R. John H. Hoxmeier

Instream Evaluation of Passive Integrated Transponder Retention in Brook Trout and Brown Trout: Effects of Season, Anatomical Placement, and Fish Length

Abstract We examined effects of tagging season, anatomical placement of tags, and fish total length (TL) at tagging on 2-month retention of passive integrated transponder (PIT) tags in 181 brook trout Salvelinus fontinalis (99–302 mm TL) and 709 brown trout Salmo trutta (122–511 mm TL) in small streams of southeastern Minnesota. A lower percentage of brown trout retained their tags in spring (56%) than in fall (68%), but season did not affect tag retention in brook trout. Retention rates varied with anatomical placement for both species. For brook trout, retention was 70% when the PIT tag was placed into the body cavity using an insertion point that was posterior to the pelvic fins and 100% when the tag was placed into the dorsal musculature. Among brown trout, PIT tag retention was 56% for body cavity placement (posterior insertion) and 95% for dorsal musculature placement. Tag retention was not associated with fish TL for brown trout and was only weakly associated with TL of brook trout. Although report...

Factors Influencing Precision of Age Estimation from Scales and Otoliths of Bluegills in Illinois Reservoirs

Abstract We examined the effects of population-specific variation on age estimates from scales and otoliths of bluegills Lepomis macrochirus from Illinois reservoirs. We divided 12 reservoirs into four groups (north stunted, north quality, south stunted, and south quality) to examine the effects of latitude and fish size distribution on the precision of estimated ages. Ages of 40 bluegills from each reservoir (total N = 480) were independently estimated by two readers. Otoliths provided more precise age estimates than scales. Population size structure and sex had no effect on precision of ages estimated from either structure; however, latitude, age, and maturity stage all affected precision of ages estimated from scales. Age also affected precision of estimates from otoliths. Percent agreement, coefficient of variation, and age bias plots all provided useful interpretations of the data. Our results demonstrate the importance of examining population-specific sources of variation with multiple statistical m...

Growth and Survival of Larval Walleyes in Response to Prey Availability

Abstract Although larval fish can be highly susceptible to changes in prey availability, the effects on growth and survival are difficult to examine in the field. In addition, previous studies often have examined these relationships only with zooplankton communities common to northern oligotrophic lakes. We used mesocosm and pond experiments to better understand the relationship between communities of larval walleye Sander vitreus (formerly Stizostedion vitreum) and zooplankton common to eutrophic midwestern USA reservoirs. Treatments of low, medium, and high crustacean zooplankton density (1–50 individuals/L) were created in mesocosms by filtering pond water. Treatments in ponds were created by adding copper sulfate to create low-density zooplankton ponds and adding liquid fertilizer to create high-density zooplankton ponds. Walleye growth rate (0.7–1.5 mm/d) increased with crustacean zooplankton density in both mesocosms and ponds. Densities necessary to maintain good growth were higher than previously ...

Direct and Indirect Effects of Gizzard Shad on Bluegill Growth and Population Size Structure

Abstract Competition with gizzard shad Dorosoma cepedianum has been shown to influence survival of larval bluegills Lepomis macrochirus as well as growth and size structure of largemouth bass Micropterus salmoides, which prey on these planktivorous species. However, little is known about how the presence of gizzard shad influences bluegills beyond the larval stage. We examined bluegill–gizzard shad interactions across 10 reservoirs with and 10 without gizzard shad to determine direct and indirect effects of gizzard shad on bluegill population size structure. In the presence of gizzard shad, bluegills exhibited smaller adult (>3 years old) size structure. Benthic invertebrate densities were higher in non-gizzard shad reservoirs, which may have contributed to increased bluegill growth in these systems. In contrast, zooplankton densities were similar in reservoirs with and without gizzard shad. Turbidity was higher in reservoirs with gizzard shad, which may have reduced foraging success and growth of bluegil...

Examining Interpopulation Variation in Bluegill Growth Rates and Size Structure: Effects of Harvest, Maturation, and Environmental Variables

Abstract Understanding how life history variation and the environment affect growth and population size structure is an important theme of fisheries ecology. However, the interactions among important biotic and abiotic factors and their relative importance in the context of population-specific variation are seldom considered. We used an information theoretic approach to investigate how environmental variables interact with important life history parameters to influence population size structure of bluegills Lepomis macrochirus. We sampled bluegill populations in 23 Illinois reservoirs to examine the effects of temperature, water transparency, and prey availability and bluegill density, harvest, and size at maturation on bluegill growth and population size structure. Good growth and large body size were associated with warm, clear lakes containing abundant prey resources. An exception to this pattern was early growth (length at age 2): Larger body size at age 2 was associated with relatively low Secchi dep...

Relative Survival of Three Sizes of Walleyes Stocked into Illinois Lakes

Abstract The ability to differentially batch-mark several size-groups of fish stocked concurrently in lakes or rivers makes it possible to compare survival within a single year. We evaluated stocking of walleyes Stizostedion vitreum in Illinois during 1991–1996. Ten lakes were stocked with combinations of two or three sizes of walleyes, including fry and small (50-mm) and large (100-mm) fingerlings. This permitted a total of 73 lake-year comparisons: fry versus large fingerlings (23 lake-years), fry versus small fingerlings (29 lake-years), and small versus large fingerlings (21 lake-years). Stocked fish were differentially marked with oxytetracycline or fin clips. Electrofishing catch per effort, relative survival, and population estimates were used in conjunction with production costs to compare size-based contributions and survival. Survival generally favored fingerlings over fry (70% of lake-years for small fingerlings, 67% for large fingerlings) and small fingerlings over large fingerlings (72% of la...

Seasonal zooplankton dynamics in main channel and backwater habitats of the Upper Mississippi River

This study used stratified random sampling to examine the spatial and temporal distribution of zooplankton communities in a large floodplain river (Mississippi River, USA). Potential mechanisms controlling zooplankton abundance and community structure were considered. Main channel and backwater habitats included in this study differed between a turbid upper pool reach where aquatic macrophytes were sparse and a lower pool reach which was considerably less turbid and had extensive aquatic macrophyte coverage. Samples were collected monthly during the summer over a 2-year period and multivariate analysis was used to examine the spatial and temporal distribution of zooplankton. Significant differences were found in zooplankton density and community composition among habitats and reaches within the pool. Rotifers were the dominant taxa and seasonality was pronounced, with peak densities often occurring in late-spring. Community structure varied by habitat and reach, which suggests that water quality, physical habitat characteristics, presence of aquatic macrophytes, and zooplankton sources can all influence the zooplankton communities of the Upper Mississippi River. Characterization of the zooplankton communities provides a basis for understanding changes in the river ecosystem and examination of zooplankton communities among habitats provides insight into the mechanisms affecting zooplankton dynamics.

Demography of Juvenile and Adult Brown Trout in Streams of Southeastern Minnesota

Abstract We assessed recruitment, survival, emigration, and immigration of brown trout Salmo trutta in six interconnected stream reaches to quantitatively estimate how much immigrants contributed to population size in reaches in southeastern Minnesota. We also examined the influence of reach and season on estimates of survival and emigration via mark and recapture of individual trout representing three groups (age-0 juveniles, age-1 and age-2 adults, and age-3+ large adults). Immigration was calculated as 1 minus emigration. Recruitment varied among the six reaches and 3 years of this study (range, 0–1,292 fish/km). Survival of the age-0 group and that comprising ages 1 and 2 varied by season but not reach. Survival was highest in winter for both groups but lowest in spring for age-0 trout and in fall for age-1 and age -2 trout. Emigration varied by season for age-0 trout but by reach for trout of ages 1 and 2. For age-3+ trout, survival and emigration only varied by reach. Survival was highest and emigra...

Factors Influencing Short-Term Hooking Mortality of Bluegills and the Implications for Restrictive Harvest Regulations

Abstract Angling can adversely affect populations of bluegill Lepomis macrochirus, and many state agencies have begun to explore restrictive creel and length limits. The fate of released fish can be influenced by a variety of factors, and the success of regulations could be reduced if the mortality of released bluegills is high. We conducted experiments using bluegills caught by the general angling public in Ridge Lake, Illinois, to quantify bluegill hooking mortality and test for the effects of bait type (live versus artificial), season (spring versus summer), retention time in live wells (1, 3, or 5 h), and retention gears (live wells versus fish baskets). Across all seasons and baits, the mortality of caught-and-released bluegills was low; the initial and short-term mortality for fish immediately released was 4.4%. There were significant differences in hooking mortality with respect to bait type, retention gear, and retention time. Bluegills caught on live bait experienced higher mortality (6.6%) than ...

Influence of Trophic Status on Larval Fish Abundance in Four Southeastern United States Reservoirs

ABSTRACT While the relationship between productivity and adult fish yield has been extensively studied, it has been viewed as a static relationship, whereas interactions among organisms and trophic levels change dramatically with the life stage of the interacting organisms. As such, little attention has been given to mechanisms that might control this relationship. Toward this end, we examined the influence of trophic status on larval fish abundance in four reservoirs in Alabama and Georgia, USA. Larval fish communities in eutrophic reservoirs were dominated by gizzard shad (Dorosoma cepedianum) and threadfin shad (D. petenense), while crappie (Pomoxis spp.) and sunfish (Lepomis spp.) contributed a relatively larger percentage of the fish community in the oligotrophic reservoir, similar to findings for older fishes from previously published work. However, while larval shad and lepomid sunfish were more abundant in eutrophic than in oligotrophic reservoirs, larval crappie showed the opposite trend. Why lar...