Includes bibliographical references. / Life history traits and tactics of commercially important Namibian shallow-water hake, Merluccius capensis, were investigated in relation to their environment. A time series of length-frequency distributions (LFDs) from otoliths collected from fur seal scat samples was used to identify cohorts and calculate the approximate hatchdates and growth rates of young M. capensis from 1994 to 2009. Monthly otolith samples of five of these cohorts (1996, 1998, 2002, 2005 and 2006) were used to evaluate the translucent zone periodicity over the first 21 months of their life. Additionally, LFDs from research surveys and commercial samples were used to calculate growth rates for M. capensis up to 65 cm total length (TL), and to further validate the translucent zone formation of three of the five cohorts (1996, 1998 and 2002) on fish up to 3.5 years old.

Includes abstract. / Includes bibliographical references (leaves 157-173). / The quality of South Africa’s over-stretched water resources is a matter of concern for all who depend on them for their survival and prosperity, so access to the relevant monitoring data is essential. Visualisation is a powerful method for analysing these data and communicating the results, because it unloads complex cognitive processes from the fairly restricted human numerical processing structures onto the highly developed visual perception system. Developments in the field of visualisation during the past two decades have yielded many practical methods that are applicable to the analysis and presentation of water quality data. Judicious use of visualisation aids aquatic scientists, water resource managers and ordinary consumers in assessing the quality of their water and deciding on remedial measures. To provide some insight into the possibilities of visualisation techniques, I analyse and discuss five visual methods that I have developed or contributed to: multivariate time-series inventory plots; multivariate map symbols; spatially-referenced inventory of water quality data; mass transfer summary plots; and the use of visual methods in communicating the ecological status of rivers to a wide audience.

Bibliography: leaves 367-404. / The ecology of three sandy beaches on the west coast of South Africa is examined in this thesis. The first chapter constitutes an introduction to the subject and presents a brief review of studies carried out on beaches in South Africa in order to place this thesis into its proper context. In the second chapter, methods of sampling sandy-beach macrofauna (in particular sampling strategies) are briefly reviewed and discussed. For this study it was decided to adopt a grid sampling strategy, and the value of this strategy was tested. In the third chapter the sedimentological characteristics of the beach were examined in considerable detail in order to determine whether these differed between beaches, between zones and seasons on individual beaches. Characteristic differences were found for all the above categories, and the reasons for these are discussed in detail. Two zonation classificatory schemes for intertidal sandy-beach fauna have been proposed: that of Dahl (1953) and that of Salvat (1964). The zonation of organisms on west coast beaches is described in chapter 4, and the results obtained are discussed in the light of the above zonation schemes. Using cluster analysis, ordination and information statistic techniques, Salvat's zonation scheme was found to best describe the situation on the west coast, and its advantages over Dahl's scheme are discussed. Chapter 5 deals with the biomass and densities of macrofauna and meiofauna on the three beaches studied and discusses these results in relation to season and results obtained on beaches elsewhere. On a very broad basis, it is found that the results from west coast beaches fall within the range of results obtained elsewhere, although they rank among the higher values. The results also show that mean individual mass of organisms is related to beach exposure - the mean mass increases with increasing exposure. The respiratory metabolisms of the three dominant isopod species are examined in chapter 6. Using multivariate analysis, the effects of mass, temperature and activity on respiratory rates were determined for each species. Analysis of the results showed that the activity potential of each species differed, and this was correlated with the degree of exposure of the zone inhabited by each species. Thus the species living at the top of the shore showed a high activity potential while that living at the bottom of the shore had the lowest activity potential. The results and the reason for these differences are discussed and related to the differences in the conditions pertaining in each species' environment. Traditionally, sandy beaches are investigated by means of one or two transects across the beach, and the results extrapolated to the remainder of the beach. The results obtained in chapter 2 show that there is considerable variation in biomass and density values along the beach, but a special study of this was made in chapter 7. This showed that all species in fact have an irregular distribution both along and across the beach. These distribution patches are described for all species on all three beaches in this chapter. In addition, interspecific competition and predator-prey relationships were investigated, to determine whether these had any influence on the distributions of the species concerned. Animal-sediment relationships are investigated in chapter 8 and two major types of relationship are described. The first or gross type occurs where species are excluded from a beach due to unfavourable grain size, or where the intertidal position of all the species is affected by the sediment coarseness. The second type is where species or size-classes within species select particular grades within a particular intertidal zone. Animal-sediment relationships are discussed for each species, although these were not detected in all cases. · In chapter 9 the biogeography of the sandy beach genera occurring on west coast beaches is investigated. It was found that genera generally made up of intertidal species consisted of fewer species, with generally larger distribution ranges, than genera that tended to consist mainly of sub-tidal species. Of the 15 genera investigated in this chapter, almost all had a greater percentage of species occurring tropically than in temperate and arctic and antarctic climatic zones. When these percentages were corrected for coastline length or oceanic area, however, the concentrations of species were found to be highest in temperate zones, in all cases. The reasons for these findings are discussed in the light of Bretsky and Lorenz's (1970) theory pertaining to genetic-adaptive strategies and mass extinctions. Finally, in chapter 10, the results of this thesis are synthesized and placed into the context of existing knowledge on sandy beach ecology. In addition, trends in sandy beach studies are discussed and future fields of research outlined.

This thesis presents ideas, techniques, results and conclusions from a 3-year research project regarding the osmotic and ionic regulation of the South African striped dogfish Poroderma africanum (Gmelin). The experiments where devised early in 1971 but due to the time required for personally constructing equipment and facilities and for modifying and equipping the laboratory and aquaria with the necessary apparatus, actual experimentation and subsequent obtaining of results was not possible before November 1971. The main theme of the research was the investigation of the major body fluids and their relationship to external conditions, in a local elasmobranch species. The topic has been extensively examined in some overseas countries hut so far very little physiological work on the osmoregulation of marine elasmobranchs has been carried out in the South African region. The species chosen was also considered interesting in view of its common occurrence around the Cape (at the time of commencement of the work) and the fact that it seemed to be relatively limited in its distribution around the African coast, although in appearance it resembles the Scyliorhinid dogfishes widely distributed around overseas coasts.

A study of 50 samples of Polychaeta mainly from a northern profile (0.5 - 550 m) and down to 800 m, reveals that the fauna is characterised by extremely small specimens and a great taxonomic divergence. Techniques of handling minute specimens are described, together with 21 new species, including three subspecies, six new genera and a new subgenus. The discovery of aberrant genera indicates a substantial endemism, the evolution of which is enabled by: (a) the narrow Straits of Tiran which separates the Gulf from the Red Sea proper; (b) the hydrographical factors causing vertical homogeneity of temperature, salinity and oxygen, as well as (c) a possible zone of convergence which isolates the Gulf's northern part to an as yet unknown degree. The pattern of family distribution and specimen frequencies confirms the existence of six successive benthic associations along an analysed sediment profile. The poor biomass of the fauna indicates that the Gulf has an overall low productivity, caused by the limited amount of fresh water run-off, low content of organic matter and small quantities of nutrients.

Bibliography: pages 281-290. / South Africa's Western Cape purse-seine fishery is situated off the country's western seaboard in the highly productive waters of the southern Benguela Current system (Cushing 1969). Management of the multi-species resource is the responsibility of the government's Department of Industries and since 1950 a large volume of data relating to performances of contributing species has been collected. Recent analyses have indicated an oversubscription of effort, a sequential depletion of the more valuable stocks and, consequently, a present reliance upon less favourable species (Newman and Crawford 1979, Crawford et al. in press). These adverse trends have been precipitated, in part at least, by ineffective legislation, which has resulted from a past failure to appreciate that exceptionally good year classes occur infrequently (Newman and Crawford in- press). Optimal ways of harvesting strong cohorts, or of avoiding overexploitation in the event of recruitment failure, remain to be explored.

Bibliography: pages 150-163. / The potential of bivalve molluscs as monitors of metal pollution in South African coastal marine environments has been investigated using the species Crassostrea gigas, Crassostrea margaritacea, Perna perna and Choromytilus meridionalis. Metal concentrations in these and other species living along an unpolluted coast have been determined by atomic absorption spectrometry following chemical oxidation of the biological tissues. Variations in concentrations within a population may depend upon the size or sex of the individual and on the season during which the sample is collected. Metal accumulation by the four study species has been investigated under controlled laboratory conditions for the elements zinc, cadmium, copper, lead, iron, manganese, nickel, cobalt and chromium. Rates of accumulation differ between species and for each element. Some of the factors affecting cadmium uptake have been studied. Rates of accumulation depend greatly upon the form of the cadmium in solution but are also affected by changes in environmental parameters. The accumulation rates of other elements are probably also affected by these factors, not necessarily in the same way. The solution concentrations tested for these accumulation experiments, and also those tested for their effects on the filtering rates of adults or on the development of larvae, are higher than those normally found in polluted areas. This implies that these species are sufficiently tolerant of the presence of metals in their environment to be able to act as monitoring organisms. However, adult oysters and mussels may react to the presence of metals or to the estuarine environment, where fluctuations in water salinity may occur regularly and where effluents may be discharged into the freshwater stream. The mollusc which has closed its valves for either of these reasons may avoid the pollutant. This reaction obviously affects the ability of molluscs to monitor such pollutant inputs. Theoretically, the four study species cannot be used to monitor metal pollution in coastal marine environments quantitatively, as metal accumulation is influenced by too many environmental variables. However, the results from field sampling surveys can be interpreted with greater confidence when the effects of these variables on metal accumulation are known. In practice, a semi-quantitative measure of metal pollution can be achieved.

Freshwater amphipods in southern Africa are divided into three distinct elements. Five ingolfiellid species occur in Namibia, six Sternophysinx species are found in the northern Cape Province and Transvaal, while 12 Paramelita species are restricted to the south-western Cape. The crangonyctoid genus Paramelita was last reviewed in 1981 based mainly on a reassessment of museum material. Thus, large scale field surveys of these amphipods have not been undertaken since they were first described by Barnard in 1916 and 1927. In addition, little is known about the ecology of these amphipods. This thesis examines the systematics, distribution and aspects of the ecology of Paramelita. After an extensive sampling programme in 1989 and 1990, several new species were discovered. Four new species, whose affinities with the known species were not immediately evident, were initially described, and later, after further analyses .of morphological and genetic differentiation amongst Paramelita populations, eight other new species were recognised. A phenetic analysis of the 24 Paramelita species revealed the existence of three distinct groups. The new genus Afrocrangonyx was proposed to accommodate seven of these species, whilst a single species was placed in the new genus Aquadulcaris. Sixteen species remained in Paramelita. Based on a cladistic analysis of morphological data, a fully resolved phylogenetic tree was obtained for Afrocrangonyx, but not for Paramelita, suggesting that the latter genus is not monophyletic. A population of P. nigroculus in Window Stream, Table Mountain, was selected for a detailed ecological study. P. nigroculus occurred at high densities, and showed no seasonal breeding patterns. An investigation of thermal acclimation and tolerances to high temperatures in P. nigroculus individuals showed that their acclimation rates and lethal limits were similar to many other crustaceans. P. nigroculus individuals feed mainly on allochthonous input. An investigation of the nature, timing and magnitude of this input indicated that litter was dominated by abscissed leaves which fall throughout the year, peaking in summer. Leaf fall values and benthic detritus standing stocks were within the range reported for headwaters worldwide. A study of leaf retention capabilities of two similar headwaters revealed that amphipod abundances were positively correlated with leaf retention characteristics. Leaf retention was strongly influenced by discharge, with increasing discharges resulting in decreases in retention and stream bed complexity. Thus the stream with higher discharges was less favourable for colonisation by amphipods. Since P. nigroculus occurred at such high densities, it was expected to play a significant role in breakdown of detritus. Breakdown of three riparian leaf species in litter bags submerged in two streams was investigated. Litter bags were designed to allow amphipod access, yet retain fragments which resulted from physical abrasion and feeding activity. Breakdown was rapid, and the decomposition rate of one of the leaf species was the highest ever recorded for a riparian leaf species. Thus, it was concluded that where they occur at high densities, Paramelita individuals play a major role in the detritus dynamics of the stream.

Bibliography: leaves 251-277. / This thesis was undertaken to provide quantitative scientific information for decision-making and conservation planning for the previously scarcely studied rocky intertidal habitats in KwaZulu-Natal on the east coast of South Africa. Biogeographic patterns were resolved and abiotic determinants and harvesting impacts were identified at three different scales. A biotope classifiadion system was developed as a new tool for assessing the conservation status of intertidal communities, evaluating conservation priorities and monitoring change in intertidal habitats. The implications of the findings of this thesis for management and conservation planning were examined.

Competition for space between humans and wildlife is prevalent worldwide. In the Cape Peninsula, South Africa, extensive land transformation has geographically isolated, fragmented and reduced the size of the local chacma baboon population and is perceived to be a major driver of human-baboon conflict. However, no data on baboon landscape use exist to verify this perception. I studied the spatial ecology of this population, identifying baboon land use patterns, determining the drivers of intrapopulation variation in spatial ecology and investigating how spatial variables could inform baboon management efforts to reduce human-baboon conflict.