Daniel J. Dembkowski

Hierarchy in factors affecting fish biodiversity in floodplain lakes of the Mississippi Alluvial Valley

River-floodplain ecosystems offer some of the most diverse and dynamic environments in the world. Accordingly, floodplain habitats harbor diverse fish assemblages. Fish biodiversity in floodplain lakes may be influenced by multiple variables operating on disparate scales, and these variables may exhibit a hierarchical organization depending on whether one variable governs another. In this study, we examined the interaction between primary variables descriptive of floodplain lake large-scale features, suites of secondary variables descriptive of water quality and primary productivity, and a set of tertiary variables descriptive of fish biodiversity across a range of floodplain lakes in the Mississippi Alluvial Valley of Mississippi and Arkansas (USA). Lakes varied considerably in their representation of primary, secondary, and tertiary variables. Multivariate direct gradient analyses indicated that lake maximum depth and the percentage of agricultural land surrounding a lake were the most important factors controlling variation in suites of secondary and tertiary variables, followed to a lesser extent by lake surface area. Fish biodiversity was generally greatest in large, deep lakes with lower proportions of watershed agricultural land. Our results may help foster a holistic approach to floodplain lake management and suggest the framework for a feedback model wherein primary variables can be manipulated for conservation and restoration purposes and secondary and tertiary variables can be used to monitor the success of such efforts.

Comparison of Fish Assemblages in Two Disjoined Segments of an Oxbow Lake in Relation to Connectivity

Abstract Disconnection between adjacent habitat patches is one of the most notable factors contributing to the decreased biotic integrity of global ecosystems. Connectivity is especially threatened in river–floodplain ecosystems in which channel modifications have disrupted the lateral links between the main river channel and floodplain lakes. In this study, we examined the interaction between the interconnectedness of floodplain lakes and main river channels and fish assemblage descriptors. Fish assemblages in two segments of an oxbow lake, one connected to and the other isolated from the Yazoo River, Mississippi, were estimated with daytime boat electrofishing during 2007–2010. The frequency of connection for the connected segment ranged from zero to seven individual events per year (mean, ∼2). The timing of most connection events reflected regional precipitation patterns. Greater species richness, diversity, and evenness were observed in the connected segment. Additionally, the connected segment had a ...

Influence of variable rainbow smelt and gizzard shad abundance on walleye diets and growth

Abstract Fincel MJ, Dembkowski DJ, Chipps SR. 2014. Influence of variable rainbow smelt and gizzard shad abundance on walleye diets and growth. Lake Reserv Manage. 30:258–267. Prey availability influences growth and condition of walleye (Sander vitreus) in large systems. In Lake Oahe, South Dakota, rainbow smelt (Osmerus mordax) and gizzard shad (Dorosoma cepedianum) are primary prey of walleye, but their abundance varies substantially year to year. To evaluate the influence of gizzard shad and rainbow smelt on walleye diets and growth in Lake Oahe, we compared recent estimates of walleye diets and growth in 2008 through 2010 with those from the late 1990s and early 2000s. Walleye diets differed seasonally with increased piscivory in July and October. In 2008, gizzard shad were the dominant prey item of walleye, representing about 60% of the diets by weight; however, by 2009, gizzard shad declined appreciably in the diet (22%) and were completely absent from walleye diets by 2010. Conversely, rainbow smelt abundance represented 12%, 27%, and 90% of walleye diets by weight in 2008, 2009 and 2010, respectively. Changes in growth corresponded to changes in diets, with the slowest growth occurring when gizzard shad were dominant in the diets and increasing growth every year thereafter. Because gizzard shad are only available during short periods (<3 months) in late summer, walleye can only achieve about 50% of their annual maintenance energy requirements from this prey source. Conversely, rainbow smelt, which are available and consumed year round, provide a continuous energy source that contributes to high growth rates. Nonetheless, when abundant, gizzard shad may provide an important subsidy to Lake Oahe walleye during periods of low rainbow smelt abundance.

Environmental variables measured at multiple spatial scales exert uneven influence on fish assemblages of floodplain lakes

We examined the interaction between environmental variables measured at three different scales (i.e., landscape, lake, and in-lake) and fish assemblage descriptors across a range of over 50 floodplain lakes in the Mississippi Alluvial Valley of Mississippi and Arkansas. Our goal was to identify important local- and landscape-level determinants of fish assemblage structure. Relationships between fish assemblage structure and variables measured at broader scales (i.e., landscape-level and lake-level) were hypothesized to be stronger than relationships with variables measured at finer scales (i.e., in-lake variables). Results suggest that fish assemblage structure in floodplain lakes was influenced by variables operating on three different scales. However, and contrary to expectations, canonical correlations between in-lake environmental characteristics and fish assemblage structure were generally stronger than correlations between landscape-level and lake-level variables and fish assemblage structure, suggesting a hierarchy of influence. From a resource management perspective, our study suggests that landscape-level and lake-level variables may be manipulated for conservation or restoration purposes, and in-lake variables and fish assemblage structure may be used to monitor the success of such efforts.

Pressures to Publish: Catalysts for the Loss of Scientific Writing Integrity?

ABSTRACT Publishing research is the final step in the scientific process and is used as the primary means for disseminating research findings to the scientific community. Publishing can embody many personal motivations (e.g., gratification, seeing a finished product in print, desire to further science) for authors as well as professional benefits (e.g., promotion, tenure, future funding opportunities). As the scientific workforce and competition for jobs and funding increase, publishing productivity has become a driving factor for many authors, which may lead to writing practices that violate integrity. In this essay, we discuss writing actions that may be considered a violation of integrity in the context of traditional manuscript sections (introduction and discussion, methods, and results). We define “integrity” as consistency of actions that reflect honesty and truthfulness. Writing the introduction and discussion can be compared to an artistic creation because the rendition of the data may vary depend...

Comparison of Four Types of Sampling Gears for Estimating Age-0 Yellow Perch Density

To aid biologists in obtaining reliable and efficient estimates of age-0 yellow perch (Perca flavescens) abundance, we compared operational effort and catch characteristics (i.e., density, length frequencies, and precision) of four gear types (beach seines, benthic sleds, drop nets, and push trawls) in littoral habitats in two South Dakota glacial lakes. Gear types were selected on the basis that the volume of water sampled could be determined and, thus, density (number/m3) of age-0 yellow perch could be computed for each. Age-0 yellow perch were collected on three occasions with each gear in both lakes in August 2011. Differences in gear operational effort (i.e., the time required for set-up, deployment, and fish sorting) and age-0 yellow perch density and length frequencies were compared among sampling gears. Mean operational effort ranged from 9 to 65 min, mean density from 0.07 to 4.1 age-0 yellow perch/m3, coefficients of variation of mean age-0 perch density from 33 to 134, and number of samples required to estimate a 25% change in mean age-0 perch abundance from 22 to 305. Beach seines and drop nets may selectively sample larger age-0 yellow perch than benthic sleds and push trawls. We recommend use of beach seines or benthic sleds for sampling age-0 yellow perch in littoral habitats of glacial lakes. However, all sampling gears tested in this study have associated costs and benefits and one may be more suitable than another under different circumstances.

Phenology of Annulus Formation in Walleye and Smallmouth Bass Otoliths

Walleye Sander vitreus and smallmouth bass Micropterus dolomieu were sampled monthly (May-October) from Lake Sharpe, South Dakota during 2006 and 2007 to estimate the timing of otolith annulus formation and to evaluate the influence of fish age, sex, and sample location (walleye only) on the timing and detection of annulus formation. Tim- ing of annulus formation was evaluated using marginal increment analysis. Walleye samples were stratified by age, sex, and sample location (i.e., upper and lower Lake Sharpe) and smallmouth bass samples were stratified by age and sex. Monthly mean marginal increment measurements for both species generally increased from May to June, declined in July, and slowly increased from August to October. Although monthly differences in marginal increment measurements across analysis strata were rarely consistent, July generally had the lowest mean marginal increment across species and strata, suggesting that annulus formation in walleye and smallmouth bass in Lake Sharpe likely occurs in July. The lack of dif- ferences in timing of annulus formation across species-specific strata was surprising given the well-known influences of age, sex, and water temperature on somatic growth. Nonetheless, results will aid managers in improving the accuracy of age estimates.

Impacts of Northern Pike on stocked Rainbow Trout in Pactola Reservoir, South Dakota

AbstractEstablishment of nonnative Northern Pike Esox lucius in Pactola Reservoir, South Dakota, has prompted concern among biologists about the influence of this species on the lake’s intensively managed salmonid fisheries. Ancedotal information suggests that catch rates of Rainbow Trout Oncorhynchus mykiss have declined while mean size and abundance of Northern Pike has increased, although quantitative information on diet and growth of the Northern Pike population is lacking. To address potential interactions between Northern Pike and Rainbow Trout, we assessed size-dependent predation by Northern Pike on Rainbow Trout and determined the relative energetic contribution of stocked Rainbow Trout to Northern Pike growth using bioenergetics modeling. Stable isotopes combined with traditional diet analyses revealed that smaller Northern Pike (<600 mm TL) consumed primarily centrarchids and Rainbow Smelt Osmerus mordax, and Rainbow Trout contributed less than 10% to their annual energy consumption. In contras...

Insights for Undergraduates Seeking an Advanced Degree in Wildlife and Fisheries Sciences

ABSTRACT In todays job market, having a successful career in the fisheries and wildlife sciences is becoming more dependent on obtaining an advanced degree. As a result, competition for getting accepted into a graduate program is fierce. Our objective for this study was to provide prospective graduate students some insights as to what qualifications or attributes would best prepare them for obtaining a graduate position (M.S.) and to excel once they are enrolled in a graduate program. A survey was sent to 50 universities within the National Association of University Fisheries and Wildlife Programs (NAUFWP) where both faculty and undergraduate students were asked questions relating to graduate school. Faculty rated the importance of various criteria and attributes of graduate school, and students answered the questions according to how they believed faculty members would respond. Overall, undergraduate students shared many of the same graduate school viewpoints as those held by faculty members. However, v...

Sampling Glacial Lake Littoral Fish Assemblages with Four Gears

Abstract Littoral zone fish assemblages are important components of freshwater lakes. Monitoring of littoral fish assemblage structure is important because littoral fishes often comprise the majority of the entire fish assemblage, and fluctuations in the structure and abundance of the littoral fish assemblage can influence trophic interactions and fishery yields at the ecosystem level. Single-gear sampling designs, however, may only capture a subset of the fish assemblage, resulting in a skewed representation of fish assemblage structure. Use of multiple gears can be justified if they provide complementary fish assemblage information. Our objective was to compare glacial lake fish assemblage structure as represented by four gears and to assess whether the gears provide redundant or complementary fish assemblage information. Two northeastern South Dakota glacial lakes were sampled with a beach seine, benthic sled, drop net, and push trawl in August 2011. Results indicated that fish assemblage structure did...