Geology topics

Ryan P. Koenigs

Publications and source records attributed to Ryan P. Koenigs.

5 recordsLinked to original sources

USGS2021

Second fin ray shows promise for estimating ages of juvenile but not adult Lake Sturgeon

The first marginal pectoral fin ray (fin spine) is the most common structure used for estimating the age of sturgeons, including Lake Sturgeon Acipenser fulvescens . However, conflicting results from studies on the effects of fin spine removal have made some managers hesitant about the practice. We investigated whether the second pectoral fin ray, which can be removed in a less invasive procedure, could be used for estimating ages of Lake Sturgeon. Ages estimated from fin spine and second fin ray samples were compared for 53 wild (470 to 1,981 mm TL) and 16 stocked, known-age (ages 8–18) Lake Sturgeon. Mean coefficient of variation for all samples was 12.4% for the fin spine and 17.5% for the second fin ray. In known-age fish, 17% of estimated ages for the fin spine and the second fin ray matched true age. For the remaining estimates, the difference between the second fin ray and true age was greater than the difference between the fin spine and true age ( P < 0.05, Wilcoxon’s signed rank test). In juvenile fish ( n = 24), 75% of ages estimated from fin spines and second fin rays were within ±4 annuli, which was similar to differences in reader agreement for the same fin spine. Age estimates for adult Lake Sturgeon ( n = 45) were less when using the second fin ray relative to the fin spine (up to –34 years). Additionally, poor annulus clarity was observed in >70% of the second fin rays sampled from adult fish. Our results suggest that the second fin ray does not provide reliable age estimates for adult Lake Sturgeon but may have some utility for estimating age of juvenile Lake Sturgeon. Additional research with a larger sample size would be required to provide more conclusive results.

Vermont, Wisconsin↗

USGS2020

Diets of double-crested cormorants in the Winnebago System, Wisconsin

Double-crested cormorant Phalacrocorox auritus Lesson (cormorant) populations have increased throughout the Great Lakes region of North America causing concern related to the impact of cormorant predation on fish communities. A recent decline in yellow perch Perca flavescens (Mitchill) abundance within the Lake Winnebago System, Wisconsin, USA, prompted an assessment of cormorant diets to evaluate potential effects of cormorant predation on the sportfish community. Diets were collected from 883 cormorants (417 from Lake Winnebago and 466 from Lake Butte des Morts) between 2015 and 2017. Cormorant diets on both waterbodies consisted mostly of freshwater drum Aplodinotus grunniens Rafinesque and gizzard shad Dorosoma cepedianum (Lesueur). Yellow perch and walleye Sander vitreus (Mitchill) observations were infrequent and represented < 5% of cormorant diets by weight each year. Under current conditions, cormorant predation likely has minimal impact on the Lake Winnebago sportfish community, but more research is needed to assess potential impacts on Lake Butte des Morts.

Wisconsin↗

USGS2019

Potential for improving among-reader precision and accuracy of Walleye age estimates with minimal training

Within most resource management agencies, fish ages assigned by multiple readers are used to estimate age-based population metrics and to develop state or regional growth standards under the assumption that among-reader precision and accuracy are high. A cursory evaluation suggested that precision of age estimates among seven individuals who routinely estimate Walleye Sander vitreus age for the Wisconsin Department of Natural Resources was remarkably low (otolith mean coefficient of variation [CV] = 37%; dorsal spine mean CV = 35%), which prompted concern and interest in whether among-reader precision could be improved with a minimal level of training. Consequently, we compared among-reader precision and accuracy before and after a 1-d training exercise. We distributed images of sectioned otoliths and sectioned dorsal spines from a random sample of 50 Walleye, along with images of structures from 25 known-age Walleye, to 21 readers grouped into beginner, intermediate, and advanced experience levels based on responses to a pretraining survey. Among-reader precision was substantially higher after training (otolith mean CV = 16%; dorsal spine mean CV = 15%) than before (otolith mean CV = 27%; dorsal spine mean CV = 26%). Accuracy of age estimates also improved after training, but greater improvements were observed for otoliths (mean difference between estimated and known ages before training = 0.80 year; after training = 0.15 year) than for dorsal spines (mean difference between estimated and known ages before training = 0.38 year; after training = 0.22 year). Similar improvements in precision and accuracy were evident for all experience levels. Our results suggest that a simple, low-cost age estimation training can substantially increase precision and accuracy of age estimates among a large group of readers. However, additional training and quality control measures may be required to achieve higher levels of precision and accuracy.

North American Journal of Fisheries Management↗

USGS2017

Walleye age estimation using otoliths and dorsal spines: Preparation techniques and sampling guidelines based on sex and total length

We used dorsal spines and otoliths from 735 Walleye Sander vitreus collected from 35 Wisconsin water bodies to evaluate whether 1) otolith and dorsal spine cross sections provided age estimates similar to simpler methods of preparation (e.g., whole otoliths and dorsal spines, cracked otoliths); and 2) between-reader precision and differences between spine and otolith ages varied in relation to total length (TL), sex, and growth rate. Ages estimated from structures prepared using simpler techniques were generally similar to ages estimated using thin sections of dorsal spines and otoliths, suggesting that, in some instances, much of the additional processing time and specialized equipment associated with thin sectioning could be avoided. Overall, between-reader precision was higher for sectioned otoliths (mean coefficient of variation [CV] = 3.28%; standard error [SE] = 0.33%) than for sectioned dorsal spines (mean CV = 9.20%; SE = 0.56%). When using sectioned otoliths for age assignment, between-reader precision did not vary between sexes or growth categories (i.e., fast, moderate, slow), but between-reader precision was higher for females than males when using sectioned dorsal spines. Dorsal spines were generally effective at replicating otolith ages for male Walleye <450 mm TL and female Walleye <600 mm TL, suggesting that dorsal spines can be used to estimate ages for male Walleye <450 mm TL and female Walleye <600 mm TL. If sex is unknown, we suggest dorsal spines be used to estimate ages for Walleye <450 mm TL, but that otoliths be used for fish >450 mm TL. Our results provide useful guidance on structure and preparation technique selection for Walleye age estimation, thereby allowing biologists to develop sampling guidelines that could be implemented using information that is always (TL) or often (sex) available at the time of fish collection.

Wisconsin↗

USGS2015

Temporal variation in viral hemorrhagic septicemia virus antibodies in freshwater drum ( Aplodinotus grunniens ) indicates cyclic transmission in Lake Winnebago, Wisconsin

Viral hemorrhagic septicemia virus (VHSV) is an emerging pathogen that causes mass mortality in multiple fish species. In 2007, the Great Lakes freshwater strain, type IVb, caused a large die-off of freshwater drum ( Aplodinotus grunniens ) in Lake Winnebago, Wisconsin, USA. To evaluate the persistence and transmission of VHSV, freshwater drum from Lake Winnebago were tested for antibodies to the virus using recently developed virus neutralization (VN) and enzyme-linked immunosorbent (ELISA) assays. Samples were also tested by real-time reverse transcription-PCR (rRT-PCR) to detect viral RNA. Of 548 serum samples tested, 44 (8.03%) were positive by VN (titers ranging from 1:16 to 1:1,024) and 45 (8.21%) were positive by ELISA, including 7 fish positive by both assays. Antibody prevalence increased with age and was higher in one northwestern area of Lake Winnebago than in other areas. Of 3,864 tissues sampled from 551 fish, 1 spleen and 1 kidney sample from a single adult female fish collected in the spring of 2012 tested positive for VHSV by rRT-PCR, and serum from the same fish tested positive by VN and ELISA. These results suggest that VHSV persists and viral transmission may be active in Lake Winnebago even in years following outbreaks and that wild fish may survive VHSV infection and maintain detectable antibody titers while harboring viral RNA. Influxes of immunologically naive juvenile fish through recruitment may reduce herd immunity, allow VHSV to persist, and drive superannual cycles of transmission that may sporadically manifest as fish kills.

Wisconsin↗