Gregory W. Whitledge

RIPARIAN SHADING AND GROUNDWATER ENHANCE GROWTH POTENTIAL FOR SMALLMOUTH BASS IN OZARK STREAMS

Moderation of stream temperatures by riparian shading and groundwater are known to promote growth and survival of salmonid fishes, but effects of riparian shade and groundwater on to be growth of warmwater stream fishes are poorly understood or assumed to be negligible. We used stream temperature models to relate shading from riparian vegetation and groundwater inflow to summer water temperatures in Missouri Ozark streams and evaluated effects of summer water temperatures on smallmouth bass, Micropterus dolomieu, growth using a bioenergetics model. Bioenergetics model simulations revealed that adult smallmouth bass in non-spring-fed streams have lower growth potential during summer than fish in spring-fed streams, are subject to mass loss when stream temperatures exceed 27 degrees C, and will likely exhibit greater interannual variation in growth during summer if all growth-influencing factors, other than temperature, are identical between the two stream types. Temperature models indicated that increased riparian shading will expand the longitudinal extent of thermal habitat capable of supporting adult smallmouth bass growth in spring-fed stream reaches when mean daily air temperatures exceed 27 degrees C. Optimum growth temperature (22 degrees C) will be present only in spring-fed streams under these conditions. Potential for increasing shade through riparian restoration is greatest for streams <5 m wide and along north-south reaches of larger streams. However, temperature models also indicated that restoring riparian shading to maximum levels throughout a watershed would increase the total stream mileage capable of supporting positive growth of adult smallmouth bass by only 1-6% when air temperatures are at or near average summer maxima; increases in suitable thermal habitat would be greatest in watersheds with higher spring densities. Riparian management for maintenance or restoration of the thermal habitat of adult smallmouth bass during summer should be focused in areas strongly influenced by groundwater. Restoring riparian shading along spring-fed warmwater streams will likely benefit adult smallmouth bass growth and may ultimately influence population sizes.

Development and Laboratory Evaluation of a Bioenergetics Model for Subadult and Adult Smallmouth Bass

Abstract A previously developed bioenergetics model for smallmouth bass Micropterus dolomieu (Hewett and Johnson 1992) was originally constructed with data exclusively from age-0 fish but has since been used to predict growth and food consumption for both age-0 and older fish, including adults. We developed a bioenergetics model for subadult and adult smallmouth bass and compared the abilities of the two models to predict growth and food consumption for fish weighing from 100 to 270 g. Model-independent laboratory growth and food consumption data for individual subadult and adult fish were used to evaluate the performance of both models. Experimental fish were subjected to three consecutive 3-week feeding regimes: an ad libitum ration at 22°C, a ration of 2.5% wet body weight/d at 22°C, and a ration of 2% wet body weight/d at 27°C. Overall, the bioenergetics model developed for subadult/adult smallmouth bass produced significantly greater accuracy in estimates of relative growth rate and cumulative consum...

Assessment of otolith chemistry for identifying source environment of fishes in the lower Illinois River, Illinois

Knowledge of habitats used by fish throughout their life history is important for the management and conservation of riverine fish populations and habitats. Naturally occurring chemical markers in otoliths have recently been used to determine natal origins and environmental history of fishes in a variety of marine and freshwater environments. However, to our knowledge, no studies have examined the applicability of this technique in large floodplain rivers in the USA. We evaluated otolith microchemistry and stable isotopic composition as tools for determining origins of fishes in the lower Illinois River, its tributaries, and floodplain lakes. Fishes were collected from eight sites during summer 2006 and two additional sites in spring 2007. Water samples were obtained from these 10 sites plus one additional tributary during summer and fall 2006 and spring 2007. Otolith and water samples were analyzed for δ18O and a suite of trace elements; otoliths were also analyzed for δ13C. Tributaries, floodplain lakes, and the Illinois River possessed distinct isotopic and elemental signatures, principally driven by differences in δ18O and δ13C among floodplain lakes, the Illinois River, and tributary streams. Otoliths reflected the differences in water chemistry among habitats. Relationships between water and otolith δ18O and Sr:Ca were not significantly different among species, but some differences in relationships between water and otolith Ba:Ca among species were detected. Linear discriminant function analysis with a leave-one-out jackknife procedure on otolith δ18O and δ13C indicated that fish may be classified back to environment (Illinois River, tributary, or floodplain lake) of capture with 80–98% accuracy. Otolith microchemistry and stable isotope analyses provide a potentially effective means for determining recruitment sources and environmental history of fishes in the Illinois River. The ability to reconstruct environmental history of individual fish using naturally occurring isotopic markers in otoliths may also facilitate efforts to quantify nutrient and energy subsidies to the Illinois River provided by fishes that emigrate from floodplain lakes or tributaries.

Laboratory Evaluation of a Bioenergetics Model for Largemouth Bass at Two Temperatures and Feeding Levels

Abstract We evaluated a bioenergetics model for adult largemouth bass Micropterus salmoides at two temperatures (22°C and 27°C) and two feeding levels (ad libitum and 2% wet body mass) in the laboratory. Three statistical methods were used to assess agreement between predicted and observed growth and consumption during a 9-week period. Multivariate profile analysis indicated no significant deviations between predicted and observed mean body masses at the end of each week of the experiment; partitioning mean square error revealed that 87% of the variance was attributed to random variation rather than to systematic variation; and a reliablility index indicated agreement between predicted and observed masses within a factor of 1.03. Predicted cumulative food consumption during the 9-week period was 9.4% less than that observed. Model predictions of mean daily consumption rates closely tracked observed values when fish were not fed to excess, but the model did not perform as well under ad libitum feeding cond...

Testing Bioenergetics Models under Feeding Regimes That Elicit Compensatory Growth

Abstract We tested bioenergetics model predictions of fish growth and food consumption under feeding regimes that elicited compensatory growth (CG) responses and for control fish fed ad libitum daily. Three treatment groups of seven juvenile hybrid sunfish (F1 hybrid of female green sunfish Lepomis cyanellus × male bluegill L. macrochirus) received repeating cycles of no feeding and refeeding; fixed no-feed periods of either 2, 4, or 14 d distinguished the treatment groups. The no-feed periods induced CG and were immediately followed by days of ad libitum refeeding. The refeeding periods for each treatment group were continued until the groups mean daily consumption no longer exceeded that of the controls, after which another no-feed period began. Bioenergetics model predictions of cumulative consumption and fish weight in 105-d experiments were not significantly different from observed values in the control group (2–3% model error). However, the model underestimated cumulative consumption (18–25%) and o...

Otolith trace element and stable isotopic compositions differentiate fishes from the Middle Mississippi River, its tributaries, and floodplain lakes

Naturally occurring stable isotope and trace elemental markers in otoliths have emerged as powerful tools for determining natal origins and environmental history of fishes in a variety of marine and freshwater environments. However, few studies have examined the applicability of this technique in large river-floodplain ecosystems. This study evaluated otolith microchemistry and stable isotopic composition as tools for determining environmental history of fishes in the Middle Mississippi River, its tributaries, and floodplain lakes in Illinois and Missouri, USA. Fishes were collected from 14 sites and water samples obtained from 16 sites during summer and fall 2006 and spring 2007. Otolith and water samples were analyzed for stable oxygen isotopic composition (δ18O) and concentrations of a suite of trace elements; otoliths were also analyzed for carbon isotopic composition (δ13C). Tributaries, floodplain lakes, and the Mississippi and Lower Missouri Rivers possessed distinct isotopic and elemental signatures that were reflected in fish otoliths. Fish from tributaries on the Missouri and Illinois sides of the middle Mississippi River could also be distinguished from one another by their elemental and isotopic fingerprints. Linear discriminant function analysis of otolith chemical signatures indicated that fish could be classified back to their environment of capture (Mississippi River, floodplain lake, tributary on the Illinois or Missouri side of the Mississippi River, or lower Missouri River) with 71–100% accuracy. This study demonstrates the potential applicability of otolith microchemistry and stable isotope analyses to determine natal origins and describe environmental history of fishes in the Middle Mississippi River, its tributaries, and floodplain lakes. The ability to reconstruct environmental history of individual fish using naturally occurring isotopic markers in otoliths may also facilitate efforts to quantify nutrient and energy subsidies to the Mississippi River provided by fishes that emigrate from floodplain lakes or tributaries.

Otolith microchemistry and isotopic composition as potential indicators of fish movement between the Illinois River drainage and Lake Michigan

ABSTRACT Naturally occurring chemical markers in otoliths offer a potential but untested means to identify source environment for fishes in the upper Illinois River system and Lake Michigan, including individuals that may breach or circumvent electrical barriers in the Chicago Sanitary and Ship Canal or be transferred via bait buckets between these formerly isolated drainages. The objectives of this study were to determine whether water and fish otolith stable isotopic and elemental compositions differ among Lake Michigan, the upper Illinois River, and three tributaries of the upper Illinois River (Fox, Des Plaines and DuPage Rivers) and to determine whether otolith isotopic and elemental signatures could be used to identify the water body from which individual fish were collected. Water and fish otolith samples were obtained from each site during 2007 and analyzed for &dgr;18O and a suite of trace element concentrations; otoliths also were analyzed for &dgr;13C. Otolith &dgr;13C values for Lake Michigan fish were distinct from individuals collected in the Illinois River and tributaries. Fish collected in the Fox and Des Plaines Rivers could be distinguished from one another and from fish captured in the Illinois and DuPage Rivers using otolith Sr:Ca and Ba:Ca ratios. Otolith isotopic and elemental compositions may enable identification of source environment for fishes that move or are transferred between the Illinois River drainage and Lake Michigan; however, temporal variation in otolith chemical signatures should be assessed.

Effects of Temperature on Specific Daily Metabolic Demand and Growth Scope of Sub-Adult and Adult Smallmouth Bass

ABSTRACT Specific daily metabolic demand (MET) and growth scope were determined for sub-adult (older juvenile) and adult smallmouth bass over the temperature range of 18–30°C. MET generally increased with increasing temperature and decreased with increasing fish weight, following patterns typically observed for fishes. Growth scope for sub-adult and adult smallmouth bass reached a maximum at 22°C and declined rapidly at higher temperatures to just 20% of maximum at 30°C. Sustained periods in which water temperatures substantially exceed 22°C are expected to lead to restrictions in growth scope for older juvenile and adult smallmouth bass, resulting in diminished growth rates, size, and fecundity.

Fin Ray Chemistry as a Potential Natural Tag for Smallmouth Bass in Northern Illinois Rivers

ABSTRACT Natural chemical markers in otoliths and fin rays have proven useful for describing environmental history of fishes in a variety of environments. However, no studies have evaluated smallmouth bass (Micropterus dolomieu) pectoral fin ray chemistry as a non-lethal alternative to otolith chemistry. We evaluated the trace element composition of smallmouth bass fin rays collected from northern Illinois rivers and determined the accuracy with which fish could be classified to their environment of capture using pectoral fin ray strontium: calcium (Sr:Ca) and barium: calcium (Ba:Ca) ratios. Fish were collected from nine sites during summer 2008. Fin ray Sr:Ca differed among some sites, reflecting previously observed differences in water and otolith chemistry for other fish species. Fin ray Ba:Ca did not differ among sites. Classification accuracy for individual fish to location of capture based on fin ray Sr:Ca was relatively poor when data from all nine sites in different watersheds were included. However, individual fish captured from the upper Illinois River watershed were accurately assigned to the river in which they were collected when data were restricted to these sites. Natural chemical signatures in fin rays will likely be effective for reconstructing environmental history of smallmouth bass when spatial differences in water chemistry are present, enabling investigations of stock mixing and recruitment sources for this species.

Benthic community metabolism in three habitats in an Ozark stream

Benthic community metabolism was measured in three habitats (riffles, runs and pools) during spring (May), summer (July) and fall (October) in the Jacks Fork River, Missouri, using an in situ chamber technique. Net community productivity (NCP) and gross community productivity (GCP) were highest in riffles, lowest in pools and intermediate in runs. Rates of NCP and GCP during spring and fall were similar for both riffles and runs, but NCP and GCP increased significantly during summer in both habitats. Pool substrates were always heterotrophic and exhibited no significant seasonal changes in NCP or GCP. Community respiration (CR) was highest in riffles, intermediate in runs and lowest in pools, but interhabitat differences in CR were generally smaller than for NCP. Rates of CR during spring and fall were similar, but CR increased significantly during summer. Results indicate that the physical conditions associated with each habitat strongly affect benthic community metabolism in this stream and that the relative proportions of these habitats will influence the ratio of living algal:detrital organic matter potentially available for consumers.