The effect of habitat and spatial management on reef fish in an established marine protected area
- Authors: Dames, Vivienne Abigail
- Date: 2021
- Subjects: iSimangaliso Wetland Park (South Africa) -- Management , Reef fishes -- South Africa -- KwaZulu-Natal , Baited remote underwater stereo-video systems (stereo-BRUVs) , Marine parks and reserves -- Monitoring -- South Africa -- KwaZulu-Natal , Fish populations -- Measurement
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/171150 , vital:42024
- Description: The persistence of harvested fish populations in the Anthropocene will be determined, above all, by how they respond to the interacting effects of climate change and fisheries exploitation. Predicting how populations will respond to both these threats is essential for any adaptive and sustainable management strategy. The response of fish populations to climate change is underpinned by physiological rates and tolerances, and emerging evidence suggests there may be physiological-based selection in capture fisheries. By quantifying important physiological rates of a model species, the endemic seabream, Chrysoblephus laticeps, across ecologically relevant thermal gradients and from populations subjected to varying intensities of commercial exploitation, this thesis aimed to 1) provide the first physiologically grounded climate resilience assessment for a South African linefish species, and 2) elucidate whether exploitation can drive populations to less physiologically resilient states in response to climate change. To identify physiologically limiting sea temperatures and to determine if exploitation alters physiological trait distributions, an intermittent flow respirometry experiment was used to test the metabolic response of spatially protected and exploited populations of C. laticeps to acute thermal variability. Exploited populations showed reduced metabolic phenotype diversity, fewer high-performance aerobic scope phenotypes, and a significantly lower aerobic scope curve across all test temperatures. Although both populations maintained a relatively high aerobic scope across a wide thermal range, their metabolic rates were compromised when extreme cold events were simulated (8 °C), suggesting that predicted future increases in upwelling frequency and intensity may be the primary limiting factor in a more thermally variable future ocean. The increment widths of annuli in the otoliths of C. laticeps from contemporary and historic collections were measured, as a proxy for the annual growth rate of exploited and protected populations. Hierarchical mixed models were used to partition growth variation within and among individuals and ascribe growth to intrinsic and extrinsic effects. The best model for the protected population indicated that the growth response of C. laticeps was poorer during years characterised by a high cumulative upwelling intensity, and better during years characterised by higher mean autumn sea surface temperatures. The exploited population growth chronology was too short to identify an extrinsic growth driver. The growth results again highlight the role of thermal variability in modulating the response of C. laticeps to its ambient environment and indicate that the predicted increases in upwelling frequency and intensity may constrain future growth rates of this species. A metabolic index (ϕ), representing the ratio of O2 supply to demand at various temperatures and oxygen concentrations, was estimated for exploited and protected populations of C. laticeps and used to predict future distribution responses. There was no difference in the laboratory calibrations of ϕ between populations, and all data was subsequently combined into a single piecewise (12 °C) calibrated ϕ model. To predict the distribution of C. laticeps, ϕ was projected across a high-resolution ocean model of the South African coastal zone, and a species distribution model implemented using the random forest algorithm and C. laticeps occurrence points. The future distribution of C. laticeps was estimated by predicting trained models across ocean model projections up to 2100. The best predictor of C. laticeps’ current distribution was minimum monthly ϕ and future predictions indicated only a slight range contraction on either edge of C. laticeps’ distribution by 2100. In order to provide policy makers, currently developing climate change management frameworks for South Africa’s ocean, with a usable output, the results of all research chapters were combined into a marine spatial model. The spatial model identified areas where C. laticeps is predicted to be resilient to climate change in terms of physiology, growth and distribution responses, which can then be prioritised for adaptation measures, such as spatial protection from exploitation. While these results are specific to C. laticeps, the methodology developed to identify areas of climate resilience has broad applications across taxa. From a global perspective, perhaps the most salient points to consider from this case study are the evidence of selective exploitation on physiological traits and the importance of environmental variability, rather than long-term mean climate changes, in affecting organism performance. These ideas are congruent with the current paradigm shift in how we think of the ocean, selective fisheries, and how they relate to organism climate resilience.
- Full Text:
- Date Issued: 2021
Towards the development of a pro-environmental strategy for improving catch-and-release behaviour in recreational fisheries – a case study on a competitive South African angling body
- Authors: Mannheim, Samantha L
- Date: 2021
- Subjects: Fishing -- Environmental aspects -- South Africa , Fishing -- South Africa , Fishers -- Attitudes -- South Africa , Fishers -- Attitudes -- South Africa -- Cast studies , Fishes -- Conservation -- South Africa , Rock and Surf Super Pro League , Southern African Fisheries Ecology Research Lab
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/171862 , vital:42133
- Description: Catch-and-release (C&R) is becoming increasingly popular in recreational fisheries with the potential to contribute towards conserving the oceans limited fish stocks. Several studies have highlighted high rates of mortality and many sub-lethal effects which ultimately have a negative impact on fish population viability. With poorly developed handling practices, the fish that are released suffer the consequences of physical and physiological stress and do not always survive, thus making the ethics of C&R fishing questionable. Many studies have contributed to our understanding of the factors that influence the fate of fish released by anglers. Despite this, few interventions have been able to improve angler C&R behaviour. Pro-environmental behavioural strategies however hold some potential for improving angler C&R behaviour. To test their potential, we partnered with the South African Rock and Surf Super Pro League (RASSPL Africa), the biggest exclusively C&R competitive shore-based angling league in South Africa. The first two years (2013 and 2014) of the partnership were purely focused on building trust and relationships and making observations on angler behaviour. In 2015, we collected baseline data on angler behaviour and fish health during the RASSPL national fishing competition. This was followed by comparable data collection at the following two national competitions in 2016 and 2017 after the introduction of a combination of pro- environmental behaviour interventions, including rule changes, improving angler knowledge, behavioural modelling, rewards, penalties and feedback to improve C&R behaviour. There were significant improvements in angler behaviour, including a decline in total air exposure from 101.93s ± 64.34 in 2015 to 77.37s ± 60.52 in 2017 (F(2,618) = 9.27, P < 0.01), and the time taken for an angler to place their fish into a bucket declined from 105.86s ± 69.47 in 2015 to 23.05s ± 24.13 in 2017 (F(2,556) = 158.71, P < 0.01). There were also improvements in the health of the fish, with a decline in the blood lactate concentration and mean reflex action mortality predictor (RAMP’s) scores for the dominant species, Diplodus capensis (lactate – 9.46 ± 3.80 mmol.l-1 in 2015 and 6.69 ± 2.99 mmol.l-1 in 2017, RAMP – 0.28 ± 0.22 in 2015 and 0.19 ± 0.17 in 2017), and Haploblapharus fuscus (lactate – 4.25 ± 1.89 mmol.l-1 in 2015 and 1.76 ± 0.78 mmol.l-1in 2017, RAMP – 0.15 ± 0.18 in 2015 and 0 ± 0 in 2017). In 2018, surveys were conducted to gain insight into angler demographics and external (social, economic, cultural and institutional) and internal factors (knowledge and awareness, motivations, attitudes and perceptions) associated with the RASSPL anglers. Surveys were also designed to assist in identifying what components were key drivers behind the angler’s behavioural changes. The demographic characteristics of RASSPL anglers were not dissimilar from the general recreational angling public in South Africa, suggesting that this kind of intervention may have potential at a broader scale. In terms of the drivers of behavioural change, the surveys revealed that 68% of respondents strongly agreed that the structural rule changes contributed to their improved behaviour. This was followed by the educational presentations (66% of the respondents) and modelling / demonstrative videos (59% of the respondents). The conservation prizes were considered less effective, with only 27% of anglers strongly agreeing that this intervention improved their C&R behaviour. Overall this study has demonstrated that it is possible to improve the C&R behaviour of anglers in a competitive setting, with the most effective component of the intervention being the use of rule changes (structural approach). These findings suggest that proenvironmental strategies hold potential for improving the C&R behaviour of anglers and the health of released fishes. It is suggested that interventions to improve C&R behaviour should aim to develop long-term relationships, and implement a broad range of well communicated strategies based on reliable data and sound rationality. Key words: marine shore-based fisheries; community engagement; pro- environmental behaviour; behavioural intervention.
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- Date Issued: 2021
Age of squid Loligo reynaudii d’Orbigny, 1845, and its possible use to test effectiveness of the closed season in protecting this resource
- Authors: Mwanangombe, Collette Habani
- Date: 2020
- Subjects: Loliginidae -- Spawning -- South Africa , Loliginidae -- Age determination , Loligo fisheries -- South Africa , Fishery management -- South Africa , Otoliths , Loliginidae – Eggs -- Incubation , Loliginidae – Growth , Fish stock assessment -- South Africa , Recruitment (Population biology) -- South Africa , Loligo reynaudii d’Orbigny
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/144333 , vital:38336
- Description: This study presents age distributions representing populations of adult Loligo reynaudii, together with the results of spawning and commercial catches to assist in understanding the beneficial role of the closed season. The results were based on 791 samples collected during three closed seasons (November: 2003, 2004 and 2005) and out of closed season during April/May 2005. Age and predicted growth were examined by counting daily rings on statolith microstructures. The age in days after hatching ranged from 168 to 484 days (71-425 mm) in males and from 125 to 478 days (83-263 mm) in females. Average age at spawning was found to be 323 days in males and 316 days in females. Population estimates of growth rates were best described by a linear growth model which revealed that males grew faster than females in length as they grew older with growth rate ranging between 0.63 to 0.83 mm per day for males and between 0.22 to 0.32 mm per day for females. Back-calculated hatch dates and later egg-laying events for parental populations were determined. Results from back calculated egg laying dates (presented as percentage of frequency of all laying dates) indicated a highest total of 36%, 39% and 15% of eggs from all samples were laid during the closed season and nine days after the closed season during year 2003, 2004 and 2005 respectively. Monthly commercial total catches (2002-2005) showed an increase from November soon after the fishery resumed, up until the month of January. Daily catches were highest in November (up to 290 tonnes) relative to the daily catches observed in December and January in all the years. Results led to the conclusion that the closed season (25 October to 22 November) is beneficial for both the chokka resource and the fishery. This is because: a) there is time for enough spawning biomass to accumulate, which subsequently results in high catches (good fishery), in the current year, best immediately after season opens in November; b) there is a link in the results between egg laying dates in the period of closed season and immediately afterwards, and the magnitude of catches in last nine days of November.
- Full Text:
- Date Issued: 2020
An assessment of temporal changes in selective biological characteristics of chokka squid (Loligo reynaudii d’Órbigny, 1845)
- Authors: Mmethi, Mpho Audrey
- Date: 2020
- Subjects: Loligo reynaudii , Squids -- Morphology , Squids -- South Africa , Squid fisheries -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/143516 , vital:38253
- Description: The biological characteristics of chokka squid, Loligo reynaudii, sampled off the south coast of South Africa, were compared between 1994 and 2017 to ascertain any temporal changes using analysis of length frequency (LF) data over 15 years (1996–2017), and mantle length (ML) and total weight (TW) relationships over 9 years (1994–2016). To investigate feeding, two caecum colours were chosen for analysis (white: no food ingested, and yellow: six to seven hours after food ingestion). Other factors were kept constant throughout: similar sampling period of 60 days in spring-summer, similar depths and areas sampled, and identical maturity stage. Anecdotal evidence from fishers suggested that the length frequency and ML_TW relationship of chokka have changed over years, with possibilities to be linked to fishing activities and environmental conditions. Also, there is evidence in the published literature that both fisheries and environment may influence length distributions in populations of fish and cephalopods over time. The results from this study showed no significant differences between length frequencies over the time series. However, a significant decrease in length frequencies between 2014 and 2016 was noted when paired data was analysed by Anova (2014:2015, 2014:2016 and 2015:2016), which was initially noted in kernel density, Figure 2, hence an additional analysis was done. These changes were not linked to sea temperature (at 9 m, 14 m, 18 m, and 21 m depth strata), with not significant (P>0.05) results when temperature was analysed by t-test between 2002 and 2015. There was also a weak correlation between length frequency and the total squid catch in a given year (F Statistic (df = 1; 13) is 3.686 and 5.394 for males and females respectively, R² is 0.221 for males and 0.293 for females), but too weak to interpret, given the lack of other supporting data and the short time series. The ML_TW relationship showed no significant trends between the years for either sex. There was also no correlation between the ML_TW and total squid catch or temperature. A white caecum occurred significantly more often in males than in females (dof = 1; p < 0.05) from General Linear Model (GLM), indicating that the presence of non-feeding males in the spawning grounds may be linked to the behaviour of spawning squid.
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- Date Issued: 2020
Assessing community structure and trophic interrelationships in three differently impacted headwater streams in the AmatholeWinterberg freshwater ecoregion, South Africa
- Authors: Matomela, Nonjabulo Happy
- Date: 2020
- Subjects: Stream ecology -- South Africa -- Eastern Cape , Freshwater animals -- Ecology -- South Africa -- Eastern Cape , Kat River (South Africa) -- , Lushington River (South Africa) , Elands River (South Africa) , Eyre River (South Africa) , Food chains (Ecology) -- South Africa -- Eastern Cape , Water quality -- South Africa -- Eastern Cape , Land use -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/147653 , vital:38658
- Description: Afromontane regions represent some of the highly threatened ecosystems on the planet as they harbour endemic and often relic freshwater fauna. These ecologically sensitive ecosystems have been altered by multiple impacts, including invasion by non-native fishes, replacement of diverse indigenous vegetation with monoculture plantations, agricultural and mining activities, hydrological modifications, and degradation of instream habitats, with potential detrimental effects on aquatic community structures and food web dynamics. The aim of the present study was to compare spatio-temporal patterns of macroinvertebrate and fish communities as well as food web dynamics in three differently impacted headwater tributaries of the Kat River in the Amathole-Winterberg freshwater ecoregion in the Eastern Cape Province of South Africa. The upper Kat River catchment was the ideal model for purposes of the present study as it contains streams with varying degrees of human impact. The streams considered in the present study were (i) the Eyre River which was considered to closely represent near-natural conditions as it is the least impacted stream in this catchment, with the riparian zone dominated by relatively intact and diverse native woody vegetation, (ii) the Elands River whose catchment has been altered by agricultural activities, and (iii) the Lushington River, whose riparian zone has been heavily invaded by black wattle. The three headwater streams were generally distinguished based on the physical-chemical variables. The Elands River was characterised by high conductivity and total dissolved solids (TDS). In addition, the Elands River was more alkaline and relatively warmer than the other two rivers. This suggested the negative influence of agriculture activities on the water quality in the Elands River. In general, the Lushington and Eyre rivers had comparable physical and chemical variables. However, the Lushington River was generally characterised by low streamflow, likely as a consequent of black wattle which is known for altering hydrological regimes of streams .The Eyre River and Lushington River were comparable in terms of macroinvertebrate richness and diversity, whereas the Elands River was characterised by low macroinvertebrate diversity and richness. Redundancy analysis indicated that the macroinvertebrate communities were mostly influenced by seasonality, with land-use accounting for a small but significant difference in community composition. In comparison, the generalised linear mixed-effects models (GLMMs) showed that chubbyhead barb abundance was significantly influenced by land-use patterns. Evaluation of food web dynamics using stable isotope analysis revealed that the food web structure in the three rivers differed substantially as a result of land-use. Specifically, the Eyre River was characterised by less variation in stable isotope values of basal food sources and consequently, the consumer groups had a narrow isotopic breadth. In contrast, the Elands River was characterised by a wide variation in basal food sources and therefore, a wider isotopic breadth for consumers. The Lushington River was spatially variable in terms of basal sources and isotopic breadth for consumers. The study concluded that food webs and trophic interrelationships were a more informative indicator of land-use than community structure was in evaluating the impact of land-use patterns on aquatic communities. In addition, future studies should seek to investigate food webs interrelationships in addition to community structure to infer a more conclusive river assessment.
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- Date Issued: 2020
Combination ecosystem green engineering and early life history processes to enhance the intertidal biodiversity in the Port of East London
- Authors: Mafanya, Sandisiwer
- Date: 2020
- Subjects: Biotic communities -- South Africa -- East London , Perna -- Ecology --South Africa -- South Africa-- East London , Mexilhao mussel -- Ecology -- South Africa -- East London , Habitat (Ecology) -- Modification -- South Africa -- East London , Benthic animals -- Effect of habitat modification on -- South Africa -- East London , Harbors -- Environmental aspects -- South Africa -- East London
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/166376 , vital:41357
- Description: Marine coastal ecosystems are highly impacted by anthropogenic activities, including the development of, and practices within, harbours and/or ports. Artificial structures associated with harbours have a different chemical composition, texture and orientation than that of the natural benthic habitats they have replaced, and are therefore not generally favourable for the settlement and occurrence of indigenous species. Attempts are being made to identify what structures and materials can be used to aid in the rehabilitation of native species within harbours. The aim of this study was to investigate the effects of utilising environmentally-friendly artificial structures (tiles) with varying complexity (crevices and ridges with different depths) with ecological engineers (the indigenous bivalve Perna perna), on the associated benthic biodiversity within an international port in South Africa (Port of East London). The objectives of the study were to test the effects of artificial habitat complexity and the presence of bivalves on 1) the growth, mortality and biomass of a selected model species of ecosystem engineer (P. perna), and 2) the associated intertidal biodiversity. Tiles seeded with bivalves (P. perna) were deployed at two sites in the Port of East London and monitored monthly over a period of 12 months (November 2016-October 2017) to assess survival, growth and associated biodiversity. Environmental variables were also measured every month. The results of the three-way repeated measures ANOVAs indicated that tile treatment (especially high complexity of 2.5 and 5 cm) had an effect on the diversity of mobile species, length, height and biomass of the bivalves used as model ecosystem engineer, indicating the potentials for protection from wave dislodgement and refuge provision. Treatment (especially flat tiles) also had an effect on sessile/sedentary species diversity, indicating the greater proportion of space provided by these non-complex tiles. In addition, month had an effect on the mortality, height and biomass of the bivalves. Mortality was highest in October 2017, while the growth in height and biomass of P. perna were largest in January and October 2017 respectively. The use of artificial tiles also had a positive effect on the survival, growth, and biomass of bivalves (especially the length, weight and dry weight in 2.5 cm and 5 cm complexity). Additionally, this research investigated patterns of settlement and recruitment of the local bivalve population (P. perna) in the Port of East London and adjacent natural coastline to understand the early life history temporal and spatial dynamics of this model ecosystem engineer species. Settlement and recruitment were assessed every month by deploying and replacing artificial collectors for a total period of 19 months (November 2016-May 2018). The results of the two-way ANOVAs indicated that month and site (port vs natural) had an effect on settlement and recruitment of bivalves. Settlement and recruitment of bivalves were highest in July 2017 (port) and March 2018 (natural rocky shore). This study has highlighted that the use of artificial concrete tiles with increased complexity, as well as the investigation of the early stages of mussel populations could be important to consider in a framework of rehabilitation of urban coastal environments such as the Port of East London. Ecological engineering (in terms of increased complexity and heterogeneity) has indeed the potentials to be incorporated in South African programmes aiming at improving natural biodiversity in coastal urban environments. Nonetheless, the spatio-temporal variability of early driver of mussel populations (settlement and recruitment) is also an important feature to be closely monitored if biodiversity in South African coastal armouring is to be enhanced effectively and in the long term.
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- Date Issued: 2020
Distribution, habitat associations and conservation of the Eastern Cape rocky Sandelia bainsii (Perciform: Anabantidae) in the Great Fish River system
- Authors: Sifundza, Delsy Sindy
- Date: 2020
- Subjects: Anabantidae -- South Africa -- Great Fish River , Perciformes -- South Africa -- Great Fish River , Labyrinth fishes -- South Africa -- Great Fish River , Fishes -- Effect of human beings on -- South Africa -- Great Fish River , Fish populations -- South Africa -- Great Fish River , Fish declines -- South Africa -- Great Fish River , Fish populations -- Monitoring -- South Africa -- Great Fish River , Anabantidae -- Evolution -- South Africa -- Great Fish River , Gene flow , Mitochondrial DNA , Microsatellites (Genetics) , Eastern Cape rocky Sandelia bainsii , Freshwater ecology -- South Africa -- Great Fish River
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/142692 , vital:38102
- Description: In South Africa, freshwater ecosystems are under pressure due to increasing anthropogenic factors degrading river systems. The Cape Fold, the lower Southern Temperate Highveld and the Amatolo – Winterberg Highlands freshwater ecoregions contain some of the heavily impacted river systems in the country. One such river system is the Great Fish River system, which has been affected by anthropogenic modification (hydrological modification, water pollution and invasion by non-native fish species). These modifications have raised conservation concerns on an imperilled anabantid fish, the Eastern Cape rocky Sandelia bainsii that is confined to the Kat and Koonap rivers, which are tributaries of the Great Fish River. Historically, the species was reportedly common and abundant, with a range spanning across seven river systems (Kowie, Great Fish, Keiskamma, Igoda, Gxulu, Buffalo and Nahoon rivers) in the Eastern Cape Province. However, surveys have indicated that the species has experienced decline in population size and distribution range, with localised extirpations being reported. This resulted in its listing on the IUCN Red List of threatened species as Endangered. The proposed shale gas exploration and potential infrastructure development in the Karoo basin, which encompasses the headwaters of the Kat River, represent a potential future threat to the remnant populations of this species. The aim of the present study was to review the past and present distribution range of S. bainsii, determine the habitat associations and assess the conservation of S. bainsii in the Great Fish River system. This information is essential for informing conservation and management decisions for this species in the Great Fish River system. This study undertook a comprehensive survey of the Kat and the Koonap rivers in 2017, and augmented this information with data from more recent surveys that were conducted from 2009 - 2014 to map the distributions freshwater fishes in the Great Fish River system. Data from these recent surveys (2009 – 2017) were compared with historical records (1961 – 2005) obtained from the South African Institute for Aquatic Biodiversity to evaluate changes in distribution patterns of S. bainsii. Historical records indicated that S. bainsii occurred at 11 localities in the Kat River and three localities in the Koonap River. Data from recent surveys indicated that the species has persisted at these historical localities, except one locality in the Koonap River where no individuals of S. bainsii were captured, despite the use of multiple sampling approaches and gears. Although the species still persists at two of the three historical localities in the Koonap River, the population sizes have considerably declined as the species was reportedly in high abundance at these localities in the 1980s. Factors threatening the continued existence of this species in the Koonap River likely include non-native species, extreme drought conditions and the associated excessive abstraction of water which has resulted in the drying of some of the refugia pools where the species was historically common and abundant. In contrast to the Koonap River, the 2017 survey indicated that in the Kat River, S. bainsii had a similar distribution range compared to historical records. The species occurred at 11 of the 41 localities that were sampled in the Kat River, and the sampled populations consisted of all size classes. Sandelia bainsii occurred with other native fish species in the system, including Labeo umbratus, Enteromius anoplus and Glossogobius callidus. A comparison of historical and recent data indicates that non-native fishes have likely not expanded their ranges in the Kat River. This is likely due to the presence of weirs and dams that have prevented upstream movement of non-native fish species L. aeneus, C. gariepinus and T. sparrmanii which are now abundant in the lower Kat and mainstem Great Fish River. Surveys from the present study indicated that although S. bainsii still persists within the Kat River, there are a number of factors that pose a considerable threat to the continued existence of this species in the Great Fish River system. Chapter 3 evaluated the habitat associations of S. bainsii based on 10 physical and chemical variables and distribution data collected from 30 localities in the Upper Kat River and seven of its tributaries. A non-metric multidimensional scaling model was used to assess the distribution patterns of S. bainsii in relation to environmental variables. Furthermore, a negative binomial generalised linear model (GLM) was used to assess the relationship between the abundance of S. bainsii and environmental variables. Results from the present study indicated that S. bainsii was a habitat generalist as the distribution of this species showed no specific association with any of the habitat variables that were considered in this study. The species occurred in a wide range of habitats, including rocky sections in the upper Kat River and its tributaries as well as the mainstem sections. The GLM however indicated that the abundance of S. bainsii was negatively associated with increasing conductivity. In addition, the Kat River contains multiple weirs of variable sizes. Future studies should therefore evaluate the effects of these weirs on population fragmentation, gene flow and long-term evolutionary potential of S. bainsii through the application of techniques such as mitochondrial DNA and microsatellites.
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- Date Issued: 2020
Do submarine canyons influence the structure and diversity of benthic fish assemblages on the continental shelf edge?
- Authors: Nyawo, Mpilonhle Aura June-Rose
- Date: 2020
- Subjects: Submarine valleys , iSimangaliso Wetland Park (South Africa) , Biotic communities -- South Africa -- iSimangaliso Wetland Park , Groundfishes -- South Africa -- iSimangaliso Wetland Park , Marine ecology -- South Africa -- iSimangaliso Wetland Park
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167264 , vital:41462
- Description: Marine ecosystems play an important role in human welfare, such as providing food security and providing social, economic and environmental benefits to an increasing human population. However, due to the deleterious impact of overfishing as well as habitat degradation, pollution and climate change, many marine ecosystems and the substantial biodiversity they support, are under increasing threats. Submarine canyon ecosystems cut into the continental margin in all our oceans and are considered regions of enhanced diversity, abundance and biomass for many marine communities, including fish. In South Africa, the tropical Delagoa Ecoregion is characterised by numerous submarine canyons that are home to coelacanths Latimeria chalumnae, and a variety of commercially important line fish species. However, there is currently a lack of information on the ecological structure and functioning of these canyons, in relation to nearby non-canyon ecosystems. The aim of this thesis was to generate knowledge on the role of submarine canyons in influencing the benthic fish assemblage structure and diversity on the continental shelf and shelf edge within the high-latitude coral reef ecosystems in the tropical Delagoa Ecoregion of South Africa. First, a systematic literature review was conducted to examine the current knowledge on the role of submarine canyons on the benthic fish assemblages occurring on continental margins, as well as outline the trends in canyon research. For the fieldwork component of this thesis, baited remote underwater stereo-video systems were utilised to gather data. The first research chapter, chapter 3, investigated the effect of ecosystem and depth on the diversity and structure of benthic fish assemblages within iSimangaliso Wetland Park in the Delagoa Ecoregion. Data were collected in 2017 from Wright Canyon (canyon ecosystem) and adjacent slope ecosystems around the canyon (non-canyon ecosystem) at depths ranging between 70–240 m. The second research chapter, chapter 4, data were collected in 2018, from 60–100 m depths in three ubmarine canyons (Wright, Diepgat,Levens) and their adjacent habitat within iSimangaliso Wetland Park to investigate the diversity patterns and community structure of benthic fish and cons ider location as a factor. The systematic review showed that canyon research is still very much in its infancy, however more papers are expected to be published in the future. There were clear location associated biases detected, with more than 90% of the canyon research being concentrated in the Mediterranean Sea, while only one study was published from South Africa. Most of the reviewed literature focused on invertebrates, with benthic fish (including cartilaginous fish) being the second most studied taxa. A wide range of methods from both fishery- dependent and fishery-independent categories were used to gather the data of benthic fish from the canyons and adjacent areas. With over 8500 submarine canyons mapped globally, the number of submarine canyon research published and the detected location bias is of great concern. More studies are needed in order to understand the role of submarine canyons on adjacent slope habitats Overall, the results from the research chapters indicated that there were higher a bundances in the canyon ecosystem compared to the non-canyon ecosystem. In contrast, evenness and beta-diversity were higher in the non-canyon ecosystem. Relief, bottom type as well as depth played a major role in explaining the observed abundance and diversity patterns. Both evenness and beta-diversity decreased with increase in depth. The canyon and non-canyon also differed in terms of habitat structure. The canyon ecosystem was characterised by patched reef and reef habitats with high relief whereas the non-canyon ecosystem was characterised by flats and habitats, especially at shallower depths. Additionally, there were clear differences in terms of the fish community structure between the canyon and the non-canyon ecosystem. The heterogeneous and complex habitats of the canyon ecosystem were typified by species such as Epinephelus poecilonotus, Polysteganus coeruleopunctatus and Chrysoblephus puniceus in comparison to the less complex habitats outside the canyons that were preferred by species such as Lagocephalus sceleratus, and Rhinobatos leucospilus. The different locations sampled demonstrated that the canyon effect was not onsistent at all locations, with varying results detected in the different sample locations. This research demonstrates that clea r differences exists between the benthic fish assemblages associated with canyon and non-canyon ecosystems and provides important information on the role of submarine canyons in the iSimangaliso Wetland Park. From this thesis, it is clear that a ‘canyon effect’ exists in the continental shelf and shelf edge. The results suggested that heterogeneity of habitats was the most important environmental factor that differed between the canyon and non-canyon ecosystems and these differences in the habitat were driving the observed patterns. This thesis has provided a reference point, with regards to investigating the role and influence of these canyons on benthic fish assemblages occurring on the continental shelf edge. The information provided by this thesis can ultimately be used in other studies investigating benthic fish assemblages in other submarine canyons within iSimangaliso Wetland Park and the rest of South Africa./
- Full Text:
- Date Issued: 2020
Evaluation of Baited Remote Underwater Video Systems (BRUVS) for monitoring fish communities in Lake Malawi/Niassa
- Authors: Van Wyk, Angus
- Date: 2020
- Subjects: Underwater videography -- Malawi , Chambo -- Malawi -- Monitoring , Fishes -- Malawi -- Monitoring , Oreochromis lidole -- Malawi -- Monitoring
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145546 , vital:38448
- Description: Baited Remote Underwater Video systems (BRUVS) have become a well-established in-situ monitoring technique in clearwater aquatic ecosystems. The relatively low cost, nondestructive and non-extractive nature of this technique permits BRUVS to be employed in a wide range of habitats. To date, the vast majority of studies using BRUVS technology have been conducted in marine habitats. Subsequently, BRUVS applications in freshwater habitats are scant, and techniques are not well developed. The primary objective of this thesis was to address this knowledge gap and develop standard operating procedures for BRUVS employment in Lake Malawi/Niassa and explore the potential of BRUVS as a monitoring tool for fish communities in the African Great Lakes. Eight easily identifiable species groups, representative of Lake Malawi/Niassa inshore fish communities, were used to develop the technique. The optimal BRUVS deployment time to obtain 95 % species accumulation was achieved in a 15-minute recording period. Power analysis, using a pre-determined 80 % power, a confidence interval of 95 % and a significance level of < 0.05 was used to determine annual sampling effort requirements for each species group. The power analysis was performed to detect a 10 % change in abundance over a hypothetical 10-year monitoring scenario. In areas where fish abundance was lower, the sampling effort required to monitor key fisheries species was significantly higher. For example, Chambo, the local Oreochromis (Nyasalapia) species flock, required an annual sampling effort of 120 deployments in Malawi compared to 56 in Mozambique ( < 0.05). Chambo had a higher detection probability in areas of lesser fishing pressure and were found in higher abundances in deeper, less accessible habitats. Deep-water (> 20 m) and rocky habitats were most important in explaining Chambo abundance and detection probability. The size-structure of Chambo in Lake Malawi/Niassa reflects size-specific depth and habitat migrations. Larger Chambo were observed aggregating in waters deeper than 20 m and a broader size range of individuals were observed utilising structured habitat. The effects of fishing are apparent in the size-structure of Chambo in the areas sampled. In study areas exposed to greater levels of fishing pressure – such as Malawi, the BRUVS detected significantly fewer individuals within sexually mature size classes, and the average size was smaller than in areas with less exploitation.
- Full Text:
- Date Issued: 2020
The effect of alginate supplementation on the growth, feed utilization, digestive enzyme activity levels, and intestinal morphology of juvenile South African abalone (Haliotis midae) fed formulated feeds
- Authors: Tlakedi, Thato
- Date: 2020
- Subjects: Abalones -- Feeding and feeds -- South Africa , Haliotis midae , Abalones -- Digestive organs , Abalones -- Morphology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145279 , vital:38424
- Description: Alginate occurs abundantly in kelp and while a few studies have quantified the effect of kelp inclusion in formulated Haliotis midae feeds, none have researched the effect of alginate inclusion on the growth of abalone fed this feed. Feeding kelp to cultured abalone affects gut structure and modulates gut bacteria, aiding digestion by upregulating enzyme activity. This farm-based experiment compared the growth, feed utilization, digestive enzyme activity levels and intestinal villi structure between abalone (1-year-old, 10 - 20 mm shell length) fed kelp-supplemented (BK) or alginate-supplemented (BA) diets and abalone fed basal (B) and fresh kelp (K) diets for a period of eight months from June 2017 to February 2018. Growth and enzyme activities were also compared between abalone that experienced dietary changes and abalone that remained on their initial diets. The tested diets were: base diet (B, 34% protein), the same base diet supplemented with fresh minced kelp (0.90% kelp [dry mass, equivalent to 0.20% alginate]; BK), base diet supplemented with sodium alginate (0.20% alginate; BA) and a fresh kelp diet (K). Alginate or kelp inclusion in a formulated feed had no significant effect on the specific growth rates (SGR), linear shell growth rates (LGR), daily percentage feeding rates (PFR), feed conversion ratio (FCR), percentage mass gain (MG) and condition factor (CF) over the eight month trial period, compared to abalone fed the base diet. In October 2017, four months since the start of the trial in June, all the groups fed formulated feeds showed significantly higher average weight gain (8.42 ± 0.72 g to 8.86 ± 0.63 g) compared to the kelp-fed group (6.68 ± 0.43 g). However, no significant differences in the average weight gain were observed between abalone fed kelp and formulated feeds at the end of this study. Furthermore, there were no significant differences in the FCR and PFR between abalone fed the base or alginate diets and abalone fed the fresh kelp diet. However, the SW diet produced significantly lower FCR (1.00 ± 0.13) and PFR (0.78 ± 0.10%) compared to the kelp diet (10.6 ± 1.40% and 8.12 ± 1.01%, respectively). All formulated diets produced non-significant LGR, MG and CF compared to the kelp diet at the end of this study. Enzyme activity levels were compared between abalone fed the test diets in July and August 2017 and February 2018. There were no significant differences in the average alginate lyase specific activity levels between abalone fed formulated diets in July and August 2017. At the end of the trial, however, the alginate diet induced significantly higher alginate lyase specific activity levels (4.89 ± 1.64 mg.mg-1 protein) compared to the base diet (1.57 ± 0.98 mg.mg-1 protein), but showed no significant differences compared to the SW (3.78 ± 0.41 mg.mg-1 protein) and fresh kelp-only diets (4.00 ± 0.62 mg.mg-1 protein). The SW diet showed no significant differences in the alginate lyase specific activity levels compared to the base diet. There were no significant differences in the chymotrypsin activity levels between the test diets throughout this study. Alginate or kelp inclusion also had no significant effect on the intestinal structure compared to the base or fresh kelp diets. This was despite a higher degree of variability in microvilli height and width being observed in abalone fed the kelp-only diet, with microvilli visibly wider and longer than in abalone fed formulated feeds. Switching abalone between some diets significantly affected the average weight gain, MG, FCR and PFR, alginate lyase, chymotrypsin and cellulase activity levels compared to abalone kept on their initial diets. The inclusion levels of kelp and alginate used in this study were likely too low to affect abalone growth as higher inclusion levels, particularly of alginate, have been found to improve fish growth. This study concluded that minced kelp and alginate inclusion in a formulated H. midae diet did not affect the SGR, FCR and intestinal morphology, but significantly affected alginate lyase and chymotrypsin activity levels. Furthermore, changes in growth and digestive enzyme activity levels coincided with dietary changes. Consequently, higher inclusion levels, particularly of sodium alginate, and the effect of dietary changes on abalone growth and digestive enzymes must be investigated in future studies.
- Full Text:
- Date Issued: 2020
Towards understanding how exploitation influences the wild energetic response of marine fish to temperature variability
- Authors: Skeeles, Michael Richard
- Date: 2020
- Subjects: Chrysoblepus laticeps -- Climatic factors , Sparidae -- Genetics , Sparidae -- South Africa -- Climatic factors
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/145133 , vital:38411
- Description: Exploitation of fish populations can exacerbate the effects of climate change, yet our understanding of their synergistic effects remains limited. As fish are increasingly exposed to temperatures on the edges of their optimal thermal performance window, their physiological response is expected to shape their future performance. It is therefore concerning that exploitation can select for specific physiological phenotypes, as this may affect fished populations’ physiological response to temperature change. A recent laboratory study revealed fewer high-performance metabolic-scope phenotypes in an exploited population of the marine Sparid Chrysoblepus laticeps across a range of experimental temperatures in comparison to an unexploited population. This suggested that individuals in exploited populations may have less available energy for aerobic performance at thermal extremes, which may reduce the resilience of the population to changes in temperature. However, since laboratory experiments exclude numerous other variables that fish encounter in the wild, it was necessary to test this finding in a natural setting. This thesis aimed to further develop the laboratory study by assessing whether exploitation effects the wild energetic response of C. laticeps to thermal variability. To achieve this, the field metabolic rate of C. laticeps, a resident and endemic South African fish, from a near-pristine population (Tsitsikamma National Park) and a heavily exploited population (Port Elizabeth) was compared using acoustic accelerometry. A laboratory-based study using a swim-tunnel respirometer and accelerometer transmitters was conducted to develop a model to predict metabolic rate from acceleration data at temperatures from 10 to 22⁰C. Acceleration, temperature, mass and population (exploited/unexploited) were found to be the best predictors of the metabolic rate of C. laticeps and were incorporated into the model to estimate the field metabolic rate of fish tagged with acoustic accelerometers in the wild. To examine the combined effects of temperature and exploitation on the field metabolic rate of C. laticeps in their natural state, two fine-scale telemetry arrays with temperature loggers were used to assess the acceleration of the fish across different temperatures in the wild for three months during a period of high thermal variability. Ten fish from the exploited and unexploited populations were caught, surgically implanted with accelerometer transmitters and released back into the wild. Close to 500 000 and 400 000 acceleration estimates were recorded from wild exploited and unexploited fish, respectively. The field metabolic rate of both populations was estimated by combining the field acceleration and temperature data with the laboratory calibration model. The field metabolic rate of C. laticeps from the exploited population was constrained near cold and warm extremes compared to no constraints observed in the unexploited population. This was attributed to reduced inter-individual variability in the field metabolic rate-temperature relationship within the exploited population. There appeared to be a greater proportion of individuals that maintained a high field metabolic rate at extreme temperatures in the unexploited population. In contrast, all but one fish from the exploited population did not maintain a high field metabolic rate at extreme temperatures. These findings aligned with the laboratory-based metabolic-scope study on both populations of C. laticeps and demonstrate that passive-fishing may be removing thermally tolerant individuals and rendering exploited populations less resilient to thermal change. These findings are discussed in the context of fisheries management and particularly on the role that marine protected areas could play in maintaining physiological diversity, and therefore the resilience of fish in the Anthropocene. This study highlights the importance of applied conservation physiology in understanding the consequences of fisheries-induced evolution in an increasingly variable climate.
- Full Text:
- Date Issued: 2020
Secret sex lives in the intertidal: insights into the mating systems of clinid fishes from molecular parentage analyses
- Authors: Scheeper, Martinus Johannes
- Date: 2019
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/72438 , vital:30048
- Description: Expected release date-April 2020
- Full Text: false
- Date Issued: 2019
The development of a larval feeding regimen for dusky kob, Argyrosomus japonicus, with a specific focus on the effect of weaning period on larval development and survival
- Authors: Keet, Thomas
- Date: 2019
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/96897 , vital:31344
- Description: One of the biggest limiting factors in marine finfish aquaculture is the low survival rate of early-stage larvae. Most mortalities can be ascribed to the poor nutritional value of live feeds, sibling cannibalism, and various stressors that result in swim bladder hyperinflation and/or starvation during the larval stage. Research results vary on the best timing for the introduction of artificial feed for good survival and growth rate in dusky kob larvae. The main objective of this experiment was to improve survival and growth rate. The experiment focused on a new feeding regime that sought to wean larvae onto an artificial diet earlier than the current Argyrosomus japonicus standard (weaning commenced at 16 days after hatch (DAH) versus 20 days after hatch), based on findings and recommendations made by Musson & Kaiser (2014). Three trials were conducted, each with five replicates of the two treatments, namely the new feeding regime and the standard feeding regime in a fully randomised design. Samples from each tank were collected every two days for the duration of the trial. Morphometric measurements (standard length; body depth; eye diameter) obtained from these sample larvae were used to compare growth rates between treatments. The ratio of BD:SL was used to assess larval condition throughout each trial. Tank survival rates were calculated on the last day of each trial.The study indicated that in mean water temperatures ranging from 24.3 – 25.2 °C, dusky kob larvae can be weaned onto an artificial pellet diet from 16 - 21 DAH without any negative effects on growth, condition and survival. Results from the highest mean temperatures of Trial 2 show a better mean condition in the treatment group during the weaning period (p < 0.05). In Trial 3, with its lower mean water temperatures of 23.2 °C, larvae in both treatments showed stunted absolute growth rates of all biometrics when compared to results from the higher mean temperatures of Trials 1 and 2. During the first 6 days of Trial 3 larvae were in relatively poor condition, BD:SL ≤ 0.30. During this same period in Trials 1 and 2, mean BD:SL ≥ 0.31, suggesting that a BD:SL ratio of ≤ 0.30 in non-weaned dusky kob larvae is an indicator of a degree of starvation. A future study on the morphology and histology of the larval gastrointestinal tract, specifically the liver and intestines, and how this early weaning regime affects their ontogeny under differing temperature conditions this needed to investigate the validity of these initial data on dusky kob larvae condition.
- Full Text:
- Date Issued: 2019
The development of a larval feeding regimen for dusky kob, Argyrosomus japonicus, with a specific focus on the effect of weaning period on larval development and survival
- Authors: Keet, Thomas
- Date: 2019
- Subjects: Argyrosomus japonicus , Argyrosomus , Argyrosomus japonicus -- Larvae , Argyrosomus -- Larvae , Argyrosomus japonicus -- Larvae -- Nutrition , Argyrosomus -- Larvae -- Nutrition
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146577 , vital:38538
- Description: One of the biggest limiting factors in marine finfish aquaculture is the low survival rate of early-stage larvae. Most mortalities can be ascribed to the poor nutritional value of live feeds, sibling cannibalism, and various stressors that result in swim bladder hyperinflation and/or starvation during the larval stage. Research results vary on the best timing for the introduction of artificial feed for good survival and growth rate in dusky kob larvae. The main objective of this experiment was to improve survival and growth rate. The experiment focused on a new feeding regime that sought to wean larvae onto an artificial diet earlier than the current Argyrosomus japonicus standard (weaning commenced at 16 days after hatch (DAH) versus 20 days after hatch), based on findings and recommendations made by Musson & Kaiser (2014). Three trials were conducted, each with five replicates of the two treatments, namely the new feeding regime and the standard feeding regime in a fully randomised design. Samples from each tank were collected every two days for the duration of the trial. Morphometric measurements (standard length; body depth; eye diameter) obtained from these sample larvae were used to compare growth rates between treatments. The ratio of BD:SL was used to assess larval condition throughout each trial. Tank survival rates were calculated on the last day of each trial.The study indicated that in mean water temperatures ranging from 24.3 – 25.2 °C, dusky kob larvae can be weaned onto an artificial pellet diet from 16 - 21 DAH without any negative effects on growth, condition and survival. Results from the highest mean temperatures of Trial 2 show a better mean condition in the treatment group during the weaning period (p < 0.05). In Trial 3, with its lower mean water temperatures of 23.2 °C, larvae in both treatments showed stunted absolute growth rates of all biometrics when compared to results from the higher mean temperatures of Trials 1 and 2. During the first 6 days of Trial 3 larvae were in relatively poor condition, BD:SL ≤ 0.30. During this same period in Trials 1 and 2, mean BD:SL ≥ 0.31, suggesting that a BD:SL ratio of ≤ 0.30 in non-weaned dusky kob larvae is an indicator of a degree of starvation. A future study on the morphology and histology of the larval gastrointestinal tract, specifically the liver and intestines, and how this early weaning regime affects their ontogeny under differing temperature conditions this needed to investigate the validity of these initial data on dusky kob larvae condition.
- Full Text:
- Date Issued: 2019
The effect of bait on fine-scale habitat associations of reef fish investigated with remote underwater video systems
- Authors: Schmidt, Nicholas C
- Date: 2019
- Subjects: Baited remote underwater stereo-video systems (stereo-BRUVs) , Remote underwater stereo-video systems , Underwater videography in wildlife monitoring -- South Africa -- Tsitsikamma , Fish stock assessment -- South Africa -- Tsitsikamma , Fish populations -- Monitoring -- South Africa -- Tsitsikamma , Fishes -- Habitat -- South Africa -- Tsitsikamma
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/68380 , vital:29249
- Description: Establishing the associations between fish and their habitats can aid in the monitoring of fish stocks and the design of effective marine protected areas (MPAs). Baited remote underwater stereo-video systems (stereo-BRUVs) are now commonly used to asses fish populations. The habitats seen in the video footage of stereo-BRUVs can be used to link fish fauna to preferred habitat types. However, the application of bait potentially attracts fish from surrounding habitats, and might result in a biased understanding of fish–habitat associations. A field study was conducted in the Tsitsikamma National Park MPA to determine the effect of bait on fine-scale fish–habitat associations, using remote photographic and video methods. The study was conducted over the summer season of 2015 and 2016. Data were collected within a 1x1 km shallow (9–44 m) reef complex. Within the sampling area, 944 photo-quadrats of the macrobenthos were taken 30 m apart by means of a drop camera. By separating the macrobenthos into broad taxonomic groups, five habitat types were identified, namely Shallow Sand, Shallow Reef, Deep Reef, Deep Sand and Patch Reef. The results show that even on a fine scale, depth is an important predictor of macrobenthic distribution and assemblage structure. Baited (stereo-BRUVs) and unbaited (stereo-RUVs) surveys were then conducted to sample the fish community in the same area during the period under study. Higher abundances of fish were observed in reef than in sandy habitats, and bait was seen to have a positive effect on species richness and fish abundance. When comparing habitats, fish abundance and composition on reef habitats were significantly different from sand habitats. This was observed in both the stereo-RUVs and stereo-BRUVs methods. High counts of roman (Chrysoblephus laticeps), fransmadam (Boopsoidea inornata) and steentjie (Spondyliosoma emarginatum) in reef habitats were contrasted by high counts of white sea catfish (Galeichthys feliceps), evil-eye puffer (Amblyrhynchotes honckenii) and lesser guitarfish (Rhinecanthus annulatus) in sandy habitats. Overall, the underlying patterns in fish diversity recorded with the two video methods were generally comparable. However, stereo-RUVs appeared to be unable to detect species that were present in sand habitats, while stereo-BRUVs increased the number and abundance of species recorded in all habitat types. In the stereo-RUVs footage, differences between reef habitats were dampened by the presence of highly abundant fish species. In the stereo-BRUVs footage, although bait appeared to have an effect on the observed fish assemblage, this manifested in an increase in species richness, higher fish abundances and a better overall ability to detect fish–habitat relationships. As such, stereo-BRUVs are considered a robust, effective and recommended method for detecting fish–habitat relationships, even over a fine scale.
- Full Text:
- Date Issued: 2019
The integration of effluent treatment using constructed wetlands, with crop production and aquaculture
- Authors: de Jong, Martyn
- Date: 2019
- Subjects: Recycling (Waste, etc.) , Brewery waste , Sewage -- Purification , Beets , Mozambique tilapia
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/95767 , vital:31197
- Description: Breweries are major consumers of water and produce nutrient rich wastewater. Therefore, it is important to research technologies that optimise the reuse and recycling of this waste. This study compared different constructed wetlands (CWs) in terms of their potential for cleaning brewery effluent and simultaneously producing crops Beta vulgaris and fish Oreochromis mossambicus. Filling and draining times (FDT; 15 min, 30 min and 60 min) in tidal CWs were compared in Experiment 1. The 15 min FDT (6.52 ± 0.09 mg/l) and 30 min FDT (5.74 ± 0.09 mg/l) had higher dissolved oxygen (DO) than the 60 min FDT (5.40 ± 0.09 mg/l; p<0.05). This resulted in the 15 and 30 min FDT treatments reaching ammonia effluent discharge standards sooner than the 60 min FDT. Total plant harvest increased with increasing FDT; therefore, 15 min FDT was used as the FDT in tidal treatments in the following experiments. The aerated CW (5.81 ± 0.07 mg/l) and tidal CW (5.67 ± 0.07 mg/l) treatments had higher DO concentrations than the unaerated CW treatment (3.76 ± 0.07 mg/l; p<0.05) in Experiment 2. This resulted in lower ammonia concentrations on day 5 in the aerated and tidal CWs compared with the unaerated treatment (p<0.05). The tidal CW (23.97 ± 2.57 kg) had a total harvest that was approximately four times higher than the unaerated CW (p<0.05), which had the highest frequency of chlorosis and plant mortality; and was unable to treat ammonia to discharge standards. In Experiment 3, the aerated and tidal CW were compared with municipal-water as water sources for aquaculture. There were no differences in fish growth (p > 0.05). However, there were differences in water quality; with the municipal treatment having the lowest pH, EC and nitrate concentration (p<0.05); but all water quality parameters remained in a range suitably for fish production. Due to the tidal CW having the highest plant harvest and lowest frequency of chlorosis and mortality; it was the most suitable CW technology to clean the brewery effluent, and to produce B. vulgaris and water that could be used downstream in aquaculture.
- Full Text:
- Date Issued: 2019
The morphological and molecular variation of southern African Nannocharax (Characiformes: Distichodontidae), and its taxonomic implications
- Authors: Smith, Timothy
- Date: 2019
- Subjects: Nannocharax -- Africa, Southern , Distichodontidae -- Africa, Southern , Freshwater fishes -- Africa, Southern , Nannocharax -- Genetics -- Africa, Southern , Distichodontidae -- Genetics -- Africa, Southern , Freshwater fishes -- Genetics -- Africa, Southern
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/69212 , vital:29446
- Description: Nannocharax is the most species rich genus in the family Distichodontidae, being currently represented by 41 species. The genus is widely distributed across much of sub-Saharan Africa, with a range extending from the Zambezi ichthyofaunal province in the south to the Nilo-Sudan ichthyofaunal province in the north. In southern Africa, the genus is currently represented by four species, Nannocharax dageti Jerep, Vari, & Vreven, 2014, N. machadoi (Poll, 1967), N. macropterus Pellegrin, 1926, and N. multifasciatus Boulenger, 1923. Each of these species exhibit considerable intraspecific pigmentation pattern variation across their respective distribution ranges, suggesting that the current taxonomy possibly underestimates the taxonomic diversity of Nannocharax species in southern Africa. Much pigmentation pattern variation within these southern African species has been observed by both collectors and scientists in the field, prompting an investigation into the extent of this morphological variation as well as what molecular variation may occur as well. The genus displays a high degree of morphological conservatisim, making it difficult to assign external morphological characters as diagnostic. To this end, this study was conducted to determine the extent of diversity of this genus in the region, employing an integrative approach with traditional morphological analysis techniques as well as sequencing the ‘barcoding gene’, cytochrome oxidase I, testing the hypothesis that there is a greater, hidden diversity of this genus in the region than currently recognised. This study aims to identify these potential lineages and accurately map their distributions. Phylogenetic analyses were performed using maximum parsimony, maximum likelihood, and Bayesian inference, using the mitochondrial cytochrome oxidase I gene region. Massive genetic divergence was detected between populations of taxa previously considered to be singular, widely distributed species. The three approaches of phylogenetic inference used in this study yielded trees of comparable overall topology, with the exception of the maximum parsimony tree which indicated additional lineages within the southern African N. multifasciatus group. These analyses revealed four deeply divergent (1.3 – 12.3%) lineages within southern African N. macropterus, as well as two deeply divergent (0.4-14.6%) populations from the Congo ichthyofaunal region, the lineages here named “N. macropterus Congo 1” and “N. macropterus Congo 2”. Within the southern African region, two deeply divergent (10.3%) lineages of N. macropterus were identified from the Okavango River system, identified as “N. macropterus Okavango 2” lineage restricted to the Cuito-Canavale tributary, and “N. macropterus Okavango 1” distributed throughout the remainder of the Okavango system. “N. macropterus Okavango 2” shares a closer relationship with the unique lineage from the Kwanza ichthyofaunal region, named N. macropterus “Kwanza”, which itself is deeply divergent from the N. macropterus “Okavango 1”, N. macropterus “Zambezi”, N. macropterus “Congo 1” and N. macropterus “Congo 2” lineages (3.1-14.4%). Principal component analyses (PCA) and discriminant function analyses (DFA) produced overlapping clusters for all identified lineages, with the exception of the N. macropterus “Kwanza” lineage, which in all analyses clustered away from the other lineages. Analysis of variance (ANOVA) and Kruskall-Wallis tests indicated significant differences in means between character traits between lineages, however, overlap in measurements and counts occurred in all instances except between the N. macropterus “Kwanza” and N. macropterus Congo lineages. However the N. macropterus “Kwanza” lineages could be distinguished from the other lineages by generally smaller fin lengths (dorsal fin 19.5%SL vs 20.0-22.1%SL in others; pectoral fin 16.5%SL vs 20.6-21.8%SL in others; pelvic fin 18.3%SL vs 21.3-22.4) and pigmentation pattern differences. The N. macropterus species group displayed extensive pigmentation pattern variation, to the extent that five pattern grades could be used to classify them. These pattern grades, while not specific to river systems, showed patterns similar to that which was seen in the molecular analyses and could be linked to lineages with only minor overlap between them. Three lineages of N. multifasciatus were identified, with two occurring in the southern African region, each corresponding to a river system, being the N. multifasciatus “Zambezi” and N. multifasciatus “Okavango” lineages. This species group displayed shallower divergence between lineages than did the N. macropterus group, at 2.5% genetic distance. Genetic analysis inferred a closer relationship between the N. multifasciatus “Zambezi” and N. multifasciatus “Congo” lineages than with the N. multifasciatus “Okavango” lineage. Morphological PCA and DFA analyses indicated morphological divergence of the N. multifasciatus “Congo” lineage, with generally larger proportional measurements than southern African specimens (body width 12.6%SL vs 9.5-9.7%SL; body depth 26.6%SL vs 21.6-21.9%SL; head width 12.0%SL vs 10.0-10.4%SL). PCA, DFA, and measurements show a near complete overlap between the N. multifasciatus “Okavango” and N. multifasciatus “Zambezi” lineages. Pigmentation pattern variation occurred within this group, but none that could be assigned to a particular lineage. The N. machadoi species group in southern Africa consists of five lineages: N. machadoi “Zambezi 1”, N. machadoi “Zambezi 2”, N. machadoi “Kafue 1”, N. machadoi “Kafue 2”, and N. machadoi “Okavango”. This group displayed shallower genetic divergence between lineages than the other southern African Nannocharax species groups (0.4-1.3%). This shallow genetic divergence is paralleled by near complete morphological overlap, with PCA and DFA producing overlapping clusters, and measurements, meristics, and pigmentation pattern metrics consisting of very similar values for the lineages. These results indicate that what is considered to be “N. macropterus” in southern Africa should not be named as such. The N. macropterus “Zambezi” and the N. macropterus “Okavango 1” lineages, are misidentifications of Nannocharax dageti. Other “N. macropterus” from the southern African region possesses fewer circumpeduncular scales than the true N. macropterus as described by Pellegrin (1926), and require taxonomic re-evaluation, each here being recognised as a unique lineage with species status, here named N. macropterus “Okavango 2” and N. macropterus “Kwanza”. In particular, N. macropterus “Kwanza” displays deep genetic divergence as well as morphological dissimilarity with the other southern African “N. macropterus” groups. Nannocharax fasciolaris and N. monardi are here placed as junior synonyms of N. multifasciatus, owing to vast overlaps in measurements and character counts of these species and N. multifasciatus, which is also known to occur within the same geographical distribution, as well as dubious arguments from the original publications in delineating these species from N. multifasciatus. Therefore, there is insufficient evidence indicating the presence of multiple species originating from the Okavango system, where it is here indicated that only a single lineage of banded, adipose fin-bearing Nannocharax occurs, namely N. multifasciatus “Okavango”.
- Full Text:
- Date Issued: 2019
The use of filter-feeding fish (Clarias gariepinus and Oreochromis mossambicus) to remove microalgae from brewery effluent treatment ponds
- Authors: Nombembe, Lwazi
- Date: 2019
- Subjects: Clarias gariepinus -- Food , Mozambique tilapia -- Food , Water -- Purification -- South Africa , Algae -- Biotechnology -- South Africa , Microalgae -- Biotechnology-- South Africa , Brewery waste -- South Africa , Fish culture -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/95745 , vital:31194
- Description: The removal of microalgae from high rate algal ponds (HRAP) in waste-water treatment systems remains a constraint to their use in effluent treatment systems. Conventional algae harvesting methods often have high energy demands, take up lots of space, are expensive to operate or are time consuming. The aim of the study was to determine if fish such as Clarias gariepinus and Oreochromis mossambicus, could be used to remove microalgae from waste-water treatment ponds (in the absence/presence of a flocculent in the former and in the absence or presence of pH moderation in the latter), and to investigate the subsequent influence of algae concentration on several water quality parameters. The age of Clarias gariepinus (3-12 months) had a positive relationship with the distance between gill rakers (98.27 to 163.34 μm; y=90.576+4.823*x: R²=0.549; F(1,18)=21.867; p<0.001) and these data suggested that these fish might be efficient at removing algae from HRAP effluent. However, this was not the case, even with flocculent application (but this result might have been confounded by very high pH readings, at which flocculation is less likely to occur). Oreochromis mossambicus removed some of this algae, but the pH was too high for tilapia culture. It was not possible to moderate the increase in pH by keeping tanks in the dark and thus preventing photosynthesis; but pH fluctuation in HRAP effluent could be moderated using CO2 sparging in an attempt to make the environment more hospitable for tilapia (the average pH that was moderated with CO2 was 8.43±0.06, whereas the unmoderated average was 10.65±0.06). However, pH moderation using CO2 sparging did not increase the rate at which algae were removed by O. mossambicus; rather, it compromised O2 concentration which dropped to 4.17±1.26 mg/l after five hours of CO2 sparging, whereas it increased to 20.50±1.41 mg/l in treatments with unadjusted pH over the same period. Fish can be used to remove algae from treated effluent, and Oreochromis mossambicus remains a recommended species. Future work needs to investigate moderating fluctuations in pH and O2 concentration to further facilitate this method of algae removal.
- Full Text:
- Date Issued: 2019
Towards defining the tipping point of tolerance to CO2-induced ocean acidification for the growth, development and metabolism of larval dusky kob Argyrosomus japonicus (Pisces: Sciaenidae)
- Authors: Mpopetsi, Pule Peter
- Date: 2019
- Subjects: Argyrosomus japonicus , Argyrosomus , Argyrosomus japonicus -- Larvae , Argyrosomus -- Larvae -- Effect of water acidification on , Argyrosomus japonicus -- Larvae -- Nutrition , Argyrosomus -- Larvae -- Nutrition , Ocean acidification
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/71602 , vital:29924
- Description: Increased CO2 production and the consequent ocean acidification (OA) have been identified as one of the greatest threats to both calcifying and non-calcifying marine organisms. Traditionally, marine fishes, as non-calcifying organisms, were considered to have a higher tolerance to near-future OA conditions owing to their well-developed ion regulatory mechanisms. However, recent studies provide evidence to suggest that they may not be as resilient to near-future OA conditions as previously thought. In addition, earlier life stages of marine fishes are thought to be less tolerant than juveniles and adults of the same species as they lack well-developed ion regulatory mechanisms for maintaining homeostasis. This study follows up on previous studies examining the effects of near-future OA on larval Argyrosomus japonicus, an estuarine-dependent marine fish species, in order to identify the tipping point of tolerance for the larvae of this species. These previous studies showed that elevated pCO2, predicted for the year 2100, had negative effects on growth, development and metabolism and ultimately, survival of larval A. japonicus from post-flexion stage. Larval A. japonicus in the present study were reared from egg up to 22 DAH (days after hatching) under three treatments. The three treatments, (pCO2 353 μatm; pH 8.03), (pCO2 451 μatm; pH 7.93) and (pCO2 602 μatm; pH 7.83) corresponded to levels predicted to occur in year 2050, 2068 and 2090 respectively under the Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (IPCC RCP) 8.5 model. Size-at-hatch, growth, development and metabolic responses (standard and active metabolic rates and metabolic scope) were assessed and compared between the three treatments throughout the rearing period. Five earlier larval life stages (hatchling – flexion/post-flexion) were identified by the end of the experiment. There were no significant differences in size-at-hatch (P > 0.05), development or the active metabolic (P > 0.05) or metabolic scope (P > 0.05) of fish in the three treatments throughout the study. However, the standard metabolic rate was significantly higher in the year 2068 treatment but only at the flexion/post-flexion stage which could be attributed to differences in developmental rates (including the development of the gills) between the 2068 and the other two treatments. Overall, the metabolic scope was narrowest in the 2090 treatment, but varied according to life stage. Although not significantly different, metabolic scope in the 2090 treatment was noticeably lower at the flexion stage compared to the other two treatments, and the development appeared slower, suggesting that this could be the stage most prone to OA. The study concluded that, in isolation, OA levels predicted to occur between 2050 and 2090 will not negatively affect size-at-hatch, growth, development, and metabolic responses of larval A. japonicus up to 22 DAH (flexion/post-flexion stage). Taken together with the previous studies of the same species, the tipping point of tolerance (where negative impacts will begin) in larvae of the species appears to be between the years 2090 and 2100.
- Full Text:
- Date Issued: 2019
Effects of CO2-induced ocean acidification on the early development, growth, survival and skeletogenesis of the estuarine-dependant sciaenid Argyrosomus japonicus
- Authors: Erasmus, Bernard
- Date: 2018
- Subjects: Argyrosomus , Argyrosomus -- Growth , Argyrosomus -- Mortality , Argyrosomus -- Ecology , Argyrosomus -- Physiology , Ocean acidification , Marine ecology -- South Africa , Carbon dioxide -- Physiological effect
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/60585 , vital:27799
- Description: Although it is increasingly accepted that ocean acidification poses a considerable threat to marine organisms, little is known about the likely response of fishes to this phenomenon. While initial research concluded that adult fishes may be tolerant to changes predicted in the next 300 years, the response of early life stages to end-of-century CO2 levels (~ 1100 µatm according to the IPCC RCP 8.5) remains unclear. To date, literature on the early growth and survival of fishes has yielded conflicting results, suggesting that vulnerability may be species dependant. The paucity of ocean acidification research on fishes is particularly evident when one considers larval skeletogenesis, with no robust studies on its impacts on bone and cartilage development. This study addresses the early life embryogenesis, hatching success, growth, skeletogenesis and survival of an estuarine-dependant species. Dusky kob (Argyrosomus japonicus) were reared in a control (pCO2 = 327.50 ± 80.07 qatm at pH 8.15), intermediate (pCO2 477.40 ± 59.46 qatm at pH 8.03) and high pCO2 treatment (pCO2 910.20 ± 136.45 qatm at pH 7.78) from egg to 29 days post-hatch (dph). Sixty individuals from each treatment were sacrificed at the egg stage and at 2, 6, 13, 18, 21 and 26 dph, measured and stained using an acid-free double- staining solution to prevent the deterioration of calcified matrices in fragile larval skeletons. The proportion of bone and cartilage was quantified at each stage using a novel pixel-counting method. Growth and skeletal development were identical between treatments until the onset of metamorphosis (21 dph). However, from the metamorphosis stage, the growth and skeletal development rate was significantly faster in the intermediate treatment and significantly slower in the high treatment when compared to the control treatment. By 26 dph, A. japonicus reared in high pCO2 were, on average, 47.2% smaller than the control treatment, and the relative proportion of bone in the body was 45.3% lower in the high pCO2 treatment when compared with the control. In addition, none of the fish in the high pCO2 treatment survived after 26 dph. It appears that the combination of the increased energy requirements during metamorphosis and the increased energy cost associated with acid-base regulation may account for reduced growth, skeletogenesis and poor survival in high pCO2. Regardless of the driver, the results of this study suggest that the pCO2 levels predicted for the end of the century may have negative effects on the growth, skeletal development, and survival during metamorphosis.
- Full Text:
- Date Issued: 2018