Adaptations in allopatric populations of Triakis megalopterus isolated by the Benguela Current: steps towards understanding evolutionary processes affecting regional biodiversity
- Authors: Soekoe, Michelle
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5389 , http://hdl.handle.net/10962/d1021264
- Description: This study was initiated to gain a better understanding of evolution and adaptation of elasmobranchs by investigating how a putative biogeographic barrier, the Benguela Current, had influenced populations of a demersal shark species, Triakis megalopterus. It was hypothesized that the Benguela Current formed a biogeographic barrier in the distribution of T. megalopterus and was responsible for the divergence between South African (SA) and Angolan (AN) populations. Since elasmobranchs are generally characterized by a slow rate of evolutionary change and conservative morphology and life history traits, it was hypothesized that there would be limited genetic, morphological and life history divergence between the populations. Both mtDNA Control Region (mtCR) and microsatellites (nDNA) were used to assess population connectivity and structure of T. megalopterus. The mtCR predominantly showed a northern (Angola, AN, and Namibia, NA) versus southern (Western Cape, WC, and Eastern Cape, EC) Benguela subsystem arrangement. This suggested that the formation of the Benguela Current had an influence on the genetic structure of T. megalopterus during the early Pleistocene. The nDNA, however, showed a distinct transoceanic, Atlantic (AN, NA, WC) versus Indian Ocean (EC) arrangement, and this was attributed to the more recent exposure of the Agulhas Bank and reduced rocky shore habitat during the glaciations of the late Pleistocene. Traditional morphological analyses on full body and tooth morphology were used to assess phenotypic plasticity and/or adaptability of T. megalopterus. A novel method of geometric morphology, with potential for non-lethal application, was developed and tested to examine interpopulation divergence in shape. Traditional morphometrics showed significant divergence between populations and this variation was congruous with the mtCR haplotypes. However, the divergence in the truss variables was not concomitant to the haplotypes and suggested that differences in shape may be attributed to phenotypic plasticity. There was limited divergence in the tooth morphology between populations. The divergence in several morphological characters associated with swimming speed and manoeuvrability may be attributed to both habitat structure and dominant prey in the different biogeographic zones. The diet of T. megalopterus consisted primarily of crustaceans, teleosts and molluscs. The significant variation in the diet between populations suggested a generalist tooth configuration and broad trophic adaptability. There was significant divergence in the interpopulation life history parameters. The AN population had the fastest growth, smallest size at maturity, and shortest longevity. Individuals in the EC population had the youngest age at maturity, while the WC population had the earliest parturition. This divergence may be attributed to the contrasting thermal regimes in the three biogeographic regions and the dissimilar exploitation rates of the three populations. The results of this thesis demonstrated that a combination of the formation of the Benguela Current and sea level change most likely contributed to vicariance of three populations of T. megalopterus. The significant interpopulation morphological and life history divergence appeared to be both phenotypic and genetic, and suggested that contrasting environmental drivers can result in relatively rapid change in elasmobranchs.
- Full Text:
- Date Issued: 2016
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
Age, growth and yield-per-recruit analysis of ndunduma Diplotaxodon limnothrissa (Teleostei: Cichlidae), in the southeastern arm of Lake Malawi
- Authors: Kanyerere, Geoffrey Zantute
- Date: 2004
- Subjects: Fishes -- Nyasa, Lake , Cichlids -- Nyasa, Lake , Fishes -- Growth -- Nyasa, Lake , Fishes -- Age -- Nyasa, Lake , Fishery resources -- Malawi , Fishery management -- Malawi
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5214 , http://hdl.handle.net/10962/d1005057 , Fishes -- Nyasa, Lake , Cichlids -- Nyasa, Lake , Fishes -- Growth -- Nyasa, Lake , Fishes -- Age -- Nyasa, Lake , Fishery resources -- Malawi , Fishery management -- Malawi
- Description: Diplotaxodon limnothrissa Turner (1995) is a widely distributed species occurring throughout Lake Malawi, extending from the surface to a depth of at least 220m. It is probably the most abundant cichlid in the lake with biomass estimates of around 87 000 tonnes in the pelagic zone alone. The species is exploited commercially in the southern part of the lake but since its inception the fishery has never been assessed. As such this study investigates some aspects of age and growth of the species besides applying a yield-per-recruit analysis to assess the status of the fishery. Analysis of sectioned sagittal otoliths revealed that D. limnothrissa is fast growing and relatively long-lived species, attaining ages in excess of 10 years. Growth in length was rapid in immature fish, with fish attaining almost half of their maximum size within their first year. Le ngth-at-age was described by the von Bertalanffy growth model with combined-sex growth described as Lt = 211.21(1-exp(- 0.24(t+1.36))) mm TL. Total, natural and fishing mortalities were estimated at 0.76 yr⁻¹, 0.31 yr⁻¹ and 0.45 yr⁻¹ respectively. Per-recruit analysis indicated that the D. limnothrissa stock in the southeast arm of the lake is fully exploited as indicated by the current spawner biomass-per-recruit ratios of 31-55% (SB/R)F=0. Modelling indicated that the current age-at-capture (2.67 years) is lower than the age at which yield is optimised (> 5 years) based on the F₀·₁ harvesting strategy. It is, therefore, recommended that the age-at-capture should be increased from 2.67 to 5 years to optimise yield.
- Full Text:
- Date Issued: 2004
Ammonia removal from water by ion exchange using South African and Zambian zeolite samples
- Authors: Mwale, Monica
- Date: 2000
- Subjects: Ammonia -- Toxicology , Water -- Purification , Zeolites , Ion exchange
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5215 , http://hdl.handle.net/10962/d1005058 , Ammonia -- Toxicology , Water -- Purification , Zeolites , Ion exchange
- Description: One problem of intensive fish culture systems is the progressive build-up of toxic wastes such as ammonia. The possibility of improving aquaculture water quality using two kinds of zeolite is discussed. Zeolites are alumino-silicates whose framework allows them to exchange cations. Ion exchange has been demonstrated to be competitive with other methods of ammonia removal due to the high selectivity for ammonia exhibited by zeolite materials. In this study an unknown Zambian zeolite (identified as laumontite by X-ray diffraction techniques) and Pratley clinoptilolite (a South African zeolite) were tested under laboratory conditions and in a fresh water recirculating system. Ammonia cation exchange capacities (CEC) and suitable application rates for efficient water treatment were determined using the batch and column ion exchange procedures. Estimated ammonia uptake, the most important criterion used to assess performance of zeolite filters was strongly influenced by zeolite type, particle size, pre-treatment, regeneration and ion exchange method used. Statistical analysis showed significant differences in average ammonia CEC values between clinoptilolite (14.94 mg g⁻¹) and laumontite (2.77 mg g⁻¹), with the former displaying a higher Na⁺ ® NH₄⁺ exchange rate especially in the early reaction stages. This difference accords with the higher purity of clinoptilolite, 47% as opposed to 4.7% for laumontite, which makes it a better zeolite for ammonium removal. CEC increased linearly as particle size of the clinoptilolite was reduced resulting in a linear regression model (y = 18.29 – 3.704 x; r² = 74%). Pre-treatment of clinoptilolite using 1N NaCl significantly improved the ammonia CEC of clinoptilolite. Overall performance of both the batch and column methods achieved after regeneration (18.3 mg g⁻¹) was 25% higher than the estimated CEC values (13.0 mg g⁻¹) for the unregenerated samples of clinoptilolite. Comparison of CEC estimates using Pratley clinoptilolite, showed that average batch CEC estimates were significantly lower than the column method estimates. The average ammonia CEC values estimated in a fresh water recirculating system (5.80 mg g⁻¹ and 4.12 mg g⁻¹ for the 0.7-1.0 and 1.0-1.4 mm particle sizes, respectively) were significantly lower than the column and batch estimates for the same particle sizes (P < 0.05). Some nitrite (NO₂) and nitrate (NO3) build up was experienced probably due to the growth of autotrophs in the filters. Mass balance of nitrogen (N) for the three treatments of the fish trial (0.7-1.0 mm, 1.0-1.4 mm and the control treatment that had no zeolite in the filter) indicated that less that 10% of the N was retained for growth. It was found that 60% of the NH₄-N present associated with the soluble N was available for absorption by the zeolite filter or biological nitrification and that a total of approximately 22% of NH₄-N available was absorbed by clinoptilolite. The results indicate that the rate of nitrification can be deductively estimated by allowing a zeolite filter to become a biological filter. It is concluded that water treatment by ion exchange using natural zeolites, provides a reliable and efficient method for ammonia removal and appears to be a viable supplementary water treatment method for fresh water systems.
- Full Text:
- Date Issued: 2000
An analysis of the early ontogeny of Aplocheilichthys johnstoni (Günter, 1893) from a life history perspective
- Authors: Haigh, Eliria H
- Date: 1990
- Subjects: Ontogeny -- History , Cyprinodontidae , Aplocheilidae , Fishes -- History
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5217 , http://hdl.handle.net/10962/d1005060
- Description: The reproductive and developmental styles of Aplocheilichthys johnstoni closely resemble those of other oviparous cyprinodont fishes reported in the literature. Reproductively it sorts to the guild of nonguarding phytophyllic broodhiders, is a daily, fractional spawner of relatively large, adhesive eggs. The length of the embryonic period varies between 14 and 19 days and the larval period can last for up to 30 days. Sexual maturity can be attained at an age of 150 days from fertilization. The embryology is described in detail and close comparison is made with the embryology of other cyprinodonts to highlight possible phylogenetic differences. Major differences with other cyprinodonts are in the rate of development, and heterochronic shifts in the appearance of certain structures in relation to each other. A discussion is included on the nature of development. It is suggested that development proceeds in a gradual stepwise fashion, interspersed with four major saltations, namely, fertilisation, onset of exogenous feeding, sexual maturity and death
- Full Text:
- Date Issued: 1990
An analysis of the trawl and longline fisheries for Merluccius capensis off the west coast of South Africa
- Authors: Fairweather, Tracey Pamela
- Date: 2002
- Subjects: Fisheries -- South Africa , Merluccius capensis -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5218 , http://hdl.handle.net/10962/d1005061 , Fisheries -- South Africa , Merluccius capensis -- South Africa
- Description: The South African hake resource faces divergent fishing pressures and management issues. Although the resource consists of two species, management was simplified because the resource was only subject to trawl effort and because of the similarity in population parameters, single species assessment models could be adopted. The impact of trawling on the stock is considered to be well understood and the resource has shown recovery since exclusion of foreign vessels. The 1990s were punctuated by major political change and the need for transformation has resulted in an expansion of the number of fishing rights holders. Longlining has been reintroduced and there is no clear understanding of how the combined fishing pressures will affect the population structure of either Merluccius capensis or M. paradoxus. Information is vital to successful management. Fisheries are complex and intricate, and at times appear impossible to control or monitor. An integrated information system provides easily understood graphical explanations of complex issues. This thesis assessed the dynamics of the trawl and longline fisheries between 1994 and 1999 using a geographical information system (GIS). The accessability of a GIS incorporates the needs of scientists, managers and fishing communities. The simple GIS developed in this study revealed shifts in effort, facilitated the calculation of spatially precise catches and biomasses and highlighted the inadequacy of current sampling coverage. Trawlers were shown to fish the same areas consistently during the years investigated, with highest fishing intensity and average CPUE achieved at depths between 300 and 500m. Analysis of the longline sector revealed several similarities to the trawl sector, fishing intensity was highest between 301 and 500m, suggesting that both sectors face a "friction of distance" dilemma. The distribution and abundance of hake, in particular the exploitable proportion of the population, was determined by a combination of depth and substrate type. The selectivity patterns of trawlers and longliners were briefly investigated with the results illustrating that gear selectivity of the M. capensis stock was depth dependent. The deeper fishing occurred, the larger the length-at-selection. As a result, the M. capensis parental stock faces unprecedented fishing pressure. In the absence of reliable species-specific catch data, logistic and linear regression models were developed to split the hake catch into its respective species components. Large discrepancies between the predicted M. capensis catch for the two models were noted. Regression estimates constructed at a finer spatial scale may provide a better fit than the current depth logistic employed by Marine and Coastal Management. A first attempt at assessing the M. capensis resource on the West Coast using an age-structured production model was presented. It was found that a lengthy and accurate M. capensis catch series is required before it is possible to successfully model the dynamics of the stock. It is necessary to incorporate finer spatial detail in the collation of catch data and collection of sampling data. It would be unadvisable to assume that the stock is stable or recovering. The implications of a size/sex relationship must be investigated and properly appraised.
- Full Text:
- Date Issued: 2002
An assessment of inland fisheries in South Africa using fisheries-dependent and fisheries-independent data sources
- Authors: McCafferty, James Ross
- Date: 2012
- Subjects: Fisheries -- South Africa , Fishery management -- South Africa , Fisheries -- Economic aspects -- South Africa , Food security -- South Africa , Poverty -- South Africa , Economic development -- South Africa , Fishing -- South Africa , Fisheries -- Catch effort -- South Africa , Fish stock assessment -- South Africa , Fish populations -- South Africa , Linear models (Statistics)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5229 , http://hdl.handle.net/10962/d1005072 , Fisheries -- South Africa , Fishery management -- South Africa , Fisheries -- Economic aspects -- South Africa , Food security -- South Africa , Poverty -- South Africa , Economic development -- South Africa , Fishing -- South Africa , Fisheries -- Catch effort -- South Africa , Fish stock assessment -- South Africa , Fish populations -- South Africa , Linear models (Statistics)
- Description: The role of inland fisheries as contributors to local and national economies in developing African countries is well documented. In South Africa, there is increasing interest in inland fisheries as vehicles for achieving national policy objectives including food security, livelihoods provision, poverty alleviation and economic development but there is surprisingly little literature on the history, current status, and potential of inland fishery resources. This lack of knowledge constrains the development of management strategies for ensuring the biological sustainability of these resources and the economic and social sustainability of the people that are dependent on them. In order to contribute to the knowledge base of inland fisheries in South Africa this thesis: (1) presents an exhaustive review of the available literature on inland fisheries in South Africa; (2) describes the organisation of recreational anglers (the primary users of the resource); (3) compiles recreational angling catch records and scientific gill net survey data, and assesses the applicability of these data for providing estimates of fish abundance (catch-per-unit effort [CPUE]); and finally, (4) determines the potential for models of fish abundance using morphometric, edaphic, and climatic factors. The literature review highlighted the data-poor nature of South African inland fisheries. In particular information on harvest rates was lacking. A lack of knowledge regarding different inland fishery sectors, governance systems, and potential user conflicts was also found. Recreational anglers were identified as the dominant user group and catch data from this sector were identified as potential sources of fish abundance and harvest information. Formal freshwater recreational angling in South Africa is a highly organised, multi-faceted activity which is based primarily on angling for non-native species, particularly common carp Cyprinus carpio and largemouth bass Micropterus salmoides. Bank anglers constituted the largest number of formal participants (5 309 anglers affiliated to formal angling organisations) followed by bass anglers (1 184 anglers affiliated to formal angling organisations). The highly structured nature of organised recreational angling and dominant utilisation of inland fisheries resources by this sector illustrated not only the vested interest of anglers in the management and development of inland fisheries but also the role that anglers may play in future decision-making and monitoring through the dissemination of catch data from organised angling events. Generalised linear models (GLMs) and generalised additive models (GAMs) were used to standardise CPUE estimates from bass- and bank angling catch records, which provided the most suitable data, and to determine environmental variables which most influenced capture probabilities and CPUE. Capture probabilities and CPUE for bass were influenced primarily by altitude and conductivity and multiple regression analysis revealed that predictive models incorporating altitude, conductivity, surface area and capacity explained significant (p<0.05) amounts of variability in CPUE (53%), probability of capture (49%) and probability of limit bag (74%). Bank angling CPUE was influenced by conductivity, surface area and rainfall although an insignificant (p>0.05) amount of variability (63%) was explained by a predictive model incorporating these variables as investigations were constrained by small sample sizes and aggregated catch information. Scientific survey data provided multi-species information and highlighted the high proportion of non-native fish species in Eastern Cape impoundments. Gillnet catches were influenced primarily by species composition and were less subject to fluctuations induced by environmental factors. Overall standardised gillnet CPUE was influenced by surface area, conductivity and age of impoundment. Although the model fit was not significant at the p<0.05 level, 23% of the variability in the data was explained by a predictive model incorporating these variables. The presence of species which could be effectively targeted by gillnets was hypothesised to represent the most important factor influencing catch rates. Investigation of factors influencing CPUE in impoundments dominated by Clarias gariepinus and native cyprinids indicated that warmer, younger impoundments and smaller, colder impoundments produced higher catches of C. gariepinus and native cyprinids respectively. A predictive model for C. gariepinus abundance explained a significant amount of variability (77%) in CPUE although the small sample size of impoundments suggests that predictions from this model may not be robust. CPUE of native cyprinids was influenced primarily by the presence of Labeo umbratus and constrained by small sample size of impoundments and the model did not adequately explain the variability in the data (r² = 0.31, p>0.05). These results indicate that angling catch- and scientific survey data can be useful in providing predictions of fish abundance that are biologically realistic. However, more data over a greater spatial scale would allow for more robust predictions of catch rates. This could be achieved through increased monitoring of existing resource users, the creation of a centralised database for catch records from angling competitions, and increased scientific surveys of South African impoundments conducted by a dedicated governmental function.
- Full Text:
- Date Issued: 2012
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
An assessment of the invasion state and fisheries suitability in four dams and a natural lake in the Western Cape, South Africa
- Authors: Dredge, Brendon Neville
- Date: 2016
- Subjects: Introduced organisms Fishery management -- South Africa -- Western Cape Fishes -- Conservation -- South Africa -- Western Cape Introduced fishes -- South Africa -- Western Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/69114 , vital:29391
- Description: Despite more than a century of introductions, fish invasions are poorly understood in South Africa. This thesis aims to: (1) provide baseline information on the fish fauna in five inland water bodies (four dams: Theewaterskloof, Clanwilliam, Quaggaskloof, and Voelvlei and a natural lake, Groenvlei) in the Western Cape; (2) determine which species were established and provide a baseline of abundance and size structure for monitoring and, (3) make preliminary recommendations for a fishery. First, criteria for determining establishment were developed by undertaking a full biological assessment of bluegill Lepomis macrochirus, a data-poor species in South Africa. This included the assessment of growth rate using validated estimates of age derived from otoliths in two dams (Clanwilliam Dam: Lt=335.9(1−eo.113(t+1.06)); Groenvlei: Lt=287.2(1-e−0.171(t+0.54)). Length at 50% maturity was similar for males (146 mmFL) and females (147 mmFL). Length frequency analysis combined with data on the age and growth and reproduction demonstrated that established populations of bluegill contained several age cohorts as well as mature and juvenile fishes. A meta-analysis was conducted to: (1) compile a list of initial stocking dates for all alien fishes in each waterbody and (2) use angler tournament data to assess for additional species and persistence over time. Data from the meta-analysis was combined with ichthyological survey data to determine establishment success. These data demonstrated that nine non-native species had established in the five water bodies. Clanwilliam Dam had the largest number (7) of non-native species established, Groenvlei (5) and Theewaterskloof, Brandvlei and Voelvlei the lowest with four species. The state of invasion of each species in the province showed that all nine species are categorised as invasive. This information on establishment was then integrated into a framework for rapidly determining what type of fishery would be most suitable for the 5 waterbodies. Potential yield was estimated using morphoedaphic models, were 260 t/yr for Theewaterskloof Dam, 93 t/yr for Voelvlei, 81 t/yr for Brandvlei, 59 t/yr for Groenvlei and 55 t/yr for Groenvlei. The CPUE for Groenvlei was the highest in gill nets with 1.32 ± 1.94 kg/h, then Voelvlei 1.05 ± 1.34 kg/h followed by Brandvlei (0.84 ± 1.48 kg/h), Clanwilliam (0.71 ± 1.55 kg/h) and lastly Theewaterskloof (0.36 ± 0.41 kg/h). Only Theewaterskloof could produce in excess of 100 t/yr but less than 400 t/yr of fish making it suitable for a small scale fishery. The CPUE values of Theewaterskloof were the lowest and a gill net fishery on this water body may not produce sufficient fish for the fishery. All water bodies had a high recreational angling usage, the opening of a small scale fishery could be detrimental to this industry. Subsistence and recreational anglers should be promoted with the possibility of a long line industry targeting Clarias gariepinus.
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- Date Issued: 2016
An assessment of the Kenyan coastal artisanal fishery and implications for the introduction of fish aggregation devices
- Authors: Mbaru, Emmanuel Kakunde
- Date: 2013 , 2013-07-30
- Subjects: Fisheries -- Kenya , Fishery management -- Kenya , Fish aggregation devices , Small-scale fisheries -- Kenya , Small-scale fisheries -- Economic aspects -- Kenya
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5341 , http://hdl.handle.net/10962/d1006055 , Fisheries -- Kenya , Fishery management -- Kenya , Fish aggregation devices , Small-scale fisheries -- Kenya , Small-scale fisheries -- Economic aspects -- Kenya
- Description: The marine fishery in Kenya is predominantly small-scale and artisanal with about 11,000 fishers intensely fishing near shore coastal reefs using minimally selective fishing gears. A large majority (88%) of fishers use outdated equipment such as basket traps, beach seines, hand lines (hook and lines), fence traps, gillnets, spearguns and cast nets. Handmade canoes propelled by paddles (kasia) or sail power are used to access offshore waters, while only a few fishers have motorized boats. Although fishers along this coast know and express the potential of offshore fishing, most of them are disempowered and unable to access any of the largely untapped offshore pelagic resources. Using a unique dataset from four distinct coastal areas: Funzi-Shirazi bay area, Diani-Chale area, Mombasa-Kilifi north coast area and the Malindi-Ungwana bay area, containing species level length frequency catch data from the multi-gear and multi-species fishery, abundance of specific species, gear use comparisons in various regions, catch per unit effort and total catch estimate over a nine year period (2001 – 2009) were evaluated. Despite high diversity in the fishery, five species (Lethrinus lentjan, Siganus sutor, Leptoscarus vaigiensis, Lethrinus harak and Parupeneus macronemus) represented over 75% of the catch. A total of 11 legitimate gears were observed in this coastal artisanal fishery with basket traps (42%) being the most popular. Fishers along the Mombasa-Kilifi area predominatly used beach seines while those in Diani-Chale, Malindi-Ungwana bay and Funzi-shirazi bay predominaltly used spearguns, gillnets and basket traps, respectively. Apart from gillnets, a general declining trend for most of the gear types was observed since 2004. Beach seines recorded the lowest (20.9±0.2 cm) mean length while gillnets recorded the highest (34.2±0.3 cm). The highest catch (~26,000 metric tons) came in 2001 and the lowest (~15,000 metric tons) in 2005. The highest number of fishers was observed in 2008 while 2009 recorded the highest (4.8±2.3) mean number of hours per outing. The mean annual CPUE per region ranged from (1.5 kg.fisher-1.hr-1) in Diani-Chale to (1.0 kg.fisher-1.hr-1) in Malindi-Ungwana bay. Making use of questionnaire data, the attitudes towards offshore fishing strategies, FADs in particular, were evaluated. Some communities (about 25% in every location) were not even aware of FAD fisheries. With the imminent introduction of a FAD fishery in Kenya, it was concluded that, for this fishery to realize its full potential, training on FAD fishing techniques has to be done. Finally, effective management is necessary if small-scale fisheries are to continue providing food security for many poor coastal communities. Gear-based management in Kenya, although under represented and under studied, has the potential to be adaptive, address multiple objectives, and be crafted to the socio-economic setting. Management effectiveness in near shore fisheries has generally been evaluated at the scale of the fish community. However, community level indicators can mask species-specific declines that provide significant portions of the fisheries yields and income. This thesis seeks to identify ways in which the Kenyan artisanal fishery can be sustained and managed from within coastal communities, giving them the resources and education to effectively improve their lives. The introduction of a offshore FAD fishery and hence access to offshore pelagic species provides an opportunity to not only alleviate pressure on coastal resources but also to empower coastal communities and contribute to the growth of Kenya’s national economy as a whole.
- Full Text:
- Date Issued: 2013
An assessment of the monkfish resource of Namibia
- Authors: Maartens, Lima
- Date: 2000
- Subjects: Lophius -- Namibia Lophius
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5231 , http://hdl.handle.net/10962/d1005074
- Description: Two monkfish species are caught off the coast of Namibia. These are Lophius vomerinus Valenciennes (1837) and L. vaillanti Regan (1903). L. vomerinus is the more abundant of the two and contributes approximately 99% to the total Namibian monkfish landings. The Namibian monkfish fishery is one of the largest and most valuable of its kind in the world. Two fishing fleets harvest the resource, viz. the monkfish and sole fleet and the hake directed fleet. In 1998 and 1999, monkfish were also harvested by one gillnet vessel that had an experimental right. In this study, the biology, abundance and exploitation patterns of monkfish were investigated and used as inputs into a stock assessment framework as a contribution towards the development of a management procedure for this species. Ground and sectioned otoliths and sectioned illicia were used to age Lophius vomerinus. The illicia provided more precise estimates of age, and growth was subsequently modelled using these age estimates. Growth in length and weight was best described by the threeparameter specialised von Bertalanffy model as Lt (cm TL) = 72.29 (1-e⁻°·¹⁴⁽t⁺°·³°⁾) and Wt (kg) = 3.96 (1-e⁻°·¹⁸⁽t⁺°·¹°⁾)²·⁹⁹ for males, and Lt (cm TL) = 111.98 (1-e⁻°·°⁸⁽t⁺°·³⁶⁾) and Wt (kg) = 6.92 (1-e⁻°·¹⁸⁽t⁻°·⁶⁴⁾)³·°³ for females. L. vomerinus is a slow-growing species with a life span in excess of 10 years. Reproductive activity was shown to occur throughout the year, with a slight peak during the winter months. The adult sex ratio of fish > 37 cm TL was biased towards females. Length-at-50% sexual maturity was attained at 32.1 cm TL for females and 23.7 cm TL for males. The rate of natural mortality was estimated at 0.15 year⁻¹, while fishing mortality rates during the 1970s, 1980s and 1990s were estimated at 0.01 year⁻¹, 0.04 year⁻¹ and 0.14 year⁻¹, respectively. Gillnetting for monkfish (300 mm stretched mesh) was highly efficient with a moderate bycatch of around 20% during the two years of operation. The main bycatch species were red crab, spider crab, squalid sharks, rays and Cape and Deep-water hake. The mean length of the monkfish caught in gillnets (67 cm TL) was significantly larger than the monkfish landed by the trawlers (38 cm TL) and less than 1% of immature fish were landed. Gillnet catch-per-unit-effort for monkfish fluctuated between 0.03 and 0.67 kg.day⁻¹.50 m net panel⁻¹, with a soak time of between one and sixteen days. More than 50% (by weight) of monkfish landed by monkfish and sole trawlers, consisted of fish below 36 cm TL. There was a significant increase in catches of juvenile monkfish during 1997 and 1998 in comparison to the period 1994 to 1996. Various types of rigid sorting grids were tested to release juvenile monkfish below 32 cm TL. Five grid designs were tested. These included an “Ex-it” grid with horizontal bars spaced at 55 mm, single grids with vertical and horizontal bars spaced at 55 mm and grids with circular openings of 110 and 168 mm in diameter. The most efficient design was the grid with circular openings of 110 cm in diameter, which ensured the escape of 66% of monkfish smaller than 31 cm TL. However, studies need to be undertaken to quantify the survival of released fish and to test the feasibility of using grid sorters on commercial monkfish and sole trawling gear. The monkfish resource was assessed by means of length cohort analyses, the Thompson and Bell predictive model and by way of a deterministic age-structured production modelling approach. The length cohort analysis models were sensitive to the rate of natural mortality and insensitive to changes in the terminal fishing mortality rate. These biases may, however, not be serious provided that estimates of abundance are used to reflect relative changes. Fish ranging between 26 and 59 cm TL are the most heavily exploited. The Thompson and Bell model predicted that the monkfish resource is exploited above MSY -levels and a reduction of approximately 40% in fishing effort would provide a higher yield. Yield-per-recruit ranged between 10 000 and 14 000 tonnes. Results should, however, be treated with caution, as the condition of steady state was not satisfied. The age-structured production model was tuned using trends in catch-per-unit-effort data, estimated by Generalised Linear Modeling, as well as relative abundance indices calculated from hake biomass surveys. The model was found to be sensitive to both the ‘steepness’ parameter h and estimates of natural mortality. The ‘depletion’ level of the monkfish resource is currently estimated to be 49%. Estimated coefficients of variation were high (> 63%) due to the lack of a consistent trend within the abundance indices to tune the model. Overall productivity of the monkfish resource was estimated to be approximately 16%, similar to other southern African demersal resources. Results of the risk analyses suggest that catches in excess of 7 000 tonnes may be unsustainable and that catches of 5 000 or 6 000 tonnes would decrease the risk of stock collapse and possibly lead to a recovery in the stock. Monkfish management strategies were reviewed and these were considered in relation to the results of this study. The following management recommendations were made: to follow the precautionary approach and implement a total allowable catch for monkfish; to implement rigid sorting grids as these would be the most appropriate way in which to reduce catches of juvenile monkfish; to restrict soak time, depth of operation and implement means to reduce ‘ghost fishing’ by gillnetting and finally, to develop a management procedure for Namibian monkfish with the main objective being the sustainable exploitation of the resource.
- Full Text:
- Date Issued: 2000
An assessment of the shore baitfishery in the Eastern Cape
- Authors: Mackenzie, Bernard Louis
- Date: 2005
- Subjects: Fishing baits -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fisheries -- South Africa -- Eastern Cape , Fishery -- Law and legislation -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5232 , http://hdl.handle.net/10962/d1005075 , Fishing baits -- South Africa -- Eastern Cape , Fishery management -- South Africa -- Eastern Cape , Fisheries -- South Africa -- Eastern Cape , Fishery -- Law and legislation -- South Africa
- Description: The collection of bait organisms goes hand-in-hand with shore-angling in South Africa, hence the level of bait-collection can be used as an indicator of fishing effort and vice versa. This emphasises the importance of understanding the fisheries for bait organisms. In 1998 the South African fisheries policy was revised, culminating in the Marine Living Resources Act No. 18 (1998) which supported sustainable development, equitable access to resources and stability of the industry. The policy also dealt with the needs of subsistence fishers who had previously been all but ignored. This study looks to continue in this direction by investigating the opportunities for the establishment and management implications of small-scale commercial baitfisheries in the Eastern Cape. Data were collected from eight clearly demarcated sampling areas using the roving survey method. A total of 97 survey trips were undertaken between September 2001 and April 2003 and 469 interviews were conducted on individual anglers. The data was analysed and discussed on the basis of three wider study regions and this allowed for a more accurate and focussed assessment of the fishery area and the potential for its formalisation. Recreational fishers (91.5%) dominated in each of the three regions surveyed. The low number of subsistence fishers encountered in this study is not a standard pattern throughout South Africa. The dominance of local residents in the shore-fishery could have an important impact on the success of a formalised baitfishery in that the greater proportion of the potential market is accessible throughout the year. Most recreational shore-anglers were middle-aged (43.8 years ± 12.9 years), and hence at the peak of their earning years and this may contribute towards the potential success of a small-scale commercial baitfishery. Most anglers and baitfishers were of the opinion that all South Africans owned and were responsible for managing the living marine resources. The vast majority of recreational users paid for and were in possession of valid permits and approved of the baitfishery regulations. This implies that the greater majority of users recognise that the state is the rightful custodian of the resource and is responsible for management. No subsistence users were in possession of permits. Resource users in the Gamtoos to Tsitsikamma National Park region, where the inspection rate was highest, had the best knowledge of the regulations regarding both baitfishing (67.2% ± 38.8%) and angling (79.8 ± 21.4%). This substantiates the hypothesis that there is a direct correlation between knowledge of the regulations and the rate of inspection. About 475 000 angler-days/year were fished in the study area, with the highest number of angler-days recorded in or near urban and peri-urban areas. Bronze bream (65.9%) and dusky kob (61.1%) were the two most commonly targeted species, followed by white steenbras (31.7%), white musselcracker (31.4%) and blacktail (20.2%). A total of four purchased and 19 collected bait species was recorded during the study. Sardine, chokka and pink prawn were the most frequently encountered purchased bait. Red bait, sand prawn, mullet, siffie, sand mussel, bloodworm and saddleback were the most frequently encountered collected bait species. Sand prawn was identified as the preferred bait species for a wide range of angling species. The total quantity of bait organisms used per fishing trip was markedly less than the total amount collected per trip. The ban of off-road vehicles (ORV's) from beaches (20 January 2002) resulted in spatial shifts in angler effort in certain areas, suggesting that total effort has reduced in areas where ORV's were commonly used. Subsequent to the ban, fishers were encountered, on average, much closer to access points. The value of small-scale baitfisheries within the total study area was estimated at about R7 million per year. Across the entire study area red bait was identified as the most valuable bait in the rock-and-surf fishery in monetary terms, while sand prawn was also important. The findings led to the conclusion that small-scale commercial baitfisheries in the study area are potentially viable. Scenarios for the establishment of baitfisheries are suggested and discussed.
- Full Text:
- Date Issued: 2005
An assessment of the small-scale fisheries in the Kogelberg district of the Western Cape, South Africa
- Authors: Jordan, Tia
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/997 , vital:20011
- Description: Small-scale fisheries play a critical role in communities by contributing to food security, poverty alleviation and source of income. The study focused on the Kleinmond small-scale fishery and estimated the current economic value of the fishery as well as exploring the potential for increasing this and also whether it is being used in a way that ensures sustainable harvesting of the marine resources. It was important to evaluate the ecological, economic and social dimensions of the fishing community in order to address the problems currently facing the community. The study draws on previous research done in the Kleinmond area. Data were collected to update and complement previous research and addresses current research. In order to investigate the fisheries catch contribution in the area, data were obtained from the Department of Agriculture, Forestry and Fisheries. Three different questionnaires were developed and conducted in face-to-face formal and informal interviews with the various stakeholders (n=42) in the value-chain. Interviews were also conducted telephonically with other stakeholders and a focus group was formed to supplement previous available data. Simple economic models were developed for the fisheries working from the Kleinmond harbour, which were used to estimate the gross and net economic value of catches for individual right-holders, as well as the Kleinmond area as a whole. The economic models used in this study showed that the West Coast rock lobster Jasus lalandii, fishery was the primary source of income for small-scale fishers. This was due to the rock lobsters being sold to the export market as a high-valued commodity, whereas the linefish were sold to the local market as a lower-valued commodity. However, linefish were found to be more of a commodity to the community as a portion would be retained for personal consumption. The linefishers were concerned in that over the past couple of years, snoek Thrysites atun have been absent the Kleinmond area, resulting in and the fishing effort shifting to a resident species Cape bream Pachymetopon blochii. Whereas West Coast rock lobster were considered to be harvested sustainably under the current total allowable catch strategy, there was concern for the future of the fishery because of the occurrence of illegal fishing, both locally and nationally. Small-scale fisheries in the Kleinmond community are largely dependent on fishing resources, even though the industry is only marginally profitable. Future management measures should concentrate on optimising the value-chain to provide both sustainability for the resources and improve the livelihoods of the community.
- Full Text:
- Date Issued: 2016
An assessment of the South African east coast linefishery from Kei Mouth to Stil Bay
- Authors: Brouwer, Stephen Leonard
- Date: 1998
- Subjects: Fisheries -- Research -- South Africa , Fisheries -- Environmental aspects -- Research -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5233 , http://hdl.handle.net/10962/d1005076 , Fisheries -- Research -- South Africa , Fisheries -- Environmental aspects -- Research -- South Africa
- Description: During the period April 1994 and February 1996 as part of an investigation into the national Iinefishery, the east coast shore fishery and the recreational and commercial ski-boat fisheries were surveyed, at eight sites between Kei Mouth in the East and Stil Bay in the West. Roving creel, access point and aerial surveys were used. A questionnaire was developed for each sector to gather data on catch and effort, fisher demographics, economics, fisher attitudes towards, and knowledge of, the current management regulations and assess the efficacy of the fisheries inspectorate. During the access point survey the catch of 3273 fishers was inspected and 1556 interviews were conducted. Questionnaires were conducted on 118 recreational ski-boaters and the catch of 165 boats was inspected. 96 commercial skippers were interviewed and 230 had their catch inspected. Three aerial surveys of the entire area were conducted during which a total of 1067 shore fishers were counted giving a shore fisher density of 0.39 fishers.km⁻¹. The majority (99%) of participants in all sectors of the linefishery were male. The greatest number of participants were white, shore fishery 77% recreational ski-boat 98% commercial skiboat 89%, followed by coloured, asian and black people. To a large extent this reflects the income of various racial groups. Most fishers supported the current linefish management plan. However, when tested on their knowledge of the size limits, bag limits and closed seasons of their target species many shore fishers (59%) did not know them and a high proportion of fishers in all sectors had disobeyed at least one of the regulations (shore 50%, recreational ski-boat 70%, commercial ski-boat 56%). When compared to historical data the present catch per unit effort (CPUE) in all sectors has decreased. Most interviewees in the various sectors did not accept responsibility for the decline in CPUE, but attributed it to three principal reasons vis their perceived direct competitors, trawling and pollution. Analysis of the catch revealed that all sectors were multispecies fisheries, with each sector being characterised by a small number of target species. Catch composition differed significantly between the shore and ski-boat sectors, but there was significant overlap between the two skiboat sectors. Analysis of the catch in comparison to that reported to the National Marine Linefish System (NMLS) revealed that there was a substantial degree of under-reporting. There was little seasonal difference in effort in the shore fishery while the recreational ski-boat effort was highest in the summer and the commercial ski-boat effort was high in the winter. Effort in the shore and recreational ski-boat fisheries was concentrated over weekends while the commercial ski-boat effort was highest during weekdays. Total effort for the entire area was estimated at 903 186 (±1913) fisher days per annum in the shore fishery, 24 357 (±685) recreational ski-boat fisher days and 64 266 (±1686) commercial ski-boat fisher days. Expenditure and capital investment in the various sectors was calculated, as were earnings of the participants in the commercial ski-boat sector. The linefishery in the Eastern Cape was estimated to have a minimum capital investment in excess of R210 million and more than R32 million is spent annually on running costs. The commercial ski-boat fishery directly employed an estimated 3184 people. The economic implications of changes in CPUE for the commercial ski-boat fishery are considered, as are the benefits of a recreational angling licence. Management of the linefishery is discussed in relation to the findings of this study.
- Full Text:
- Date Issued: 1998
An assessment of the South African longline fishery with emphasis on stock integrity of kingklip, Genypterus capensis (Pisces : ophidiidae)
- Authors: Japp, David William
- Date: 1989
- Subjects: Genypterus capensis , Ophidiidae , Fisheries -- South Africa , Longlining (Fisheries) -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5209 , http://hdl.handle.net/10962/d1004660 , Genypterus capensis , Ophidiidae , Fisheries -- South Africa , Longlining (Fisheries) -- South Africa
- Description: The South African demersal longline experiment is assessed with emphasis on the target species, kingklip Genypterus capensis. The hypothesis that kingklip on the South African coast comprise a unit stock is tested. Recommendations for the management of the fishery are made. Longlining was found to be commercially viable. Techniques have been developed to target on either kingklip or the Cape hakes, Herluccius capensis and H. paradoxus. Longline fishermen exploit the kingklip spawner stock from August to No v ember by taking advantage of prespawning aggregations on the South-East Coast . Effort switches to the West Coast in late summer and early winter where kingklip are less abundant and a larger proportion of hake is caught. Catch rates of kingklip on the South Coast have declined sharply and the resource there has been exploited at a rate greater than that required to retain 50% of the unexploited biomass . There is a 17,6% probability that the spawner biomass on the South Coast has already been depleted below its pristine level. On the West Coast the catch rates of kingklip are lower than on the South Coast and have not changed significantly, although within the 95% confidence limits there is a possibility that the resource there has also been depleted below 50% of its pristine level. Genypterus capensis on the South African coast comprise a unit stock. Comparison of kingklip morphology using multivariate and discriminant function analysis and of otolith morphology using univariate statistics shows that there are no significant differences between the fish on the West and South Coasts. They are a slow growing species and were aged up to 25 years. Kingklip on the West Coast are smaller and have a lower L~ than those on the South Coast, but this is not a characteristic of discrete stocks. Kingklip on the South Coast mature earlier than those on the West Coast and aggregate to spawn on the South - East Coast in spring. There is no obvious spawning period on the West Coast. It is hypothesized that kingklip spawning on the South-East Coast is in response to favourable environmental conditions that enhances the survival of their eggs and larvae. It is recommended that demersal longlining be established as a permanent kingklip-directed fishery but that effort should not be allowed to increase. The West and South Coasts should be managed .separately. A TAC of 5 OOOt for kingklip should be introduced for 1989 of which 2 OOOt should be allocated to the West Coast and 3 OOOt to the South Coast . A closed season for kingklip from 1 August to 30 September on the South-East Coast is recommended. Hake-directed longlining should not be allowed as its effect on the hake spawner stocks are unknown and could be a potential threat to the stability of the demersal trawl fishery.
- Full Text:
- Date Issued: 1989
An eco-physiological investigation of fisheries-induced evolution: comparing the resilience of larvae from exploited and unexploited commercial reef fish populations to projected ocean acidification
- Authors: Muller, Cuen
- Date: 2022-04-08
- Subjects: Ocean acidification , Fishes Climatic factors , Fishes Physiology , Fishes Metabolism , Fishes Respiration , Fishes Larvae , Fishery management , Chrysoblephus laticeps (Red roman)
- Language: English
- Type: Doctoral thesis , text
- Identifier: http://hdl.handle.net/10962/232579 , vital:50004 , DOI 10.21504/10962/232579
- Description: It is now accepted that anthropogenic-induced climate change is resulting in unprecedented rates of change to marine environments. Marine organisms are being challenged by rapidly increasing temperatures, acidification, expansion of oxygen dead zones, and higher frequencies and magnitudes of extreme weather events. Exploited fish populations are also undergoing selective harvesting. Certain traits, such as large size, fast growth, and/or bold/active behaviours, are being actively targeted and removed from the population gene pool. This selective removal of individuals may compromise the capacity of fish populations to resist or recover from environmental disturbances and reduce their ability to adapt to a changing environment as many of these traits are heritable. As most marine fishes' embryonic and larval stages represent the period when individuals are most sensitive to environmental disturbances, they are a critical bottleneck to population persistence in the face of exploitation and climate change. This thesis aimed to quantify and compare the metabolic physiology, growth, and development of an exploited and endemic sparid, the roman seabream Chrysoblephus laticeps, during the early larval stages under 1) ocean acidification conditions expected by the year 2100 and 2) from populations experiencing dissimilar rates of exploitation. To quantify and compare the physiology of larvae, adult C. laticeps from an exploited population were captured and field-spawned. Fertilised eggs were placed into either control/present-day conditions (pH = 8.03, pCO2 ≈ 420 μatm) or high-pCO2/hypercapnic treatment conditions (pH = 7.63, pCO2 ≈ 1400 μatm). The metabolic physiology of individual larvae was determined using a novel rolling-regression technique on static respirometry data. Here, estimates of the minimum and maximum oxygen consumption rates (VO2) could be determined with high test-retest reliability. The very early developmental stages (yolk-sac stage) appeared resilient to high pCO2 conditions despite being exposed to treatment conditions throughout the embryonic stage. Preflexion larvae showed sensitivity to treatment conditions by exhibiting reduced metabolic and growth rates, consistent with metabolic depression, associated with environmental stress. However, by the onset of flexion, which coincides with gill development, acid-base regulation, and muscle differentiation, metabolic and growth rates of treatment larvae were significantly greater than that of controls. This suggests that acid-base regulation imposes a high cost to maintain internal pH homeostasis. Importantly, these elevated metabolic costs were likely mediated through increased feeding rates in experimental conditions where food was ad libitum. In natural conditions, where food availability may be varied, high pCO2 conditions could be associated with higher mortality rates. Based on evidence that protected/unexploited populations are more genetically diverse and are composed of individuals representing a greater range of metabolic phenotypes, offspring were collected from a protected population experiencing otherwise similar environmental conditions to the exploited population. Metabolic rates of control larvae were generally similar to those of the exploited population. However, minimum rates of VO2 were typically higher for larvae from the protected population at comparable life stages. Preflexion treatment larvae from the protected population did not appear to undergo a period of reduced metabolism or growth compared to their control counterparts. While metabolic rates at the onset of flexion were significantly higher for treatment larvae, this was not associated with growth differences. Growth over-compensation following periods of growth depression is often associated with deleterious effects, such as organ damage and body or developmental malformations. This suggests somewhat improved resilience to ocean acidification conditions. This thesis found evidence that larval C. laticeps are sensitive to ocean acidification conditions expected by 2100. When this stressor is combined with increasing thermal variability, changing current coastal regimes, and heterogeneous food availability, also expected to occur by 2100, ocean acidification may compromise the population persistence of this species. However, an energetics approach to stress-tolerance suggests that larvae from the protected population may inherently show greater resilience to climate change-related environmental stressors. Evidence that exploitation affects the resilience of fish larvae to climate change highlights the need for an evolutionary approach to fisheries management and the importance of spatial protection in maintaining larger and more resilient populations while providing the raw material essential for adaptation. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
- Full Text:
- Date Issued: 2022-04-08
An ecological study of territoriality in four Cichlid species resident on rocky shores near Monkey Bay, Lake Malawi
- Authors: Sharp, Bradley John
- Date: 1982
- Subjects: Cichlids -- Nyasa, Lake , Cichlids -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5340 , http://hdl.handle.net/10962/d1005927 , Cichlids -- Nyasa, Lake , Cichlids -- Behavior
- Description: This study centres on a diverse assemblage of epilithic algal grazing fish (17 cichlids and 2 cyprinids) found on the rocky shores near Monkey Bay, Lake Malawi. Diet overlap among these species is large, but competitive exclusion is apparently avoided by the species having different feeding structures, behaviour and distribution on the shore. In many respects the ecology and behaviour of the cichlid fishes inhabiting the rocky zones of Lake Malawi parallel those of coral reef fish. In both communities there are species which are highly territorial, resulting in resource subdivision and, in some cases, the development of algal gardens. As this behaviour has not been previously reported for cichlid species, this thesis describes the territoriality of the rock-dwelling cichlids of Monkey Bay, Lake Malawi, and poses three specific questions: 1. What is the function of territoriality? 2. How do the territorial species subdivide the space resource? 3. What prevents one species taking over all the available space? It is suggested that interspecific territoriality evolved in response to a shortage of food, and, at present, serves principally to defend an algal garden i.e. a food supply of high standing crop. The species studied are extremely site specific. The rocky shore is subdivided among the four species according to the rock configuration, size, algal mat composition and position on the shore, of the available sites. An experimental study of the space utilization of the two common territorial species, referred to as 'Pseudotropheus orange cheek' and 'Pseudotropheus aggressive', showed that suitable territory sites are in short supply and that these species are in competition for some sites. These results do not support those of Fryer (1959) who suggested that a superabundance of food enabled fish to coexist by sharing the same food resource. Indeed it now appears that a shortage of food may have been a major driving force during the recent evolution of the species studied.
- Full Text:
- Date Issued: 1982
An evaluation of sampling and statistical methods for long-term monitoring of subtidal reef fishes : a case study of Tsitsikamma National Park marine protected area
- Authors: Parker, Denham
- Date: 2016
- Subjects: Reef fishes -- South Africa -- Monitoring , Tsitsikamma National Park (South Africa)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5385 , http://hdl.handle.net/10962/d1019991
- Description: Tsitsikamma National Park (TNP) possesses the oldest (established 1954), and one of the largest (350 km2) ‘no-take’ marine protected areas (MPA) in South Africa. A long-term monitoring (LTM) programme to observe the subtidal reef fishes in the TNP MPA was established in 2007. To date, 243 angling replicates have been completed, and a total of 2,751 fish belonging to 41 different species have been caught and released. In an era of unprecedented global biodiversity loss, data that can be used to monitor ecosystems and gauge changes in biodiversity through time are essential. This thesis aims to improve the methodological and statistical processes currently available for LTM of subtidal reef fish by providing an evaluation of the TNP MPA LTM programme. Angling data revealed definitive spatial structuring, in the form of spatial autocorrelation, and a shift in viewing spatial dependency as a statistical obstacle to a source of ecological information created a new avenue of data inference. Species-specific distribution maps identified localized habitat as the main predictor variable for species abundance, emphasizing the need for accurate a priori bathymetric information for subtidal monitoring. ‘Random forest’ analyses confirmed spatial variables are more important than temporal variables in predicting species abundance. The effectiveness of Generalized Linear Mixed Models (GAMMs) to account for spatial autocorrelation was highlighted, and evidence that disregarding spatial dependencies in temporal analyses can produce erroneous results was illustrated in the case of dageraad (Chrysoblephus cristiceps). Correlograms indicated that the current sampling strategy produced spatially redundant data and the sampling unit size (150 m2) could be doubled to optimize sampling. Temporal analyses demonstrated that after 50 years of ‘no take’ protection the TNP MPA ichthyofauna exhibits a high level of stability. Species-specific size structure was also found to be highly stable. Dageraad was the only species to exhibit a definitive temporal trend in their size structure, which was attributed to recruitment variation and the possibility that large individuals may migrate out of the study area. The inadequacy of angling as a method for monitoring a broad spectrum of the fish species was highlighted, particularly due to its selectivity towards large predators. As a result, a new sampling technique known as Stereo Baited Remote Underwater Videos (stereo-BRUVs) was introduced to the LTM programme in 2013. Stereo-BRUVs enabled sampling of 2640 fish belonging to 52 different species, from 57 samples collected in less than two years. A comparison of the sampling methods concluded that, compared to angling, stereo-BRUVs provide a superior technique that can survey a significantly larger proportion of the ichthyofauna with minimal length-selectivity biases. In addition, stereo-BRUVs possess a higher statistical power to detect changes in population abundance. However, a potential bias in the form of ‘hyperstability’ in sites with unusually high fish densities was identified as a possible flaw when using stereo-BRUVs. In an attempt to provide a more rigorous method evaluation, simulation testing was employed to assess the ability of angling and stereo-BRUVs to accurately describe a decreasing population. The advantage of this approach is that the simulated population abundances are known, so that each sampling method can be tested in terms of how well it tracks known abundance trends. The study established that stereo- BRUVs provided more accurate data when describing a distinct population decline of roman (Chrysoblephus laticeps) over 10- and 20-year periods. In addition, spawner-biomass was found to be a more accurate population estimate than relative abundance estimates (CPUE and MaxN) due to the inclusion of population size structure information, highlighting the importance of length-frequency data. The study illustrated that an evaluation framework that utilizes simulation testing has the potential to optimize LTM sampling procedures by addressing a number of methodological questions. This includes developing a procedure that aligns data collected from different sampling methods by applying correction factors, thus ensuring LTM programmes are able to adapt sampling strategies without losing data continuity.
- Full Text:
- Date Issued: 2016
An investigation into the captive spawning, egg characteristics and egg quality of the mud crab (Scylla serrata) in South Africa
- Authors: Churchill, Giles John
- Date: 2004
- Subjects: Scylla serrata , Crabs -- South Africa , Scylla serrata -- South Africa , Crabs -- Eggs -- Incubation , Crabs -- Spawning
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5376 , http://hdl.handle.net/10962/d1015963
- Description: The source of a reliable supply of seed is one of the most important factors determining the success of aquaculture. At present mud crab culture is reliant on wild caught juveniles, which limits the expansion of mud crab farming globally. This, coupled with the paucity of knowledge of the spawning and egg characteristics of mud crabs, prompted the investigation into the captive spawning, incubation and egg quality of Scylla serrata in South Africa. A total of 112 mature females were caught from three estuaries in northern KwaZulu Natal and acclimated to captive conditions. Mature females were present in the estuaries throughout the year and ranged from 90 to 200 mm carapace width. Except for 40 crabs all the females spawned in captivity. On average spawning took place 38 ± 23 days after capture but was not dependent on crab size. Fecundity was significantly correlated to crab size (p = 0.026), with larger females producing more eggs. The average fecundity per batch was 5.79 ± 2.07 million eggs. Hatch success rate for all egg batches was high averaging 84 ± 6 %. Egg dropping occurred in all egg batches during incubation. On average 6.5 % of the egg mass was dropped during incubation. At the average temperature of 27⁰C eggs in the incubation system hatched within 292 ± 12 hours after extrusion. In-vitro incubation of eggs proved to be an ineffective means of incubating Scylla serrata eggs with a hatch success rate of only 25 ± 5 %. Egg quality was assessed both directly, using variables such as hatch success rate and hatch synchronicity and retrospectively by using stress tests and comparing survival of larvae from different coloured egg batches. Lipid class composition and fatty acid methyl ester content for 28 batches of eggs and 16 batches of larvae were analyzed. The biochemical composition of the egg was correlated to survival of larvae in the stress tests to ascertain if the lipid content of the eggs determines their quality. Stress tests were used to retrospectively assess egg quality. Four stressors were administered to newly hatched larvae and the LD50 values recorded. An average LD50 of 64 hours was recorded for the starvation tests, 40% for the salinity tests, 37 ppm for the formalin tests and 39.7 mg/l NH3 for the ammonia stress tests was recorded. Egg colour ranged from pale yellow to orange-red. Egg colour was not influenced by female size or the time the females spent in captivity prior to spawning. Egg colour can therefore not be used as an indicator of quality. The lipid profiles of newly extruded eggs had no effect on hatch synchronicity or hatch success rate. However, the stress tests identified female size (p ≤ 0.02), DHA content of the egg (p ≤ 0.02), Σ omega-3 fatty acids of eggs (p ≤ 0.02) and EPA content of eggs (p ≤ 0.007) as possible determinants of egg quality. Larger crabs tended to produce poorer quality eggs. Egg quality also decreased as the amount of DHA, EPA and the Σ omega-3 fatty acids decreased in the eggs. To summarize, the results of this study indicated that the following parameters affect egg quality - crab size, DHA, EPA and Σ omega-3 fatty acid content of eggs.
- Full Text:
- Date Issued: 2004
An investigation into the dietary requirements of Oreochromis Mossambicus fry and the formulation and preparation of a dry food for use in aquaculture
- Authors: Thorpe, Peter Stuart
- Date: 1989
- Subjects: Cichlids , Tilapia -- Nutrition , Aquaculture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5184 , http://hdl.handle.net/10962/d1001960 , Cichlids , Tilapia -- Nutrition , Aquaculture
- Description: The need for developing a dry feed which satisfied the nutrient requirements of Oreochromis mossambicus fry was identified. The spawning and grading techniques which resulted in a higher fecundity and ensured uniformity within and between samples of fry are discussed. Preparation techniques were developed which met the physical requirements of fry feeds. An analysis of the flesh and yolk sac fry for amino acid composition was undertaken. The initial test diet was based on these results, as well as on the natural feeding ecology of the species. Feeding trials were undertaken and growth responses monitored to determine the optimum levels of the various dietary components. A feed was developed which gave superior growth to that obtained with natural food organisms. This feed consisted of Torula yeast (47%), Weider Super Protein (44.39%), Vitamin supplement (0.45% - multivitamin), additional vitamin C supplement (0.16%), Spirulina (5%), and methionine supplement (3%). An optimum particle size range for O. mossambicus fry (between 5 & 25mm) was established at 125-200um. The fry should be fed the following feed ratios depending on age: 30.4% body weight/day up to day 5, 30.6% body weight/day up to day 10 and 25.1% body weight/day up to day 15. An optimum feeding frequency of 8/10hr day was recommended. A feed conversion ratio of 1.24:1 and a protein efficiency ratio of 0.682:1 was obtained. Digestable energy of the feed was determined at 16.1 kj/g feed. The established dry feed is suitable for use in commercial hatcheries, and as a formulation for further research on the intensive rearing of O. mossambicus fry.
- Full Text:
- Date Issued: 1989