Justin A. VanDeHey

Genetic structure of lake whitefish (Coregonus clupeaformis) in Lake Michigan

Genetic relationships among lake whitefish (Coregonus clupeaformis) spawning aggregates in Lake Michigan were assessed and used to predict a stock or management unit (MU) model for the resource. We hypothesized that distinct spawning aggregates represented potential MUs and that differences at molecular markers underlie population differentiation. Genetic stock identification using 11 microsatellite loci indicated the presence of six genetic MUs. Resolved MUs corresponded to geographically proximate spawning aggregates clustering into genetic groups. Within MUs, analyses suggested that all but one delineated MU was a stable grouping (i.e., no between-population differences), with the exception being the Hog Island – Traverse Bay grouping. Elk Rapids was the most genetically divergent population within Lake Michigan. However, low Fst values suggested that moderate to high levels of gene flow occur or have occurred in the past between MUs. Significant tests of isolation by distance and low pairwise Fst valu...

Age-Structured Assessment of Walleyes, Saugers, and Naturally Produced Hybrids in Three Missouri River Reservoirs

Abstract Walleye Sander vitreus and sauger Sander canadensis naturally hybridize in many populations, but the factors influencing the recruitment of hybrids are unknown. We determined relative year-class strength for 1,454 saugers, walleyes, and naturally produced hybrids from three Missouri River reservoirs. Hybridization rates varied from 4% in Lakes Sharpe and Francis Case to 21% in Lewis and Clark Lake. Hybrids comprised multiple year-classes in each system, indicating that hybridization does not occur in erratic pulses but at a consistent low-level recruitment rate. The year-class strength of hybrids was not correlated with that of either walleyes or saugers. Our models suggest that higher than average recruitment of walleyes, saugers, and hybrids can be expected during years with warmer spring and early summer water temperatures in Lake Sharpe and Lewis and Clark Lake and during years when inflow (from main-stem discharge for hybrids and tributary inputs for saugers and walleyes) is reduced in Lewis...

Genetic Diversity of Lake Whitefish in Lakes Michigan and Huron; Sampling, Standardization, and Research Priorities

ABSTRACT We combined data from two laboratories to increase the spatial extent of a genetic data set for lake whitefish Coregonus clupeaformis from lakes Huron and Michigan and saw that genetic diversity was greatest between lakes, but that there was also structuring within lakes. Low diversity among stocks may be a reflection of relatively recent colonization of the Great Lakes, but other factors such as recent population fluctuation and localized stresses such as lamprey predation or heavy exploitation may also have a homogenizing effect. Our data suggested that there is asymmetrical movement of lake whitefish between Lake Huron and Lake Michigan; more genotypes associated with Lake Michigan were observed in Lake Huron. Adding additional collections to the calibrated set will allow further examination of diversity in other Great Lakes, answer questions regarding movement among lakes, and estimate contributions of stocks to commercial yields. As the picture of genetic diversity and population structure of lake whitefish in the Great Lakes region emerges, we need to develop methods to combine data types to help identify important areas for biodiversity and thus conservation. Adding genetic data to existing models will increase the precision of predictions of the impacts of new stresses and changes in existing pressures on an ecologically and commercially important species.

Assessing Length-Related Bias and the Need for Data Standardization in the Development of Standard Weight Equations

Abstract The recently developed empirical percentile (EmP) method, a technique for deriving standard weight (Ws ) equations, putatively reduces the length-related biases that often plague such equations. To determine whether the EmP method is superior to the regression line–percentile (RLP) method in reducing length-related biases, we developed new Ws equations by applying both methods to two morphologically distinct species, walleye Sander vitreus and black crappie Pomoxis nigromaculatus. We also investigated diagnostic approaches to provide quality control for weight–length data. We evaluated the new Ws equations with filtered independent data to determine which equation reduced length bias the most. We suggest a protocol for evaluating length-related bias using an independent data set. Our results showed that for randomly selected walleye populations, the RLP method did not have any length-related biases when relative weight (Wr ) was plotted as a function of length. However, the Wr values calculated f...

Survival, reproduction, and recruitment of gizzard shad (Dorosoma cepedianum) at the northwestern edge of its native range

South Dakota (SD) represents the northwestern edge of gizzard shads (Dorosoma cepedianum) native range. However, with recent climate warming the gizzard shad is experiencing a natural range expansion northward. Little knowledge exists regarding temperatures that are required for overwinter survival, and less is known regarding population dynamics of gizzard shad in these populations. The objectives of this research were to determine the extent of reproduction, recruitment, and overwinter survival after annual introductions of adult gizzard shad in two northeastern SD glacial lakes relative to other SD systems. Prior to spawning, the gizzard shad was introduced into East Krause Lake and Middle Lynn Lake and successfully spawned during 2008 and 2009. Mean (±SE) peak larval abundances (number/100 m3) were 3.87 (±1.87) and 1.72 (±0.89) in East Krause Lake and 0.79 (±0.22) and 0.17 (±0.11) in Middle Lynn Lake in 2008 and 2009, respectively. Larval abundances were lower than those observed in most other SD populations. Survival to fall age-0 was documented in both years in Middle Lynn Lake, but only during 2008 in East Krause Lake. No overwinter survival was documented. Low water temperatures and rapidly cooling water likely caused overwinter mortality of gizzard shad in these systems. Temperature at the sediment–water interface during the winter of 2009–2010 was below 2.2°C for 114 and 62 consecutive days in East Krause Lake and Middle Lynn Lake, respectively.

Assessing Length-Related Biases in Standard Weight Equations: Response to Comment

Assessing Length-Related Biases in Standard Weight Equations: Response to Comment Steven H. Ranney a , Mark J. Fincel b , Melissa R. Wuellner b , Justin A. VanDeHey b & Michael L. Brown b a Gateway Environmental, Post Office Box 103, Gallatin Gateway, Montana, 59730-0103, USA b Department of Wildlife and Fisheries Sciences, South Dakota State University, Box 2140B, Northern Plains Biostress 138, Brookings, South Dakota, 57007-1696, USA

Comparing isotope signatures of prey fish: does gut removal affect δ13C or δ15N?

Stable isotope analysis is a quick and inexpensive method to monitor the effects of food web changes on aquatic communities. Traditionally, whole specimens have been used when determining isotope composition of prey fish or age-0 recreational fishes. However, gut contents of prey fish could potentially alter isotope composition of the specimen, especially when recent foraging has taken place or when the gut contains non-assimilated material that would normally pass through fishes undigested. To assess the impacts of gut content on prey fish isotope signatures, we examined the differences in isotopic variation of five prey fish species using whole fish, whole fish with the gut contents removed, and dorsal muscle only. We found significant differences in both δ15N and δ13C between the three tissue treatments. In most cases, muscle tissue was enriched compared to whole specimens or gut-removed specimens. Moreover, differences in mean δ15N within a species were up to 2‰ among treatments. This would result in a change of over half a trophic position (TP) based on a 3.4‰ increase per trophic level. However, there were no apparent relationships between tissue isotope values in fish with increased gut fullness (more prey tissue present). We suggest that muscle tissue should be used as the standard tissue for determining isotope composition of prey fish or age-0 recreational fishes, especially when determining enrichment for mixing models, calculating TP, or constructing aquatic food webs.

Size and Age at Maturity of Bluegill (Lepomis macrochirus) in Southeastern South Dakota Impoundments

ABSTRACT Both social and demographic factors can affect size structure of bluegill (Lepomis macrochirus) populations, but these two factors have not been assessed in South Dakota impoundments. We compared length and age at maturity of bluegill in four southeastern South Dakota impoundments (two with historically low size structure and two with historically high size structure and related bluegill growth patterns to size structure and relative abundance. Despite large differences in size structure and maximum observed total lengths among lakes, all males from three of four populations were mature by age 3, with the only exception being Lake Mitchell (high size structure population; 89% mature). Mean total length at 100% maturity was lower in the two low size structure populations, and bluegill in the two low size structure populations matured at a smaller length than in the two high size structure populations; however, at least 50% of males in all four systems reached sexual maturity by 140mm in all years. Negative relationships between mean catch-per-unit-effort and both proportional size distribution (r2 =0.47) and proportional size distribution of preferred length fish (r2 =0.86) values for all populations indicated that density-dependence was likely in these systems. Indications of social influence on bluegili behavior were observed; however, density-dependence was likely more influential on size structure.