ISSN:0035-919X    

DOI:10.1080/00359198109520583

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Research on pelagic birds and mammals in the southern Benguela region has to date concentrated on the breeding species of seabirds and on the Cape fur sealArctocephalus pusillus.The status of knowledge of non-breeding seabirds and cetaceans is poor to non-existent. Research has so far concentrated on distribution, abundance, diet and land-based observations of breeding biology. Future research should include those species as yet little known and should aim at collecting information which can be used to obtain a real understanding of the relationships between pelagic birds and mammals and their prey within the southern Benguela region. This knowledge should then be used to predict the effect of changes within the system such as those due to the commercial fishery.

ISSN:0035-919X    

DOI:10.1080/00359198109520584

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Growth rates of rock-lobstersJasus lalandiivaried considerably along the west coast of southern Africa. As small differences affect the productivity of individual fishing grounds, an attempt was made to identify the major environmental factors influencing growth. Six widely-spaced areas were studied over a period of nine years. Tagging and short-term holding experiments were used to measure rock-lobster growth rates, while diving and hydrological surveys provided detailed information on rock-lobster populations and their environment. Relatively rapid growth was found in the southern part of the Cape west coast (except for the extreme south, off the Cape Peninsula) where depths occupied by rock-lobsters extend to at least 50 m. Further north, rock-lobsters and associated benthos were limited to shallower depths and growth was generally slower. Food availability is probably the most important factor influencing growth rates, while differences in water temperature were not considered to be significant. Ribbed musselsAulacomya ater(Molina) are the most important food source for rock-lobsters, and these occur in high densities throughout the geographic range ofJ. lalandii. However, most rock-lobsters are limited to feeding only on certain sizes of mussels, so that food may be limited even in areas of comparatively high mussel biomass. Density-dependent effects on feeding and growth are likely to be important, and these intensify in the northern areas of the coast owing to the restriction in depth range of the benthos. Extremely low dissolved-oxygen values (a phenomenon linked with the azoic muds off the central and northern coast) limit the northern extent of distribution of dense stocks ofJ. lalandiito about 25°20'S. Factors limiting the distribution of commercially exploitable stocks ofJ. lalandiiat the southward edge of the range (Cape Point) are related to the distribution of phyllosoma larvae in offshore waters and to recruitment inshore of puerulus larvae.

ISSN:0035-919X    

DOI:10.1080/00359198109520585

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

ISSN:0035-919X    

DOI:10.1080/00359198109520586

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The filtering rates ofCrassostrea gigas, Crassostrea margaritacea, Perna pernaandChoromytilus meridionalishave been determined by measuring the removal of neutral red particles from a known concentration of neutral red suspension in a given time. The effects of copper, zinc, cadmium and lead on these filtering rates have been investigated and of these metals, copper was found to be the most toxic to both oysters and mussels. The effective concentrations are compared with the results of conventional lethal toxicity tests.

ISSN:0035-919X    

DOI:10.1080/00359198109520587

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The interannual variability in rainfall over South Africa is shown to be composed of a number of uncorrelated components that are spatially dependent. There is a little evidence to support the view that interannual variability in rainfall has been increasing over the last twenty to thirty years. For the most part its temporal variation appears to be random. There seems to be little doubt, however, that a biennial oscillation is present in one of the uncorrelated components associated with the interannual variability in rainfall over South Africa. The period covered by the investigation is from 1921 to 1975 inclusive.

ISSN:0035-919X    

DOI:10.1080/00359198109520588

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Several Australian members of the genus Acacia L. have attained weed status in the Cape Province, South Africa. It is shown that in the Cape the plants are pollinated but lack effective seed predators. Mature plants drop seeds numbering usually in the range 1 100 to 7 000 m−2yr−1. They have a seed-bank in the soil about two to five times this magnitude, about 95 per cent of which is dormant. It appears that the decline of viability with age may be relatively very slow. These findings are shown to be critical in planning control-methods.

ISSN:0035-919X    

DOI:10.1080/00359198109520589

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

ISSN:0035-919X    

DOI:10.1080/00359198109520590

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

ISSN:0035-919X    

DOI:10.1080/00359198109520592

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor