Marine Biology

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Biology and population dynamics of the King Mackerel (Scombereomorous commerson, Lacepede, 1800) off the coast of Natal .
(1992) Govender, Anesh.; De Freitas, A. J.; Van der Elst, Rudy P.
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.
Association of juveniles of four fish species with sandbanks in Durban Bay, KwaZulu Natal.
(1994) Graham, M. A.; Forbes, Anthony Tonks.; Cyrus, Digby Paul.
Estuaries in South Africa are important nursery areas for the juveniles of many fish species. The condition of many of these systems has, however, deteriorated as a result of degradation caused by urban, industrial and agricultural development. An assessment of the role of harbours, particularly in KwaZulu Natal, as nursery grounds has therefore become an important issue. Durban Bay has undergone considerable changes since the mid-1800s and further developments are proposed. If these developments continue, they will result in the loss of large areas of the sandbanks, but Portnet has recognised the need to integrate environmental considerations into future port developments and operations. It was the overall aim of this study to establish the nature of the association of the juveniles of four common fish species viz. Pomadasys commersonnii, Gerres filamentosus, Liza dumerilii and Leiognathus equula with these sandbanks and, thereby assess the impact of their removal. It was found that all species were abundant on the sandbanks and that the diets of P. commersonnii, G. fiiamentosus and L. equuia were very similar, consisting primarily of bivalve siphon tips, benthic crustaceans and polychaetes. The respective contributions of each food type to the diet varied with species. The diet of L. dumerilii differed from that of the other three species, consisting primarily of benthic floc, foraminiferans, ostracods and sponge spicules. Despite differences in selectivity, it was concluded, from studies of the benthos in the harbour, that all four species, irrespective of size, were feeding on these sandbanks, as opposed to in the channels, throughout the year. Removal of the sandbanks for the construction of a new pier would, thus, result in the elimination of important feeding grounds for the juveniles of these four species.
Biology and stock assessment of the coastal fish, Sarpa Salpa (Sparidae), off the KwaZulu-Natal coast, South Africa.
(1995) Van Der Walt, Bryan Anthony.; Govender, Anesh.; Beckley, Lynnath E.
This study investigated aspects of the biology of Sarpa salpa, such as reproduction, age and growth, and mortality, which are necessary for an assessment of the status of this species off the KwaZulu-Natal (KZN) Coast. The importance of S. salpa to the shore-based fishery in KZN was evaluated using Natal Parks Board shore patrol data. These data were validated by analysing preliminary results of an independent shore-angling survey along the KZN Coast. Despite differences in the catch composition and catch rates between the two analyses, both data sources highlighted the importance of S. salpa to the shore-based fishery in KZN. Shore-based catches were markedly seasonal coinciding with the breeding season of the species. The species in KZN is targeted primarily to provide a supplementary source of animal protein. An investigation of the reproductive biology of S. salpa indicated a protracted spawning period for the species. Size at 50 percent maturity for combined sexes was attained at 145 mm fork length. The sex ratio in shore-based catches was 1:1.6 in favour of males. A frequency distribution by size indicated that males dominated the smaller size classes while females dominated the larger size classes. Detailed histological examination of gonadal development showed that S. salpa has the potential for protandrous sex change. An age and growth study based on the examination of whole otoliths indicated that S. salpa was relatively fast-growing and a maximum age of six years was recorded for the species. One opaque band was laid down per year. This was validated by marginal increment analysis and by an oxytetracycline labelling experiment using captive fish. Growth in S. salpa was described by a Von Bertalanffy growth function: Lage (mm FL) = 224mm(1 -e-o.55 year-1(age+o.51years)) The natural mortality rate (M = 0.6 year-1) was derived using Pauly's equation and the current fishing mortality (F) rate was estimated at 0.8 year-1. The current status of S. salpa in the shore-based fishery was assessed by determining the effects of F and age-at-capture on the yield- and spawner biomass-per-recruit. Current levels of fishing pressure on S. salpa appeared to be appropriate for utilisation of the stock off the KZN South Coast. In terms of management, S. salpa appears to be in no need of any restrictive measures at present.
Mark-recapture models for determination of mortality, migration and growth in Pomatomus saltatrix (Teleostei)
(1996) Govender, Anesh.; Beckley, Lynnath E.; Cochrane, Kevern.
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.
Age and growth of the Queen Mackerel (Scomberomorus plurilineatus) and Seventy-four (Polysteganus undulosus) of KwaZulu Natal, South Africa.
(1996) Chale-Matsau, Jacobeth R.; Beckley, Lynnath E.; Govender, Anesh.
This study provides information on the age and growth of two important Iinefish species, Scomberomorus pluriline~tus and Polysteganus undulosus. Age determination for both species was carried out using otoliths and growth was modelled using age- and length-based methods. For the age-based method various growth models were evaluated to determine which growth function best described the age-length data, whilst Shepherd's Length Composition Analysis was used to estimate growth parameters from length-frequency data. Preliminary stock assessments, based on limited catch data, were also attempted for both species. Age estimates for the pelagic migrant S. plurilineatus, derived from reading whole otoliths, ranged from 0 + to 6 + years. As validation by marginal increment analysis was inconclusive because of the seasonal occurrence of this species in KwaZulu-Natal waters, it was assumed that a single opaque band was laid down in the otolith annually. Reproducibility of age estimates evaluated using the average percentage error (APE) technique was good (9.4%). Von Bertalanffy growth parameters were poorly estimated from length-frequency data because multiple maxima were encountered on the fitting surface. However, from the age-length data, growth was adequately modelled by the von Bertalanffy growth equation: L t =9 3 5mmFL (l-e -0. 583yr-1 (t+o. 991yr) ) S. p!urilineatus are fully recruited to the fishery at the age of 1 + year and the ageiv at-50% maturity is 2 + years. Preliminary per-recruit analyses indicated that the spawner biomass of S. plurilineatus is at 50% of its unfished level. Polysteganus undulosus is an endemic, reef-dwelling sparid and large catches weremade earlier in the century. Age determination was carried out using sectioned otoliths collected in 1962 and 1963 before the collapse of the fishery. Age estimates ranged from 3 + to 20 + years. Marginal increment analysis indicated that active deposition of opaque bands occurred during winter but, because of the seasonal occurrence of P. undulosus in KwaZulu-Natal, validation was inconclusive. Reproducibility of the age estimates was low (APE = 18.2%) because of difficulties with band interpretation as a result of stacking on otolith margins in old fish. Von Bertalanffy growth parameters could not be adequately estimated from length frequency data because of the slow growth and longevity of this species. However, from the age-length data, no difference in growth rate between the sexes was observed, and growth for the combined sexes is described by the following logistic equation: L = 942mmTL t 1+e-O.277yr-l(t-S.178yrs) The age at full recruitment was found to be 12 + years and the age-at-50% maturity was 8.8 years. A preliminary stock assessment revealed that the spawner biomass of P. undulosus was already at 25% of its unfished level in the early 1960s.
Artisanal fishery in socio-economic development of rural communities in Malawi : a case study of enclave villages of Lake Malawi National Park.
(1998) Kumchedwa, Brighton Kalembeni.; Breen, Charles Mackie.
Fishing, and artisanal fishing in particular, plays a key role in the provision of rural employment and more importantly, household food security in the developing nations. The importance of artisanal fishery is shown in Malawi where artisanal fishery produces between 85-95% of the total fish production, and about 70% of the animal protein in human consumption comes from fish. About 43,000 people are employed directly in artisanal fisheries and approximately 100,000150,000 are indirectly employed within the artisanal fishery. Owing to increasing human population in the developing countries coupled with the common property, open-access nature of the fish resource, the resource has not been able to cope with the ever-increasing socio-economic demand placed on it. The resource is so degraded that it is has started to decline beyond capacity to sustain itself. This study was an attempt to examine and understand the artisanal fishery as it contributes to the socio-economic well being of the rural population particularly, the enclave communities of Lake Malawi National Park. The present study used structured interviews, focus group interviews, key informant interviews and personal observation to collect socio-economic information of the fishery. These research tools revealed that among the enclave communities income levels are low and unsustainable due to declining productivity of fishing. The decline may be a result of increasing human population, weak community-based institutions, limited agriculture, poor infrastructure with regard to processing and marketing of fish, limited supplementary and alternatives economic activities, and the fishing methods. Documentary information was used to contextualize artisanal fishery, to examine and understand the common-property and open-access nature of the fish resource as it relates to the exploitation Of fish among the enclave communities. Integrated development that brings together conservation and socio-economic development is the only option that will increase the income of the enclave communities to sustainable levels and achieve the Park's conservation objectives. The socio-economic intervention options should include provision of basic social facilities such as education, health, safe water etc, increase the economic power of the enclave communities through irrigation, adding more value to the fishery, engaging in aquarium trade, community-based eco-tourism and beekeeping. These options would lead to socio-economic sustainability among the enclave communities and would bring about the conservation objectives of the Park.
Comparative life histories and stock assessments of rockcods (family Serranidae) from the east coast of South Africa.
(2000) Fennessy, Sean Thomas.; Beckley, Lynnath E.; Sadovy, Yvonne.
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.
The status of the riverbream Acanthopagrus berda (Sparidae) in estuarine systems of northern KwaZulu-Natal, South Africa.
(2001) James, Nicola Caroline.; Beckley, Lynnath E.; Mann, Bruce Quintin.
Acanthopagrus berda is an estuarine-dependent fish species which is widespread in the tropical Indo-Pacific. In South Africa, it is particularly abundant in the three large northern KwaZulu-Natal estuarine systems, namely Kosi Bay, St Lucia and Richards Bay. In these systems, A. berda is harvested by a variety of methods, including traditional fish traps, gillnets and hook and line. The importance of A. berda to the different fisheries was evaluated by analysing all the available monitoring data specific to catches in these three systems. A. berda was found to be one of the five most important species taken in both the gill net and recreational fisheries at Kosi Bay and St Lucia. It was less important in the marine-dominated Richards Bay system. Catches were generally seasonal, with trends in catch per unit effort (cpue) for A. berda related to annual spawning migrations. The long-term trend in cpue for this species in the Kosi recreational fishery showed a disturbing downward trend. Ages of A. berda specimens caught in northern KwaZulu-Natal estuaries were determined by examining whole otoliths. Age estimates were validated by marginal zone analysis and oxytetracycline labelling, which indicated that opaque deposition occurs primarily from September to November each year. The reproducibility of age estimates was described by a coefficient of variation of 10%. The special von Bertalanffy growth curve was found to best describe the growth of A. berda. The parameters of the von Bertalanffy growth curve indicated that A. berda in northern KwaZulu-Natal is slow growing, attaining at least 16 years of age. The age and growth parameters and mortality estimates from catch curves were used to complete a per-recruit stock assessment of the species. The results of the spawning biomass per-recruit model using different ages of first capture indicate that A. berda is at 47% to 55% of its unfished level. Although these results may indicate that A. berda in northern KwaZulu-Natal is not at present overexploited, longevity coupled with late maturation, sex change, estuarine dependency, increasing catches of A. berda and poor monitoring give cause for concern for the continued sustainable use of this species in northern KwaZulu-Natal.
Modelling streamflow and sediment yield on the lower Mgeni catchment.
(2001) Singh, Michael Lutchman.; Garland, Gerald George.
This study involves the application of the ACRU Agrohydrological Model to a selected study catchment in the Lower Mgeni Catchment, and its discretized subcatchments, immediately downstream of the Inanda Dam. This study was initiated on the assumption that the Inanda Dam, which came into operation in 1989, would have significant impacts on the downstream (Lower Mgeni) hydrology, geomorphology and ecology. The overall aim of this study, to set up and run the ACRU model for the delimited study catchment, was successfully accomplished. This aspect of the study involved firstly, the setting up of an input database for each distributed catchment within the catchment; secondly, the processes and techniques used to translate data into hydrological information; and finally the "running" of the hydrological model, which in turn "drives" the system and simulates the catchment hydrology. Specific objectives of the study entailed the simulation of hydrology, which focussed on simulated runoff and streamflow; and sediment yield responses of the subcatchments and the total study catchment of the Lower Mgeni, with respect to gross volumes and sediment yield rates produced. The streamflow results reported indicated a season of "Iow" flow, with a monthly flowrate ranging from 1155m3s-1 to 2735m3s-1 , from April to September; and is identified and distinguished from the period of "high" flowrate, ranging from approximately 483m3s-1 to 1747m3s-1 , for the remaining months of the year. The mean annual volume for the delimited subcatchment is 22 278.5 million m3 , exceeding the annual volume required to maintain riverine and estuarine ecology, which according to DWAF (1990) is 18.5 million m3 . The simulated results of sediment yield indicate that Subcatchment 3 and 4 have the lowest sediment yield rates of 32.3 t km-2 a-1 and 32.6 t km-2 a-1 , respectively. Subcatchment 2 has the highest yield rate at the value of 617 t km-2 a-1 , while subcatchment 1 has a rate of 53.2 t km-2 a-1 . Annual sediment production in the Lower Mgeni subcatchment is 10 855.1 tons per annum with respect to gross mass, resulting in a sediment yield rate of 73.8 t km-2 a-1 . The outcomes of this study compare very favourably with other studies conducted on hydrology and sediment yield, especially those undertaken within this geographical area. It may be assumed therefore, that the results produced herein can be applied with confidence to enable appropriate planning and management of resources within this catchment. Modelling of hydrology in the Lower Mgeni is expected to contribute significantly towards meeting riverine and estuarine ecological and geomorphological streamflow requirements. It would facilitate the development of an appropriate management and dam release strategy of Inanda Dam, in order to meet these requirements. The modelling of sediment yield is expected to contribute to the development of a sustainable sandwinning policy and strategy for the Lower Mgeni, as current extraction rates exceed the annual sediment production. Once the model has been applied to a selected catchment, it has the ability to consider different scenarios, providing an invaluable tool for planning. Based on the results of this study, the ACRU model may be applied, with confidence, to other similar ungauged catchments.
The vegetation ecology of the lower Mkuze river floodplain, Northern KwaZulu-Natal : a landscape ecology perspective.
(2001) Neal, Marian J.; Ellery, William Nolan.
The overall aim of this study was to develop an understanding of the vegetation ecology of the lower Mkuze River floodplain from a landscape ecology perspective. The lower Mkuze River floodplain and its associated wetlands are located east of the Lebombo Mountains and north of Lake St. Lucia on the Maputaland Coastal Plain in northern KwaZulu-Natal. This system is defined as a storage floodplain wetland and comprises a mosaic of different wetland types. In addition it has a complex history of resource use and management. Landscape ecology proved to be an ideal theoretical framework for this study because it enables the examination of complex ecological processes and phenomena in an integrated and holistic manner. It achieves this by explicitly recognizing the spatial heterogeneity, dynamics and hierarchical organization of the landscape; concepts that proved useful in developing an understanding of the ecological patterns and processes operating within the lower Mkuze River floodplain. The vegetation of the study area was classified, using multivariate techniques, into six plant communities. The distribution of these plant communities was correlated with underlying environmental gradients that summarized the interactions between hydrology, substrate properties and topography within the floodplain system. Within the study area the Phragmites mauritianus reed swamp community was found where there was slow moving water, in semi- to permanently saturated soil. This was usually around the edges of pans or in extensive stands in low-lying areas in the distal reaches of the floodplain. The Imperata cylindrica hygrophilous grassland community was uncommon and was found in isolated stands towards the edge of the region of seasonal flooding. The Echinochloa pyramidalis backswamp community was the most extensive of all the plant communities identified. This community was tolerant of flooding and was found in damp places such as seasonal pans, backswamps and riverbanks as well as in standing water. The distribution of the Ficus sycomorus riparian forest community was restricted to elevated levees adjacent to the river channel that experienced inundation when floods were large enough to overtop channel banks. The Cynodon dactylon floodplain community was generally found towards the floodplain-terrestrial upland boundary in elevated areas with sandy well-drained soils. The Acacia xanthophloea woodland community was distributed on the floodplain margin in elevated areas on sandy soils, primarily fringing the linear pans draining towards the Mkuze River from the north. The description of the plant community types and the underlying environmental determinants of their distribution provided a useful foundation for the examination of ecological processes and phenomena operating at spatially coarser levels within the landscape hierarchy. Plant communities were aggregated into functional types based on criteria such as exposure to similar flooding and sedimentation regimes. The identification and mapping of these functional types, using a Geographical Information System (GIS), enabled one to identify a hydrogeomorphic continuum that described the interaction between floodplain processes and vegetation distribution. Within the study area the proximal-seasonally inundated functional type comprised plant community types found on channel levees and within backswamp areas. These areas were functionally connected to the Mkuze River in that they were exposed to seasonal flood events and associated sedimentation. The distal-permanently inundated functional type was typically found in the lower reaches of the floodplain that were rarely exposed to hydrological and sedimentological inputs from the Mkuze River. This functional type was permanently inundated and characterized by standing water and/or permanently saturated soils that were generally associated with the large floodplain pans. The distal-infrequently inundated functional type was typically located in sandy areas along the southern distal reaches of the floodplain. These areas were infrequently inundated by overbank floodwaters from the Mkuze River and were not characterized by substantial clastic sedimentation. The distribution and interaction between these functional types made it possible to develop process-based understanding of the ecosystem patterns and processes operating within the lower Mkuze River floodplain. Landscape ecology theory emphasises the importance of a temporal analysis of spatial heterogeneity and the role of disturbance in ecosystem patterns and processes. Therefore a temporal analysis of the landscape mosaic from 1937 to 1996 was undertaken, using a GIS, in order to quantify landscape change over time. The landscape characteristics utilised to examine this change were total category area, percentage contribution to the total landscape area, number of patches, mean patch size, median patch size, patch size standard deviation and the mean perimeter-area ratio. These spatial statistics were calculated for each year using PATCH ANALYST, an ArcView GIS extension and they were used to illustrate the role of anthropogenic disturbance on the landscape mosaic at a variety of levels within the landscape hierarchy. Anthropogenic disturbance was found to affect landscape content and configuration and therefore had the potential to undermine the underlying environmental determinants of landscape patterns and processes. Once the underlying functional processes are undermined, irreversible ecosystem degradation is a possible outcome. The examination of the different levels within the landscape hierarchy and the dynamics of ecosystem patterns and processes operating within the Mkuze River floodplain made it possible to develop deeper insights into ecosystem patterns and processes than a conventional vegetation ecology study that typically focuses primarily on plant community classification. The use of landscape ecology as an overarching theory that guided the research process and aided the interpretation of findings by explicitly recognising the importance of examining spatial heterogeneity, hierarchical organisation and dynamics, proved invaluable in developing process-based understanding of the lower Mkuze River floodplain.
Management of the linefish resource in Southern Mozambique : a case study for Marreco (Chrysoblephus puniceus).
(2001) Lichucha, Ivone Delfina Lourenco Tivane.; Govender, Anesh.; Van der Elst, Rudy P.
This study provides information on the biology, stock status and the management of C. puniceus, a key linefish resource in southern Mozambique. This is regionally endemic to Mozambique and KwaZulu-Natal. Fairly resident species, is found on the continental shelf ranging north to Zavora and south to KwaZulu-Natal and Transkei, and inhabits rocky seabeds, ranging between 20 and l00m. In Mozambique is manly exploited by semi-industrial fleet, and exported to South Africa. The reproductive biology, assessed through gonad somatic index as well as microscopic and macroscopic assessment, indicates that spawning extends over the spring months from August to November, peaking in September. It is a protogynous hermaphrodite, relatively slow growing and long lived species. The length-weight relationships for male and female C. puniceus show to be different, and the overall length frequency distribution shows clear difference in size between male and female C. puniceus, with male length frequency distribution restricted to the larger size classes. The monthly length frequency distribution of female C. puniceus is unimodal and peak at 300 mm FL, male shows unclear year classes. Age determination was carried out using otoliths and growth was estimated using the model developed by Punt et al (1993) for protogynous hermaphrodites reproductive styles. Validation of annuli was done by examining the outer margin of otolith, and also through mark and recapture information. Validation following the first method indicated that the opaque band is laid down twice a year, but the mark recapture results were inconsistent. This contradicts previously published information on C. puniceus, and thus; both single and double scenarios were modelled. The Von Bertalanffy growth parameters found for C. puniceus suggest relatively slow-growth, with the number of rings found from reading the sectioned otolith ranging from 2 to 18. Reproducibility of age estimates was evaluated using the average percentage error (APE) technique, and was equal to 22%. The age at full recruitment was found to be 2.5 and 5 years for bi-annual and annual banding, respectively. The analysis of the age-at-50% maturity, based on double band scenario, suggests that C. puniceus mature at 1.5 year-old, which corresponds to a mean FL of 240mm. A preliminary yield per recruit assessment revealed that at the current fishing mortality, C. puniceus fishery is moderately overfished, with the spawning biomass-per-recruit at 35.43% and 36.57%, for one and two bands, respectively, of its unexploited level. Fishing mortality was equal to 0.2 year-1 and 0.41 year-1, for single and double band, respectively. YPR analysis shows that the single band scenario is less conservative than the double band assessment, which has a bearing on the management approach. It is suggested as the preliminary management strategy a reduction of the number of boats. Indeed the average number of crew per boat, needs to be evaluated in terms of overall effort. To complement this management measures, there is a strong and urgent need to establish marine reserves in order to protect spawning stock, and also, to develop an overall linefish management plan, which will help in the management of the whole linefish resource in Mozambique. Furthermore, an age and growth study for C. puniceus over a larger geographical area needs to be done as a mean to overcome the differences between previous study and this study, once C. puniceus is being shared between the two countries (Mozambique and KwaZulu-Natal).
Coral propagation for aquarium specimens.
(2001) Jordan, Ingrid Elizabeth.; Schleyer, Michael H.
Coral reefs are being destroyed and degraded by natural and anthropogenic processes. Live corals are becoming increasingly popular as marine aquarium specimens, in both the commercial and private sectors, leading to the degradation of coral reefs. This often has serious economic implications for the fishing, aquarium and tourist industries. It is clear that there is a need for the management and protection of these fragile ecosystems. The artificial propagation of coral is desirable as it will alleviate the demand for wild coral specimens, and will also provide a stock for the rehabilitation of damaged reefs. Although corals are being propagated worldwide by hobbyists, reports on their work are mainly anecdotal and there is little in the scientific literature on the specific requirements for optimal growth rates and survival in suitable coral species. This study thus focused on developing techniques to propagate a range of appropriate coral species and to promote their optimal growth. The results revealed that different morphological groups of scleractinian corals require specialised techniques of fragmentation and attachment to ensure survival. The corals were broken using a hammer and chisel. Attachment techniques varied from the use of superglue (which is widely used in the United States), to thermoplastic glue. The mean mortality using superglue was 73% (n=120, ±0.167), using epoxy, 62% (n=120, ±0.127) and with thermoplastic glue it was 11% (n=120, ±0.108) Superglue was extremely difficult to work with and proved ineffective, especially when attempting to glue uneven surfaces. Certain species did not survive using this adhesive due to exposure of the coral to air. The most effective method of rapid attachment was the use of thermoplastic glue that set rapidly underwater. The use of electrolysis to promote the attachment of coral nubbins was tested as an alternative to the various adhesives. This method increased the survival of the nubbins and eliminated exposure to air. It has proven suitable for both coral propagation and in situ reef rehabilitation. Growth experiments revealed that the manipulation of current flow, light and the addition of different feeds had different effects on the growth rates of selected candidate species. A suite of optima was thus developed for each species. The majority of species grew best in a bi-directional current flow, with yeast as feed, under actinic blue light. An experiment that combined the optimal current flow, feed and light conditions, revealed that the majority of species grew best under mixed light with yeast as feed. The trade in corals is sensitive in terms of their handling, transportation and CITES (Convention on International Trade in Endangered Species) status. Having established the viability of their propagation, consideration was given to appropriate regulatory and marketing procedures to accommodate this sensitivity of the cultivated material.
Transboundary water resource management of the Pongolo River/Rio Maputo.
(2002) Tompkins, Robyn.; Quinn, Nevil Wyndham.
In the Twenty-first Century, sustainable water management is likely to be humanity's greatest challenge in a world of ever-increasing demand. Legal instruments both international and national regulate and provide a general framework for the use and management of international waters. Future basin management agreements can be informed by examining the degree of success, in terms of sustainability and equity, achieved by such agreements. That success can be influenced by the degree to which such agreements support the human right to water implicitly stated in international customary law, through a collaborative management approach. Since 1988, attempts by communities on the Pongolo floodplain to be involved in Pongolopoort Dam releases, have met with little success. Recently, the Department of Water Affairs and Forestry has begun to support those efforts, but the approach remains a sectoral one, and is primarily concerned with water issues. The South African National Water Act 36 of 1998 provides for environmental management and public participation, as well as providing explicitly for the rights of individual water users, but its implementation is hampered by an overwhelming emphasis on technical considerations and a lack of political will to embrace collaborative management systems. Little effort is expended on collaborative management methods, though the level of transparency in water management is improving, despite remaining highly centralised. The level and extent of incentives for local community participation is low, and systematic monitoring is in its early development. International river basin agreements generally take a top-down or state-driven approach, though there are some examples where local cross-border communities have participated successfully in the implementation of international agreements and management of transboundary basins. South Africa, Swaziland and M09ambique signed the Interim Incomaputo Agreement, which includes the Maputo basin, in August 2002. Once again, the approach to this agreement has been highly sectoral in that negotiations were handled entirely by water officials in the relevant countries. A lack of transparency has prevailed in the negotiation stages, though through the basin studies, which will inform implementation plans, the level of participation should improve. There is overwhelming consensus that integrated management is the key to sustainable international river basin management. Formal and systematic methods for inter-departmental communication, both nationally and internationally are currently not being implemented, which has significant negative impacts on integrated management. Research in this area represents an opportunity to explore collaborative management of an international river basin in an area that is, as yet, unstressed in terms of population and water supply.
The macrobenthos of the Little Lagoon, Durban Bay.
(2002) Pillay, Deena.; Forbes, Anthony Tonks.
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.
The dynamics of microphytobenthos in the Mdloti and Mhlanga estuaries, Kwazulu-Natal.
(2004) Iyer, Kogilam.; Perissinotto, Renzo.; Nozais, C.
Microphytobenthos (MPB) generally dominates total autotrophic biomass in temporarily open/closed estuaries (TOCEs) of South Africa. A comparative study of MPB biomass was undertaken in two KwaZulu-Natal TOCEs, the Mdloti and the Mhlanga. Both estuaries receive different volumes of treated sewage waters. The Mdloti receives 8 ML.d-1, while the Mhlanga receives 20 ML.d-1, resulting in a capping flow of 0.092 and 0.23 m3.s-1, respectively. Through these effluents, eutrophication is enhanced and periods of mouth opening are also increased and prolonged, particularly at the Mhlanga. The aim of this study was to investigate fluctuations in MPB biomass in the Mdloti and the Mhlanga systems, with emphasis on freshwater flow and the alternation of closed and open phases. Sediment samples for MPB biomass were collected on a monthly basis, between March 2002 and March 2003, in the lower (mouth), middle, and upper (head) reaches of the two estuaries. MPB biomass ranged from 1.33 to 391 mg chI a m-2 and from 1.7 to 313 mg chI a m-2 in the Mdloti and the Mhlanga, respectively. A I-way ANOVA revealed no significant differences in MPB chI a concentrations between the two estuaries for the entire data set (Fl, 76 =1.48, P > 0.05). At the Mdloti, MPB biomass varied considerably, with values ranging from 1.33 to 131 mg chI a m-2 during the open phase, and from 18 to 391 mg chI a m-2 during the closed phase. A Mann-Whitney U test confirmed the high significance of these differences between open and closed phases (U= 29, P < 0.001). At the Mhlanga, MPB biomass ranged from 7.0 to 313 mg chI a m-2 during the open phase, and from 1.7 to 267 mg chI a m-2 during the closed phase. Unlike what was observed at the Mdloti, the higher MPB values at the Mhlanga were not always associated with the closed mouth state. In relation to key physico-chemical and biological factors, grazing pressure exerted by the zooplankton community appeared to have played a major role in controlling MPB biomass. Zooplankton biomass was consistently and positively correlated to MPB biomass throughout the study period both at the Mdloti (r = 0040, P < 0.001) and at the Mhlanga (r = 0.33, p < 0.05). Unlike what was shown in previous studies, light attenuation was not significantly correlated with MPB biomass during the period ofthe study, either at the Mdloti or the Mhlanga. These results show that the opening and closing of the mouth play a key role on the MPB biomass of both estuaries. The Mdloti seems to function as a typical TOCE, with prolonged open and closed phases. The Mhlanga, on the other hand, lacks a prolonged closed phase. This, in turn, affects its entire trophic structure and functioning.
The commercial and recreational marine skiboat linefisheries in Richards Bay, KwaZulu-Natal.
(2005) Jairam, Sureka.; Van der Elst, Rudy P.
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.
The zooplankton of temporarily open/closed estuaries : case studies of the Mdloti and the Mhlanga estuaries, KwaZulu-Natal North Coast.
(2005) Thwala, Xolani Christopher.; Perissinotto, Renzo.
The zooplankton communities of the Mdloti and Mhlanga estuaries were studied over a 13-month period (March 2002-March 2003). Monthly daytime samples were collected from both estuaries at the lower, middle and upper reaches using a WP-2 net and a hyperbenthic sled. Throughout the study period, the Mdloti Estuary experienced nine breachings, while the Mhlanga experienced 16 such events. Significant differences in zooplankton abundance were observed between the two estuaries (F I, 73 = 5.2; P<0.05), with the Mdloti consistently exhibiting higher values than the Mhlanga. No significant differences were, however, observed in zooplankton biomass between the two estuaries (U = 634; P>0.05). At the Mdloti, zooplankton abundance ranged from 20 ind.m-3 to 5.4 x 106 ind.m-3 , while at the Mhlanga this ranged from 76 ind.m-3 to 2.0 x 105 ind.m-3 • Zooplankton biomass ranged from 0.08 mg.m-3 (OW) to 2010 mg.m-3 (OW) at the Mdloti, and from 0.18 mg.m-3 (OW) to 1210 mg.m-3 (OW) at the Mhlanga. A one-way ANOV A revealed significant differences in zooplankton abundance between the open and the closed phase, both at the Mdloti (FI, 30 = 59; P<0.05) 'and the Mhlanga (FI, 38 = 7.3; P<0.05), with the closed phase exhibiting consistently higher values than the open. Similarly, biomass was significantly higher during the closed than the open phase, both at the Mdloti (U= 16.5; P
An assessment of changes in the Ichthyofaunal bycatch of the Tugela Bank prawn trawlers in KwaZulu-Natal.
(2006) Mkhize, Mbali.; Fennessy, Sean Thomas.; Van der Elst, Rudy P.
Bycatch refers to the portion of the catch that is captured incidentally to the target species and is one of many growing problems facing the world's marine fisheries in recent years. Prawn trawling is one of the world's most lucrative marine fisheries, contributing about 3% to the total annual production of the world's marine fisheries. It is also one the most wasteful because it is associated with large quantities of bycatch. This is because of the high diversity and abundance of other organisms in areas where prawn trawling occurs, and the non-selective nature of the otter trawl used to land prawns. The South African shallow water prawn trawl fishery is typical of penaeid fisheries, and operates on the Tugela Bank off northern KwaZulu-Natal. The bycatch of penaeid prawn trawlers operating on the Tugela Bank was analysed between March 2003-July 2004 as a follow up to an initial study between May 1989-June 1992. The aim of this study was to determine if there has been any change in bycatch species composition over the 13-years and to determine the impacts of trawling on the environment. Catch composition data were recorded from 168 trawls processed onboard trawlers and on-shore. A total of 122 species was identified with teleosts contributing more than 60% to relative abundance by number. Comparison between the 1989-1992 and 2003-2004 data sets showed that although the species compositions were similar, there was an increase in the relative abundance of pelagic species. It is not clear if the change is due to trawling impacts or due to fluctuations in recruitment of these taxa. The annual discarded bycatch was estimated at 88 tonnes in 2003 and the prawn catch was estimated at 1 1 tonnes, both substantially lower than in 1 989-1992. There was no difference in discard rate between trawls from shallow and medium depths. However, there were significant differences in discard rates between large and medium gears, and warm (December-April) and cool (May- November) seasons. Kolmogorov-Smirnov tests revealed that there were significant differences between the 1990s and 2000s length frequency distributions of three sciaenid species (Otolithes ruber, Johnius dorsalis and J. fuscolineatus), which all showed an increase in fish size for the 2003- 2004 data. This assessment, however, is confounded by a gear effect as mesh size differs between the two sample periods. Based on the results of the study, management recommendations were made to improve the management of the Tugela Bank prawn trawl fishery by reducing bycatch. It was recommended that the observer programme continue for further investigation into the changes in species dynamics. Further research on BRDs (Bycatch Reducing Devices) and gear types that reduce bycatch is also recommended.
Genetic diversity of symbiodinium in selected corals in the Western Indian Ocean.
(2007) Starzak, Dorota Ewa.; Schleyer, Michael H.; Lamb, Jennifer Margaret.
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.
Responses of Avicennia marina (Forssk.) Vierh. to contamination by selected heavy metals.
(2008) Hiralal, Tisha.
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.

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