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Brainerd, MN, United States

Schultz D.W.,7316 State 371 Northwest | Carlson A.J.,601 Minnesota Drive | Mortensen S.,Leech Lake Band of Ojibwe | Pereira D.L.,00 Lafayette Road
North American Journal of Fisheries Management

The recovery of the double-crested cormorant Phalacrocorax auritus throughout North America has led to increased human-cormorant competition over fishery resources and has forced managers to evaluate cormorant effects and consider management alternatives at local and broader scales. We present a method for modeling local double-crested cormorant populations under varying levels of culling intensity based on a colony managed at Leech Lake, Minnesota, during 2005-2011. In this case study, the cormorant colony was evaluated under no, moderate, and intensive control rates and compared with the observed population response. Cormorant diets for fledged (adults and subadults) and nestling cormorants were described during 2004-2007 and 2010. Annual fish consumption and 95% confidence intervals were estimated from 1992 to 2011 using a bioenergetics model and Monte Carlo methods. Total feeding effort and fish consumption has been reduced by nearly 90% since cormorant control began in 2005 (consumption reduced from 20.01 kg/ha in 2004 to 1.98 kg/ha in 2011) and by 46-73% annually, depending on the number of birds arriving each spring and the applied culling intensity. Averaged across all years and periods, fledged cormorants consumed 0.75 kg·bird-1·d-1 and nestlings consumed 0.45 kg·bird-1·d-1. Respectively, average fledged and nestling diets were comprised of Yellow Perch Perca flavescens (61.0% and 77.4%), Coregonus spp. (12.3% and 9.4%), minnows Notropis spp. (9.9% and 2.2%), Trout-perch Percopsis omiscomaycus (4.1% and 0.4%), and Walleye Sander vitreus (4.6% and 3.6%), though considerable seasonal and temporal variability was observed. The bioenergetics model used to estimate total fish consumption was sensitive to this variability, which was strongly associated with the dynamics of the population of Cisco Coregonus artedi. Some fish population and fishery statistics were described by changes in cormorant predation pressure, but these relationships were compromised by other concurrent management activities. Received April 1, 2013; accepted August 20, 2013. © 2013 Copyright Taylor and Francis Group, LLC. Source

Pierce R.B.,1201 East Highway 2 | Carlson A.J.,601 Minnesota Drive | Carlson B.M.,University of Michigan | Hudson D.,U.S. Geological Survey | Staples D.F.,463 C West Broadway
Transactions of the American Fisheries Society

We monitored depths and temperatures used by large (>71-cm) versus small Northern Pike Esox lucius in three north-central Minnesota lakes with either acoustic telemetry or archival tags. Individual Northern Pike demonstrated flexibility in depths used within a season and between years. The fish had some tolerance for low levels of dissolved oxygen (<3 mg/L), but depth selection was generally constrained by low dissolved oxygen in summer and winter. The fish more fully exploited all available depths during winter and thermal turnover periods. During July and August, large Northern Pike tended to follow the thermocline into cooler water as upper water layers warmed. Selection ratios indicated that large Northern Pike preferred water temperatures of 16-21°C during August when temperatures up to 28°C were available. In two lakes providing dense overhead cover from water lilies in shallow water, small Northern Pike used warmer, shallower water compared with large fish during summer. In a third lake providing no such cover, small fish were more often in deeper, cooler water. For small Northern Pike, temperature seemed to be a secondary habitat consideration behind the presence of shallow vegetated cover. This study provided detailed temperature selection information that will be useful when considering temperature as an ecological resource for different sizes of Northern Pike. Received March 27, 2013; accepted June 27, 2013. © 2013 Copyright Taylor and Francis Group, LLC. Source

Radomski P.,601 Minnesota Drive | Holbrook B.V.,601 Minnesota Drive
Journal of Aquatic Plant Management

Hydroacoustic systems have been used for > 30 yr to survey aquatic plant communities. The objective of this study was to collect and analyze data using two commonly available but different hydroacoustic systems to determine whether both sets of gear yielded similar estimates of aquatic plant abundance and height statistics. There were appreciable differences in the estimates of submerged macrophyte abundance, plant height, and variability in plant height estimated from data collected with a Lowrance HDS transducer and processed with BioBase compared with data collected with a BioSonics transducer and processed with Echoview. Both approaches produced estimates of plant abundance that deviated from plant community observations. Compared with the those plant community observations and the BioSonics/Echoview system, the Low-rance/BioBase system produced higher estimates of plant height by depth stratum with higher variability, likely because of lower occurrences of registered aquatic plants in each depth stratum, and may have overestimated plant heights in shallow waters. In contrast, BioSonics/Echoview produced a higher frequency of submerged macrophyte occurrences at all depths and may have overestimated occurrences in deep water. Differences appeared to be mostly due to the signal processing approaches. Investigators should tailor a system for their specific survey objectives, needed accuracy, and resources. The use of this technology for long-term monitoring will likely require standardization of data collection equipment and signal processing. Source

Knapp M.L.,601 Minnesota Drive | Mero S.W.,1202 East Highway 2 | Bohlander D.J.,601 Minnesota Drive | Staples D.F.,463C West Broadway | Younk J.A.,114 Bemidji Avenue
North American Journal of Fisheries Management

The popularity of sportfishing for muskellunge Esox masquinongy in Minnesota has increased substantially during the last 20 years and has resulted in a call for creating more fishing opportunities. As new waters are considered for muskellunge management, some anglers have expressed concern over the effects on other popular game fish species of adding a top-level predator. We evaluated the responses of seven fish species to muskellunge by comparing gill-net and/or trap-net catch per unit effort (CPUE) before and after muskellunge were stocked in 41 Minnesota lakes composed of 12 lake-classes. The species examined were northern pike Esox lucius, walleye Sander vitreus, yellow perch Perca flavescens, bluegill Lepomis macrochirus, black crappie Pomoxis nigromaculatus, white sucker Catostomus commersonii, and cisco Coregonus artedi. We found no significant decreases among the lakes in the mean CPUE of any species after muskellunge stocking, either for the stocked lakes as a whole or within lake-classes. There was a significant increase in the mean CPUE for bluegills over the entire group of lakes and within lake-class 24 in addition to an increase in the mean CPUE for black crappies sampled by gill nets in lake-class 25. Nevertheless, there was large variability in the changes in CPUE among lakes, and several individual lakes had significant changes in mean CPUE for some species following muskellunge stocking. The trend in CPUE increased for yellow perch and declined for white suckers over the entire group of lakes after muskellunge stocking. Because Minnesota follows established, biologically based guidelines for selecting new muskellunge lakes, the study lakes were not chosen at random and therefore the study conclusions most appropriately apply to lakes chosen in this manner. The lack of consistent negative changes in CPUE after stocking suggests that these fish species have generally coexisted well with muskellunge in these lakes at the densities that have resulted from stocking. © American Fisheries Society 2012. Source

Radomski P.,601 Minnesota Drive | Perleberg D.,601 Minnesota Drive
Ecological Indicators

The objective was to develop a Minnesota aquatic macrophyte integrity index that can use plant checklist data from existing and ongoing lake plant survey programs without alteration. Using the extensive lake survey data collected by numerous state programs, we created a suite of predictive models for macrophyte richness and floristic quality and identified aquatic macrophyte community outliers to set potential impairment thresholds. The highest-ranked predictive models included total phosphorus, disturbance indices, and ecoregion variables. Models with all in-lake macrophyte taxa generally performed better than those based on just submerged aquatic macrophyte or those based on submerged and floating-leaf taxa. The best generalized linear mixed model for aquatic macrophyte richness was a model containing total phosphorus, alkalinity, lake size, maximum depth, ecoregion, survey type, and several interactions. The best linear mixed effects model for floristic quality also included these predictive variables. Richness and floristic quality thresholds were calculated using these models with associated disturbance-response breakpoints. The approach took sampling protocol into account by providing different thresholds based on sample design. These thresholds then identify potentially biologically impaired lakes. There appeared to be no disturbance-response breakpoints between aquatic macrophyte richness and floristic quality for the Northern Lakes and Forest ecoregion of northeastern Minnesota. © 2012 Elsevier Ltd. Source

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