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Kaisets ge ge nauhe

Jacob ge !gasase

The Port Elizabeth disturbances of October, 1920

  • Authors: Baines, Gary F, 1955-
  • Date: 1988
  • Subjects: Black people -- South Africa -- Port Elizabeth -- Social conditions , Police shootings -- South Africa -- Port Elizabeth , Labor movement -- South Africa -- Port Elizabeth -- History
  • Language: English
  • Type: text , Thesis , Masters , MA
  • Identifier: vital:2529 , http://hdl.handle.net/10962/d1001858
  • Description: Chapter one suggests thet trade and merchant capital, which were crucial to Port Elizabeth's economic development during the nineteenth century, was subsumed by the rise of manufactures and industrial capital after the First World War. Industrial expansion was cut short by the post-war recession, which caused un- and underemployment. The black worker, who experienced a severe loss in real earnings on account of the increased cost of living, became involved in a struggle with employers for wage increases. Chapter two shows how the policy of segregation was applied in Port Elizabeth, which meant that the workers were subjected to an increasing degree of control and regulation of their daily lives. The conditions of reproduction in the black townships fostered inter-racial and cross-class mobilisation which culminated in the formation of a general labour union, the Port Elizabeth Industrial and Commercial Workers' Union (PEICWU). Chapter three will suggest links between the tradition in Port Elizabeth of worker resistance and the unionisation of black workers in the post-war period. Thus, the first three chapters attempt to provide a historical perspective for analysing the underlying causes of the 1920 Port Elizabeth disturbances. The immediate cause of the disturbances was the arrest of the Union leader, Masabalala, after he called for a general strike. Chapter four will show how the intervention of the local authorities provoked a spontaneous act of defiance on the part of Union members. A demonstration outside the Baakens Street Police Station to demand the release of Masabalala, precipitated the tragic shootings of 23 October 1920. The repressive violence which left 22 dead (with two further deaths resulting indirectly from the incident) was unprecedented in South African history. The resolution of the crisis brought the workers no nearer to obtaining a reasonable settlement of the wage issue. If anything, the resolve of employers to deny wage demands was hardened by the actions of the local authorities, who attributed the disturbances to ' agitation '. Such thinly-disguised justifications of the shootings by the dominant classes, however, provoked recriminations from other quarters. Chapter five examines the legal and political ramifications of the Port Elizabeth shootings. The circumstances of the shootings prompted the Smuts Government to appoint a Commission of Enquiry in the face of public pressure. The Commission found that the Police and vigilantes were largely to blame for the high death toll. But the Government's 'whitewash' of the findings could not absolve the Police from culpability entirely, nor could it sidestep its own responsibility and liability to victims of the shootings. Finally, in Chapter six, an attempt will be made to assess the long term impact of the shootings on the PElCU and the black labour movement in Port Elizabeth generally. The outcome of the episode was a victory for employers, which dealt a body blow to worker organisation which only became resurgent in the 1950s.
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  • Date Issued: 1988

The development of a concept of psychological well-being

  • Authors: Bar-On, Reuven
  • Date: 1988
  • Subjects: Mental health -- Psychological aspects Personality
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:2928 , http://hdl.handle.net/10962/d1002437
  • Description: This thesis focuses on the development of an operational and theoretically eclectic concept of psychological well-being. A comprehensive research strategy was employed to examine various personality factors thought to be components of psychological health (i.e., the basis of the proposed concept). The general approach involved four major phases: (1) the clustering of various variables and identification of underlying key factors purported to be related to psychological health based on the writer's clinical experience and review of the mental health literature, (2) the formulation of an ~ priori concept of psychological well-being based on the operational definition of those factors, (3) the construction of an inventory designed to examine the proposed concept, and (4) the interpretation of the results and their implications for the development of the overall concept based on the examination of the factorial structure, validity and reliability of the inventory. The"a posteriori concept" evolved out of this process. The results of the present study indicate that the most valid and reliable factorial components of psychological well-being are self regard,interpersonal relationship, independence, problem-solving, assertiveness,reality testing, stress tolerance, self-actualization and happiness; social responsibility and flexibility emerged as questionable components of the a posteriori concept. The inventory which was designed to study the concept was successful in significantly differentiating various levels of psychological health. This way of conceptualizing and assessing psychological well-being has potential applicability for mental health practitioners and researchers.
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  • Date Issued: 1988

An analysis of the structural use of music, song and dance in certain novels by West African writers in relation to concepts of time

  • Authors: Baxter, Marion
  • Date: 1988
  • Subjects: Music and literature
  • Language: English
  • Type: text , Thesis , Masters , MA
  • Identifier: vital:2174 , http://hdl.handle.net/10962/d1001825
  • Description: The topic of this thesis is time in the West African novel in English and French, and the key approach is that West African time is readily grasped through a study of West African music. Though Western time is not exclusively or only linear, mechanical and exploitative, and African time not exclusively cyclic, synchronic and experiential, yet there is a characteristically African view of time and preferred modes of its employment in West African fiction. The novelists considered here wrote in European languages, yet each was a member of a specific cultural group and concerned to portray the aesthetics of his inheritance, an important aspect of which is the predominance of repetitive formulae, both in music and in oral literature. The Introduction offers an historical survey of some of the main notions of time that have been manifest in the West, and compares them with notions of African time. Chapter One examines the structural use of rhythm and repetition in the novels of Camara Laye. Chapter Two discusses the griot and other traditions of oral literature in the novels of Ayi Kwei Armah and Yambo Ouologuem, novels which are concerned with the griot 's continuing role in the creation and dissemination of historical perspective. Chapter Three analyses Chinua Achebe 's portrayal of the values of pre-colonial life in Igbo society where the role of music is to limit behaviour through the structures of ritual which thus create static/cyclic time. Chapter Four describes the syncretic art-form, 'highlife', as used by novelists such as Wole Soyinka, which, because it is transitory and always changing, underscores the ironies of modern city life. The thesis concludes that the authors discussed above are aware that music, because it is predominantly social in Africa, is a powerful medium for achieving a healing synthesis between the traditional past when communalistic values were binding, and the urban-orientated present with its insistence on individuation and material enrichment.
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  • Date Issued: 1988

Fishes of the family Mullidae in the Red Sea, with a key to the species in the Red Sea and the Eastern Mediterranean

  • Authors: Ben-Tuvia, Adam , Kissil, Geerge Wm
  • Date: 1988
  • Subjects: Mullidae -- Red Sea , Mullidae -- Mediterranean Sea
  • Language: English
  • Type: Text
  • Identifier: vital:15011 , http://hdl.handle.net/10962/d1019744 , ISSN 0073-4381 , ISBN 0-86810-175-3 , Ichthyological Bulletin of the J.L.B. Smith Institute of Ichthyology; No. 52
  • Description: Thirteen species of Mullidae (goatfishes or red mullets) occur in the Red Sea: Mulloides flavolineatus, M. vanicolensis, Parupeneus cyclostomus, P. forsskali, P. heptacanthus, P. macronemus, P. rubescens, Upeneus asymmetricus, U. moluccensis, U. subvittatus (previously known only from the western Pacific), 0. sulphureus, U. tragula and U. vittatus. Descriptions, biological observations and black and white photographs are given for each of these 13 species. Keys are provided to the genera of Mullidae, to the species occurring in the Red Sea, and to the two Mediterranean species of Mullus that have been reported from the Suez Canal. The distinction between the genera Pseudupeneus and Parupeneus is discussed. , Rhodes University Libraries (Digitisation)
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  • Date Issued: 1988

Cleavage of the precursor coat protein of black beetle virus strain w17 in rabbit reticulocyte lysate

  • Authors: Blackhurst, Diane Mary
  • Date: 1988
  • Subjects: Beetles , Insects -- Viruses
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:3880 , http://hdl.handle.net/10962/d1001614
  • Description: Black beetle virus (BBV) is a bipartite single-stranded RNA virus belonging to the family Nodaviridae. Its host range has been found to be limited to insects. RNA 1, the larger of the two RNA molecules, with a MW of 1,15 x 10⁶ and the smaller RNA 2 with a MW of 0,46 x 10⁶, are both packaged in the same virus particle. The two RNA molecules are translated separately, with RNA 1 coding for protein A of MW 105 x 10³ and RNA 2 coding for protein α of MW 47 x 10³. Protein α is the major capsid protein precursor, which during in vivo maturation is cleaved to form the coat protein β of MW 43 x 10³, and protein γ of MW 5 x 10³. Cell-free translation of BBV (strain W17) mRNA was carried out in rabbit reticulocyte lysates. Protein α was detectable between 0 and 30 minutes after RNA addition. A protein 'β', which was found to co-electrophorese on polyacrylamide gels with authentic β and which was immunoprecipitated by anti-BBV antiserum, was detectable after 30 minutes. Results of this work show that the formation of 'β' could be prevented by the addition of RNase to the lysate, indicating that intact RNA is necessary for α to β cleavage. Arresting protein synthesis by the addition of cycloheximide to the lysate mix did not inhibit the cleavage. The formation of β could also be prevented by cooling the lysate mix to 1°C. Cleavage of α to β still occurred when RNA 2, without the presence of RNA 1, was translated. Therefore the cleavage is not dependent on a translation product of RNA 1. Sedimentation of lysate on sucrose density gradients showed that α to β cleavage was not accompanied by assembly of BBV RNA and protein lnto a viral substructure as has been shown to occur with some viruses, for example certain picornaviruses. Serial dilution of lysate containing α showed that the level of β decreased with increasing dilution, indicating that the cleavage is not mediated by autocatalysis, but by some other unknown factor. Although much work has been carried out on black beetle virus, no work has been published to date concerning α to β cleavage as an indication of assembly in rabbit reticulocyte lysates. Results of these cell-free translation experiments thus indicate that BBV coat protein precursor α, in association with its messenger RNA 2, undergoes a maturation cleavage in the lysate to produce BBV coat protein β. In addition, this cleavage seems to occur without assembly into any intermediate viral structure
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  • Date Issued: 1988

Lo tla utwa go twe ka Disontaga

Jesu rato lwa gaga

Petrology and geochemistry of the lower group chromitites and host rocks on the farm Zandspruit 168 JP, Western Bushveld Complex

  • Authors: Botha, Michael James
  • Date: 1988
  • Subjects: Petrology -- Africa, Southern , Geochemistry
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4905 , http://hdl.handle.net/10962/d1001565
  • Description: The eight Lower Group chromitite layers of the Ruighoek Pyroxenite in the area west of the Pilanesberg (LGl - LG7), on the farm Zandspruit 168 JP, were sampled in borehole cores drilled through the succession. The stratigraphic succession faIls within Cameron's (980) units B to E of the Critical Zone. The lowermost layer of the Lower Group, the LG 1 chromitite, is located some 440 metres below the MG 2 (Middle Group) chromitite layer, above which the first appearance of cumulus plagioclase in the Complex is seen. By convention, this horizon is designated the top of the Ruighoek Pyroxenite in the Western Bushveld Complex. Homogeneous units of chromite-bearing orthopyroxenite (bronzitite), exhibiting inconspicuous layering defined in terms of variations in orthopyroxene grain-size host all but one of the Lower Group layers; the LG 4 chromitite layer is exposed within an olivine-rich subunit 23 metres in thickness (C₃ subunit). The cumulative thickness of chromitite is 2,92 metres or 0,8 per cent of the studied section, which is 381 metres in thickness. Minimum and maximum thicknesses of the LGl - LG7 layers exposed in drill core are 17 and 81 centimetres, respectively, with minor chromitite layers ranging between 2 and 5 centimetres in thickness. Weighted mean Cr₂0₃ contents of units B to E vary between 1,17 and 3,22 per cent, with the latter estimate representative of the D₂ subunit which hosts the LG 6 chromitite layer. The LG 6 is correlated with the Steelpoort layer of the Eastern Bushveld Complex, and varies between 76 and 81 centimetres in thickness under a large portion of the farm Zandspruit. An undisturbed succession striking N15°E and dipping 12 - 15°E is depicted within the studied area, which is bounded on the eastern side by the north-striking Frank fault. Major folding of the layered succession is evident to the north of the area, where the layering adjacent to the trace of the fault dips 35° to the southwest. Particular attention is paid in the present study to (a) the nature of chromitite layers and their host rocks, (b) the contrast between the mineral chemistry of weakly disseminated chromite and grains within massive ore layers, (c) concentrations of Cr, V, Ni, Co, Sc and Ti in orthopyroxene in relation to stratigraphic height, and levels of Sr, Ba and Zr associated with hypothetically pure, intercumulus plagioclase feldspar, and (d) possible mechanisms which induce crystallization of chromitite layers containing 50 per cent Cr₂0₃ from magma with a Cr content of less than 1 000 ppm. Electron microprobe studies of chromite in relation to mineralogical and textural environment clearly reveal that (a) the proportions of Cr and Al cations are linked to paragenesis: higher Al/Cr ratios characterize olivine-bearing domains, whereas grains intergrown with plagioclase feldspar exhibit low AI/Cr ratios, and (b) Al contents rise with a decline in Mg/(Mg + Fe²⁺) from high values to a value of 0,450, then decrease with a further decline in Mg/(Mg + Fe²⁺). The paragenetically later trend is emphasized in a large population of chromite grains which escaped early encapsulation in orthopyroxene crystals and continued to grow in the environment of intercumulus plagioclase. Within-and between-sample compositional variation of grains in silicate-rich domains is modelled in terms of in situ growth increments, diffusive homogenization of zonal structures, and residence time within interstitial melt. Fractionation trends, as measured by Mg/(Mg + Fe²⁺) ratios in whole-rock and/or microprobe studies of orthopyroxene, are reversed in relation to stratigraphic height towards the top of the B unit and in the overlying C unit. These data are supported, for example, by lower vanadium contents and higher Ni/Sc ratios in hypothetically pure orthopyroxene. Small olivine crystals in chromite-rich domains are enriched in Ni relative to coarse-grained olivine in adjacent dunite: a feature attributed to early isolation of primocrysts from magma in the former case, and in situ equilibration between olivine crystals and Ni-depleted residual melt in the latter case . Similarly, rising Ni contents and Mg/(Mg + Fe²⁺) ratios of orthopyroxene with increasing stratigraphic height in the footwall of the LG 6 chromitite layer, linked to a progressive decline in orthopyroxene grain-size, are effects which may arise out of early separation of interstitial melt from orthopyroxene cumulates. A model is thus proposed which (a) links the thickness of chromitite layers to the vertical separation between successive layers or the thickness of fine-grained orthopyroxenite in the footwall, (b) ascribes copious nucleation of chromite to liquid mixing of this footwall derived, Cr - depleted contaminant with influxes of hot, primitive magma, and (c) tenders the notion that the present modal proportion of mesostasis in the footwall of a chromitite layer serves as a reciprocal measure of the volume of fractionated exudate
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  • Date Issued: 1988

Pandene Hompa Karunga

  • Authors: Boys' Choir , Lucretia, Sister , Dargie, Dave
  • Date: 1988
  • Subjects: Folk music , Field recordings , Africa, Sub-Saharan , Africa Namibia Nyangana f-sx
  • Language: Mbukushu
  • Type: sound recordings , field recordings , sound recording-musical
  • Identifier: http://hdl.handle.net/10962/305380 , vital:58563 , International Library of African Music, Rhodes University, Makhanda, South Africa , Dave Dargie Field Tapes, Rhodes University, Makhanda, South Africa , DD111-08
  • Description: Church composition performed by boys' choir with drum and clapping accompaniment.
  • Full Text: false
  • Date Issued: 1988

Mbudi yaruhafo

  • Authors: Boys' Choir , Likuwa, E , Dargie, Dave
  • Date: 1988
  • Subjects: Folk music , Field recordings , Africa, Sub-Saharan , Africa Namibia Nyangana f-sx
  • Language: Mbukushu
  • Type: sound recordings , field recordings , sound recording-musical
  • Identifier: http://hdl.handle.net/10962/305389 , vital:58564 , International Library of African Music, Rhodes University, Makhanda, South Africa , Dave Dargie Field Tapes, Rhodes University, Makhanda, South Africa , DD111-09
  • Description: Church composition performed by boys' choir.
  • Full Text: false
  • Date Issued: 1988

Hompa tupeko mpora

  • Authors: Boys' Choir , Lucretia, Sister , Dargie, Dave
  • Date: 1988
  • Subjects: Folk music , Field recordings , Africa, Sub-Saharan , Africa Namibia Nyangana f-sx
  • Language: Mbukushu
  • Type: sound recordings , field recordings , sound recording-musical
  • Identifier: http://hdl.handle.net/10962/305488 , vital:58575 , International Library of African Music, Rhodes University, Makhanda, South Africa , Dave Dargie Field Tapes, Rhodes University, Makhanda, South Africa , DD111-13
  • Description: Church composition with clapping, drum and rattles accompaniment.
  • Full Text: false
  • Date Issued: 1988

Jungene muliwiru

  • Authors: Boys' Choir , Likuwa, E , Dargie, Dave
  • Date: 1988
  • Subjects: Folk music , Field recordings , Africa, Sub-Saharan , Africa Namibia Nyangana f-sx
  • Language: Mbukushu
  • Type: sound recordings , field recordings , sound recording-musical
  • Identifier: http://hdl.handle.net/10962/305448 , vital:58571 , International Library of African Music, Rhodes University, Makhanda, South Africa , Dave Dargie Field Tapes, Rhodes University, Makhanda, South Africa , DD111-11
  • Description: Church composition performed by boys' choir.
  • Full Text: false
  • Date Issued: 1988

Karunga Hompawetu

  • Authors: Boys' Choir , Likuwa, E , Dargie, Dave
  • Date: 1988
  • Subjects: Folk music , Field recordings , Africa, Sub-Saharan , Africa Namibia Nyangana f-sx
  • Language: Mbukushu
  • Type: sound recordings , field recordings , sound recording-musical
  • Identifier: http://hdl.handle.net/10962/305466 , vital:58573 , International Library of African Music, Rhodes University, Makhanda, South Africa , Dave Dargie Field Tapes, Rhodes University, Makhanda, South Africa , DD111-12
  • Description: Church composition performed by boys' choir.
  • Full Text: false
  • Date Issued: 1988

Tu pandure Hompa

  • Authors: Boys' Choir , Likuwa, E , Dargie, Dave
  • Date: 1988
  • Subjects: Folk music , Field recordings , Africa, Sub-Saharan , Africa Namibia Nyangana f-sx
  • Language: Mbukushu
  • Type: sound recordings , field recordings , sound recording-musical
  • Identifier: http://hdl.handle.net/10962/305430 , vital:58569 , International Library of African Music, Rhodes University, Makhanda, South Africa , Dave Dargie Field Tapes, Rhodes University, Makhanda, South Africa , DD111-10
  • Description: Indigenous music.
  • Full Text: false
  • Date Issued: 1988

Sequence in the mathematics syllabus : an investigation of the Senior Secondary Mathematics Syllabus (July 1984) of the Cape Education Department attempting to reconcile the demands of the strictly mathematical order and the developmental needs of pupils, modified by the mathematical potential of the electronic calculator : some teaching strategies resulting from new influences in the syllabus

  • Authors: Breetzke, Peter Roland
  • Date: 1988
  • Subjects: Mathematics -- Study and teaching (Secondary) -- South Africa , Calculators , Mathematics -- South Africa -- Outlines, syllabi, etc.
  • Language: English
  • Type: Thesis , Masters , MEd
  • Identifier: vital:1364 , http://hdl.handle.net/10962/d1001430
  • Description: This study was motivated by the latest revision of the mathematics syllabuses of the Cape Education Department. The most important changes to content in the Senior Secondary Mathematics Syllabus (July 1984) are the introduction of calculus and linear programming, the substitution of a section on analytical geometry for vector algebra and the recall of the remainder and factor theorems. The way in which these changes were introduced left the task of integrating them into the teaching process in the hands of individual teachers. This is a task of extreme importance. If one's classroom practice is to simply plough one's way through the syllabus, one loses many opportunities to make the study of mathematics meaningful and worthwhile. Accepting the view of the spiral nature of the curriculum where one returns to concepts and procedures at increasing levels of sophistication, one needs to identify the position of topics in this spiral and to trace their conceptual foundations. Analytical geometry is in particular need of this treatment. Similarly there are many opportunities for preparing for the introduction of calculus. If the teaching of calculus is left until the last moments of the Standard 10 year without proper groundwork, the pupil will be left with little time to develop an understanding of the concepts involved. It is the advent of calculators which presents the greatest challenge to mathematics education. We ignore this challenge to the detriment of our teaching. Taken seriously calculators have the potential to exert a radical influence on the content of curricula and examinations. They bring into question the time we spend on teaching arithmetic algorithms and the priority given to algebraic manipulation. Numercial methods gain new prominence. Calculators can even breathe new life into the existing curriculum. Their computing power can be harnessed not only to carry out specific calculations but also to introduce new topics and for concept reinforcement. The purpose of this study has been to bring about a proper integration of the new sections into the existing syllabus and to give some instances of how the calculator can become an integral part of the teaching/learning process
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  • Date Issued: 1988

The selection and evaluation of grey-level thresholds applied to digital images

  • Authors: Brink, Anton David
  • Date: 1988
  • Subjects: Image processing -- Digital techniques
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5443 , http://hdl.handle.net/10962/d1001996
  • Description: Many applications of image processing require the initial segmentation of the image by means of grey-level thresholding. In this thesis, the problems of automatic threshold selection and evaluation are addressed in order to find a universally applicable thresholding method. Three previously proposed threshold selection techniques are investigated, and two new methods are introduced. The results of applying these methods to several different images are evaluated using two threshold evaluation techniques, one subjective and one quantitative. It is found that no threshold selection technique is universally acceptable, as different methods work best with different images and applications
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  • Date Issued: 1988

Environmental requirements for the hatchery rearing of African catfish Clarias Gariepinus (Pisces: Clariidae) larvae and juveniles

  • Authors: Britz, P J (Peter Jacobus), 1959-
  • Date: 1988
  • Subjects: Catfishes -- Africa , Fish culture , Clariidae , Clarias
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5188 , http://hdl.handle.net/10962/d1001964 , Catfishes -- Africa , Fish culture , Clariidae , Clarias
  • Description: Inadequate seed production has historically been a factor limiting the commercial culture of Clarias gariepinus. The need to determine the environmental requirements of larvae was identified, in order to facilitate their successful mass rearing in hatcheries. The effects of key environmental factors on the growth, survival and aspects of the behaviour of C. gariepinus larvae and juveniles were investigated under controlled conditions. A strong emphasis was placed on the interpretation of the observed responses in terms of the natural history of the animal. Larvae were obtained by artificially inducing and spawning feral adult broodfish. Larval growth rates were highest in the temperature range 26-33ºC, with a peak at 30ºC. Survival of larvae was high between 22 and 33ºC. The final temperature preferendum of juveniles, determined in a thermal gradient was 30ºC, and it was concluded that this temperature is probably optimal for most of the physiological processes of the animal. Larvae and juveniles displayed strong negative phototaxis. When reared under different photoperiod regimes, larval growth increased with longer dark periods, however a similar rate of mortality was recorded in all photoperiod treatments. The provision of cover was found to enhance larval growth under conditions of continual light (24L/OD), however under conditions of continual darkness (OL/24D) similar growth rates were recorded regardless of the presence or absence of cover. All growth rates in continual darkness (OL/24D) were higher than those in continual light (24L/OD), regardless of whether cover was provided or not. It was concluded that a OL/24D photoperiod is optimal for larval rearing. At salinities between 0 and 5% similar growth and mortality rates of larvae were recorded. At 7.5 % larval growth and survival rates were lower, and at 10 % all larvae died within 48 hours. The 96h-LCSO for unionised ammonia was found to be 2.3 mg/l. The cytological effects of unionised ammonia were evident as degenerative changes in the gill and liver tissues. In an investigation of tank hygiene, it was found that larval growth and survival rates were highest in tanks not cleaned at all. As the frequency of tank cleaning increased, the growth and survival rates of larvae decreased. When reared at densities ranging from 45-450/1, larval growth was found to be density dependent. A model of hatchery productivity (number larvae of standard size produced/time/vol.) was developed based on the density dependent nature of larval growth. The model predicts that maximum productivity, will be achieved at a rearing density of 1400/1. The high growth and survival rates obtained over a broad range of each environmental parameter investigated serve to explain how larvae survive and grow in their unstable floodplain habitat in nature. The broad environmental tolerances of C. gariepinus are of benefit with respect to the culture of larvae, as successful larval rearing is possible over a fairly wide range of environmental conditions.
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  • Date Issued: 1988

Life history changes of two reef fish species in exploited and unexploited marine environments in South Africa

  • Authors: Buxton, Colin David
  • Date: 1988
  • Subjects: Reef fishes -- Africa, Southern Chrysoblephus laticeps Chrysoblephus cristiceps
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:5189 , http://hdl.handle.net/10962/d1001965
  • Description: A detailed investigation into the life histories of Chrysoblephus laticeps and c. cristiceps in exploited and unexploited marine environments on the south-east coast of southern Africa is presented. The study provided information necessary for the evaluation of marine reserves as a management option for these and similar reef species. Visual underwater assessments showed a clear spatial separation between adults and juveniles of both species, suggesting a recruitment of juveniles into shallow water followed by a gradual outward migration into deeper water with age. Denslty estlmates of C. laticeps in the Noordhoek (0.0064 fish/m²) and Tsitslkamma (0.0254 fish/m²) areas were significantly different and were attributed to exploitation. Within area differences in density were also significantly correlated with temperature) depth and substratum relief. Similar comparisons for C. cristiceps were not possible because these fish shied away from divers. Habitat preferences were mirrored in the diets of both species which fed on a wide variety of reef associated benthic animals. Size of prey appeared to be gape limited, only larger fish being able to manipulate prey. Quantitative differences between the diets of fish sampled in different areas were a reflection of differences in available prey and not related to the relative density of predators. The dietary characteristics recorded in these fish were typical of search hunters. An age and growth study based on the examination of sectioned otoliths showed that both species were slow growing and long lived. Maximum recorded ages were 18 and 22 years for C. laticeps and C. cristiceps respectively. Growth rates in exploited and unexploited areas were not significantly different although there was an indication that growth was slower in the exploited areas for C. cristiceps. Several inconsistencies in otolith interpretation and terminology were evaluated. Contrary to other South African studies the results suggested that somatic growth was fastest just after spawning. This coincided with the winter months and was reflected by the deposition of a hyaline zone in the otolith. Two independent estimates, the Pauli derivation and visually assessed length frequency analysis, produced the same value for total mortality of C. laticeps in the Tsitsikamma area (0.2). This result, together with a significant difference in the rate of fishing mortality at different areas along the coast suggested that the populations sampled were discrete and supported the postulate that both species were sedentary. Further support was obtained from a mark-recapture study. Although sample numbers were low the results showed no evidence of large scale migratory patterns in these fish. An investigation of the reproductive biology of both fish showed that they were protogynous hermaphrodites, all males being derived from females with no evidence for polyandry. Males were shown to be capable of mating with a number of females and this, together with monandry, monochromatism and a small testis size, suggested a polygynous mating system in both species. Observations of the courtship behaviour in captive c. laticeps also supported polygyny. A significant difference in the mean size at sex reversal between unexploited and exploited populations supported the postulate that sex reversal was independent of the size or age of the animal. The size at which sex reversal occurred appeared to be dependent on sex ratio. A detailed yield per recruit analysis of the response of the population to different levels of fishing mortality and size at recruitment (t [subscript]r), showed that sex reversing species were particularly vulnerable to over fishing. This was due to a dramatic decline in the number of surviving individuals past t[subscript]r which resulted in a skewing of the sex ratio towards females. Evidence is presented to show that current legislation is inadequately protecting the spawner stock of both species. In conclusion it is shown that longevity, sex reversal, restricted movements and the occupation of a demersal habitat make these species particularly vulnerable to over exploitation in a size- selective fishery. The sustained yield in the linefishery is suggested to be a result of distant recruitment from relatively unexploited populations rather than the adequacy of current conservation measures. The need to protect the spawner stock is emphasised and the use of marine reserves as an additional protection for sedentary reef-dwelling species is therefore advocated.
  • Full Text:
  • Date Issued: 1988
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