Large-scale exploitation of sacred chank Xancus pyrum using modified trawl net along Rameswaram Coast, Tamil Nadu

The sacred chank, Xancus pynim is a gregarious, large gastropod and its habitat forms distinct chank bed. Homell as early as 1922 described the chank beds in depths of 10 to 20 metres in the Gulf of Mannar and are considered as the most important ones in the country although there are other chank beds along the Gulf of Kutch and the southwest coast of India

Sardines of the Gulf of Mannar ecosystem - fishery and resource characteristics of major species

Fishery, species diversity and resource characteristics of exploited sardine resources of the genera Sardinella were studied during 2000-2008. Sardines were exploited by sardine gillnets, trawls and shore seine. Annual average production for the period was 20,249 t. They formed about one fourth of the total marine fish production (77,443 t) of the region. Fishery was supported by eight species dominated by Sardinella gibbosa, followed by S. sirm, S. albella and S. longiceps. Fishery fluctuated widely with declining trend over the years mainly due to reduction in the fishing effort following destruction of traditional crafts and gears during the Tsunami in 2004. Oilsardine in the fishery registered an increasing trend with wide annual fluctuation during the period. Stock assessment studies show that the exploitation rate of major species ranged between 0.45 and 0.62, against the EMSY value of 0.72 and 0.86. This indicated that sardine resource as a whole is under-exploited, offering considerable scope for enhancing their yield. Despite contributing a higher share to marine fish production, sardines, along with other small pelagics, play a vital ecological role in sustaining the stock and fishery of other predatory groups especially large pelagics by providing them a major share of their forage. They support 46 to 87% of the total food of pelagic predators and 14 to 29% of demersal predators

Temperature and terahertz frequency dependence of the dielectric properties of Fe3O4 thin films deposited on Si substrate

The Fe$_3$O$_4$/Si films are considered to be promising materials for THz spintronic applications due to their high temperature magnetic transition and semiconducting properties. In this article, we present the real part of the dielectric constant ($\epsilon_1$) and the optical conductivity ($\sigma_1$) of Fe$_3$O$_4$ films of different thicknesses deposited on Si substrate (Fe$_3$O$_4$/Si) in the THz range at temperatures 2- 300 K. Although the magnetization of the films with thickness $\geq$ 115 nm shows a clear change at the Verwey transition temperature T$_v$ = 121 K, their optical properties in the THz frequency range are drastically different from each other. We have shown that $\sigma_1$ is maximum and $\epsilon_1$ is minimum when the Fe$^{+2}$/Fe$^{+3}$ ratio is equal to 0.54 which is the ratio of Fe+2/Fe+3 for pure Fe$_3$O$_4$. The $\sigma_1$ reduces and $\epsilon_1$ increases at all temperatures when the Fe$^{+2}$/Fe$^{+3}$ ratio deviates from 0.54. We have shown that a slight change in the Fe$^{+2}$/Fe$^{+3}$ ratio can induce large changes in the optical properties which shall have implications in the application of the Fe3O4 films in THz spintronics.Comment: 18 pages, 6 figure

Feeding congregation of ribbonfish, Trichiurus lepturus juveniles in oceanic waters and their targeted exploitation by deepsea trawlers along the Tuticorin coast in Gulf of Mannar

Ribbonfishes supported commercial fishery at Tuticorin prior to nineteen nineties. But reports suggested that their stock and fishery declined considerably thereafter. Their fishery during 2000- 2006 was represented by occasional landings of small quantity of ribbonfish by trawls. Average production by trawls at Tuticorin fishing harbour during the period was 250 t. They represent about 0.7% of the total fish catch of the period

Exploited marine fishery resources off Tuticorin along the Gulf of Mannar coast

Tuticorin coast of Gulf of Mannar is endowed with rocky bottom, coral reefs and sea grass beds with characteristic flora and fauna. It also acts as home for several endangered marine mammals, sea cows and marine turtles. These resources were exploited by a variety of gears during 2000-2005