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Harvest Strategies (harvest + strategy)
Selected AbstractsClimate change and the future for coral reef fishesFISH AND FISHERIES, Issue 3 2008Philip L Munday Abstract Climate change will impact coral-reef fishes through effects on individual performance, trophic linkages, recruitment dynamics, population connectivity and other ecosystem processes. The most immediate impacts will be a loss of diversity and changes to fish community composition as a result of coral bleaching. Coral-dependent fishes suffer the most rapid population declines as coral is lost; however, many other species will exhibit long-term declines due to loss of settlement habitat and erosion of habitat structural complexity. Increased ocean temperature will affect the physiological performance and behaviour of coral reef fishes, especially during their early life history. Small temperature increases might favour larval development, but this could be counteracted by negative effects on adult reproduction. Already variable recruitment will become even more unpredictable. This will make optimal harvest strategies for coral reef fisheries more difficult to determine and populations more susceptible to overfishing. A substantial number of species could exhibit range shifts, with implications for extinction risk of small-range species near the margins of reef development. There are critical gaps in our knowledge of how climate change will affect tropical marine fishes. Predictions are often based on temperate examples, which may be inappropriate for tropical species. Improved projections of how ocean currents and primary productivity will change are needed to better predict how reef fish population dynamics and connectivity patterns will change. Finally, the potential for adaptation to climate change needs more attention. Many coral reef fishes have geographical ranges spanning a wide temperature gradient and some have short generation times. These characteristics are conducive to acclimation or local adaptation to climate change and provide hope that the more resilient species will persist if immediate action is taken to stabilize Earth's climate. [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] 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] An ecosystem modelling approach to deriving viable harvest strategies for multispecies management of the Northern Gulf of CaliforniaAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2009Diego Lercari Abstract 1.An ecosystem analysis was developed focusing on resource exploitation and biodiversity conservation for the Northern Gulf of California. The main tools employed were a trophic ecosystem model and time dynamic simulations. 2.The ecosystem was represented by an Ecopath model that included 34 functional groups, from primary producers to top predators. It included relevant species in the area such as commercially important shrimp (e.g. Litopenaeus stylirostris) and highly endangered species (Phocoena sinus and Totoaba macdonaldi). 3.Temporal simulations of changing fishing effort allowed the evaluation of fishing impact on the ecosystem components and, particularly, on protected species. Formal optimization methods were applied with the purpose of searching viable temporal patterns of fishing effort that might minimize social, economic and conservationist conflicts in the area. 4.The results of those simulations showed the capability of the model to represent reference temporal series of relative biomass. The search for viable fishing strategies resulted in effort allocation consistent with those proposed by other studies; that is, a decrease in the industrial shrimp fleet (35,65%), a decrease in the gillnet fishing fleet (52,57%), and an increase of the artisanal shrimp fishery (63,222%). 5.The main conflicts in the Northern Gulf of California seem to take place between social and conservation interests, while the economic and ecological benefits seem to be relatively independent. The next steps towards conflict resolution and ecosystem management should consider the design and operation of MPAs already established in the region. Copyright © 2008 John Wiley & Sons, Ltd. [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] Dynamic and spatial models of kelp forest of Macrocystis integrifolia and Lessonia trabeculata (SE Pacific) for assessment harvest scenarios: short-term responsesAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 5 2010Marco Ortiz Abstract 1. Dynamic and spatial models of the kelp forest off northern Chile (SE Pacific coast) were constructed using the Ecosim and Ecospace theoretical frameworks based on a previously mass-balanced trophic model using Ecopath II software. 2. The biomass of Macrocystis integrifolia and Lessonia trabeculata blades constituted the most relevant compartments or variables of the ecosystem studied. 3. The relative ascendency (A/C) of 35.5% suggests that this ecosystem is immature, but resistant to disturbances (e.g. fisheries). 4. The results obtained using mixed trophic impacts (MTI) show that both brown macroalgae produced relatively similar quantitative and qualitative effects, however, the predictions based on Ecosim clearly show that L. trabeculata experienced the most relevant direct and indirect effects. 5. The highest values of system recovery time obtained by Pinguipes chilensis and the other seastar group suggest that both compartments could be considered to be top predator species with strong top-down control. 6. The exploitation of kelp blades as a new harvest strategy appears to be ecologically sustainable. 7. The Ecospace trophic-spatially explicit model shows that exploitation exerted separately by habitat generates a similar pattern of direct and indirect effects. These results suggest that a habitat rotation of fisheries would not be justified.Copyright © 2010 John Wiley & Sons, Ltd. [source] | |||||||||||||