The St. Lucia Estuary, Africa’s largest estuarine lake, is currently experiencing an unprecedented crisis related to freshwater deprivation. This has resulted in a reversed salinity gradient and drastically reduced water levels. These harsh environmental conditions, combined with the limited connection with the open ocean have lead to a loss of biodiversity in the system. The dominant zooplankton taxa include the copepods Pseudodiaptomus stuhlmanni and Acartia natalensis and the mysid Mesopodopsis africana. In March 2007, the closed-mouth state was briefly interrupted by an open-mouth phase, induced by a unique combination of extreme climatic events. With the incoming seawater, previously excluded marine taxa re-entered the system, increasing its diversity significantly. Salinity and temperature have been referred to as driving forces in aquatic ecosystems. The tolerance limits of the key mysid species were, therefore, investigated. Results showed that M. africana has some of the highest recorded upper salinity and temperature tolerances for a mysid. Because of their high biomass, mysids have the potential to affect microalgal standing stocks. Their grazing dynamics (in relation to autotrophic food availability) were investigated in two contrasting environments within the estuary. Ingestion rates and subsequently population grazing impacts on the total microalgal standing stocks were higher at the Mouth than at Charters Creek. This was attributed to the harsh environmental conditions in the latter region. Despite the lower ingestion rates exhibited here, these mysids seem capable of meeting their energetic requirements from a microalgal diet alone. Stable isotope data, though, show that they also utilise a heterotrophic diet. Results of the mixed model SIAR v 4 revealed the contribution of the different carbon sources to the diet of M. africana. Most unique was this mysid’s ability to modify its diet on both short temporal and spatial scales. Resource utilization between the dominant taxa was also compared. All three taxa appear to be opportunistic feeders, capable of incorporating a number of food items in their diet. Between food partitioning, predator avoidance strategies, and their common ability to survive in highly dynamic environments, these species are capable of co-existing, and together contribute to the overall resilience so far shown by the system. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2011.

During long-term studies of dolphins, the number of individuals in the population being studied are constantly monitored using the technique of photo-identification. This constant monitoring makes use of different researchers over time. Therefore, measurement of photographic quality and individual distinctiveness for photo-identification analyses was incorporated in this dissertation to provide an additional data set for analysis. Researchers with differing levels of experiences did not obtain the same information from the same photograph and were unable to reliably quantify variables of photo quality and individual distinctiveness, but experienced researchers were found to be more adept than inexperienced researchers in counting notches on the dorsal fin of bottlenose dolphins. These results highlight the necessity for researchers to be trained in photo-identification techniques prior to carrying out their study. This study theodolite tracked dolphins off Durban from June 2004 to Feb 2005 to assess habitat utilization of bottlenose dolphins (Tursiops aduncus) in the Durban bay region. Dolphins were seen in all months surveyed and throughout the survey area. Temporal distribution of dolphins was skewed with 91% of dolphins seen before midday and 98% of sightings observed in water depths less than 30m. Six behavioural categories were recorded, including: social, fast travel, slow travel, feeding, resting and milling. The most dominant behaviour exhibited by dolphins was slow travel (46%) followed by feeding (27%). Resting was not observed at all. Of the feeding behaviour 88% occurred in the southern end of the bay whereas other behaviours occurred randomly throughout the survey area. Additional theodolite tracks were conducted during experimental boat approaches (before, during and after boat approaches) to determine potential short-term reactions of dolphins to dolphin watching boats. Two speeds of approach (slow ~ < 5 km/hr and fast ~ > 40 km/hr) and two distances of approach (20m and 80 m) were tested. The bottlenose dolphin groups did not change their behaviour in response to boat approaches during any of the periods of experimentation. Short-term changes in group speed, group size and spread were not statistically significant. Dolphin groups continued with their ‘normal’ behaviour and spent the same amount of time in the bay when compared to their distribution and behaviour in the absence of the experimental boat. These findings indicate that the experimental boat did not affect the behaviour of dolphins at either a slow or fast approach and even at a close distance. This is interpreted as being as a result of habituation of the dolphins due to their residency in a busy port. This work is crucial in developing guidelines for the development of a sustainable dolphin watching industry off Durban. / Thesis (M.Sc.) - University of KwaZulu-Natal, Durban, 2008.

The family Serranidae is a diverse group of fishes, of which the genus Epinephelus (rockcods or groupers) is the largest. Serranids are commonly caught in reef fisheries in tropical and warm-temperate latitudes, and are targeted because of their tasty flesh and high value. In South Africa, epinepheline serranids mainly occur in hook and line fisheries in the province of KwaZulu-Natal. Mostserranids are caught by the boat-based (skiboat) fishery, and the commonestspecies are the endemic catface rockcod (Epinephelus andersoni), thehalfmoon rockcod (E. rivulatus), the yellowbelly rockcod (E. marginatus) and the endemic white-edge rockcod (E. albomarginatus). Although serranids contribute about ten percent to catches by the commercial and recreational skiboat sectors in KwaZulu-Natal, representing an estimated total catch of around 200 mt per year, little is known about these fishes in South Africa. From the mid-1980s to the mid-1990s, the mean lengths of E. marginatus and E. albomarginatus in the region declined significantly. Over this period, lengths of E. andersoni remained the same, while those of E. rivulatus increased. Lengths of E. marginatus and E. albomarginatus from Mozambique, where fishing effort was low at the time of sampling, were significantly greater than in KwaZulu-Natal. Monthly biological data were mostly collected from commercial skiboat catches on the northern and southern coast of KwaZulu-Natal. Additional data for E. marginatus and E. albomarginatus were also collected irregularly from commercial catches made in Mozambique. Unless the fish had ripe ovaries, all gonads had to be sectioned to establish sex and stage. Histology revealed that all gonads had a female-like appearance, with lamellae and a central lumen. In E. andersoni, there was a complete overlap of male and female length frequencies, and their meanlengths were not significantly different. Some males and inactive bisexuals were both smaller and younger than the female size and age at first maturity. Together with the occurrence of mature bisexual fish (transitionals), these observations indicate that males are derived from immature or mature females, hence this species is a diandric protogynous hermaphrodite. The other three species exhibit typical signs of monandric protogynous hermaphroditism. Males and females had significantly different mean lengths, and age and length frequencies by sex werebimodal. Transitional individuals were recorded in E. rivulatus. E. andersoni and E. rivulatus matured at small sizes and early ages relative to E. marginatus and E. albomarginatus. Ripe ovaries were much larger than ripe testes in all four species. E. andersoni, E. marginatus and E. albomarginatus spawned in spring and summer, while E. rivulatus spawned in winter and spring. There were no indications of spawning in E. andersoni in the southern sampling region, and few ripe individuals of E. albomarginatus were encountered in KwaZulu-Natal samples. Size at maturity of this species was much smaller in Mozambique samples. Large, reproductively inactive individuals of E. andersoni were frequently observed in the spawning season. The lack of reproductive activity of E. andersoni and E. albomarginatus in KwaZulu-Natal may be because this area represents thesouthernmost limit of the distribution of these species. Ageing of the four species was undertaken using sectioned otoliths. Age validation was undertaken by a combination of tetracycline marking in captive fishes, and analysis of the marginal zone in otoliths. All four species are relatively long-lived, although estimates of maximum age may be under-estimated because of long-term harvesting. In all four species, fish from the southern sampling region were larger than fish from the northern region at the same age. Only in the case of E. rivulatus were these significant enough to warrant the fitting of two growth curves to the northern and southern populations. Males in all four species tended to be larger than females at the same age, suggesting that there may be a growth spurt following sex change, or that faster-growing females changed sex. A logistic growth curve was fitted to the age-length data for E. andersoni, while von Bertalanffy curves produced the best fit for the other species. Based on the rates at which L∞ attained in these four species, E. marginatus and E. albomarginatus are slow-growing species, while E. andersoni and, particularly, E. rivulatus arefaster growing. Rates of total mortality and natural mortality were estimated using length-converted catch curves and the Rikhter and Efanov equation, respectively. Stock assessments undertaken by yield per recruit and spawner biomass per recruit analyses indicate that E. andersoni in KwaZulu-Natal is currently optimally exploited, while E. rivulatus is lightly exploited. Both E. marginatus and E. albomarginatus are over-exploited. The potential problems in applying standard per recruit models to species with complex life histories are discussed. Support for the reduced stock status of the latter two species is provided by the observed changes in lengths of these species over a ten-year period, and their relatively small size in KwaZulu-Natal compared to the lightly-fished Mozambique populations. Local fishers in KwaZulu-Natal have also reported declines in sizes and reduced catches of these two species.The life history styles and other features of the four species are compared and discussed with reference to the resilience of these species to harvesting. Two of the species (E. marginatus and E. albomarginatus) are monandric protogynous hermaphrodites, which grow slowly, mature late and attain large sizes. E.andersoni and E. rivulatus grow faster, mature earlier and are smaller species. The normally deleterious effects of fishing on sex-changing species are not manifested in these two species, possibly because E. rivulatus is so small, that males are not selectively removed. In contrast, E. andersoni is a diandric protogynous hermaphrodite, and hence, does not rely on sex-change as a source of males. The current management methods for serranids in KwaZulu-Natal are presented, and suggestions for future approaches are discussed. / Thesis (Ph.D.)-University of Natal, Durban, 2000.

This study primarily attempts to develop models to estimate population dynamic parameters from mark-recapture data. Model implementation is illustrated using data collected from the South African Pomatomus saltatrix fishery . The models developed allow for the estimation of mortality, survival and migration rates in exploited fish stocks. A growth model is also developed which simultaneously estimates growth parameters as well as validates the hard structure banding using age-length and markrecapture data. There are number of advantages to these models . Given appropriate datasets the mark-recapture models developed in this study can be applied to others species of interest. The models can be modified easily e.g. the growth model can incorporate growth functions other than the von BertalanfIy model. The models can be programmed into a spreadsheet which facilitates the estimation of parameter variances using likelihood profile or bootstrapping methods and allows the testing of model assumptions based on simulations. A general mortality model is developed and is illustrated with mark-recapture data from the P. saltatrix fishery. The model provides an estimate of the average fishing mortality for the Cape and KwaZulu-Natal and is then extended to include movement between the Cape and KwaZulu-Natal. It utilises mark-recapture data from the Sedgwick's-ORI Tagging Programme as well as effort and catch data from the National Marine Linefish System (NMLS). Estimates of annual fishing mortality rates in KwaZulu-Natal are derived from the model which takes into account immigration of P. saltatrix into KwaZulu-Natal from the Cape as well as emigration from KwaZulu-Natal to other areas including the Cape. The average fishing mortality rate was estimated to be 0.27 year" between 1984 and 1993 in the Cape and KwaZulu-Natal combined. This is likely to be underestimated because of non-reporting of tags, shedding of tags and tag-induced mortality. The model is shown to be robust for estimating the average fishing mortality rate and exploitation rate only when annual variability in fishing mortality is small during the study period. The second model to quantify migration into and out of KwaZulu-Natal waters suggested that the whole adult Cape stock migrates into KwaZulu-Natal during winter. Further, this whole stock is available to fishing in KwaZulu-Natal although there is probably large exchange between inshore and offshore areas and, in the latter zone, P. saltatrix is inaccessible to shore-based fishing. Large fishing mortality rates for the years 1987 to 1993 were estimated in KwaZulu-Natal. These large fishing mortality rates may prevent the return migration of P. saltatrix to the Cape and the model predicts that possibly less than 4% actually return to the Cape. An age and growth study based on otolith readings was also undertaken. Validation of the growth banding as annual was confirmed by developing a model that estimated growth parameters using age-length data and simultaneously estimating times-at liberty of tagged individuals based on arbitrarily chosen band deposition periodicities. It is shown that the assumption of annual banding led to the best prediction of periods of liberty of tagged individuals with small coefficients of variations in the parameter estimates. However, since only a few tagged animals were used in the analysis more research is needed to verify the robustness of this technique for use on other fish. The growth of P. saltatrix in the present study was found to be faster than that of a previous study in South Africa. A modified delay-difference model was developed to estimate relative biomass and relative catch based on observed mean body weights and effort indices. For the period 1956 to 1972 the model predicts that there was a decline in P. saltatrix abundance with corresponding declines in mean weight of the catch. Although during this period there was a general decline in fishing mortality, the fishing mortality was sufficiently high for growth overfishing to occur. It was found that during the 17 year period there was a 44% reduction in biomass which is similar to an estimate in another study. Catch during the period was annually variable but generally declined with time especially in the later years. The decline in average weight harvested and the variable but lower catches during this period are consistent with observations by fishers . An evaluation of the present closed season for P. saltatrix in conserving egg production was performed. It showed that better conservation of egg production is possible by shifting the present closed season (September to November) to extend over the October to December season but this may adversely affect the tourism industry in KwaZulu-Natal. Shortening the present closed season by one month (September) does not affect egg production but increases present yield levels. This study suggests that the closed season may not be useful in terms of reducing the fishing mortality rate on P. saltatrix as fishers may be encouraged to fish harder in the open season to make up for the lost yields of the closed season. Moreover, lengthy closed seasons may also increase fishing mortality because fishers tend to fish harder in the months open to fishing. Assuming no large annual recruitment variations the P. saltatrix stock is presently optimally exploited as current fishing mortality rates are just below the MSY or optimum yield levels. / Thesis (Ph.D.)-University of Natal, 1996.

Heavy metal contamination of mangroves is of critical concern due to its accumulative and adverse effects in aquatic ecosystems. This study was undertaken to investigate the effects of mercury (Hg ), lead (Pb ), copper (Cu ) and zinc (Zn ) on plant responses, specifically growth and productivity, in Avicennia marina (Forssk.) Vierh. A. marina plants were grown for twelve months in pots contaminated with Hg +, Pb +, Cu2+ and Zn2+ at concentrations of 0, 40, 80, 120 and 160 ppm (1 ppm = 1 (agmf1). Accumulation and distribution of the heavy metals in shoot and root tissues were determined using atomic absorption spectroscopy (Perkin-Elmer Model 303) while secretion of the heavy metals from leaves was studied using scanning electron microscopy and energy dispersive X-ray microanalysis. I hypothesized that heavy metals have deleterious effects on plant growth and that they are absorbed by roots and secreted from salt glands present on the leaves. SEM X-ray microanalyses confirmed secretion of Cu + and Zn + ions as well as salt (NaCl) from glandular structures on both the adaxial and abaxial surfaces of leaves; however Hg2+ and Pb2+ were not detected in the secretion. Ion concentrations were significantly higher in plant roots than in shoots, particularly at 160 ligml"1 for all heavy metals. In addition, toxic levels of Hg and Pb were detected in the shoot tissue; however, Cu2+ and Zn2+ were within the normal ion concentration in the shoots. Plant height, number of leaves, biomass accumulation and chlorophyll content were significantly lower at 160 ugml" than the control values for all heavy metals. Carbon dioxide exchange, transpiration and leaf conductance generally decreased with increasing metal concentration. CO2 exchange at a concentration of 160 (J-gmf1 was significantly lower than the control for all metals. CO2 exchange at 160 ugml"1 for Hg2+, Pb2+, Cu2+ and Zn were 49.6 %, 55 %, 47.6 % and 63.6 % respectively lower than the control values. Photosystem II (PS II) quantum yield, photochemical efficiency of PSII (Fv/Fm) and electron transport rate (ETR) through PS II generally decreased with increasing concentration for all heavy metals. XV This study has shown that A. marina experiences dose-dependent stress responses to Cu2+, Zn2+, Hg2+ and Pb2+ in shoot and root tissue at a concentration of 160 lagmi"1, evidenced by decreases in growth and photosynthetic performance. The results also ~)A- "7-1- 9-1- "J-\-indicate that CuZT, Znz\ HgZT and PbZT are taken up by roots and transported to shoots. In addition, only Cu and Zn are secreted via the glands while Hg and Pb accumulate within the shoots. / Thesis (M.Sc.)-University of KwaZulu-Natal, 2008.

In order to assess and improve their management, a survey of the commercial and recreational marine linefisheries in Richards Bay was conducted from June 2002 to July 2004. The ultimate aim of this survey was to develop a sound management framework for the commercial and recreational marine Iinefisheries in Richards Bay. Skippers on both commercial and recreational skiboats were all white males in their mid-40s whom were fairly experienced. There were twice as many crew on commercial than recreational skiboats. The crew on commercial skiboats were mostly black males while on recreational skiboats, crew were mostly white males. Slinger was the most important species caught by commercial fishermen off Richards Bay, accounting for the vast majority of catches by number and mass. The total contribution by sparids to commercial catches amounts to approximately 93 % by number and 81 % by mass. Recreational catches comprised a greater variety of species (73 recreational species versus 54 commercial species), signifying a less focussed targeting approach compared to commercial skiboat fishermen. Although slinger also numerically dominated recreational linefish catches, catface rockcod were most important by mass. Although there were five times more recreational outings during the study, total catch by commercial skiboat fishermen was five times higher than that of recreational fishermen. This was expected, as the average duration of each commercial outing is more than twice that of recreational outings and the crew numbers are higher. Commercial skiboat fishermen in Richards Bay are also more effective, as the average number of fish caught per man per hour on commercial skiboats was approximately 4 times greater than that on recreational skiboats. Total estimated catch for the commercial sector was 28 tonnes and 173 tonnes for the recreational sector. Comparison of data between this survey and commercial data available on NMLS showed similar species composition, although the dominance of slinger was 20 % higher in this survey compared to data. Similarly, within the recreational sector, there was a close similarity in catch composition between this survey and that catch inspections. The profit (excluding the costs of fixed assets) that each commercial fisherman earns per month was estimated to be in the region ofR8 500. However, if one examines the value of the commercial linefishery as a whole, it appears that there is a net loss of R90 000 per year, excluding the costs of fixed assets. The discrepancy stems from the disparity between the recorded number of launches and the number reported by skippers. Most of the commercially caught fish are not sold in Richards Bay, but are exported to Gauteng. The average monthly Iinefish catch by commercial fishermen was less than half the average estimated consumption of Iinefish in Richards Bay, and the difference appears to be made up from recreational catches, with many consumers indicating that they either caught their own fish or were given it. Knowledge of and compliance with fishing regulations by commercial and recreational skiboat fishermen in Richards Bay was reasonably good. The main recommendations emanating from this study include continuous monitoring of the Richards Bay commercial and recreational line fishery in order to determine the efficacy of the new regulations, the development of area-based commercial linefishing permits and the possible introduction of restrictions on the sale of fish outside of the Richards Bay area. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2005.

Coastal communities along the east African coastline rely on coral reefs and their associated resources for food security and income. However, increases in the frequency and severity of episodes of coral bleaching have resulted in mass coral moralities in many locations around the world including the western Indian Ocean (WIO). Reef corals obligately host dinoflagellate algal symbionts of the genus Symbiodinium. Coral bleaching is caused by the loss of these symbionts from the host, resulting from a variety of stresses, the major ones being increased seawater temperature and irradiance. The Symbiodinum genus is diverse and the distribution of symbionts is influenced by the host biology, external light environment and geographic location. Ten distinct clades of Symbiodinium have been identified. Although the Caribbean and Great Barrier Reef have been studied intensively with respect to Symbiodinium diversity in many locations in the WIO Symbiodinium diversity is unknown. The aim of this study was to determine diversity, distribution and prevalence of Symbiodinium types in corals along the east African coastline. The Symbiodinium ssrDNA region was analysed using restriction fragment length polymorphism (RFLP) in order to assess the cladal diversity of Symbiodinium. The results showed all samples analysed to belong to clade C. To gain more insight into Symbiodinium genetic diversity, the ITS region was employed to assess Symbiodinium diversity at the subcladal level. Twenty ITS types were identified. The most prevalent type was found to be subclade C1. No phylogeographic structuring was found amongst the symbiont types, however, specificity of symbiont types to coral hosts was demonstrated indicating potential susceptibility to perturbations such as increased seawater temperature. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2007.

The Little Lagoon is a shallow sandflat habitat situated in Durban Bay, which has been earmarked for removal, as part of the port expansion. In order to prevent the possible loss of such a significant habitat, it was proposed that this habitat be re-created elsewhere in the Bay. The aims of this project were therefore to provide a detailed assessment of the macrobenthic habitat of the Little Lagoon, and to identify the major determinants of the community structure. The ultimate goal was to provide essential background information to assess the success of the recreation of the Little Lagoon. Apart from seasonal changes in water temperature, no ecologically significant temporal fluctuations in the physical environment of the Little Lagoon were detected. This was directly translated into an extremely stable macrobenthic community, in which negligible seasonal changes to its composition were recorded. The polychaetes Prionospio sexoculata, Glycera sp, the isopod Leptanthura laevigata and cumaceans dominated the community during every sampling season. From a spatial perspective, particle sizes and organic contents of surficial sediments were the major determinants of macrobenthic community structure. Densities of macrofauna were three to five times higher in organically rich sediments, and were dominated by surface and sub-surface deposit feeders such as the tanaid Apseudes digitalis and cirratulid polychaetes. In organically poor sediments, burrowing infauna such as Prionospio sexoculata and Glycera sp. dominated. Significantly though, biological interactions, specifically bioturbation by the sandprawn Callianassa kraussi, was an important determinant of community structure in the Little Lagoon. Two zones of high and low abundance of C. kraussi were recorded in the Little Lagoon. Abundance, species richness and diversity of macrofauna were significantly lower in the zone of high C. kraussi abundance. These parameters were significantly and negatively influenced by the abundance of C. kraussi, indicating that C. kraussi may act as a disturbance organism. Surface dwelling macrofauna were recorded in the zone of low C. kraussi abundance, but not in the zone of high C. kraussi abundance. It appeared that the bioturbative activity of C. kraussi of expelling sediment from burrows to the sediment surface resulted in the exclusion surface dwelling fauna, and played a major role in structuring the Little Lagoon macrobenthic community. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

The purpose of this study was to evaluate the current management effectiveness of the KwaZulu-Natal linefishery (i.e. the shore linefishery and the offshore boat-based linefishery). Methods used included a stratified-random creel sampling technique and an associated questionnaire survey for the shore-based linefishery and a random access-point technique and associated questionnaire survey for the offshore boat-based linefishery. Additional catch and effort data for the offshore boat-based linefishery was also obtained from Marine and Coastal Management’s (MCM) Linefish Observer Programme. The study was undertaken between February 2009 and April 2010. Total participation within the two linefisheries ranged between 41283-68200 shore-anglers and 21220-28857 boat-fishers (2001-4445 boats). Excluding the increase in the number of boat-fishers that fish off charter vessels (i.e. charter clients), it seems that there have been relatively few new entrants into the marine linefishery of KZN since 1994-96. In contrast, total angler effort in both the shore (779382-1287548 angler-days.annum-1) and offshore (39664 boat outings annum-1) linefisheries has decreased substantially in the past 12 years. Overall catch per unit effort (CPUE) for the KZN shore linefishery amounted to 0.18 ±0.3 fish.angler-1.hour-1 or 0.07 ±0.13 kg.angler-1.hour-1. Eighty-four fish species, belonging to 39 families were recorded in catches of shore-anglers during the study period. Only five species accounted for 75% of the catch recorded along the coast (Sarpa salpa 34.8%, Pomatomus saltatrix 14.7%, Diplodus capensis 14.5%, Pomadasys olivaceum 6.5% and Rhabdosargus holubi 4.9%). The total annual catch for the KZN shore linefishery was estimated between 249.2 and 276.7 metric tonnes (mt).annum-1 (636589 - 706995 fish.annum-1). Overall CPUE was significantly different between the various sectors of the KZN offshore boatbased linefishery. The commercial boat sector had the highest CPUE both numerically (p < 0.05; 307.4 fish.outing-1) and by weight (p < 0.05; 235.6 kg.outing-1). Contrastingly, the recreational boat sector had the lowest CPUE both numerically (p < 0.05, 8.6 fish.outing-1) and by weight (p < 0.05, 15.0 kg.outing-1). The charter boat sector (p < 0.05, 26.6 fish.outing-1 or 41.6 kg.outing-1), although far lower than commercials, had a CPUE slightly higher than the recreational boat sector. In total, 86 fish species, belonging to 27 families were recorded in catches of boat-fishers (all sectors) during the study period. The top five species that comprised the bulk of the commercial catch numerically included Chrysoblephus puniceus (66.0%), Cheimerius nufar (22.4%), Lethrinus nebulosus (4.6%), Pachymetopon aeneum (1.9%) and Chrysoblephus anglicus (0.9%). Similarly, recreational catch composition was dominated by C. iii puniceus (33. 9%), L. nebulosus (9.0%), Thunnus albacares (7.4%), Scomber japonicus (5.3%) and C. anglicus (4.4%). The top five species in charter boat-fishers’ catches comprised C. puniceus (34.4%), L. nebulosus (16.7%), T. albacares (13.1%), C. anglicus (8.1%) and P. aeneum (4.6%). The socio-economic characteristics of the KZN shore and offshore linefisheries have changed very little since the last national linefish assessment conducted during 1994-96. Recreational (both shore and boat-based) and charter anglers generally agree with most of the linefishery regulations, with exception of the beach vehicle ban. However, knowledge and compliance with the current fishery regulations by recreational and charter anglers was limited. Commercial fishers had good knowledge of all the fishery regulations, but did not agree with the minimum legal size and daily bag limits that are in place on certain fish species. Subsequently, the majority of commercial skippers interviewed stated that they disobeyed these two regulations frequently. General policing of the KZN linefishery by EKZNW seems to be more focused on permit requirements rather than enforcing species-specific linefish regulations. Comparison of the catch and effort results of this study with the long-term monitoring data stored on the NMLS showed that while the NMLS data is limited by a number of biases, it still provides a valuable system for monitoring long-term trends in the KZN linefishery. Analysis of overall CPUE, catch composition and total catch in both the shore and offshore linefisheries of KZN suggested that both fisheries are currently in a relatively stable condition and that little change has occurred in the past 12 years. However, comparisons of speciesspecific CPUE values from this study with recent literature suggest that some species (i.e. Argyrosomus thorpei and Scomberomorus commerson) are severely overexploited. Furthermore, in relation to the catches recorded throughout most of the 20th century, current catch trends suggest that linefish resources have been fished to very low levels which are only ‘superficially’ sustainable at current levels of fishing effort. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.

This thesis provides a study on aspects of the biology and population dynamics of Scomberomorus commerson off the south east coast of southern Africa. This is necessary for the evaluation of the current management policies and for the selection of the "best" management strategy for this species off the coast of Natal. The current status of S. commerson off the Natal coast was assessed in terms of yield-per-recruit and spawning biomass-per-recruit analyses. Input parameters to these per-recruit models include growth and mortality rates and basic biological data. Estimates of these parameters and the methods employed are detailed in the thesis . S. commerson has a protracted spawn ing period rang ing from November to March. The principal spawning area is Mozambique. Fifty percent sexual maturity is attained at 1096mm and 706mm(FL) for females and males, respectively. The, ratio of males to females in the sampled catches is approximately 1:2 with females attaining a significantly larger mean size: females (926mm,FL) and males (898mm , FL). The masslength relationsh ip for both sexes can be described by the following equation: Ma s s ( g ) = O.1353X10-5 • [FL(mm) J3.25 15 Growth parameter estimates for the combined sexes were estimated from a lengthbased as well as an age-based method. An objective technique was utilised to determine which growth function best describes the age-length data of S. commerson. Age data were obtained from otolith readings. The precision of otolith readings was described by an index. This index, the average percent error, which is equal to 20.25%, is higher than that recorded in other studies. Two opaque bands are laid down annually. This was validated by marginal increment analyses as well as from tagging data. The age-length relationship , assuming biannual periodicity of the opaque band, is best described by a Von Bertalanffy growth function: L age(mm, FL) = 134 4mm (l-e ...{).292 yr-'Cage-+2.999 yrs») The instantaneous natural mortality rate (M) was estimated using two different techniques: the Pauly equation and the Rihkter and Efanov equation. The former equation was very sensitive to changes in the mean environmental temperature and both techniques produced different estimates. The average of both methods was, therefore, taken as an estimate of M which is 0.5 yr'. The instantaneous fishing mortality rate (F) is currently estimated to be 0.25 vt", This estimate is, however, positively biased as the effects of emigration have not been taken into account. The per-recru it analyses were conducted for three different growth equations for the same values of F and M, age-at-maturity and age-at-first-capture. For all growth equations the yield-per-recruit increased with increased fishing with maximum yield-perrecruit attained either at infinite F or at very high values of F (> 5 yr'), FO.1 was attained between 0.6 and 0.8 v' for all growth equations. The Von Bertalanffy growth function, assuming annual periodicity of the opaque band, was the most unrealistic. It predicted a virtual collapse of the fishery When F=M and a reduction of the spawning biomass to 50% of its unfished level at F=0.1 yr'. The length based derived growth equation and the Von Bertalanffy growth function, assuming biannual periodicity of the opaque band, predicted that spawning biomass dropped to 50% of the pristine level at F=0.19 and 0.16 vr' . respectively. It is believed that the current restrictions on sport catches of 10 fish/person/day offers adequate protection for the Natal king mackerel stock. These restrictions should be maintained in Natal. However, if fishing effort on this species continues to increase (as is anticipated in an open access fishery) or if there is increased commercial interest or if there is renewed fishing in Mozambique, a minimum size is recommended to adequately protect the spawning stock. Such a minimum size should be implemented in Mozambique which is the principal spawning area for king mackerel. Setting a minimum size in Natal, above the size-at-50% maturity may substantially reduce catches in the short and medium term because at least 90% of the catch currently taken will be inaccessible to fishermen. Restrictions of king mackerel catches in Natal, alone, is not considered a viable management option as Natal's commercial and to a certain extent recreational fishermen may turn to Mozambican waters to harvest king mackerel. Management options should be implemented and enforced both in Natal and Mozambique. / Thesis (M.Sc.)-University of Natal, Durban.