoidesfloridanus was monitored weekly for 1 year by radiotelemetry in 80-hectare Lake Baldwin, Florida. The lake contained grass carp Ctenopharyngodon idella, which had elminiated all submersed aquatic macrophytes. Six of the largemouth bass stayed predominantly (87% of tracking locations) in water deeper than 3.5 m (60% of lake surface area), where they established home ranges averaging 21.0 hectares (range, 0.6–39.5 hectares); the offshore region had no natural or artificial structures. The other radio-tagged fish were relocated a majority of times in water depths of 3.5 m or less. Five of these fish established year-round home ranges averaging 4.1 hectares (range, 1.0–9.8 hectares) in the inshore region where water depths were less than 2.0 m, and had significant (P < 0.05) preferences for habitats with water tupelo Nyssa aquatica. The remainder of the largemouth bass used both the inshore region and water depths out to 3.5 m and had significant preferences for the 11 piers in Lake Baldwin.

An infestation of hydrilla Hydrilla verticillata caused an 85% reduction in angler effort at Orange Lake, Florida, in 1977 when plant coverage exceeded 80% of the lake. Nonlocal anglers were only 3% of the total number of anglers fishing the lake in 1977, but were 37% of the anglers during 1978 and 1979, when hydrilla coverage was less than 19%. Although angler use of Orange Lake was greatly reduced during the peak 1977 hydrilla infestation, the number of fish caught per hour during 1977 was equivalent to or greater than that of all other study years for all species of sport fish. The almost complete plant coverage did not lower the population of harvestable largemouth bass Micropterus salmoides or black crappie Pomoxis nigromaculatus. Numbers of harvestable bluegill Lepomis macrochirus and redear sunfish Lepomis microlophus were, however, negatively correlated with hydrilla coverage. Reduction in angling caused a 90% loss in revenue from the Orange Lake sport fishery that is valued at approximately $1 million (U.S.) annually. Benefit: cost (B:C) ratios of sportfishing expenditures to aquatic plant control costs during the 2 years in which there were no major aquatic plant problems were estimated to be 300:1 and 69:1. The B:C ratio decreased to 1:1 when hydrilla severely limited access to the lake. Excessive growths of hydrilla, which limited access to Orange Lake, tripled the aquatic plant control costs. These data are offered as an economic case for the control of nuisance aquatic vegetation because the total economic benefits far exceeded the cost of aquatic plant control.

Selective removal of grass carp was attempted in an 80-hectare Florida lake by means of a 0.1-mg/liter treatment of rotenone. A mark-recapture procedure was used to obtain a population estimate. Prior to the lake treatment, a field bioassay conducted in large polyethylene bags containing lake water and suspended in the lake, revealed that a 0.1-mg/liter concentration of rotenone killed grass carp but had little effect on sport fish. Fish collected from block nets set within the lake revealed lake-wide rotenone treatment removed more than half of the threadfin shad (Dorosoma petenense), grass carp, and golden shiners less than 100 mm. Appreciable numbers (20-50%) of largemouth bass (Micropterus salmoides), lake chubsuckers (Erimyzon sucetta), larger golden shiners, and redear sunfish (Lepomis microlophus) less than 100 mm were affected. Larger redear sunfish, bluegill (Lepomis macrochirus), warmouth (Lepomis gulosus), and black crappie (Pomoxis nigromaculatus) were abundant within the lake, as shown by quantitative block net sampling; however, their mortality from the selective treatment was less than 20% for all size classes.

The sampling effectiveness of rotenone applied within large (0.41 hectare) and small (0.08 hectare) blocknetted areas was compared at open-water and vegetated sites in Orange Lake, Florida. Eighteen fish species were collected within the large nets and 21 species within the small nets; 16 species were common to both nets. Total fish biomass (kg/hectare) and abundance (number/hectare) estimates did not differ significantly (P = 0.10) between areas in either open-water or vegetated habitats; abundance estimates (number/hectare) did not differ between large and small open-water areas. Significantly higher abundance estimates were obtained in the smaller nets in vegetated habitats due to more efficient pickup of small fish. For larger size game fish, total abundance, biomass, and individual species estimates were not significantly different between sample areas in either habitat. The smaller experimental nets provided inventories of fish populations that were as accurate as those from large-area samples, with much lower labor and equipment requirements.

Five thousand grass carp (Ctenopharyngodon idella) fry were stocked into a 0.81-hectare pond in Marion County, Florida. The fry grew from 48.2 mm to 186 mm total length in 6 months with a survival rate of less than 7%. Food consumption decreased to near maintenance ration when water temperature fell below 14 C and growth was reduced. The 76 grass carp which contained food (63-220 mm) were strict herbivores, and ate animal material only in trace quantities (<0.1%). Mean electivity indices indicated positive selection for Sagittaria graminea, slight selection for Eleocharis sp., and discrimination against Najas flexilis, Ceratophyllum demersum, and Potamogeton illinoensis.

Coefficients of condition were calculated seasonally for largemouth bass (Micropterus salmoides), bluegill (Lepomis macrochirus), and redear sunfish (Lepomis microlophus) for three years from two hydrilla-infested Florida lakes, Baldwin and Wales. Hydrilla coverage was altered with aquatic herbicides and grass carp (Ctenopharyngodon idella) during the study period in both lakes. Bluegill and redear sunfish condition was not adversely affected until hydrilla occupied the majority of the water column. The reduction in condition which occurred with near total occupation of the water column by hydrilla was probably due to the elimination of a foraging gradient between the submersed macrophytes and open water. Harvestable (creelable) largemouth bass had low condition values once hydrilla coverage was above 30%; however, smaller largemouth bass were not as adversely affected until percent coverage exceeded 50%.

The external distance between the cleithrum bones was used to estimate the sizes of grass carp (Ctenopharyngodon idella) that could be ingested by Florida largemouth bass (Micropterus salmoides floridanus). The equations for mouth width vs. total length (TL) of largemouth bass were: Mouth (mm): 0.0968 (mm TL) for bass <200 mm TL (r2= 0.89); and mouth (mm) = -11.102 + 0.1567 (mm TL) for bass >200 mm (r2= 0.95). The equation for body depth vs. total length of grass carp was: depth (mm) = 0.629 + 0.204 (mm TL), r2= 0.98. Five thousand grass carp fingerlings were stocked in a 0.81-hectare vegetated pond. Initial predation was high in the sportfish pond, as only one grass carp was recovered at termination. Stocking of grass carp >450 mm is necessary to totally eliminate the possibility of piscivorous predation in lakes with established Florida largemouth bass populations.