Mark J. Fincel

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...

Otolith Microchemistry Reveals Natal Origins of Walleyes in Missouri River Reservoirs

AbstractReproductive habitats are vital for sustaining fish populations, but their location and relative natal contributions are often unknown or poorly understood. We used otolith microchemistry to examine natal origins of Walleyes Sander vitreus in Missouri River reservoirs (i.e., Lake Oahe, Lake Sharpe, Lake Francis Case, and Lewis and Clark Lake) in North Dakota and South Dakota. Water Sr:Ca and Ba:Ca were spatially heterogeneous and temporally consistent in all impoundments. Otolith Sr:Ca and Ba:Ca from age-0 Walleyes permitted the reclassification of fish to known natal habitats (i.e., tributary, embayment, main stem) and individual sites with 87% and 75% accuracy, respectively. Natal contributions were highest in tributaries, particularly those in Lake Oahe, where 32% of all adults and 77% of Lake Oahe adults hatched. Embayments and main-stem environments had high natal contributions (67–78%) in Lakes Sharpe and Francis Case and Lewis and Clark Lake, where tributaries are less abundant. Our researc...

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.

Larval gizzard shad characteristics in Lake Oahe, South Dakota: a species at the northern edge of its range

Gizzard shad, Dorosoma cepedianum, have generally been restricted to the lower Missouri River impoundments in South Dakota. In recent years, gizzard shad numbers have increased in Lake Oahe, marking the northern-most natural population. These increases could potentially affect recreational fishes. Specifically, questions arise about larval gizzard shad growth dynamics and if age-0 gizzard shad in Lake Oahe will exhibit fast or slow growth, both of which can have profound effects on piscivore populations in this reservoir. In this study, we evaluated larval gizzard shad hatch timing, growth, and density in Lake Oahe. We collected larval gizzard shad from six sites from May to July 2008 and used sagittal otoliths to estimate the growth and back-calculate the hatch date. We found that larval gizzard shad hatched earlier in the upper part of the reservoir compared to the lower portion and that hatch date appeared to correspond to warming water temperatures. The peak larval gizzard shad density ranged from 0.6 to 33.6 (#/100 m3) and varied significantly among reservoir sites. Larval gizzard shad growth ranged from 0.24 to 0.57 (mm/d) and differed spatially within the reservoir. We found no relationship between the larval gizzard shad growth or density and small- or large-bodied zooplankton density (p > 0.05). As this population exhibits slow growth and low densities, gizzard shad should remain a suitable forage option for recreational fishes in Lake Oahe.

Entrainment of Rainbow Smelt through Oahe Dam during the 2011 Missouri River Flood

AbstractEntrainment of fishes through impoundments is common, and Rainbow Smelt Osmerus mordax, which is the dominant forage fish species in the Missouri River reservoir, Lake Oahe, is frequently entrained through Oahe Dam at low rates. In 2011, the Missouri River endured a flood of a magnitude never before experienced in recorded history. Concerns regarding Rainbow Smelt entrainment were numerous; thus we sought to determine Rainbow Smelt entrainment rates. To evaluate entrainment, we used stationary trawls downstream from each Oahe Dam outlet structure and repeated hydroacoustic sampling above Oahe Dam on Lake Oahe. Trawl sampling estimated that 231 million adult and 433 million age-0 Rainbow Smelt were entrained during the summer of 2011. Hydroacoustic sampling estimated a loss of 213 million adult and 520 million age-0 Rainbow Smelt from Lake Oahe. Thus, both gears provided an estimate of Rainbow Smelt loss that was surprisingly similar. Additionally, Rainbow Smelt entrainment rates were substantially...

Otoliths as elemental tracers of walleye environmental history: insights for interjurisdictional fisheries management

ABSTRACT Carlson AK, Bailey PE, Fincel MJ, Graeb BDS. Otoliths as elemental tracers of walleye environmental history: insights for interjurisdictional fisheries management. Lake Reserve Manage. 32:329–340. Understanding fish natal origins and movement is important for managing interjurisdictional fisheries. We used otolith microchemistry to assess walleye (Sander vitreus) provenance, movement, and natal homing in Lake Oahe, an interjurisdictional reservoir fishery in North Dakota and South Dakota. Historical (1983–1989) water chemistry varied among 6 tributaries for strontium:calcium (Sr:Ca; μmol/mol) and barium:calcium (Ba:Ca) and between 2 main-stem sites for Ba:Ca. Current (2012) water chemistry was spatially heterogeneous for Sr:Ca and Ba:Ca. Both ratios were consistent between the historical and current periods in tributaries and main-stem sites. Sr:Ca and Ba:Ca of age-0 walleye otolith cores varied in proportion to water chemistry, resulting in high reclassification accuracies to habitat types (87%) and individual sites (78%). For adult walleye, contributions of South Dakota natal sites to the North Dakota population (48%, n = 30) and North Dakota natal sites to the South Dakota population (48%, n = 29) were highest for tributaries and embayments (e.g., Moreau and Cannonball rivers, Beaver Bay). Annual downstream movement was more prevalent than upstream movement, particularly during a flood in 2011. An average of 36% of North Dakota walleye and 33% of South Dakota walleye exhibited natal homing each year from 2009 to 2013. Otolith element:Ca ratios are effective natural tracers for evaluating walleye natal origins, movement within and between states, and natal homing. Otolith microchemistry is a tool for interjurisdictional walleye management in reservoirs, providing a methodology for assessing natal origins and movement and designing spatially informed habitat conservation programs and harvest regulations.

Effects of historic flooding on fishes and aquatic habitats in a Missouri River delta

Understanding the effects of disturbances on aquatic biota is important for management of the worlds rivers. Riverine deltas are among the most biologically productive ecosystems, yet the ecological effects of floods in deltas are poorly understood. Therefore, the goal of this study was to examine impacts of an historic flood in the Missouri River basin in 2011 on fishes and aquatic habitats in the Lewis and Clark Delta, located in South Dakota and Nebraska, USA. Fish community structural indices declined in the six years preceding the flood, with species richness and diversity (Fishers α) decreasing from 25 to 22 and 4.56 to 3.48, respectively. However, the fish community exhibited short-term resistance to the flood as both metrics were similar to pre-flood levels after the disturbance in 2012. Evenness (J′) declined from 0.88 to 0.73 before the flood but increased to 0.84 after the disturbance. The majority of species exhibited greater relative abundance after the flood regardless of age class (i.e., juvenile, adult), morphology (i.e., small-bodied, large-bodied), introduction history (i.e., introduced, native), or recreational importance (i.e., sport fish, non-recreational). However, the flood reduced relative abundance of juvenile freshwater drum (Aplodinotus grunniens) and white crappie (Pomoxis annularis) and did not affect the three small-bodied species that were studied, including emerald shiner (Notropis atherinoides), red shiner (Cyprinella lutrensis), and spotfin shiner (Cyprinella spiloptera). The flood decreased side channel and backwater frequency and width/area but increased sandbar abundance. Physical alterations evidently had minimal effects on structural indices of the fish community. However, an overall increase in relative abundance across species suggests that interspersed fluvial and slackwater habitats in the delta provided refuge from floodwaters during the disturbance. Maintaining habitat connectivity in deltas during and after floods is particularly important for fisheries conservation. Illustrating the ecological effects and implications of a major flood, this study contributes to the nascent field of delta ecology.

Using cumulative diet data and stable isotope analysis to determine trophic position of walleye Sander vitreus in a large, complex system

Diet studies have traditionally been used to determine prey use and food web dynamics, while stable isotope analysis provides for a time-integrated approach to evaluate food web dynamics and characterize energy flow in aquatic systems. Direct comparison of the two techniques is rare and difficult to conduct in large, species rich systems. We compared changes in walleye Sander vitreus trophic position (TP) derived from paired diet content and stable isotope analysis. Individual diet-derived TP estimates were dissimilar to stable isotope-derived TP estimates. However, cumulative diet-derived TP estimates integrated from May 2001 to May 2002 corresponded to May 2002 isotope-derived estimates of TP. Average walleye TP estimates from the spring season appear representative of feeding throughout the entire previous year.

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.