Aquatic ecosystem management requires knowledge of the links among landscape-level anthropogenic disturbances and aquatic ecosystem properties. With large catchment area to surface area ratios (CA:SA), reservoirs often receive substantial terrestrial subsidies and can be particularly sensitive to eutrophication. Reservoir numbers and attendant management problems are increasing, and tools are needed to categorize their eutrophication status. We analyzed a dataset of 109 reservoirs in Ohio (USA) in an effort to classify eutrophication status using landscape-level features and reservoir morphometry. These predictor variables were selected because they are relatively stable and easily measured. We employed regression tree analysis and used a composite eutrophication variable as our response variable. Our regression tree analysis accurately divided 67% of Ohio reservoirs into 4 eutrophication status groups using 3 predictor variables: percentage of catchment area composed of agriculture versus forest; maximum reservoir depth; and CA:SA. We can infer that reservoirs with catchments containing >71% forest will likely be oligotrophic to mesotrophic. For reservoirs with <71% catchment forest, trophic status is determined by the relative extent of catchment row crops and either CA:SA or maximum depth. We applied our regression tree to a subset of reservoirs in the Environmental Protection Agency's National Lakes Assessment (NLA; n = 339 reservoirs). With a few exceptions, we categorized NLA reservoirs by eutrophication status despite their broad geographical range across the contiguous USA. Our results show that a few easily measured, stable parameters can classify reservoir eutrophication status. Models like ours may be useful for broad-scale management decisions.

Community structure and species composition may be strongly influenced by predator-prey interactions resulting from and leading to episodes of population abundance or scarcity. We quantified diets of stocked saugeyes (female walleye Sander vitreus × male sauger S. canadensis) and estimated biomass of their primary prey, gizzard shad Dorosoma cepedianum, in three Ohio reservoirs at quarterly intervals during July 2002-July 2003 to determine whether saugeye consumptive demand could exceed the supply of available gizzard shad prey, resulting in a shift to alternative prey. We incorporated water temperature and saugeye diet composition, growth, and mortality into walleye bioenergetics models, which allowed us to compare estimated prey-specific consumption rates by saugeyes with gizzard shad standing stocks estimated with acoustics. Spring and summer were critical seasons. During spring, gizzard shad biomass was low, saugeye consumptive demand was low, and saugeyes consumed primarily alternative prey. During summer, when age-0 gizzard shad became available as prey, saugeyes consumed similar proportions of gizzard shad and alternative prey. Saugeye cumulative consumptive demand in summer was high and approached the gizzard shad standing stock. However, during fall and winter, gizzard shad supply was adequate to support high (fall) or declining (winter) saugeye consumptive demand. Across reservoirs and seasons, saugeyes consumed alternative prey to varying degrees, primarily sunfishes Lepomis spp., yellow perch Perca flavescens, logperch Percina caprodes, and minnows Pimephales spp. Seasonal asynchrony between saugeye consumptive demand and gizzard shad biomass during spring and summer indicated that a saugeye population with high survival, growth, and consumptive demand will opportunistically increase use of prey other than gizzard shad. The manner in which saugeye predation quantitatively influences these prey species could not be assessed. However, overexploitation of gizzard shad prey appears to be unlikely at current saugeye population sizes, particularly considering the opportunistic use of alternative prey and the high reproductive potential of gizzard shad.

Mechanisms associated with habitat selection by fishes are often unknown and require both physical habitat and growth environment considerations. We used spatially explicit prey biomass estimates, predator growth rate potential (GRP), bottom slope, predator distance from shore, and substrate data to predict habitat use of the saugeye (walleye Sander vitreus × sauger S. canadensis), a popular sport fish that is stocked throughout the central United States. We used telemetry to determine saugeye locations, acoustics to estimate prey biomass and distributions, and a bioenergetics model to aid in calculation of GRP. Akaike's information criterion was used to determine which habitat variables were most important in explaining saugeye location. Models that included both physical habitat and either GRP or prey density performed better than models that considered only one of these parameter types. The resulting models provided the data to create location suitability maps. In general, saugeyes favored steep slopes over hard substrates in nearshore areas with high biomass of gizzard shad Dorosoma cepedianum or high GRP. This comprehensive analysis suggests that the consideration of both spatial habitat suitability and temporal prey availability may improve fisheries management and conservation through a quantitative appreciation of available resources.An understanding of habitat selection and use by animals requires an understanding of both physical habitat and the growth environment. Through its effects on population dynamics and community structure, habitat has the ability to shape life his-

Hybridization and introgression continue to gain recognition as important issues in the management and conservation of native fishes. It is often necessary to identify hybrids in natural populations and to distinguish among individuals of various hybrid categories. Molecular methods are important for these purposes, and it is valuable if researchers have a range of molecular methods to apply, since each method has unique advantages and disadvantages. The determination of the best class of marker for a particular study depends on various factors, including the goals of the study, the resolution required, and the genomic and marker information already available for the taxa of interest. We modified a protocol to generate fluorescent randomly amplified polymorphic DNA (FRAPD) markers for hybridization studies. To our knowledge, this type of marker has not previously been used for hybrid identification. To demonstrate the utility of the modified methods, FRAPD markers were used to evaluate potential reproduction by saugeye (female walleye Sander vitreus × male sauger Sander canadensis) in a central Ohio reservoir. Our approach successfully generated a battery of diagnostic genetic markers that were used to test the hypothesis that young-of-year saugeye were later-generation offspring of saugeye cohorts previously stocked into the reservoir. Alternatively, the fish may have been immigrant first-generation saugeye from other sources. Data obtained from the FRAPD markers provided strong support favoring the alternative hypothesis. These methods provide a very useful tool for distinguishing between pure parentals and various classes of hybrid individuals, both in Sander spp. and in other taxa, offering a powerful and easily developed alternative to other molecular methods of generating informative genetic markers for hybridization studies.Hybridization and genetic introgression are important factors to consider in the management and conservation of native fishes (Epifanio and Nielsen 2000;Laikre et al. 2010;Sato et al. 2010). In turn, the need for powerful and efficient methods for identifying hybrids, and for distinguishing among various hybrid categories, continues to grow. Molecular methods can provide much more power for identifying hybrid individuals than morphological approaches. This is especially true when 671 672 SOVIC ET AL.