The Cyclic Stocking of Parentals in a Farm Pond to Produce a Population of Male Bluegill x Female Green Sunfish F\u3csub\u3e1\u3c/sub\u3e Hybrids and Male Redear Sunfish x Female Green Sunfish F\u3csub\u3e1\u3c/sub\u3e Hybrids

A population of male bluegill (Lepomis macrochirus) x female green sunfish (Lepomis cyanellus) F1 hybrids was established by parental stocking in a southern Illinois farm pond containing male redear sunfish (Lepomis microlophus) x female green sunfish F1 hybrids and largemouth bass (Micropterus salmoides). In 1967, male redear sunfish and female green sunfish parentals, along with fingerling bass, were stocked into a new farm pond. Nine years later in 1976, male bluegill and female green sunfish were stocked into the same pond. At the time of sampling in the fall of 1978, bluegill x green sunfish F1 hybrids weighed an average of 3 g at annulus I, 24 g at annulus II, and 171 g at annulus III. Growth rates among the three year classes varied widely. The best growth was exhibited by the 1976 year class of bluegill x green sunfish F1 hybrids. Redear x green sunfish F1 hybrids sampled in 1969 weighed an average of 32 g at annulus I, 118 g at annulus II, and 217 g at annulus III. Both F1 hybrid sunfish crosses produced fish that reached the theoretical minimum harvestable size of 110 g at annulus III

Gear-Specific Population Demographics of Channel Catfish in a Large Midwestern River

Various gear types have been used to sample populations of channel catfish Ictalurus punctatus in lotic systems. However, these gears produce different population characteristics (i.e., recruitment, growth, and mortality). We compared the population demographics of channel catfish in the Wabash River, Indiana, sampled with baited 25- and 32-mm-bar mesh hoop nets and three-phase alternating current (AC) electrofishing. Based on catch per unit effort, the relative abundance of channel catfish sampled with 32-mm hoop nets was lower than that of fish sampled with 25-mm hoop nets and AC electrofishing. Each gear type also resulted in a different length frequency, mean length increasing progressively in sampling with 25-mm hoop nets, 32-mm hoop nets, and AC electrofishing. Similarly, age-frequency distributions differed among gears. The 25-mm hoop nets biased the age structure toward younger individuals (mean age = 2.5), whereas both 32-mm hoop nets (mean age = 4.0) and AC electrofishing (mean age = 5.8) included older fish. Catch-curve analysis generated different mortality rates for the three gear types, the mortality rate being highest (50%) in fish sampled with 25-mm hoop nets. Gear-specific size and age structures led to differences in von Bertalanffy statistics among the 25-mm hoop nets and AC electrofishing, while the results for 32-mm hoop nets were uninterpretable. Because the different gears led to conflicting parameter estimates, management practices based on sampling with single gears may be contradictory. Given the differences in gear selectivity, biologists need to approach management cautiously until calibration to the true size and age structure is conducted

Protracted treatment with corticosterone reduces breeding success in a long-lived bird

Determining the physiological mechanisms underpinning life-history decisions is essential for understanding the constraints under which life-history strategies can evolve. In long-lived species, where the residual reproductive value of breeders is high, adult survival is a key contributor to lifetime reproductive success. We therefore expect that when adult survival is compromised during reproduction, mechanisms will evolve to redirect resources away from reproduction, with implications for reproductive hormones, adult body mass, nest attendance behaviour and breeding success. We investigated whether manipulating corticosterone, to simulate exposure to an environmental stressor, affected the secretion of prolactin and breeding success in the black-legged kittiwake Rissa tridactyla. We used implanted Alzet® osmotic pumps to administer corticosterone to incubating kittiwakes at a constant rate over a period of approximately eight days. Manipulated birds were compared with sham implanted birds and control birds, which had no implants. There was no significant difference in the body mass of captured individuals at the time of implantation and implant removal. Corticosterone-implanted males showed lower nest attendance during the chick rearing period compared to sham-implanted males; the opposite pattern was found in females. Corticosterone treated birds showed a marginally significant reduction in breeding success compared to sham-implanted individuals, with all failures occurring at least one week after implant removal. However, prolactin concentrations at implant removal were not significantly different from initial values. We were unable to measure the profile of change in corticosterone during the experiment. However, our results suggest a delayed effect of elevated corticosterone on breeding success rather than an immediate suppression of prolactin concentrations causing premature failure

Evaluation of Walleye Stocking Program January 1, 1991 to December 31, 1998

Illinois Department of Natural Resources Division of Fisheries Federal Aid Project F-118-Runpublishednot peer reviewedOpe