Reservoirs are important resources utilized by millions of freshwater anglers annually, but as reservoirs age the quality of the habitat that they provide for fish deteriorates. In 2007, a large‐scale habitat improvement project began on Table Rock Lake, Missouri, with the goal of supplementing existing fish habitat in this large reservoir. Over 2,000 habitat structures composed of cedar, pine, hardwoods, stumps, and rocks were installed between 2007 and 2013. By means of scuba surveys, we evaluated the use of these structures by black bass Micropterus spp. and crappies Pomoxis spp. to determine whether it varied among fish species, fish sizes, and structure types. Black bass were observed utilizing all structure types but appeared to utilize hardwoods most. Covariates such as water depth and visibility at the structure confounded our analysis of black bass use, however, limiting our ability to clearly document differences in use. Crappies never used rock structures, and more crappies were observed on cedar structures than any other type. In Table Rock Lake, black bass were attracted to all structure types and crappies were attracted to all structure types except rock. Since fish use is similar across nearly all habitat types, other factors such as cost and installation times should be considered when planning habitat enhancement projects on large reservoirs.Received August 12, 2013; accepted October 30, 2013
Mortality is a key parameter in understanding the dynamics of any fish population. We examined three methods to evaluate Shovelnose Sturgeon Scaphirhynchus platorynchus mortality (e.g., ratio of first year recruits to all recruits [Heincke's method], a linearized weighted catch curve, and an open system mark–recapture mortality approach). The Mississippi River was sampled in two distinct but connected geomorphic sections: upper Mississippi River (UMR; river kilometer 323–587) and the middle Mississippi River (MMR; river kilometer 0–322). All analyses were pooled across these areas due to potential emigration or immigration throughout both study reaches. Heincke's method estimated annual mortality at 16.9% for the full range of ages (9–23 years) with generally increasing estimates with decreasing age ranges considered (10–23, 11–23, 12–23, and so on). A linearized weighted catch curve that considered increasing estimates of mortality for the shorter age ranges generated an annual mortality estimate of 29.0%.d Four mark–recapture models were considered using the program MARK. The model with the greatest support was the model that provided estimates of annual mortality for each year and a single recapture probability. The annual mortality estimates from this model varied from 2.7% to 70.7% after correcting for tag loss. The best fit model with a single estimate of annual mortality was the one that estimated annual recapture probabilities for each year and had a mortality estimate of 34.6% (after correcting for tag loss, but not for immigration, emigration, or sampling effort). The three methods provided varying results, and our data indicated that a single method to estimate Shovlenose Sturgeon mortality rate may not be appropriate. As such, biologists must recognize that disparities in Shovelnose Sturgeon mortality rates may exist using various methods and should use caution when choosing which method will be employed to estimate sturgeon mortality.Received August 1, 2012; accepted May 16, 2013
Occupancy models have been underused in multispecies plant studies. We evaluated the effectiveness of occupancy models to document impacts of management on grassland plant species populations in a pilot study. The study was designed to answer three questions: (1) From a list of 44 plant species, how many will have sufficient frequency to be analyzed? (2) Within a single site, which factor (sampling year or unit) influences occupancy and detection of each plant species? (3) How does the number of plots and visits affect the number of species with sufficient frequency for analysis? In 2012 and 2013, occupancy and detection probabilities of 44 plant species were assessed using permanently marked plots on two different grassland sites. Within each site, a fire and grazing managed unit and a burn-only control unit were used to test the efficacy of occupancy modeling for multiple plant species and study design. Four of the 44 species had sufficiently high known presence (π) on both sites and years to be analyzed. There was little evidence to support that occupancy was different between years, despite very different weather patterns. There was support that occupancy was different in the burned and grazed unit compared with the control for Rhus copallinum L. Detection was highest (≥0.8) for R. copallinum, while the other species analyzed varied. In 2012, eight species had sufficient π for analysis. In 2013, 12 species had sufficient π for analysis. Occupancy models can be useful for investigating multiple plant species; however, a priori investigation of species' distribution is necessary to ensure species can be analyzed. Detection of plants was never 1, and therefore, detection should continue to be incorporated in plant population models, regardless of modeling technique.
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