4 resultados para DISORDERS OF EXCESSIVE SLEEPINESS

em Aquatic Commons


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Florida’s large number of shallow lakes, warm climate and long growing season have contributed to the development of excessive growths of aquatic macrophytes that have seriously interfered with many water use activities. The introduction of exotic aquatic macrophyte species such as hydrilla ( Hydrilla verticillata ) have added significantly to aquatic plant problems in Florida lakes. The use of grass carp ( Ctenopharyngodon idella ) can be an effective and economical control for aquatic vegetation such as hydrilla. Early stocking rates (24 to 74 grass carp per hectare of lake area) resulted in grass carp consumption rates that vastly exceeded the growth rates of the aquatic plants and often resulted in the total loss of all submersed vegetation. This study looked at 38 Florida lakes that had been stocked with grass carp for 3 to 10 years with stocking rates ranging from < 1 to 59 grass carp per hectare of lake and 1 to 207 grass carp per hectare of vegetation to determine the long term effects of grass carp on aquatic macrophyte communities. The median PAC (percent area coverage) value of aquatic macrophytes for the study lakes after they were stocked with grass carp was 14% and the median PVI (percent volume infested) value of aquatic macrophytes was 2%. Only lakes stocked with less than 25 to 30 fish per hectare of vegetation tended to have higher than median PAC and PVI values. When grass carp are stocked at levels of > 25 to 30 fish per hectare of vegetation the complete control of aquatic vegetation can be achieved, with the exception of a few species of plants that grass carp have extreme difficulty consuming. If the management goal for a lake is to control some of the problem aquatic plants while maintaining a small population of predominately unpalatable aquatic plants, grass carp can be stocked at approximately 25 to 30 fish per hectare of vegetation.

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The paper critically examines the trend in fish production in Nigeria. The problem of excessive mismanagement and lack of attention by relevant agencies are still common place in inland water bodies. The paper discusses these mismanagement practices which are non compliance with the existing rules and regulations on good fishing methods, uncontrollable, unorthodox and obnoxious fishing practices, destruction of the natural breeding grounds and the collapse of the fishery due to massive over fishing. The challenges posed by the fishing methods as well as the effect of different gears and mechanization of fishing crafts on fish production are discussed. The paper recommends ways to increase domestic fish production in inland water bodies, which include a well planned strategy of restocking the existing reservoirs after careful scientific study, enforcement of the existing laws and regulation based on community participation. Training of stakeholders on the code of practice for responsible fisheries (CPRF), extension of subsidies to fisher folks, the traditional practices, which encourage the adherence to close season and other fish conservation and utilization strategies, are also advocated

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A first assessment ofimportant East China Sea fisheries was carried out using data from 1956 to 1993. Two different data sets were available: 1) catch and effort data taken from landings and boat registrations and 2) catch and effort data from skipper's logs taken at sea. The two sets provided similar trends in CPUE over the study period. Stocks of high value, low volume species have been fished heavily and now produce very low landings or have been depleted (e.g. small and large yellow croaker). Some high volume and low value species have also been heavily fished (e.g. green filefish) while others (e.g. hairtail) are still producing high landings. Surplus production models were fitted to seven stocks. All showed considerable fluctuations in landings around MSY. The green filefish stock had an estimated MSY of around 160,000 tlyr at an effort of 2,500,000 kw and was depleted by a combination of excessive effort (around 4,000,000 kw in 1993) and marked fluctuations in landings (up to 70,000 tlyr above or below MSY). A sustainable policyfor managing ECS fisheries should address the effects ofboth effort and environmental variation.

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It is global concern that soil and water were contaminated with organic substances such as BTEX (benzene) (B), toluene (T) and xylene (x) .The presence of excessive amounts of BTEX in aqueous surroundings may have a greatly adverse impact on water quality and thus endanger public health and welfare. Carbon nanotubes (CNT) have aroused widespread attention as a new type of adsorptions due to their outstanding ability for the removal of various inorganic and organic pollutants from large volume of wastewater. Due to variety of adsorbent and their ability to adsorb pollutant, it is possible to reduce expenses and completely omit pollutant. In this CNT is used as a new adsorbent for removal pollutant such as benzene, toluene, and xylene. The result in the area of adsorbing benzene, toluene, and xylene is as follows: the changes of pH don’t affect the capacity of adsorption and the greatest amount of adsorption occurs in pH. The greatest amount of adsorption occurs when using 0.01gr CNT oxidized. Comparing CNT with CNT oxidized in term of adsorption capacity, it is proved that the adsorption capacity of CNT oxidized is much more than CNT. The result of comparing the percentage of adsorption of mentioned elements (B, X, T) is as follows; the amount of adsorption of xylene is more than toluene and toluene is more than benzene. It should be mentioned that in this research the percentage of adsorption to measure is between to 70-80.