Effects of Commercial Harvest on Shovelnose Sturgeon Populations in the Upper Mississippi River

Shovelnose sturgeon Scaphirhynchus platorynchus have become an increasingly important commercial species in the upper Mississippi River (UMR) because of the collapse of foreign sturgeon (family Acipenseridae) populations and bans on imported caviar. In response to concerns about the sustainability of the commercial shovelnose sturgeon fishery in the UMR, we undertook this study to describe the demographics of the shovelnose sturgeon population and evaluate the influence of commercial harvest on shovelnose sturgeon populations in the UMR. A total of 1,682 shovelnose sturgeon were collected from eight study pools in 2006 and 2007 (Pools 4, 7, 9, 11, 13, 14, 16, and 18). Shovelnose sturgeon from upstream pools generally had greater lengths, weights, and ages than those from downstream pools. Additionally, mortality estimates were lower in upstream pools (Pools 4, 7, 9, and 11) than in downstream pools (Pools 13, 14, 16, and 18). Linear regression suggested that the slower growth of shovelnose sturgeon is a consequence of commercial harvest in the UMR. Modeling of potential management scenarios suggested that a 685-mm minimum length limit is necessary to prevent growth and recruitment overfishing of shovelnose sturgeon in the UMR

Fundamental Science Investigations to Develop a 6-MV Laser Triggered Gas Switch for ZR: First Annual Report.

In October 2005, an intensive three-year Laser Triggered Gas Switch (LTGS) development program was initiated to investigate and solve observed performance and reliability issues with the LTGS for ZR. The approach taken has been one of mission-focused research: to revisit and reassess the design, to establish a fundamental understanding of LTGS operation and failure modes, and to test evolving operational hypotheses. This effort is aimed toward deploying an initial switch for ZR in 2007, on supporting rolling upgrades to ZR as the technology can be developed, and to prepare with scientific understanding for the even higher voltage switches anticipated needed for future high-yield accelerators. The ZR LTGS was identified as a potential area of concern quite early, but since initial assessments performed on a simplified Switch Test Bed (STB) at 5 MV showed 300-shot lifetimes on multiple switch builds, this component was judged acceptable. When the Z{sub 20} engineering module was brought online in October 2003 frequent flashovers of the plastic switch envelope were observed at the increased stresses required to compensate for the programmatically increased ZR load inductance. As of October 2006, there have been 1423 Z{sub 20} shots assessing a variety of LTGS designs. Numerous incremental and fundamental switch design modifications have been investigated. As we continue to investigate the LTGS, the basic science of plastic surface tracking, laser triggering, cascade breakdown, and optics degradation remain high-priority mission-focused research topics. Significant progress has been made and, while the switch does not yet achieve design requirements, we are on the path to develop successively better switches for rolling upgrade improvements to ZR. This report summarizes the work performed in FY 2006 by the large team. A high-level summary is followed by detailed individual topical reports

Importance of Groundwater Inflows for Maintenance of Striped Bass Habitat in the Flint River and Lake Seminole

Proceedings of the 1989 Georgia Water Resources Conference, May 16-17, 1989, Athens, Georgia.Adult striped bass are heavily dependent on habitats influenced by the inflows of cool water from groundwater sources in the Flint River between Albany, Georgia, and Lake Seminole. Fish tracked with radio transmitters in 1984-85 moved into isolated spring-fed areas during May, when ambient river temperatures reached 24° C, and remained in these areas until October or early November, when the river cooled to 20° C. The duration of habitation of the spring-fed areas averaged 160 days per year (range 137-182), illustrating the vulnerability of the species to habitat changes that would occur if groundwater inflows were reduced or eliminated. Knowledge of the distribution of spring-fed areas that serve as important striped bass habitat provides a basis for linking fisheries concerns with other groundwater demands in this part of Georgia.Sponsored by U.S. Geological Survey, Georgia Department of Natural Resources, the University of Georgia, Georgia State University, and Georgia Institute of Technology.This book was published by the Institute of Natural Resources, The University of Georgia, Athens, Georgia 30602 with partial funding provided by the U.S. Department of the Interior, Geological Survey, through the Georgia Water Research Institute as authorized by the Water Resources Research Act of 1984 (P.L. 98242). The views and statements advanced in this publication are solely those of the authors and do not represent official views or policies of The University of Georgia or the U.S. Geological Survey or the conference sponsors

A modeling analysis of lake ecosystem responses to inorganic fertilization

Vita.Separate mathematical models for phytoplankton and fish were developed to describe nominal dynamics and responses to single applications of fertilizer in Postoak Lake, Texas. Models were based on data from three fertilization experiments and interim periods between 1966 and 1976. Simulations were used to identify factors regulating primary productivity and fish growth and to evaluate pathways through which fertilization affected biotic ecosystem components. Phytoplankton biomass and productivity were formulated as functions of nutrient concentrations, temperature, illumination, grazing, and sinking losses. Nominal simulations which treated the phytoplankton as a single homogeneous unit indicated that phytoplankton dynamics were primarily regulated by the feedback of chlorophyll on light attenuation. Following simulated fertilization of the lake, predicted carbon uptake rates were approximately equal to observed values, but chlorophyll concentrations were overestimated. These results, in combination with those from previous studies of Postoak Lake, suggested that the phytoplankton did not respond homogeneously to fertilization and that a significant portion of phytoplankton biomass was lost from the photic zone immediately after nutrient enrichment. An energetic model for bluegills, largemouth bass, and warmouth incorporated the influences of food availability, feeding selectivity, and temperature on growth of individual fish. Fertilization effects were evaluated by examining growth responses to simulated increases of zooplankton, benthos, and forage fish biomass within ranges suggested by previous studies on Postoak Lake.

A modeling analysis of lake ecosystem responses to inorganic fertilization

Vita.Separate mathematical models for phytoplankton and fish were developed to describe nominal dynamics and responses to single applications of fertilizer in Postoak Lake, Texas. Models were based on data from three fertilization experiments and interim periods between 1966 and 1976. Simulations were used to identify factors regulating primary productivity and fish growth and to evaluate pathways through which fertilization affected biotic ecosystem components. Phytoplankton biomass and productivity were formulated as functions of nutrient concentrations, temperature, illumination, grazing, and sinking losses. Nominal simulations which treated the phytoplankton as a single homogeneous unit indicated that phytoplankton dynamics were primarily regulated by the feedback of chlorophyll on light attenuation. Following simulated fertilization of the lake, predicted carbon uptake rates were approximately equal to observed values, but chlorophyll concentrations were overestimated. These results, in combination with those from previous studies of Postoak Lake, suggested that the phytoplankton did not respond homogeneously to fertilization and that a significant portion of phytoplankton biomass was lost from the photic zone immediately after nutrient enrichment. An energetic model for bluegills, largemouth bass, and warmouth incorporated the influences of food availability, feeding selectivity, and temperature on growth of individual fish. Fertilization effects were evaluated by examining growth responses to simulated increases of zooplankton, benthos, and forage fish biomass within ranges suggested by previous studies on Postoak Lake.

Blue crab /

"TR EL-82-4.""March 1989."Includes bibliographical references (p. 13-18).Mode of access: Internet