Variable Gizzard Shad Recruitment with Reservoir Productivity: Causes and Implications for Classifying Systems

Achieving sustainable prey fish assemblages that support sport fish predator populations is a fundamental challenge to fisheries managers. Among Midwestern and Southeastern (USA) reservoirs, gizzard shad, Dorosoma cepedianum, have been widely stocked to improve predator growth. However, these stockings have yielded highly variable effects on sport fish, due in part to highly variable recruitment of gizzard shad. To determine whether reservoir productivity can be used to classify reservoirs according to recruitment of gizzard shad, we quantified gizzard shad recruitment along a mesotrophic to hypereutrophic productivity gradient. We sampled 12 reservoirs during May through June 1993, to evaluate the hypothesis that larval gizzard shad foraging success and survival increase with reservoir productivity. Both hatch abundance and survival of larval gizzard shad correlated positively with total phosphorus concentrations (TP), an indicator of reservoir productivity. Abundance of 15-mm (total length) larval gizzard shad survivors, an indicator of age-0 year class strength, increased by two orders of magnitude across TP concentrations. Larval gizzard shad foraging success increased with availability of preferred, small zooplankton prey. However, abundance of small zooplankton did not increase with reservoir TP concentrations, and larval survival did not increase with foraging success. These results provide mechanistic understanding for the relative lack of gizzard shad in mesotrophic reservoirs, and the dominance of gizzard shad in hypereutrophic reservoirs. In hypereutrophic reservoirs, negative effects of gizzard shad on sport fish may be alleviated by reducing phosphorus loading from the watershed, suggesting a watershed approach to this fishery and water quality problem.This work was funded by the Department of Zoology at The Ohio State University, Electric Power Research Institute grant 91-07, National Science Foundation grants DEB 9107173 and DEB 9407859, and the Federal Aid in Sport Fish Restoration Project F-69-P, administered jointly by the U.S. Fish and Wildlife Service and the Ohio Division of Wildlife

Aquatic Vegetation, Largemouth Bass and Water Quality Responses to Low-Dose Fluridone Two Years Post Treatment

Whole-lake techniques are increasingly being used to selectively remove exotic plants, including Eurasian watermilfoil ( Myriophyllum spicatum L.). Fluridone (1-methyl-3-phenyl- 5-[3-(trifluoromethyl)phenyl]-4(1 H )-pyridinone), a systemic whole-lake herbicide, is selective for Eurasian watermilfoil within a narrow low concentration range. Because fluridone applications have the potential for large effects on plant assemblages and lake food webs, they should be evaluated at the whole-lake scale. We examined effects of low-dose (5 to 8 ppb) fluridone applications by comparing submersed plant assemblages, water quality and largemouth bass ( Micropterus salmoides ) growth rates and diets between three reference lakes and three treatment lakes one- and two-years post treatment. In the treatment lakes, fluridone reduced Eurasian watermilfoil cover without reducing native plant cover, although the duration of Eurasian watermilfoil reduction varied among treatment lakes. (PDF has 11 pages.

Prey Selection by Larval Fishes as Influenced by Available Zooplankton and Gape Limitation

Feeding success during the first weeks of life is critical to determining survival and ultimate year-class strength of fishes. To compare the relative influence of gape limitation and available zooplankton on prey size selection among the larvae of three species of freshwater fishes, we gathered data on fish gape size, prey size, and size-specific prey selection in lakes and reservoirs. These variables were compared among black crappies Pomoxis nigromaculatus from a lake that contained large zooplankton as prey and white crappies P. annularis and gizzard shad Dorosoma cepedianum (a potential competitor of white crappie) from reservoirs that contained small zooplankton. In three Ohio reservoirs (i.e., small-zooplankton systems), available zooplankton and larval stages of white crappies and gizzard shad were collected once per week during April through September 1987 and 1988. Although mean prey size of white crappies continued to increase with fish size, mean prey size of smaller-gaped gizzard shad did not. However, as documented for black crappies in north-temperate lakes, white crappies in reservoirs continued to consume prey that were smaller than other available prey, even when they were no longer gape limited. Thus, although the potential for gape limitation differed between large- and small-zooplankton assemblages, prey selection did not differ as expected. Given between-species prey size selection, gizzard shad (that prefer small zooplankton) should be relatively more successful in reservoirs with small zooplankton, whereas white and black crappies (that prefer large zooplankton) should have better success in lakes with large zooplankton.This work was supported in part by DEB- 9108986 and DEB-9410323 to D.R.D., and by NSF BSR-8705518, DEB-9107173, DEB-9407859, and Federal Aid in Fish Restoration, project F-57-R to R.A.S., administered through the Ohio Division of Wildlife

Nuclear Imperialism: Examining Atomic Test Reactions and UN Intervention in Kwame Nkrumah’s Ghana, 1957-1966

France’s decision to test their nuclear weapons program in the Sahara in 1960 wholly reshaped how the Cold War infiltrated into West Africa. During a time of nation building, Ghanaian President Kwame Nkrumah urged Ghana and Africa, more broadly, to break ties with colonial powers and rebuke further attempts of what he declared to be “nuclear imperialism” on the part of France. This thesis explores the ways in which Nkrumah navigated this ever-changing landscape, as global politics forced him to maintain fluidity in his response. I argue that from the late 1950s through the 1960s, Nkrumah used nuclear opposition as a political tool to promote pan-African unity, sharpening and wielding it as he entered into continental, intergovernmental, and international political conversations. He did this over the course of his time in office from 1957 through 1966 in three distinct phases. First, I will show how in his early years of leadership, Nkrumah explicitly rejected the French nuclear testing in Africa in 1960, expressing concerns over fallout and the nuclearization of the African continent. Secondly, through 1960 and 1961, Nkrumah embraced the opportunity to express his concerns over the French testing and nuclear matters in front of the United Nations, influencing their continued denunciation of the nuclearization of Africa. This reliance of the UN as an amplifying body, I assert, faltered as he witnessed the UN complacency in the assassination of Congolese leader Patrice Lumumba. Finally, following this loss of trust, Nkrumah continued to advocate for nonproliferation from 1962 through 1966, though he did so on an international level beyond the UN. Over the course of his presidency, Kwame Nkrumah adjusted and sharpened in his anti-nuclear response, with three phases of raising awareness in Africa through pan-African unity, at the United Nations, and lastly to the broad international nonproliferation community