Representation and its Relationship with Cartographic Visualization

A research agenda is presented which addresses the current role and potential of map displays. By considering the geospatial data used in visualization, the form and design of maps, the purposes for which map displays are created, the nature of the map user community, and the technology employed to visualize geospatial data, a thorough overview of the nature of cartographic visualization is given. Under the same themes, and sourced in cartographic tradition, cartographic practice and technological opportunities, a series of possible research avenues are highlighted. The important links between representation and the user interface, map user cognition and the geospatial database are stressed.     

Socio-economic characteristics of gillnet and beach-seine fishers in the Western Cape,South Africa

Data collected by questionnaire and telephone surveys conducted during 1998 and 1999 are used to describe the socio-economic characteristics of inshore netfishers in the Western Cape. Approximately two-thirds of netfishers work or have worked in other fishing sectors and a further 6–50%, depending on the area surveyed, are retired. Very few (0–11%) permit-holders in most areas classified their occupations as netfishers and the majority claimed to make <5% of their income from netfishing. Estimated costs and returns to net permit-holders suggest that, in most areas, commercial netfishing at current levels of catch and effort is not economically sustainable in the long-term. Only Saldanha-Langebaan gillnetters and beach-seine permit-holders, on average, manage to cover their opportunity costs and make an economic profit. The lack of profits in other areas is compelling evidence that the net fisheries are at or beyond the open access equilibrium point, suggesting that effort reduction in the order of 60% is necessary if maximum economic yield is to be obtained from the fishery. The netfisheries provide part-time employment for approximately 2 000 crew in the Western Cape. Additional economic benefits and employment directly related to the fishery in the form of equipment and fuel purchases made by fishers, maintenance of fishing gear and the sale of fish are estimated to contribute at least R15 million to the regional economy annually. Between 42 and 76% of respondents felt that their catches had declined since they had started netfishing and most felt that no new permits should be issued. Knowledge of catch restrictions among respondents was low (53–73%), indicative of a lack of communication between management and fishers, poorly defined permit conditions and a lack of enforcement. Many fishers interviewed feel it is unfair that they are restricted to catching only low-value target species and do not adhere to the catch restrictions, even if they do know them. The importance of the netfishery for participants varies greatly between and within areas. In order to reduce effort equitably, current and potential new permit-holders should be assessed on an individual merit basis.     

Stock separation and life history of Argyrozona argyrozona (Pisces: Sparidae) on the South African east coast

Fishery independent biomass surveys and commercial linefish catch returns were used to elucidate the spatial patterns of carpenter Argyrozona argyrozona distributed along the South African continental shelf. Two distinct areas of abundan ce ere determined, one on the central and the other on the eastern Agulhas Bank. Tagging studies revealed little exchange between them. Nurseries were identified in Algoa Bay on he eastern Agulhas Bank and on the central Agulhas Bank (CAB). Early juveniles (<100mm total length) on the CAB were found offshore in the vicinity of the Alphard Bank. They were found to move inshore with growth and then back offshore as they approached maturity. Juveniles in Algoa Bay dispersed both eastwards and westwards with growth. Otoith readability and growth rates varied between regions, with fish from the Eastern Cape (Port Elizabeth and Port Alfred combined) having the lowest average percentage error (4.82 vs 5.33 and 7.03) and the slowest growth rates. Size-at-50 % mturity (L₅₀) varied regionally, female fish in the Eastern Cape maturing at a smaller size (L₅₀ = 206mm fork length) than in the Tsitsikamma National Park (L₅₀ = 292mm) or the CAB (L₅₀ = 267mm). Mass-at-length varied between regions, with carpenter in the Park having the highest mass-at-length and those in the Eastern Cape having the lowest. Based on the distribution of carpenter, variability in otolith readability, mass-at-length, variation in growth and size-at-maturity, it is concluded that carpenter exist as two separate stocks and should be managed accordingly.     

Life strategies,energetics and growth characteristics of Calanoides carinatus (Copepoda) in the Angola-Benguela frontal region

Rates of daily egg production, moulting and egg hatching success, as well as total lipid content and composition of Calanoides carinatus, were measured in the region of the southern Angola Curre nt SAC), the Angola-Benguela Front (ABF) and the coastal upwelling area of the northern Benguela Current (NBC) system during February–March 2002. There were distinct differences in the vertical distribution, growth characteristics, lipid content and composition of populations in the SAC/ABF and NBC regions, indicative of different physiological states. Whereas in the NBC, C. carinatus was actively growing in response to elevated chlorophyll a levels associated with coastal upwelling, it comprised deep-living C5 copepodids with very large wax ester reseves (c. 40–50% dry mass) and extremely low metabolism in the SAC/ABF, suggesting diapause. This study provides the first data on lipid composition (lipid classes, fatty acids and alcohols) of this copepod in the region; in particular, the diapausing C5 contained high-levels of long-chain, mono-unsaturated fatty acids (23% of all fatty acids) and alcohols (69% of all fatty alcohols) in addition to trophic markers of diatoms, viz. 16:1(n-7) and 20:5(n-3). Based on total lipidcontent, the maximum survival time of the diapausal component of C. carinatus was estimated to be 149–192 days, whereas active surface-dwelling C5s and females could not survive for more than 10 days without feeding.     

Catch and effort of the shore and skiboat linefisheries along the South African Eastern Cape Coast

An assessment of catch and effort in the Eastern Cape shore and skiboat linefisheries was undertaken between 1994 and 1996 by means of roving creel and access point surveys. Catch-and-effort data were obtained from direct observation of 3 273 shore-fishers, 172 recreational and 223 commercial skiboat outings. Total effort in the region was high at 903 186 fisher-days year^?1 in the shore fishery and 64 266 and 24 357 fisher-days year^?1 in the commercial and recreational skiboat sectors respectively. The fisheries are multispecies in nature. The shore fishery consisted of 66 species, the recreational skiboat fishery 44 species and the commercial skiboat fishery 48 species. Just 10 species accounted for 75, 83 and 90% of the catch of the shore, recreational and commercial skiboat fishery respectively. The average catch per unit effort (cpue) was low in all sectors, 1.15 kg fisher^?1 day^?1 in the shorefishery, 9.4 kg fisher^?1 day^?1 in the recreational skiboat fishery and 21.5 kg fisher^?1 day^?1 in the commercial skiboat fishery. Catch data showed that professional and club anglers are more successful fishers. Comparisons with historic records for Port Elizabeth revealed that the cpue in the shore fishery had declined markedly, whereas the total effort increase was negligible (0.1%). In addition, the species composition of the fishery has changed.     

伽师地震与区域断层活动研究

利用GPS、连续倾斜和地震活动性资料分析了伽师地区构造活动的特点和伽师强震群的动力背景，结果表明：在印度洋板块的挤压下，塔里木盆地的右旋腑冲运动是造成南天山区地震活动的主要原因；1996年3月19日伽师阿图什6．7级地震，强烈地影响了该地区块体由向西南倾斜转向北向倾斜，并可能成为诱伽师地区强震群活动的主要动力因素，利用1998年和1999年对该地区GPS测量的结果，给出了该地区断层活动的水平。