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《African Journal of Marine Science》2013,35(3):517-528
Between 1978 and 1998, a total of 3 385 scalloped hammerhead sharks Sphyrna lewini was caught in the protective nets off KwaZulu-Natal. The mean annual catch was 166 sharks (range 60–279). There was a significant decrease in catch rate with time, but the relationship with the population size in KwaZulu-Natal waters is unknown. Size and sex segregation is indicated. Sizes-at-50% maturity were 161.5cm (males) and 183.1cm (females). Most of the catch (91%) was immature, but neonates are poorly sampled by the 51-cm meshed nets. In small animals (<160cm precaudal length, PCL), males significantly outnumbered females by 2.2:1, and in large animals by 3.6:1. The length-mass relationship differed between sexes. Catches of both small and large animals were highest in summer. Most of the large males were caught in November and December, consistent with an inshore movement of mature animals to breed in summer, but no evidence of recent mating was observed in either sex. Females pregnant with term embryos (median embryo length per litter 30.4–36.2cm) were caught between October and March. These females tended to have maximum ovarian follicle diameters of ≥30mm, indicating that mating would occur shortly after parturition. The median size of 11 litters was 10 embryos. The Tugela Bank to the north of the netted region appears to be a nursery ground. Teleosts, comprising 42 families and 60 identified species, dominated the diet in terms of frequency of occurrence (77%), followed by cephalopods (25%). 相似文献
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《制图学和地理信息科学》2013,40(2):110-116
This paper presents a method for terrain generalization using Laplacian pyramids. The method pre-processes digital terrain for generating cartographically generalized 3D maps. Map authors can attenuated or amplify selected frequency bands of the terrain with a graphical interface imitating an audio equalizer. Ridge lines and valley lines are localized by curvature indices, and their characteristic shapes are preserved or emphasized using additional sets of equalizer controls. Frequency bands are adjusted separately for the foreground and the background to remove visually disturbing terrain detail in the background. This is relevant for 3D maps in central perspective projection that considerably compresses distant terrain features. The proposed generalization method was implemented in Terrain Equalizer, a free and open-source application providing a graphical interface with interactive 3D previews (available at http://www.terraincartography.com/). Using this application, disturbing high frequency details can be easily removed and major mountain forms can be accentuated. The level of generalization can be adjusted seamlessly from the foreground to the background of the 3D map. Topographic break lines, such as ridge or valley lines, are successfully preserved, which is important for conveying the characteristic shape of a generalized terrain. 相似文献
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《African Journal of Marine Science》2013,35(1):107-120
The surface and subsurface waters of the Angola and Agulhas Current systems significantly influence the Benguela region and its living resources, and it is probable that the movement of Central Water, which plays a key role in the coastal upwelling process, is controlled by circulation of underlying Antarctic Intermediate Water (AIW) as well as by the dynamics of the overlying subtropical water. The movement of AIW can be inferred from a study of the t-s characteristics, and the data holdings and data base of the South African Data Centre for Oceanography facilitated this investigation. Key findings of the investigation, some confirming earlier theories and hypotheses, are as follows. The mean depth of the AIW core in the South-East Atlantic is 750 m, and in the South-West Indian Ocean, 1 100 m. Agulhas Current AIW, which is modified by Red Sea Water, becomes fresher en route because of entrainment and mixing of water from the south and west. Most of the Agulhas Current AIW per se retroflects east of 18°E. A poleward movement of AIW along the West Coast to around 32°S may be inferred from the salinity and oxygen data, with a freshening en route analogous to the Agulhas Current. Relatively fresh AIW (s < 34,35 × 10?3) is present off the South-Western Cape, the only part of the Benguela where the overlying virgin Central Water upwells. No statistically significant seasonal differences could be resolved. 相似文献
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《African Journal of Marine Science》2013,35(3-4):581-588
Between 1980 and 2001, a total of 661 African angel sharks Squatina africana was caught in the protective nets off KwaZulu-Natal, South Africa. The mean annual catch was 30 sharks (range = 11–69, SD = 12.4), with no trend in catch rate over the study period. Individuals were caught throughout the year and through much of the netted region, with a higher catch to the south. The sex ratio of the catch was 2.9 females:1 male. Males matured between 640mm and 700mm and females at about 700mm precaudal length (PCL). Mature males had clusters of thorn-shaped denticles, each about 2mm high, near the anterio-dorsal margins of both pectoral and pelvic fins. Of the mature females, 44% were pregnant, many of which contained only ova in utero. Embryos were present from April through to January. The average litter size was six, with length at parturition at least 240mm PCL. Most early-term pregnant females and all mature males were caught in the south. The reproductive cycle showed some seasonality and appeared to be biennial, with a gestation of about one year. Teleosts were the most common prey (76% of stomachs with food), followed by cephalopods (52%). 相似文献
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《制图学和地理信息科学》2013,40(4):257-268
Much progress has been made in the field of web-based cartography through standards developed by the Open Geospatial Consortium (OGC). While automated access and presentation of cartographic data have been defined, the services for automated generalization are yet to be standardized. This paper aims to show advantages of applying the service concept to generalization and suggests several classification schemas of generalization services at different levels of granularity. A detailed explanation of a real implemented Generalization Service is provided. We show how software developers can make their generalization functionality available as a service and how these services can be accessed dynamically. For the implementation, the open source Java Unified Mapping Platform (JUMP) was extended to work as a framework for generalization. Generalization services could be used in different application scenarios, for instance as a middleware component extending a web map service with adaptive zooming or as stand-alone services supporting the production of topographic maps by national mapping agencies. They may also allow the development of a common research platform, where researchers would have access to a common generalization framework. 相似文献
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《制图学和地理信息科学》2013,40(4):217-236
This article presents the use of the frequency histogram legend (FHL) as a substitute to traditional legends in both classed and unclassed choropleth maps. Great variation in the size of mapping units can hinder readers' ability to comprehend statistical distributions from a choropleth map. Replacing conventional legends with FHL can aid readers in their understanding of spatial as well as statistical distributions of the mapped data simultaneously. A customized mapping application was designed in ArcInfo 9.0 to test the use of FHL in both classed and unclassed choropleth maps. Frequency histogram legends were tested on different types of statistical distributions. Although the comparison of the results shows that the FHL works best for a Gaussian or close to a Gaussian distribution for eight or fewer classes, the customized application permits users to generate choropleth maps with frequency histogram legends for any type of statistical distribution with any number of classes. The analysis reveals that readers' background in statistics helped them to effectively utilize and interpret frequency histogram legends in the choropleth maps. 相似文献
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