Otoliths, calcium carbonate (CaCO
) ear bones, are among the most commonly used age and growth structures of fishes. Most fish otoliths are comprised of the most dense CaCO
polymorph, aragonite. ...Sturgeon otoliths, in contrast, have been characterized as the rare and structurally enigmatic polymorph, vaterite-a metastable polymorph of CaCO
. 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 CaCO
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 P6
22 model, a = 7.1443(4)Å, c = 25.350(4)Å, V = 1121.5(2)Å
provides the best fit to the neutron powder diffraction data, and allows for a structure refinement using rigid carbonate groups.
The spatial distribution of benthic invertebrates is fundamental to the ecology of lakes and has implications for higher trophic levels and ecosystem processes. We conducted a lake-wide study of the ...spatial variation of benthic invertebrates in Lake Winnebago, Wisconsin (USA) with emphasis on the chironomid community. We asked: 1) What is the extent of spatial variation in benthic invertebrate community structure and abundance among and within major lake zones in the lake? 2) What factors are correlated with spatial variation of benthic invertebrates at multiple scales? 3) How has the chironomid community and the abundance of Chironomus varied temporally at the multidecadal scale in the lake? We collected benthic invertebrates from the profundal (33 sampling locations), offshore reef (17), and littoral (15) zones in August 2013. Profundal locations were sampled again in August 2014. Habitat variables, including water depth and temperature, Secchi depth, and benthic organic matter were measured with the goal of investigating potential causes of variation in the biota. The highest mean invertebrate densities occurred in the offshore reef and littoral zones (13,987 and 10,638 individuals ind/m², respectively), relative to the profundal zone (2103 ind/m²). Zebra mussels were the numerically dominant taxon in both the littoral and offshore reef zones, whereas chironomids were the most abundant macroinvertebrates in the profundal. Large differences in chironomid community composition occurred among the 3 major zones. Within the profundal zone, the pattern of spatial variation in total chironomid abundance differed between the 2013 and 2014 sampling events. Local factors (e.g., sediment characteristics) and stochastic factors (e.g., wind and current speed) probably interact to influence the spatial distribution of chironomid taxa between and within zones in large shallow lakes, such as Lake Winnebago.
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.
•Compared dorsal spine and otolith derived age estimates from 299 known age walleye (ages 0–10, 16, 18) and more than 2000 additional walleye.•Correlated catch curve residuals from structure and ...sex-specific catch curves to standard walleye recruitment indices.•Otoliths yielded accurate age estimates for known age walleye, while dorsal spines underestimated the age of walleye age-6 and older.•Otoliths yielded older age estimates than dorsal spines for both male and female walleye.•Catch curve residuals derived from otolith age estimates correlated well with recruitment indices while residuals derived from dorsal spine age estimates did not.
Although accurate age data are essential when estimating somatic growth and mortality rates required to effectively manage exploited walleye (Sander vitreus) populations, aging structures have not been validated for age ranges present in most walleye populations. Otoliths and dorsal spines were collected from 302 walleye considered known age in the Winnebago System, Wisconsin, USA: 142 that were assigned ages via progression of discrete length modes following an individual strong year class (ages 0–3), and 160 (ages 4–10, 12–13, 16, 18) that were initially tagged at lengths small enough to accurately assign age ±1 year (<380mm) and later recaptured and assigned an age (assigned age at tagging plus number of years at liberty). Paired aging structures were also collected from over 2000 additional walleye sampled during spawning assessments, tournament monitoring, and other surveys to better understand the relationship between spine and otolith age estimates and to compare catch curve residuals from structure and sex-specific catch curves to standard walleye recruitment indices. We found otoliths were accurate for walleye ages 0–10, while dorsal spines yielded relatively accurate age estimates for walleye ages 1–5, but underestimated age of walleye age-6 and older. Age distributions within catch curves constructed from otolith age estimates correlated well with measured year class strength, while age distributions from dorsal spine age estimates correlated poorly. Our results from fish considered known age validate the accuracy of otolith age estimates for walleye up to age-10, with corroborating evidence from catch curves and accurate recruitment indices strongly suggesting that otoliths are valid for all ages of Winnebago System walleye. We recommend the use of otoliths to accurately estimate walleye age, growth, and mortality, and to provide accurate age data for other population analyses.
Acipensericola glacialis
n. sp. infects the heart of lake sturgeon,
Acipenser fulvescens
(Rafinesque), in the Lake Winnebago System and differs from its only congener,
Acipensericola petersoni
...Bullard, Snyder, Jensen & Overstreet, 2008, by having a dendritic intestine, deeply-lobed testes, a post-ovarian oötype, and a common genital pore that is medial to the dextral caecum.
Acipensericola petersoni
has a non-dendritic intestine, testes that are not deeply lobed, an oötype that is at level of the ovary (ventral to the ovary), and a common genital pore that is dorsal to the dextral caecum. Comparison of the large (28S) and small (18S) sub-unit ribosomal DNA and internal transcribed spacer 2 (ITS2) regions between specimens of
A. glacialis
n. sp. and
A. petersoni
revealed 13 (of 1,621 nt; 99.2% similarity in the 28S), 8 (of 1,841 nt; 99.9% similarity in the 18S), and 11 (of 442 nt; 97.5% similarity in the ITS2) nucleotide differences. Collectively, these results comprise an unexpectedly high degree of morphological and molecular similarity given the geographical (Mississippi River Basin
vs
Great Lakes Basin) and phylogenetic (Polyodontidae
vs
Acipenseridae) separation of these hosts but seemingly did not reject a previous hypothesis concerning lake sturgeon dispersal from the Mississippi Refugium following the Wisconsin glaciation ~18,000 years ago. The new species is the first nominal blood fluke described from a sturgeon.
A common guideline for attaching or imbedding transmitters for fish is that the transmitter weight should not exceed 2% of the total weight in air of a fish. This guideline is thought to limit the ...negative effects of tagging, but little research supports it. Our objectives were to compare the postrelease dispersal rates of 48 hatchery-reared fingerling Lake Sturgeon Acipenser fulvescens (265–305 mm, 80–100 g) surgically implanted with sonic transmitters equating to 2% and 4% of fish body weight, and to compare the dispersal rates between fish stocked in two river systems in Wisconsin. Downstream dispersal rates of the 2% and 4% treatments were not significantly different within the individual rivers but were significantly different between rivers. We recommend that transmitters weighing up to 4% of total body weight can be used without effects on the movement of fingerling Lake Sturgeon. Received January 6, 2015; accepted June 29, 2015
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 (which rely heavily on von Bertalanffy model parameters) incorporating spine age data produced average yield estimates 50–70% lower than the models developed from otolith ages. The yield-per-recruit models derived from spine-determined ages also resulted in lower recommendations as to the age and size of fish for maximum yield at all exploitation levels than the models developed from otolith age data. The mean dorsal spine and otolith age estimates were similar for male Walleyes <457 mm and female Walleyes <508 mm, but for larger fish otoliths yielded significantly older ages than spines. Given the economic and social impacts of the Winnebago system Walleye fishery, we recommend exclusive use of otoliths to obtain the most accurate estimates of fish age, growth, mortality, and yield. In populations in which the sacrifice of large quantities of fish is not acceptable, we recommend using spines to estimate the ages of smaller fish (males <457 mm, females <508 mm) and otoliths to estimate the ages of fish larger than these critical lengths. Received December 26, 2012; accepted June 10, 2013
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 both sexes) than not accounting for any tag loss. Higher exploitation rates resulted in higher estimates of fishing mortality and lower estimates of natural mortality. When used in yield‐per‐recruit models, the estimated natural mortality rates derived from exploitation rates that accounted for tag loss resulted in higher yields through the implementation of larger minimum length limits to maximize yield. We recommend that managers evaluate the effectiveness of their tagging operations by estimating tag loss and assessing the potential impacts of quantified loss on management metrics. We also caution against the application of population models without an accurate estimate of tag loss and the associated impacts on estimates of population abundance and exploitation and, in turn, fishing and natural mortality rates.
Received May 22, 2013; accepted June 11, 2013
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.
Understanding sampling efficiency and movements of subadult Lake Sturgeon Acipenser fulvescens is necessary to facilitate population rehabilitation and recruitment monitoring in large systems with ...extensive riverine and lacustrine habitats. We used a variety of sampling methods to capture subadult Lake Sturgeon (i.e., fish between 75 and 130 cm TL that had not reached sexual maturity) and monitored their movements using radio telemetry in the lower Wolf River, a tributary to the Lake Winnebago system in Wisconsin. Our objectives were to determine whether (1) capture efficiency (expressed in terms of sampling time) of subadult Lake Sturgeon using multiple sampling methods was sufficient to justify within‐river sampling as part of a basin‐wide recruitment survey targeting subadults, (2) linear home ranges varied in relation to season or sex, and (3) subadult Lake Sturgeon remained in the lower Wolf River. From 2013 to 2014, 628 h of combined sampling effort that included gill nets, trotlines, electrofishing, and scuba capture was required to collect 18 subadult sturgeon, which were then implanted with radio transmitters and tracked by boat and plane. Linear home ranges did not differ in relation to sex but did vary among seasons, and the majority of movement occurred in spring. Seven of the 18 (39%) Lake Sturgeon left the river and were not detected in the river again during the study. Between 56% and 70% of subadult fish remaining in the river made definitive movements to, or near, known spawning locations when adult Lake Sturgeon were actively spawning. Our results suggest only a small proportion of subadult Lake Sturgeon in the Lake Winnebago population use the lower Wolf River, indicating that riverine sampling may not always be warranted when targeting subadults in large lake–river complexes. More information is needed on distribution of subadult Lake Sturgeon to develop sampling protocols for this population segment.
Received January 27, 2017; accepted May 19, 2017 Published online August 7, 2017
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