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Harvesting Strategies (harvesting + strategy)
Selected AbstractsEstimating age and season of death of pronghorn antelope (Antilocapra americana Ord) by means of tooth eruption and wearINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 3 2001Patrick M. Lubinski Abstract Age and season of death information for prey animals at archaeological sites can address issues such as season of site occupation and prey hunting or harvesting strategies. Unfortunately, adequate reference information for estimating age and season is lacking for many wild species, including pronghorn antelope. To address this problem, new methods of scoring tooth eruption and wear have been developed and have been applied to a sample of over 500 pronghorn mandibles to obtain improved eruption and wear schedules. One implication of this study is that ,age class discreteness' is an unreliable method for demonstrating mass mortality of prey. This study provides a much larger comparative sample than previously available, although larger known-age mandible samples are still needed for pronghorn and many other wild species. Copyright © 2001 John Wiley & Sons, Ltd. [source] Lichen acclimatization on retention trees: a conservation physiology lessonJOURNAL OF APPLIED ECOLOGY, Issue 4 2009Kadi Jairus Summary 1.,Green-tree retention (GTR) has been suggested as a means to effectively support epiphytic lichen species in managed forests, given the low lichen mortality on retention trees in the short term. However, a long-term perspective requires a physiological understanding of lichen responses to logging. This study compares anatomical, morphological and physiological traits of lichens on retention trees and on intact forest trees. 2.,Thalli of nine taxa (Buellia griseovirens, Cladonia digitata, Hypogymnia physodes, Lecanora allophana, Lecanora pulicaris, Lepraria spp., Peltigera praetextata, Pertusaria amara and Phlyctis argena) were sampled from birch Betula spp. and aspen Populus tremula in GTR cuts, where they had previously been reported to survive well, and in adjacent managed forests. In the laboratory, chlorophyll fluorescence parameter Fv/Fm, thickness of the upper cortex, photobiont to mycobiont ratio and (in Lecanora species) the relative area of the apothecia were measured. 3.,All the lichen samples collected from GTR cuts appeared alive, but their Fv/Fm was significantly lower, relative areas of the apothecia were larger and the upper cortices of thalli were thicker compared with the samples from adjacent forests. No difference in photobiont to mycobiont ratio was found. These patterns were broadly consistent among species, indicating a common mechanism: while suffering from photoinhibition, the lichens had acclimatized to the open conditions and increased their investment to sexual reproduction in a few years. 4.,Synthesis and applications. The study highlights the value of a morpho-physiological framework for conservation management by pointing out that, in GTR areas, lichen survival is high-irradiation limited and heavily dependent on phenotypic plasticity. A thin upper cortex may be a common feature of the most sensitive species. To sustain epiphyte populations in managed forests, precautionary harvesting strategies (gradual felling; group-retention; extended rotations) should be preferred and large-enough populations should be preserved, even though short-term studies suggest a high survival of lichens in cut areas. [source] Effect of partial harvesting strategies on Artemia biomass production in Vietnamese salt worksAQUACULTURE RESEARCH, Issue 9 2010Nguyen Thi Ngoc Anh Abstract The effect of partial harvest strategies on the production of Artemia biomass was evaluated for 12 weeks under Vietnamese salt farm conditions. The initial stocking density was 100 nauplii L,1. After 3 weeks of inoculation, Artemia adults were partially harvested at intervals of 1, 3, 6 and 9 days starting with an initial quantity of 30 kg ha,1 day,1 at first harvest, and then the quantity of harvestable biomass was adjusted according to the standing stock present in the culture pond, combined with the time needed to harvest these quantities and with the weight of biomass harvested in each pond. The results showed that in most cases, the total densities were not significantly different among harvesting frequencies (P>0.05). However, a relatively higher Artemia adult density and its standing stock were better maintained in the 3-day than in the 1-day interval, and were significantly higher compared with the other two harvesting frequencies. The total biomass yields were the highest (1587 kg ha,1) in the 3-day harvesting interval, followed by 1-, 6- and 9-day harvesting interludes, corresponding to 1323, 1091 and 975 kg ha,1 respectively. However, no statistical difference was observed between the 1- and the 3-day interval as well as between the 6- and the 9-day harvest schemes (P>0.05). The results of this study suggest that partial harvest of Artemia biomass performed every 3 days appears to be an appropriate strategy to enhance biomass productivity. [source] Simulation of optimal harvesting strategies for small-scale mixed-sex tilapia (Oreochromis shiranus Boulenger 1896) ponds using a bio-economic modelAQUACULTURE RESEARCH, Issue 4 2007Francis Saiti Abstract A cohort-based bio-economic biomass growth and economic model, validated with data from experiments conducted in Malawi, was used to identify an optimal harvesting strategy for mixed-sex tilapia ponds. Three harvesting scenarios (baseline, economic optimum time +10 days and economic optimum time) were used. In each harvesting scenario four options were explored: (i) no further harvest, harvest every (ii) 60 days, (iii) 90 days and (iv) 120 days after initial harvest. The lowest simulated yield (487 kg ha,1 year,1) was obtained when no partial harvesting was carried out and fish were harvested after 365 days. Maximum yield (4416 kg ha,1 year,1) was obtained when partial harvests were carried out every 90 days starting with a first harvest of fish weighing 60 g or more at day 90. Maximum financial returns (US$2561 ha,1 year,1) were obtained when partial harvests were carried out every 120 days starting with the first harvest at day 90 and removing all fish ,60 g. The model simulations indicate that mixed-sex tilapia culture may be profitable for tilapia farmers in Africa where markets accept small (60,150 g)-sized fish. The study further shows that a cohort-based population growth model can be reliably incorporated in tilapia production models to simulate fish yields in mixed-sex tilapia production systems. However, incorporation of intergenerational competition effects could improve the model's utility as a decision support tool for managing mixed-sex tilapia production. [source] SUSTAINABLE YIELDS IN FISHERIES: UNCERTAINTY, RISK-AVERSION, AND MEAN-VARIANCE ANALYSISNATURAL RESOURCE MODELING, Issue 3 2010CHRISTIAN-OLIVER EWALD Abstract We consider a model of a fishery in which the dynamics of the unharvested fish population are given by the stochastic logistic growth equation Similar to the classical deterministic analogon, we assume that the fishery harvests the fish population following a constant effort strategy. In the first step, we derive the effort level that leads to maximum expected sustainable yield, which is understood as the expectation of the equilibrium distribution of the stochastic dynamics. This replaces the nonzero fixed point in the classical deterministic setup. In the second step, we assume that the fishery is risk averse and that there is a tradeoff between expected sustainable yield and uncertainty measured in terms of the variance of the equilibrium distribution. We derive the optimal constant effort harvesting strategy for this problem. In the final step, we consider an approach that we call the mean-variance analysis to sustainable fisheries. Similar as in the now classical mean-variance analysis in finance, going back to Markowitz [1952], we study the problem of maximizing expected sustainable yields under variance constraints, and with this, minimizing the variance, e.g., risk, under guaranteed minimum expected sustainable yields. We derive explicit formulas for the optimal fishing effort in all four problems considered and study the effects of uncertainty, risk aversion, and mean reversion speed on fishing efforts. [source] A BIOECONOMIC APPROACH TO THE FAUSTMANN,HARTMAN MODEL: ECOLOGICAL INTERACTIONS IN MANAGED FORESTNATURAL RESOURCE MODELING, Issue 4 2008JULIA TOUZA Abstract This paper develops a bioeconomic forestry model that makes it possible to take ecosystem services that are independent of the age structure of trees into account. We derive the Faustmann,Hartman optimal harvesting strategy as a special case. The bioeconomic model is then extended to account for the fact that forest harvesting decisions impact on other ecological resources, which provide benefits for the wider community. The paper focuses on impacts associated with disturbance caused by logging operations and habitat destruction due to tree removal. This enables us to explore the interactions between forest management and the dynamics of ecological resources. The optimal rotation rule is obtained as a variation on the traditional Faustmann,Hartman equation, where an additional term captures the potential benefits derived from the growth of the ecological resource valued at its shadow price. The steady-state solutions to the problem and sensitivity to model parameter are identified using numerical analysis. [source] Simulation of optimal harvesting strategies for small-scale mixed-sex tilapia (Oreochromis shiranus Boulenger 1896) ponds using a bio-economic modelAQUACULTURE RESEARCH, Issue 4 2007Francis Saiti Abstract A cohort-based bio-economic biomass growth and economic model, validated with data from experiments conducted in Malawi, was used to identify an optimal harvesting strategy for mixed-sex tilapia ponds. Three harvesting scenarios (baseline, economic optimum time +10 days and economic optimum time) were used. In each harvesting scenario four options were explored: (i) no further harvest, harvest every (ii) 60 days, (iii) 90 days and (iv) 120 days after initial harvest. The lowest simulated yield (487 kg ha,1 year,1) was obtained when no partial harvesting was carried out and fish were harvested after 365 days. Maximum yield (4416 kg ha,1 year,1) was obtained when partial harvests were carried out every 90 days starting with a first harvest of fish weighing 60 g or more at day 90. Maximum financial returns (US$2561 ha,1 year,1) were obtained when partial harvests were carried out every 120 days starting with the first harvest at day 90 and removing all fish ,60 g. The model simulations indicate that mixed-sex tilapia culture may be profitable for tilapia farmers in Africa where markets accept small (60,150 g)-sized fish. The study further shows that a cohort-based population growth model can be reliably incorporated in tilapia production models to simulate fish yields in mixed-sex tilapia production systems. However, incorporation of intergenerational competition effects could improve the model's utility as a decision support tool for managing mixed-sex tilapia production. [source] | |||||||||||||