Ronald M. Bruch

Lake Sturgeon Age Validation using Bomb Radiocarbon and Known-Age Fish

Abstract Pectoral fin spines have been the accepted structure for estimating the age of various sturgeon species for nearly 100 years, though other structures have also been used (otoliths, pectoral girdle, scutes, and caudal fulcra). Accuracy of age estimates using any of these structures has not been validated, so we report the first use of bomb radiocarbon (14C) assays to assess the validity of ages estimated using growth increments on pectoral fin spine and otolith frontal cross sections from lake sturgeon Acipenser fulvescens; we also assessed age estimates from pectoral fin spines of known-age lake sturgeon. Growth increments on pectoral fin spine cross sections underestimated true age of fish older than 14 years and error increased with age, whereas otoliths accurately estimated true age up to at least 52 years. Increment formation on pectoral fin spine and otolith cross sections from juvenile lake sturgeon (ages 2-11) was similar, although pectoral spines were clearer and easier to interpret. A po...

Calcium regulation in wild populations of a freshwater cartilaginous fish, the lake sturgeon Acipenser fulvescens

Lake sturgeon, Acipenser fulvescens, are one of a few species of cartilaginous fishes that complete their life cycle entirely in freshwater. Sturgeons maintain very low concentrations of circulating calcium (Ca(2+)) compared with other vertebrates, and therefore, face unique challenges in regard to Ca(2+) regulation, which are likely to be magnified during vitellogenic stages of the reproductive cycle. In the present study, Ca(2+) concentrations and associated hormones of female and male lake sturgeon were examined in two wild populations, and were related to reproductive stage. In both populations, free, bound and total Ca(2+) were low, peaking in mid-late vitellogenic females. Internal Ca(2+) and phosphate (PO(4)(3-)) concentrations were inversely related to environmental concentrations, suggesting that these ions are preferentially retained and that mechanisms for mobilization are up-regulated under diminished environmental concentrations. Plasma 17beta-estradiol, 11-ketotestosterone and testosterone, peaked in mid-late vitellogenic females, while the androgens peaked in spawning males. Urine Ca(2+) was more tightly regulated than other divalent ions and decreased in spawning fish. Therefore, the increases in free plasma Ca(2+), the very low circulating concentrations of free and total Ca(2+), and the increase in PO(4)(3-) and bound Ca(2+) in low Ca(2+) environments indicate unique adaptations to Ca(2+) regulation in the lake sturgeon.

Carbon sources for lake sturgeon in Lake Winnebago, Wisconsin.

Abstract Because lake sturgeon Acipenser fulvescens, like other sturgeon species, are threatened or endangered in many aquatic ecosystems, it is imperative that we increase our understanding of their role in food webs. Our main objective was to determine the carbon sources for lake sturgeon in Lake Winnebago, Wisconsin, which contains one of the largest populations of lake sturgeon in North America. Gut content analysis revealed that gizzard shad Dorosoma cepedianum and Chironomus plumosus larvae (56% and 33% by gut content mass, respectively) were the primary prey items for lake sturgeon in the winter. Larger lake sturgeon were more piscivorous than smaller individuals. A mixing model using δ13C and δ15N suggests that Chironomus contributes 49% and gizzard shad 37% to the carbon assimilated by lake sturgeon. We estimated the carbon half-life in lake sturgeon to be about 0.6-3.0 years based on a model incorporating metabolism and growth. Thus, the stable isotope results integrate over a considerably longe...

Walleye and Sauger Mortality Associated with Live-Release Tournaments on the Lake Winnebago System, Wisconsin

Abstract Mortality was estimated for three, 2- or 3-d, professional, live-release tournaments for walleye Stizostedion vitreum and sauger S. canadense held on the Lake Winnebago system, Wisconsin, in 1991 and 1992. Estimated initial mortalities for the three tournaments were high—48%, 34%, and 80%—perhaps because the lake temperature exceeded 20°C. Estimated delayed mortalities (within 1 week of release of tagged fish) were 18%, 9%, and 0%. Estimated tournament-related long-term mortalities, based on tag return rates during the ensuing year, were 1%, 2%, and 0% of the total catch for each tournament. Comparison of the estimated harvest for tournament and nontournament anglers for the month of tournament activity indicated that the tournaments accounted for up to 25% of the estimated total harvest of walleyes in June. Tournament mortality might be reduced by holding tournaments when water is cool, by limiting stress on fish (e.g., by requiring aeration of live wells and holding tanks and by avoiding large ...

Age Validation of Freshwater Drum using Bomb Radiocarbon

Abstract The ages of freshwater drum Aplodinotus grunniens have typically been estimated by counting the growth increments on their scales or otoliths, but the accuracy of these estimates has not been validated. We used accelerator mass spectrometry (AMS) bomb radiocarbon dating to validate age estimates from sagittal otoliths of freshwater drum from the Lake Winnebago system, Wisconsin. The freshwater drum Δ14C chronology from the AMS assay closely reflects the timing and shape of other bomb radiocarbon chronologies, thus validating the accuracy of otolith growth increments to at least age 52 ± 2 years. The progression of a strong 1983 year-class, which was detected every year sampled over the course of the study (1986, 2003-2007), and indices of year-class abundance calculated from trawling assessments on Lake Winnebago (1986-2007) corroborated otolith ages. Age estimate comparisons between scales, anal spines, dorsal spines, and otoliths showed scales and spines to be completely unreliable as aging str...

Sturgeon and paddlefish (Acipenseridae) sagittal otoliths are composed of the calcium carbonate polymorphs vaterite and calcite.

This study sought to resolve whether sturgeon (Acipenseridae) sagittae (otoliths) contain a non-vaterite fraction and to quantify how large a non-vaterite fraction is using neutron diffraction analysis. This study found that all otoliths examined had a calcite fraction that ranged from 18 ± 6 to 36 ± 3% by mass. This calcite fraction is most probably due to biological variation during otolith formation rather than an artefact of polymorph transformation during preparation.

Impacts of Aging Error on Walleye Management in the Winnebago System

Abstract The age data used to manage Walleye Sander vitreus fisheries are not always accurate, as otoliths typically provide more accurate age estimates for larger, older Walleyes than dorsal spines. We assessed the impacts that the aging error associated with the use of dorsal spines has on the estimated age distribution, growth and mortality rates, and yield per recruit for Walleyes in the Winnebago system, Wisconsin. Age distributions derived from otolith age estimates more accurately portrayed variable recruitment than those derived from dorsal spine age estimates. The mean estimates of instantaneous total annual mortality developed from sex-specific catch curves were greater when dorsal spine age estimates were used (0.515 for males, 0.493 for females) than when otolith age estimates were (0.349 for males, 0.396 for females), with most of the differences being observed in natural mortality estimates. The von Bertalanffy growth models were not significantly different, but the yield-per-recruit models ...

Empirically testing vaterite structural models using neutron diffraction and thermal analysis

Otoliths, calcium carbonate (CaCO3) ear bones, are among the most commonly used age and growth structures of fishes. Most fish otoliths are comprised of the most dense CaCO3 polymorph, aragonite. Sturgeon otoliths, in contrast, have been characterized as the rare and structurally enigmatic polymorph, vaterite—a metastable polymorph of CaCO3. Vaterite is an important material ranging from biomedical to personal care applications although its crystal structure is highly debated. We characterized the structure of Lake Sturgeon otoliths using thermal analysis and neutron powder diffraction, which is used non-destructively. We confirmed that while Lake Sturgeon otoliths are primarily composed of vaterite, they also contain the denser CaCO3 polymorph, calcite. For the vaterite fraction, neutron diffraction data provide enhanced discrimination of the carbonate group compared to x-ray diffraction data, owing to the different relative neutron scattering lengths, and thus offer the opportunity to uniquely test the more than one dozen crystal structural models that have been proposed for vaterite. Of those, space group P6522 model, a = 7.1443(4)Å, c = 25.350(4)Å, V = 1121.5(2)Å3 provides the best fit to the neutron powder diffraction data, and allows for a structure refinement using rigid carbonate groups.

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

ABSTRACT 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.

Impacts of Anchor Tag Loss on Walleye Management in the Winnebago System

Abstract Rates of tag loss should be estimated and accounted for when using mark–recapture surveys and angler tag returns to estimate fish population abundance and exploitation rates. Walleyes Sander vitreus sampled during April 2010 spawning assessments conducted in the Winnebago system, Wisconsin, were marked with anchor tags and upper caudal fin clips to estimate tag loss rates during three time intervals: 0–11 d posttagging, 0–90 d posttagging, and 1 year posttagging. Tag loss was negligible (<0.5%) within the first 11 d but increased to 4.7% within the first 90 d and to 21.9% after 1 year. After we corrected for the tag loss occurring within the first 90 d, estimates of population abundance decreased 4.3% for females and 4.4% for males, while estimates of exploitation increased 4.9% for both sexes. Accounting for 21.9% annual tag loss led to more severe decreases in the estimates of population abundance (20.0% for females and 21.2% for males) and increases in the estimates of exploitation (28.0% for ...