Biology, Fishery, Conservation and Management of Indian Ocean Tuna Fisheries

The focus of the study is to explore the recent trend of the world tuna fishery with special reference to the Indian Ocean tuna fisheries and its conservation and sustainable management. In the Indian Ocean, tuna catches have increased rapidly from about 179959 t in 1980 to about 832246 t in 1995. They have continued to increase up to 2005; the catch that year was 1201465 t, forming about 26% of the world catch. Since 2006 onwards there has been a decline in the volume of catches and in 2008 the catch was only 913625 t. The Principal species caught in the Indian Ocean are skipjack and yellowfin. Western Indian Ocean contributed 78.2% and eastern Indian Ocean 21.8% of the total tuna production from the Indian Ocean. The Indian Ocean stock is currently overfished and IOTC has made some recommendations for management regulations aimed at sustaining the tuna stock. Fishing operations can cause ecological impacts of different types: by catches, damage of the habitat, mortalities caused by lost or discarded gear, pollution, generation of marine debris, etc. Periodic reassessment of the tuna potential is also required with adequate inputs from exploratory surveys as well as commercial landings and this may prevent any unsustainable trends in the development of the tuna fishing industry in the Indian Ocean

Laboratory simulation of the surface morphology of self-mulching and non self-mulching vertisols. I. Materials, methods and preliminary results

To date, the definitions of ‘self-mulching’ in Vertisols describe the phenomenon only in the air-dry state with no details of the dynamics of the system. A laboratory study was carried out to simulate the field morphological features of the soil surface of three Vertisols, one self-mulching and two non self-mulching. The soils differedin shear strength in the field, clay type, ESP and exchangeable Ca/Mg ratio. The laboratorysimulation involved both repeated wetting/drying cycles with 6 mm of water every 48 h, anda continuous drying phase. These were imposed on ponded and puddled samples of thesoils. With repeated wetting and drying the self-mulching soil developed a surface with amore complex organization of structural features than either of the non self-mulching soils.The self-mulching soil generated a granular structure and developed the widest cracks. Mostelements of the surface morphology observed in the field were achieved in the laboratorysimulation

Phytase supplemented poultry diets affect soluble phosphorus and nitrogen in manure and manure-amended soil

Understanding P and N dynamics in manure-amended soil is essential for estimating the environmental impact of manure utilization in land applications. A laboratory incubation study was conducted to assess, (i) the effect of feeding a standard Australian commercial diet, and diets modified with phytase supplementation and reduced nonphytase phosphorus (NPP), on the concentrations of P and N (total and soluble) in the manure derived from layer hens (Gallus domesticus L.), and (ii) the change in water-soluble phoshorus (P) and mineral N (NH-N and NO-N) when used as a soil amendment, applied at rates equivalent to 200 kg ha (200N) and 400 kg ha (400N). Phytase supplementation increased %P by 8 to 12% in the manures, regardless of the levels of NPP in the diets, and in the manure-amended soils by 27 to 30% at the 200N application rate, and up to 54% at the 400N rate. Phytase significantly (P < 0.05) reduced total nitrogen (TN) content (by 12-31%) of the manures but generally produced greater nitrate accumulation in the manure-amended soils. Net nitrification, which commenced 4 wk after incubation, was accompanied by a simultaneous decrease in soil pH (by one pH unit) and a concomitant decline in %P. The decline in %P was primarily attributed to Pretention by the soil as it became more acidic. This study suggests that phytase addition not only reduces manure total N content, and increases watersoluble P, but its effects on manure total phosphorus (TP) and 2 mol L KCl extractable mineral N is influenced by the NPP level in the diet