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Saint Paul, MN, United States

Dieterman D.J.,Lake City Fisheries Research Office | Walker T.S.,University of Minnesota | Cochran P.A.,University of Minnesota | Konsti M.,Section of Fisheries
North American Journal of Fisheries Management | Year: 2016

Brown Trout Salmo trutta are widely distributed fish that display substantial interpopulation variation in fundamental reproductive traits due to differences in local environmental conditions. This wide variation necessitates regional determination of key traits to aid local management efforts. In addition, several populations demonstrate a trade-off between fecundity and egg size, often as a function of growth history in response to environmental conditions. To determine these traits in the Driftless Area of the Upper Midwest, we identified two streams with contrasting environmental conditions and quantified reproductive traits just prior to the fall-spawning period in 2012. Reproductive traits included growth, length- and age-at-maturity, gonadosomatic index, and female fecundity and egg size. Environmental conditions were considered harsher at one site based on warmer water temperatures, more sand substrate, less adult fish cover, and presence of more potential interspecific competitors than at the other site. At both sites, Brown Trout of both sexes were short-lived; few Brown Trout older than age 3 were collected, and both sexes matured at age 2. Length-at-maturity ranged from 226 to 230 mm TL for males and from 214 to 238 mm TL for females. Fecundity and egg size were both positively related to female size, and females produced up to about 800 eggs. Ovaries represented a maximum of about 15% of female body weight. Female Brown Trout growth differed between the two sites, but most reproductive traits and growth of males did not. There was no evidence of a trade-off between fecundity and egg size, but length-adjusted egg sizes were significantly larger at the site with harsher environmental conditions. Differences in egg size probably were not due to the presence of competitors but may have been due to warmer water temperatures. Collectively, these fundamental reproductive data will prove useful for future population modeling efforts to support evaluation of several management strategies. © American Fisheries Society 2016. Source

Isermann D.A.,Section of Fisheries | Isermann D.A.,University of Wisconsin - Stevens Point | Thompson A.L.,Section of Fisheries | Talmage P.J.,Section of Fisheries
North American Journal of Fisheries Management | Year: 2010

We examined differences in sex-specific growth and weight-length relationships for five Minnesota populations of black crappies Pomoxis nigromaculatus. Male black crappies typically grew slightly faster than females, but observed differences in mean total lengths (TLs) at age were always 15 mm or less and were typically less than 10 mm. We detected few differences in log10(weight)-log10(TL) regressions between sexes, and predicted weights at 200 and 250 mm differed between sexes by less than 10 g. Our results indicate that biologists are justified in pooling sexes when estimating population metrics such as growth and condition because the minor differences in growth and weight-length relationships we observed would be unlikely to affect management decisions. Furthermore, while our evaluation did not specifically examine angler harvest selectivity, the small differences in growth and weight-length relationships observed between sexes seemed unlikely to promote sexselective angler harvest within the lakes we examined. However, it remains possible that male growth advantages of more than 10 mm may promote selective removal of male fish in black crappie fisheries regulated by minimum length limits, where anglers may use the minimum length limit as a target when selecting fish for harvest and are more likely to measure individual fish. © American Fisheries Society 2010. Source

Isermann D.A.,Section of Fisheries | Isermann D.A.,University of Wisconsin - Stevens Point
North American Journal of Fisheries Management | Year: 2010

I evaluated the accuracy of using differences in body coloration, gamete stripping, and abdominal distension in females as a nonlethal method for determining the sex of black crappies Pomoxis nigromaculatus collected from two Minnesota lakes during spring (late April-early June). Sex assignments based on these three attributes were 93% accurate for all black crappies (211 of 227) and 98% accurate (174 of 177) for black crappies of 200 mm or more total length. The difference in body coloration between sexes was the most useful trait for identifying sex, but the distended abdomen of females and gamete stripping aided in identifying sex in some instances. Nonlethal sex assignment was less reliable for black crappies less than 200 mm (74% accurate; 37 of 50), largely because of the lack of dark coloration in males. The sex of black crappies of 200 mm or more can be identified accurately without killing the fish, but that of smaller crappies should be determined by means of visual inspection of the gonads. © American Fisheries Society 2010. Source

Isermann D.A.,Section of Fisheries | Isermann D.A.,University of Wisconsin - Stevens Point | Schultz D.W.,Section of Fisheries | Carlson A.J.,Section of Fisheries
North American Journal of Fisheries Management | Year: 2010

Sex-selective fishing mortality can alter the demographics and life history patterns of fish populations, yet the extent of this mortality is rarely investigated in harvest-oriented recreational fisheries. Potential differences in habitat use between sexes and nest-guarding behavior suggest that male black crappies Pomoxis nigromaculatus could dominate angler harvest during spring fisheries. We examined the potential for male-dominated harvest in spring (late April to mid-June) recreational fisheries for black crappies occurring on two north-central Minnesota lakes. In the three spring fisheries we examined, males represented between 45% and 57% of all black crappies harvested by anglers, but sex ratios (expressed as the percentages of males) did not significantly deviate from 1:1. However, a temporal pattern in sex ratios was observed on Lake Hubert, where female black crappies dominated angler harvest before 19 May in both 2005 and 2006 (41-42% male) while the harvest on or after 19 May was dominated by males (69-75% male); this shift appeared to coincide with peak nesting periods. In fall electrofishing samples, the sex ratios of black crappies that had been exposed to exploitation during spring fisheries (i.e., fish age 4 and older) did not significantly deviate from 1:1, suggesting that total annual mortality rates were similar between sexes. The sex ratios of black crappies harvested by anglers during spring can vary within and among lakes and will not always be skewed toward male fish. Estimating population sex ratios and the sex ratio of black crappies harvested by anglers may improve our understanding of the effects of exploitation on crappie populations, particularly when fishing intensity during nesting is high and nests are easily located by anglers. © American Fisheries Society 2010. Source

Herwig B.R.,Populations and Community Ecology Research Group | Zimmer K.D.,Thomas University | Hanson M.A.,Wetland Wildlife Populations and Research Group | Konsti M.L.,Section of Fisheries | And 3 more authors.
Wetlands | Year: 2010

Fish exert strong influences on shallow lakes, but managers lack empirical models useful for predicting fish distributions at landscape scales. We used classification and regression tree analysis (CART), and regression to predict fish presence/absence (P/A), richness, and community composition in 82 shallow lakes distributed among two regions (prairie and prairie-parkland) along the eastern margin of the Prairie Pothole Region in western Minnesota, U.S.A. A CART model for fish P/A using downstream connections to fish sources and maximum depth correctly classified ≥92% of our study sites, indicating the rare fishless sites observed in our study were either isolated or shallow. Fish richness was positively related to both lake and watershed size. Given that many fish species have strong negative influences on shallow lake ecological characteristics, we conclude that future conservation efforts should focus on protecting shallow, isolated basins, or reducing surface connectivity among basins as these factors were decisive in promoting fish populations. Such management strategies should help to maintain current levels of fish richness and enhance richness of aquatic birds, amphibians, plants, and invertebrates. © 2010 Society of Wetland Scientists. Source

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