Growth Rates of Yellow Perch, Perca Flavescens (Mitchell), in two North Dakota Lakes After Population Reduction with Toxaphene

Fishery waters overpopulated with desirable species generally produce few harvestable fish because of slow growth rates. In 1962 Bennett stated that no fish of harvestable were found in some waters thus affected. Eschmeyer (1936) made a similar observation concerning overcrowded populations of yellow perch (Perca flavescens). For lack of more efficient remedial measures the use of piscicides has been recommended to reduce the numbers the numbers of the problem species. Relatively low toxaphene concentrations in two North Dakota lakes substantially reduced the density of the yellow perch population the effect on other fish species was less obvious. The results reported (Henegar,1961) were incidental to the determination of the minimum toxaphene concentration necessary for fish eradication in that state. The present study was initiated in 1960 to determine the growth rates of the yellow perch surviving in Brush and Long lakes, and thus gain information concerning the suitability of toxaphene tor reducing the numbers of fish in overpopulated waters. The scale method was employed to calculate the growth rates of Brush Lake fish for the 1960 and 1961 growing seasons. Post-treatment growth rates of Long Lake fish were determined tor part of the 1960 growing season and. for all of the 1961 season. Several authors reporting the use of rotenone to thin overcrowded populations or to restore balance between fish species considered the results to be favorable. Beckman (1941) noted that the growth rates of fish surviving the treatment of one-half of Booth Lake, Michigan were too great to be accounted for by normal variation. Substantially increased harvests, apparently the results of accelerated growth rates of remaining fishes, were reported by Swingle, Prather, and Lawrence (1953) subsequent to the poisoning of some Alabama ponds. Hooper and Crance (1960) stated that the use of rotenone was an affective and economical method to restore balance to certain fish populations. Reports of unfavorable results rotenone, or of similar use of other pesticides, were not found. However, the use of toxaphene was recommended by several authors including Hemphill (1954) who first used the chemical for fish eradication. The cost of fish eradication with toxaphene is approximately 15 per cent of the cost with rotenone. On the basis of recommended concentrations and methods for thinning overcrowded fish populations with these chemicals, the use of toxaphene would be even more economical. Definite information relevant to this use of this poison and the subsequent results is conspicuously absent. [Introduction – -page 1-2

The geometry of sound rays in a wind

We survey the close relationship between sound and light rays and geometry. In the case where the medium is at rest, the geometry is the classical geometry of Riemann. In the case where the medium is moving, the more general geometry known as Finsler geometry is needed. We develop these geometries ab initio, with examples, and in particular show how sound rays in a stratified atmosphere with a wind can be mapped to a problem of circles and straight lines.Comment: Popular review article to appear in Contemporary Physic

The Klein-Gordon equation on the toric AdS-Schwarzschild black hole

We consider the Klein-Gordon equation on the exterior of the toric anti de-Sitter Schwarzschild black hole with Dirichlet, Neumann and Robin boundary con- ditions at I. We define a non-degenerate energy for the equation which controls the renormalised H1 norm of the field. We then establish both decay and integrated de- cay of this energy through vector field methods. Finally we demonstrate the necessity of ‘losing a derivative’ in the integrated energy estimate through the construction of a Gaussian beam staying in the exterior of the event horizon for arbitrary long co- ordinate time

Universal properties of the near-horizon optical geometry

We make use of the fact that the optical geometry near a static non-degenerate Killing horizon is asymptotically hyperbolic to investigate universal features of black hole physics. We show how the Gauss-Bonnet theorem allows certain lensing scenarios to be ruled in or out. We find rates for the loss of scalar, vector and fermionic `hair' as objects fall quasi- statically towards the horizon. In the process we find the Lienard-Wiechert potential for hyperbolic space and calculate the force between electrons mediated by neutrinos, extending the flat space result of Feinberg and Sucher. We use the enhanced conformal symmetry of the Schwarzschild and Reissner-Nordstrom backgrounds to re-derive the electrostatic field due to a point charge in a simple fashion

An Evaluation of the Relative Importance of Tourism for Islands

The purpose of this study was to compare islands and regular countries to determine if islands depend more on tourism in their economies than regular countries. In fact, it is possible that islands depend too much on tourism. A literature review covers the various areas of research regarding island tourism, including economic impact, sustainability, forecasting, and destination management. Data from the World Bank Group was used to form a panel of 140 countries for the period 1995 through 2006. Islands and regular countries were compared on economic factors such as GDP per capita, travel receipts, and travel receipts as a percentage of exports. The results indicate that islands have a lower level of travel receipts than regular countries, but travel receipts represent a higher percentage of exports for islands

Applications of the Gauss-Bonnet theorem to gravitational lensing

In this geometrical approach to gravitational lensing theory, we apply the Gauss-Bonnet theorem to the optical metric of a lens, modelled as a static, spherically symmetric, perfect non-relativistic fluid, in the weak deflection limit. We find that the focusing of the light rays emerges here as a topological effect, and we introduce a new method to calculate the deflection angle from the Gaussian curvature of the optical metric. As examples, the Schwarzschild lens, the Plummer sphere and the singular isothermal sphere are discussed within this framework.Comment: 10 pages, 1 figure, IoP styl

A Note on the Instability of Lorentzian Taub-NUT-Space

I show that there are no SU(2)-invariant (time-dependent) tensorial perturbations of Lorentzian Taub-NUT space. It follows that the spacetime is unstable at the linear level against generic perturbations. I speculate that this fact is responsible for so far unsuccessful attempts to define a sensible thermodynamics for NUT-charged spacetimes.Comment: 13 pages, no figure

Simple generalizations of Anti-de Sitter space-time

We consider new cosmological solutions which generalize the cosmological patch of the Anti-de Sitter (AdS) space-time, allowing for fluids with equations of state such that $w\neq -1$. We use them to derive the associated full manifolds. We find that these solutions can all be embedded in flat five-dimensional space-time with $--+++$ signature, revealing deformed hyperboloids. The topology and causal-structure of these spaces is therefore unchanged, and closed time-like curves are identified, before a covering space is considered. However the structure of Killing vector fields is entirely different and so we may expect a different structure of Killing horizons in these solutions.Comment: 6 Pages, 5 Figures, Corrections and additions made for publication in Journal of Classical and Quantum Gravit