Daniel A. Isermann

Estimating Black Crappie Age: An Assessment of Dorsal Spines and Scales as Nonlethal Alternatives to Otoliths

Abstract Otoliths generally provide more accurate and precise age estimates for crappies Pomoxis spp. than do scales, but sacrificing crappies for otolith removal may not be desirable in all situations. We evaluated the use of dorsal spines and scales as nonlethal alternatives to otoliths for estimating the ages of black crappies P. nigromaculatus using 111 fish collected from two Minnesota lakes. Among-reader precision was similar for ages estimated from scales and dorsal spines (coefficients of variation [CVs] = 10–14%), but the precision associated with both structures was substantially lower than that observed for otoliths (CVs = 0.12–1.3%). Complete reader agreement (i.e., all three readers agreed on age) for dorsal spines (44–51%) and scales (33–36%) was substantially lower than that observed for otoliths (87–98%). Partial agreement (i.e., at least two of three readers agreed on age) was 100% for both otoliths and dorsal spines and between 79% and 89% for scales. Scale ages assigned by individual re...

Diet Overlap and Predation Between Largemouth Bass and Walleye in Wisconsin Lakes Using DNA Barcoding to Improve Taxonomic Resolution

AbstractOver the last decade, the abundance of Largemouth Bass Micropterus salmoides has increased in many northern Wisconsin lakes, causing concern among anglers and biologists regarding the potential for Largemouth Bass to negatively affect populations of Walleye Sander vitreus through predation or competition for prey. Our objectives were to determine whether (1) diet overlap and predation occurred between adult Walleyes and Largemouth Bass in four northern Wisconsin lakes and (2) the use of DNA barcoding to reduce unidentifiable fish in diet samples affected conclusions regarding diet overlap. A single occurrence of Walleye predation was observed in the diets of 945 Largemouth Bass. Moderate to high diet overlap was observed between Largemouth Bass and Walleyes throughout much of the study period. The use of DNA barcoding reduced the amount of unidentified fish in diets to <1% and showed that failure to identify fish or fish parts can affect conclusions regarding diet overlap. Largemouth Bass predatio...

Temporal and Regional Trends in Black Bass Release Rates in Minnesota

Abstract Determining the prevalence of voluntary catch and release occurring in recreational fisheries for black bass Micropterus spp. is important in selecting and evaluating harvest regulations. Voluntary release rates of black bass have increased in some southern U.S. fisheries, but release rates could vary spatially. We used angler interviews from 245 open-water creel surveys conducted on 167 Minnesota bodies of water during 1984–2006 to determine whether black bass release rates differed among anglers specifically targeting black bass and anglers that were not targeting black bass, among geographic regions within the state, and among time periods. Ranked values of release rate did not significantly differ between anglers targeting black bass and anglers not targeting them for any of the four time periods. Before 1990, median black bass release rates were similar in northern and southern regions of the state and did not exceed 80% in either region. During 1990–1994 and 1995–1999, median release rates ...

Walleye Population and Fishery Responses after Elimination of Legal Harvest on Escanaba Lake, Wisconsin

AbstractImplementing harvest regulations to eliminate or substantially reduce (≥90%) the exploitation of Walleyes Sander vitreus in recreational fisheries may increase population size structure, but these measures also could reduce angler effort because many Walleye anglers are harvest oriented. We analyzed data collected during 1995–2015 to determine whether Walleye population and fishery metrics in Escanaba Lake, Wisconsin, changed after a minimum TL limit of 71 cm with a one-fish daily bag limit was implemented in 2003. This change eliminated the legal harvest of Walleyes after several decades during which annual exploitation averaged 34%. We detected a significant increase in the loge density of adult females after the regulation change, but the loge density of all adults and adult males did not differ between periods. Mean TL of adult males was significantly greater after the regulation change, but the mean TL of females and the proportional size distribution of preferred-length fish (≥51 cm TL) were...

Relationships among Walleye Population Characteristics and Genetic Diversity in Northern Wisconsin Lakes

AbstractThe maintenance of genetic integrity is an important goal of fisheries management, yet little is known regarding the effects of management actions (e.g., stocking, harvest regulations) on the genetic diversity of many important fish species. Furthermore, relationships between population characteristics and genetic diversity remain poorly understood. We examined relationships among population demographics (abundance, recruitment, sex ratio, and mean age of the breeding population), stocking intensity, and genetic characteristics (heterozygosity, effective number of alleles, allelic richness, Wrights inbreeding coefficient, effective population size [Ne], mean d2 [a measure of inbreeding], mean relatedness, and pairwise population ΦST estimates) for 15 populations of Walleye Sander vitreus in northern Wisconsin. We also tested for potential demographic and genetic influences on Walleye body condition and early growth. Combinations of demographic variables explained 47.1–79.8% of the variation in ge...

Validation of a Side-Scan Sonar Method for Quantifying Walleye Spawning Habitat Availability in the Littoral Zone of Northern Wisconsin Lakes

AbstractPrevious research has generally ignored the potential effects of spawning habitat availability and quality on recruitment of Walleye Sander vitreus, largely because information on spawning habitat is lacking for many lakes. Furthermore, traditional transect-based methods used to describe habitat are time and labor intensive. Our objectives were to determine if side-scan sonar could be used to accurately classify Walleye spawning habitat in the nearshore littoral zone and provide lakewide estimates of spawning habitat availability similar to estimates obtained from a transect–quadrat-based method. Based on assessments completed on 16 northern Wisconsin lakes, interpretation of side-scan sonar images resulted in correct identification of substrate size-class for 93% (177 of 191) of selected locations and all incorrect classifications were within ± 1 class of the correct substrate size-class. Gravel, cobble, and rubble substrates were incorrectly identified from side-scan images in only two instances...

Walleye Age Estimation Using Otoliths and Dorsal Spines: Preparation Techniques and Sampling Guidelines Based on Sex and Total Length

Abstract 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 esti...

Muskellunge growth potential in northern Wisconsin: implications for trophy management

AbstractThe growth potential of Muskellunge Esox masquinongy was evaluated by back-calculating growth histories from cleithra removed from 305 fish collected during 1995–2011 to determine whether it was consistent with trophy management goals in northern Wisconsin. Female Muskellunge had a larger mean asymptotic length (49.8 in) than did males (43.4 in). Minimum ultimate size of female Muskellunge (45.0 in) equaled the 45.0-in minimum length limit, but was less than the 50.0-in minimum length limit used on Wisconsins trophy waters, while the minimum ultimate size of male Muskellunge (34.0 in) was less than the statewide minimum length limit. Minimum reproductive sizes for both sexes were less than Wisconsins trophy minimum length limits. Mean growth potential of female Muskellunge in northern Wisconsin appears to be sufficient for meeting trophy management objectives and angler expectations. Muskellunge in northern Wisconsin had similar growth potential to those in Ontario populations, but lower growth ...

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.

Short-term Mortality and Retention Associated with Tagging Age-0 Walleye Using Passive Integrated Transponders (PITs) in the Absence of Anesthesia

Abstract The ability to individually mark juvenile fishes has important implications for fisheries management. For example, marking age-0 Walleye Sander vitreus could provide important information not provided by batch-marking, including individual variation in growth and estimates of length-dependent survival and recruitment. However, the relatively small size of age-0 Walleye in northern temperate lakes has precluded use of many common tagging methods that provide information on individual fish (e.g., various anchor tags, jaw tags). Consequently, we evaluated short-term mortality and retention associated with using 12-mm passive integrated transponders (PITs) to mark age-0 Walleye (total length range = 93–216 mm; mean total length = 157 mm) by conducting 48-h within-lake net-pen trials and 7-d hatchery trials during September–October of 2015 and 2016. We did not anesthetize age-0 Walleye prior to PIT tagging. Our assessment allowed us to determine whether post-tagging mortality and PIT retention varied ...