Direct hydroacoustic observations of chokka squid Loligo vulgaris reynaudii spawning activity in deep water

Unusual and distinct hydroacoustic targets were observed in November 1996, May 1998 and November 1998 during routine pelagic biomass surveys off the south coast of South Africa. During the November 1996 survey, seven such targets were observed near the bottom at depths of 115–125 m, directly south of the traditional inshore spawning grounds of chokka squid Loligo vulgaris reynaudii at Cape St Francis. The targets were close to prominent seabed ridges and extended 30–40 m off the bottom. In May 1998, three similar targets were observed at depths 55–80 m off Plettenberg Bay, another well-known squid spawning site. The shallowest target was identified, by means of a midwater trawl, as a mixture of mature male and female chokka. During the November 1998 survey, nine similar targets were again observed on the squid spawning grounds at Cape St Francis, also adjacent to seabed ridges. Drawing on fisheries hydroacoustic experience and knowledge of chokka squid spawning behaviour, the targets are believed to be aggregations of spawning squid.     

Early post-cleavage stages and abnormalities identified in the embryonic development of chokka squid eggs Loligo vulgaris reynaudii

Six early, post-cleavage embryonic stages for chokka squid Loligo vulgaris reynaudii eggs that were developed in an aquarium are identified and described, expanding the embryonic stages for this species from 14 to 20. The influence of water temperature on embryonic development is described. At temperatures <12 and >15°C, high percentages of morphological abnormalities were observed in embryonic development. Gross forms are described and illustrated.     

Life cycle of chokka-squid Loligo reynaudii in South African waters

This short note summarises past and current knowledge of the life cycle of chokka-squid Loligo reynaudii d’Orbigny, 1845, in South African waters. Prior to approximately 2010, the chokka-squid stock was considered simple and uniform, with one paralarval pool, the drift of paralarvae westwards, one main nursery area and one main, long spawning migration of adult squid eastwards, back to the main spawning grounds. Based on new information, this life-history scheme has been revised. Genetically, the stock is uniform; however, morphologically, it comprises three main geographic groups. It is proposed that the differences between the groups originate from many different paralarval events and that short (not long) migrations dominate the life cycle.     

An assessment of the current status of the chokka squid fishery in South Africa and an evaluation of alternative allocation strategies

The South African squid fishery is based on a single species, Loligo reynaudi, locally referred to as chokka and commonly found around the Agulhas Bank and West Coast shelf of South Africa. The existing long term rights for participation in the fishery expire at the end of 2013 and a new set of rights will have to be issued. Progress made to date in achieving the objectives of the South African Marine Living Resources Act of 1998 (MLRA), including progress towards greater equity, will be an important consideration in allocation decisions. The draft Small-Scale Fisheries Policy, scheduled to be adopted in 2013, could also influence the criteria to be used. This study updates the information on the current structure and functioning of the squid jig sector and considers the likely performance of two alternative access allocation scenarios against the current and evolving policy goals. The study reaffirms that the squid fishery is an important contributor to human well-being in South Africa and particularly in the Eastern Cape Province but there is scope for improvement in the extent of transformation and equity. The study concludes that, as a result of a common lack of experience and capital amongst potential new entrants, the risks associated with transformation in this fishery are likely to be high, especially if the option of allocating rights to community-based legal entities was to be used. The risks could be reduced by ensuring that a number of pre-conditions were met. These include, amongst others, not allowing total effort in the fishery to increase; ensuring effective management by the responsible government authorities; adequate capacity building of new entrants, whether individuals or cooperatives; and ensuring new entrants have viable business plans.     

海沟影响下深水海洋管线成环行为研究

在深水海洋管线的安装过程中,制造工艺的偏差和外部环境的影响易导致管线上不均匀的扭矩分布,在张力的共同作用下,管线在其触地区可能出现“成环”现象,受到严重损伤,而海洋管线的触地区也是海沟集中形成的区域。为了研究海沟对海洋管线成环行为的影响,基于OrcaFlex软件和构建海沟模型的经验公式,建立了深水悬链线立管和海沟的三维数值模型。就海沟轮廓、位置和土壤属性对立管成环行为的影响展开参数分析,并研究了不同工况下成环的临界载荷。研究表明：海沟的产生和扩展、立管相对海沟的合理位置以及土壤参数中海床表面不排水抗剪强度和吸力因子的增加,可有效降低立管成环过程中的最大压缩力和最大弯矩,从而减少成环引起的损伤;临界载荷的分析则有助于对成环的临界条件进行预测,避免成环现象的发生。