Home About us Contact
|
Home About us Contact | ||
|
|
||
Harvest Rate (harvest + rate)
Selected AbstractsManagement and Recovery Options for Ural River Beluga SturgeonCONSERVATION BIOLOGY, Issue 3 2010PHAEDRA DOUKAKIS caviar; CITES; criadero; Mar Caspio; puntos de referencia; sobrepesca Abstract:,Management of declining fisheries of anadromous species sometimes relies heavily on supplementation of populations with captive breeding, despite evidence that captive breeding can have negative consequences and may not address the root cause of decline. The beluga sturgeon (Huso huso), a species threatened by the market for black caviar and reductions in habitat quality, is managed through harvest control and hatchery supplementation, with an emphasis on the latter. We used yield per recruit and elasticity analyses to evaluate the population status and current levels of fishing and to identify the life-history stages that are the best targets for conservation of beluga of the Ural River. Harvest rates in recent years were four to five times higher than rates that would sustain population abundance. Sustainable rates of fishing mortality are similar to those for other long-lived marine species such as sharks and mammals. Yield per recruit, which is maximized if fish are first harvested at age 31 years, would be greatly enhanced by raising minimum size limits or reducing illegal take of subadults. Improving the survival of subadult and adult females would increase population productivity by 10 times that achieved by improving fecundity and survival from egg to age 1 year (i.e., hatchery supplementation). These results suggest that reducing mortality of subadults and adult wild fish is a more effective conservation strategy than hatchery supplementation. Because genetics is not factored into hatchery management practices, supplementation may even reduce the viability of the beluga sturgeon. Resumen:,El manejo de pesquerías de peces anádromos en declinación a veces depende estrechamente de la suplementación de poblaciones mediante la reproducción en cautiverio, no obstante la evidencia de que la reproducción en cautiverio puede tener consecuencias negativas y no abordar la causa principal de la declinación. El esturión beluga (Huso huso), una especie amenazada por el mercado de caviar negro y por reducciones en la calidad del hábitat, es manejado mediante el control de la cosecha y suplementación de poblaciones, con énfasis en esta. Utilizamos análisis de producción por recluta y de elasticidad para evaluar el estatus de la población y los niveles de pesca actuales y para identificar las etapas de la historia de vida que son los mejores blancos para la conservación del beluga en el Río Ural. Las tasas de cosecha en años recientes fueron cuatro a cinco veces mayores que las tasas que sustentarían la abundancia de la población. Las tasas sustentables de mortalidad por pesca son similares a las de otras especies marinas longevas como tiburones y mamíferos. La producción por recluta, que es maximizada si los peces son cosechados a la edad de 31 años, podría incrementar significativamente elevando los límites de talla mínima o reduciendo la captura ilegal de subadultos. La mejora de la supervivencia de hembras subadultas y adultas incrementaría la productividad de la población 10 veces más que la mejora obtenida incrementando la fecundidad y supervivencia de huevo a 1 año de edad (i. e., suplementación de poblaciones mediante reproducción en cautiverio). Estos resultados sugieren que la reducción de la mortalidad de peces silvestres subadultos y adultos es una mejor estrategia de conservación que la suplementación. Debido a que la genética no es considerada en las prácticas de manejo en los criaderos, la suplementación incluso puede reducir la viabilidad del esturión beluga. [source] Tunneling enhanced by web page content block partition for focused crawlingCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 1 2008Tao Peng Abstract The complexity of web information environments and multiple-topic web pages are negative factors significantly affecting the performance of focused crawling. A highly relevant region in a web page may be obscured because of low overall relevance of that page. Segmenting the web pages into smaller units will significantly improve the performance. Conquering and traversing irrelevant page to reach a relevant one (tunneling) can improve the effectiveness of focused crawling by expanding its reach. This paper presents a heuristic-based method to enhance focused crawling performance. The method uses a Document Object Model (DOM)-based page partition algorithm to segment a web page into content blocks with a hierarchical structure and investigates how to take advantage of block-level evidence to enhance focused crawling by tunneling. Page segmentation can transform an uninteresting multi-topic web page into several single topic context blocks and some of which may be interesting. Accordingly, focused crawler can pursue the interesting content blocks to retrieve the relevant pages. Experimental results indicate that this approach outperforms Breadth-First, Best-First and Link-context algorithm both in harvest rate, target recall and target length. Copyright © 2007 John Wiley & Sons, Ltd. [source] Spatial patterns of kangaroo density across the South Australian pastoral zone over 26 years: aggregation during drought and suggestions of long distance movementJOURNAL OF APPLIED ECOLOGY, Issue 5 2007ANTHONY R. POPLE Summary 1Wildlife surveys usually focus on estimating population size, and management actions such as commercial harvesting, culling and poison baiting are referenced commonly to population size alone, without taking into account the way in which those animals are distributed. This paper outlines how point-based aerial survey data can be converted to continuous density surfaces using spatial analysis techniques. Using this approach, we describe and explore the spatial patterns of density of two species of kangaroos in an area exceeding 200 000 km2 in South Australia over a 26-year period. 2Densities of red and western grey kangaroos were estimated in 2 km2 segments along aerial survey transect lines, yielding point density estimates. Universal kriging provided an unbiased interpolation of these data using the spatial autocorrelation structure described by the semi-variogram. The Getis statistic identified clusters of high and low kangaroo density. 3Considerable year-to-year variation in the spatial patterns of kangaroo density was observed. In many cases, annual rates of increase over large areas were too high to be explained by vital rates alone, implying immigration from surrounding areas. These large shifts in distribution were occasionally to areas that had received better rainfall than the surrounding areas. For both species, there was no obvious local spatial autocorrelation pattern or clustering of kangaroo density beyond that described by average density and the present set of management regions, suggesting the latter are appropriate divisions for harvest management. 4Data for both species fitted the power law relationship extremely well. During dry times, red kangaroos, but not western grey kangaroos, were more aggregated, supporting past ground observations at a fine spatial scale. 5Synthesis and applications. Kriged density surfaces enable estimation of kangaroo density on individual properties, which are the management units at which harvest quotas or culling approvals are allocated. These estimates will be marked improvements over systematic sampling estimates when sampling intensity is low. Predictions of shifts in kangaroo distribution using rainfall or satellite imagery will allow more accurate allocation of harvest quotas. Similarly, predictions of more even kangaroo dispersion following high rainfall will allow managers to anticipate downturns in harvest rate. [source] Effective size of harvested ungulate populationsANIMAL CONSERVATION, Issue 5 2009B.-E. Sæther Abstract The harvest of ungulate populations is often directed against certain sex or age classes to maximize the yield in terms of biomass, number of shot animals or number of trophies. Here we examine how such directional harvest affects the effective size of the population. We parameterize an age-specific model assumed to describe the dynamics of Fennoscandian moose. Based on expressions for the demographic variance for a small subpopulation of heterozygotes Aa bearing a rare neutral allele a, we use this model to calculate how different harvest strategies influence the effective size of the population, given that the population remains stable after harvest. We show that the annual genetic drift, determined by , increases with decreasing harvest rate of calves and increasing sex bias in the harvest towards bulls 1 year or older. The effective population size per generation decreased with reduced harvest of calves and increased harvest of bulls 1 year or older. The magnitude of these effects depends on the age-specific pattern of variation in reproductive success, which influences the demographic variance. This shows that the choice of harvest strategy strongly affects the genetic dynamics of harvested ungulate populations. [source] Perfusion Culture of Hybridoma Cells for Hyperproduction of IgG2a Monoclonal Antibody in a Wave Bioreactor-Perfusion Culture SystemBIOTECHNOLOGY PROGRESS, Issue 1 2007Ya-Jie Tang A novel wave bioreactor-perfusion culture system was developed for highly efficient production of monoclonal antibody IgG2a (mAb) by hybridoma cells. The system consists of a wave bioreactor, a floating membrane cell-retention filter, and a weight-based perfusion controller. A polyethylene membrane filter with a pore size of 7 ,m was floating on the surface of the culture broth for cell retention, eliminating the need for traditional pump around flow loops and external cell separators. A weight-based perfusion controller was designed to balance the medium renewal rate and the harvest rate during perfusion culture. BD Cell mAb Medium (BD Biosciences, CA) was identified to be the optimal basal medium for mAb production during batch culture. A control strategy for perfusion rate (volume of fresh medium/working volume of reactor/day, vvd) was identified as a key factor affecting cell growth and mAb accumulation during perfusion culture, and the optimal control strategy was increasing perfusion rate by 0.15 vvd per day. Average specific mAb production rate was linearly corrected with increasing perfusion rate within the range of investigation. The maximum viable cell density reached 22.3 × 105 and 200.5 × 105 cells/mL in the batch and perfusion culture, respectively, while the corresponding maximum mAb concentration reached 182.4 and 463.6 mg/L and the corresponding maximum total mAb amount was 182.4 and 1406.5 mg, respectively. Not only the yield of viable cell per liter of medium (32.9 × 105 cells/mL per liter medium) and the mAb yield per liter of medium (230.6 mg/L medium) but also the mAb volumetric productivity (33.1 mg/L·day) in perfusion culture were much higher than those (i.e., 22.3 × 105 cells/mL per liter medium, 182.4 mg/L medium, and 20.3 mg/L·day) in batch culture. Relatively fast cell growth and the perfusion culture approach warrant that high biomass and mAb productivity may be obtained in such a novel perfusion culture system (1 L working volume), which offers an alternative approach for producing gram quantity of proteins from industrial cell lines in a liter-size cell culture. The fundamental information obtained in this study may be useful for perfusion culture of hybridoma cells on a large scale. [source] A framework for incorporating climate regime shifts into the management of marine resourcesFISHERIES MANAGEMENT & ECOLOGY, Issue 2 2006J. R. KING Abstract, It is possible to use an ecosystem-based management approach to incorporate knowledge of climate regime impacts on ecosystem productivity to manage fishery resources. To do so, it requires the development of a coherent framework that can be built using existing stock assessment and management activities: ecosystem assessment, risk analyses, adaptive management and reference points. This paper builds such a framework and uses two population simulations to illustrate the benefits and tradeoffs of variable regime-specific harvest rates. The framework does not require prediction of regime shifts, but assumes that detection can occur soon after one has happened. As such, decisions do not need to be coincident to regime shifts, but can be delayed by an appropriate period of time that is linked to a species' life history, i.e. age of maturity or recruitment. Fisheries scientists should provide harvest recommendations that reflect a range of levels of risk to the stock under different assumptions of productivity. Coupling ecosystem assessment with ecosystem-based management would allow managers to select appropriate regime-specific harvest rates. [source] Corn stover feedstock trials to support predictive modelingGCB BIOENERGY, Issue 5 2010DOUGLAS L. KARLEN Abstract To be sustainable, feedstock harvest must neither degrade soil, water, or air resources nor negatively impact productivity or subsequent crop yields. Simulation modeling will help guide the development of sustainable feedstock production practices, but not without field validation. This paper introduces field research being conducted in six states to support Sun Grant Regional Partnership modeling. Our objectives are to (1) provide a fundamental understanding of limiting factor(s) affecting corn (Zea mays L.) stover harvest, (2) develop tools (e.g., equations, models, etc.) that account for those factors, and (3) create a multivariant analysis framework to combine models for all limiting factors. Sun Grant modelers will use this information to improve regional estimates of feedstock availability. A minimum data set, including soil organic carbon (SOC), total N, pH, bulk density (BD), and soil-test phosphorus (P), and potassium (K) concentrations, is being collected. Stover yield for three treatments (0%, 50%, and 90% removal) and concentrations of N, P, and K in the harvested stover are being quantified to assess the impact of stover harvest on soil resources. Grain yield at a moisture content of 155 g kg,1 averaged 9.71 Mg ha,1, matching the 2008 national average. Stover dry matter harvest rates ranged from 0 to 7 Mg ha,1. Harvesting stover increased N,P,K removal by an average of 42, 5, and 45 kg ha,1 compared with harvesting only grain. Replacing those three nutrients would cost $53.68 ha,1 based on 2009 fertilizer prices. This first-year data and that collected in subsequent years is being used to develop a residue management tool that will ultimately link multiple feedstock supplies together in a landscape vision to help develop a comprehensive carbon management plan, quantify corn stover harvest effects on soil quality, and predict regional variability in feedstock supplies. [source] | |||||||||||||||||||