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.
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- Date Issued: 2012
Movement bahaviour of three South African inshore sparid species in rocky intertidal and shallow subtidal habitats
- Authors: Watt-Pringle, Peter Andrew
- Date: 2009
- Subjects: Sparidae -- South Africa , Diplodus , Sparodon Durbanensis , Fisheries -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5302 , http://hdl.handle.net/10962/d1005147 , Sparidae -- South Africa , Diplodus , Sparodon Durbanensis , Fisheries -- South Africa
- Description: This study investigated the movement behaviour of three inshore South African sparids – blacktail (Diplodus sargus capensis), zebra (Diplodus cervinus hottentotus) and white musselcracker (Sparodon durbanensis), popular inshore fishery species caught in appreciable numbers along much of the South African coast. The first study component examined movements of juveniles in a rocky intertidal nursery area at Schoenmakerskop near Port Elizabeth. Juveniles in a single gully were tagged with Visible Implant Elastomer (VIE) and resighted at the study site on snorkelling gear over a seven-month period. Tagged zebra and musselcracker displayed limited movement between potential low tide refuges, being observed repeatedly in the same gully over the full duration of the study. However, blacktail displayed greater movements and were seen infrequently in the later period of the study, probably having undergone an ontogenetic habitat shift to subtidal areas. There was evidence that blacktail maintain use of their intertidal nursery over high tide, during which the other two species moved into shallower areas adjacent to their low tide refuge. The results of three national tagging programs were analysed to determine the movement patterns of adolescent and adult fishes. The coast-wide ORI-WWF National Voluntary Tagging Program and two dedicated research programs in marine protected areas (MPAs) at De Hoop MPA and Tsitsikamma National Park (TNP) recorded few large-scale movements of tagged adult blacktail, zebra and juvenile musselcracker. High spatial-resolution data from the TNP suggested movements were usually on scales far smaller than one km. Together with long periods at liberty for many recaptured individuals, this suggests these fishes are longterm residents of small home range areas. However, tagged musselcracker over 600 mm forklength (adults) were observed to make large-scale movements, including some in excess of 800 km from Eastern Cape to KwaZulu-Natal waters. Predominantly eastward movements of adults recaptured during the spawning season indicate seasonal spawning migrations that occur in different regions of the coast. These enable the use of prevailing oceanographic currents to disperse eggs and larvae to suitable rocky nursery habitat. The third component of this study made use of high-resolution data on the temporal and spatial distribution of catches by scientific angling in the TNP to examine the daily activity patterns of the study species in relation to diel and tidal cycles, and habitat use. Blacktail capture probability was correlated with the diurnal light cycle, with peaks close to twilight suggesting elevated crepuscular foraging activity. Catches of blacktail, zebra and small musselcracker were correlated with the tidal cycle, foraging peaking over high tide periods. All three species used shallow inshore habitats extensively for foraging, blacktail showing a preference for sandy areas, while zebra and small musselcracker preferred shallow reef. Capture probability of larger musselcracker, however, was unrelated to habitat, possibly evidence of increasing area and habitat use with an ontogenetic change in diet. The lifetime movement patterns of these three species are discussed in relation to conservation measures and their management in South African fisheries. Restricted movement throughout post-settlement life for blacktail and zebra, and during the juvenile phase for musselcracker, makes local populations vulnerable to overexploitation. At present, MPAs probably play an important role in protecting local blacktail and zebra populations from overexploitation, and limited post-settlement movements mean the degree of larval dispersal between protected and adjacent areas will likely determine the effectiveness of MPAs in enhancing fisheries for these species. By contrast, MPAs likely provide recruits to fisheries for musselcracker during ontogenetic movements and dispersal from MPAs during spawning migrations. MPAs only offer partial protection to adult musselcracker populations in the spawning season, but this could nevertheless be significant under high levels of exploitation.
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- Date Issued: 2009
The feasibility of stock enhancement as a management tool for dusky kob (Argyrosomus japonicus) in South Africa
- Authors: Palmer, Ryan Michael
- Date: 2008
- Subjects: Argyrosomus -- South Africa , Argyrosomus -- Genetics , Fishery management -- South Africa , Fish stocking -- South Africa , Fisheries -- South Africa , Marine ecology -- South Africa , Fish culture -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5281 , http://hdl.handle.net/10962/d1005125 , Argyrosomus -- South Africa , Argyrosomus -- Genetics , Fishery management -- South Africa , Fish stocking -- South Africa , Fisheries -- South Africa , Marine ecology -- South Africa , Fish culture -- South Africa
- Description: The dusky kob, Argyrosomus japonicus, is a popular South African “line fish” whose stocks have dwindled to dangerously low levels of between 1% and 4.5% of pristine spawner biomass per recruit. A. japonicus stocks are currently managed by means of minimum size restrictions and daily bag limits, and as a result of the inability of these measures to facilitate the recovery of the species over a realistic time frame, the need for an alternative management plan has become apparent. Given the status of the stock and management regime, stock enhancement appears to be an appropriate option to be investigated. This study evaluates the feasibility of stock enhancement as a possible management tool to assist with the recovery of this important South African linefish species. By evaluating the genetic and ecological implications related to stock enhancement, identifying a suitable tagging method for post-release monitoring, and evaluating the economic feasibility of such a programme, any fatal flaws would become immediately apparent. This coupled with the required framework for the development of a management plan for stock enhancement of A. japonicus provides direction further research and actions required in order to utilise stock enhancement as a management tool. Due to the nature of stock enhancement, there are several ecological and genetic issues that arise from such a programme. These issues were reviewed and the issues that were relevant to stock enhancement of A. japonicus identified. Ecological concerns that arose included those of competition, disease and seed quality, while genetic issues were concerned mainly in the possible loss of genetic variability and consequent reduction in fitness of the stock. Fortunately the technology exists to evaluate the effects and likelihood of these problems occurring as well as to minimise the likelihood of them occurring. By taking a scientific approach to stock enhancement, hatchery management, and release strategies can be manipulated in such a way as to minimise any negative effects that may be caused. Both ecological and genetic effects of stocking indicate a need for post-release monitoring of stock enhancement programmes. Stock enhancement requires a post-release monitoring programme, which in turn relies on an ability to distinguish between hatchery reared and wild fish. A study was conducted to evaluate the suitability of coded wire tags (CWT), visual implant fluorescent elastomers (VIFE), and oxytetracycline (OTC) as a means of distinguishing between hatchery reared and wild A. japonicus, for the purpose of a post-release monitoring programme. OTC appeared to be the most suitable as it produced 100% retention over a five month period compared to 62% and 61% for VIFE and CWT respectively. OTC is therefore suggested as a tagging method for the purpose of post-release monitoring of the stock enhancement of A. japonicus. To evaluate a possible funding option for stock enhancement of A. japonicus in South Africa, a willingness-to-pay survey, based on a “user pays” approach using recreational fishing permits as a vehicle for payment, included 102 recreational anglers in the Plettenberg Bay area. The survey showed that generally anglers were willing to pay more than the current amount for the recreational fishing permit. This promising result, coupled with the fact that there are approximately 450 000 recreational anglers leads to the belief that there is potential for a substantial increase in the funds generated for the Marine Living Resources Fund through recreational anglers. Stock enhancement should not be ruled out on the basis of economic feasibility yet as there is potential for it to be sustained by the users of the resource. An A. japonicus juvenile production costing model was created taking into account setup and running costs of a hatchery for A. japonicus, based on known parameters from existing facilities, and adjusting them to meet the requirements of a stock enhancement facility. Estimates varied according to the number and size of fish for release (values which can only be decided upon after further research), with setup estimated to be between R 10 000 000 and R 30 000 000 and annual running costs between R 2 400 000 and R 6 700 000 annually. These figures were dependant on the size and number of fish being produced, with production ranging between 100 000 and 5 000 000 fish of between 50 mm and 150 mm, and a broodstock of 150 individuals. Given the need for alternative management of A. japonicus in South Africa and the lack of evidence to suggest that it is an unfeasible option, this project has found no reason why further investigation into the use of stock enhancement for the management of A. japonicus should not proceed further provided the fishery is shown to be recruit limited. The technology and ability to overcome possible ecological and genetic problems exists, a suitable means of tagging for post-release monitoring exists, as does a realistic funding option. There is a substantial amount of research that must be done prior to stocking, for which a base framework is provided.
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- Date Issued: 2008
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.
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- Date Issued: 2002
Environmental influences on the daytime vertical distribution of Cape hakes and implications for demersal trawl estimates of hake abundance off the west coast of South Africa
- Authors: Maree, R C
- Date: 2000
- Subjects: Hake , Fisheries -- Environmental aspects -- South Africa , Fisheries -- South Africa , Trawls and trawling
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5278 , http://hdl.handle.net/10962/d1005122
- Description: The demersal fishery off the west coast of South Africa experiences decreased catches per unit effort of hake, Merluccius capensis and M. paradoxus, following the onset of strong south easterly winds. Research has demonstrated that, during daylight hours, Cape hakes migrate vertically in the water column in response to strong south easterly winds, decreasing their availability to the bottom trawl. Hydroacoustic, trawl and environmental data were collected off the West Coast during both calm and wind-swept periods in an attempt to understand the forces that initiate this behaviour, its spatial variability and the implications for demersal trawl estimates of abundance. Near-bottom currents appear to be the primary factor influencing the vertical distribution of the demersal fish community, of which hake constitutes a large proportion, during daylight hours. Correlation between wind and near-bottom currents suggest that the poleward component of the currents increase in velocity within eight hours following the onset of south easterly winds. The fish avoid boundary layers where currents change direction and speed dramatically, and seem to concentrate in waters with relatively stable current regimes. This result questions the assumption of CPUE-based assessment models that hake availability to the bottom trawl is constant or varies randomly. The incorporation of acoustic assessment techniques to demersal surveys has potential, but may be most valuable by supplementing swept-area estimates of abundance, since the sampling efficiency of these methods varies within the water column. The incorporation of wind indices and gear performance data to Cape hake assessment models have been identified as useful considerations for the future.
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- Date Issued: 2000
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.
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- Date Issued: 1989