Gamtoos River Research Articles

The Nature, Causes and Extent of Land cover Changes in Gamtoos River Estuary, Eastern Cape Province, South Africa: 1991–2017

Multi-date remotely sensed SPOT images of 1991, 2000, 2009 and 2017 were used to reconstruct changes in land cover in the Gamtoos River Estuary, Eastern Cape province, South Africa. These images were complemented by near-anniversary aerial photographs and Google Earth images that were used as ancillary sources of ground truth. The long-term trend direction of change was determined by calculating percentage changes and performing linear trend analysis. The magnitude of change was established by calculating Sen Slope estimates (SSE) and the influence of climate change on changes in land cover tested by correlating changes in rainfall and different cover types. The greatest and lowest changes were for noncultivated land and surface water (−7.94%, y = −1.2032x + 21.275, SSE = −0.292, and 0.44%, y = −0.4261x + 9.657, SSE = 0.007, respectively). Correlations between rainfall and all cover types were weak and ranged between 0.453816 and −0.643962. Rainfall exhibited a significant decrease (p = 0.0411, σ 0.05; y = −7.175x + 734.55, SSE = −11.130) that was highly correlated with changes in surface water distribution (0.813709, Critical R = 0.805). Overall, the results of this investigation point to the combined influence of climate change and human agency, with the latter tending to play a more prominent role by exerting increasing pressure on the environment’s natural supporting potentials. We therefore urge the scientific community to continue exploring actionable interventions that can be used to enhance the sustainability of this ecosystem and others elsewhere.

Identifying multiple geographically restricted phylogeographic lineages of Moggel (Cyprinidae: Labeo umbratus) in South Africa

Labeo umbratus (Smith, 1841) is a widespread species with populations distributed across isolated southern African river systems. Given that cryptic lineages have been detected in freshwater fishes with a similar distribution, a phylogeographic study of L. umbratus was conducted, considering populations sampled from nine currently isolated river systems between 2008 and 2013. Analyses of mitochondrial DNA (cyt b) and nuclear DNA (S7) sequence data demonstrated that two unique lineages occur in the west-flowing Orange River and south-flowing drainages, respectively. The southern lineage was further divided into three sublineages: one restricted to the Gouritz River, the second largely confined to the Gamtoos River and the last distributed across catchments to the east (the Sundays, Bushmans, Great Fish, Keiskamma, Buffalo and Nahoon rivers). The Great Escarpment and deep incisions along the south coast were identified as potentially influencing the geographic genetic structure of this species. For conservation purposes and pending future taxonomic assessment, the two major lineages were identified as Evolutionarily Significant Units, and Management Units were identified within the southern lineage.

Development of the Sterile Insect Technique to Suppress Thaumatotibia leucotreta (Lepidoptera: Tortricidae) in Citrus Fruit: Commercialisation and Expansion (Part 2)

Progress since 2007 with the commercial implementation of the sterile insect technique (SIT) for Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) in citrus orchards in South Africa is discussed. To enable expansion of the SIT programme, rearing equipment was developed and adapted where necessary. Production monitoring systems for traceability, cold chain management and quality management of reared insects were developed and constantly improved. The initial 3300-ha SIT-treated area in the Citrusdal region was increased to 4800 ha by incorporating parts of the Olifants River Valley and sterile insect releases were also introduced into 6500 and 2200 ha of the Sundays River and Gamtoos River Valleys (Eastern Cape Province), respectively. There was a progressive, seasonal improvement in wild T. leucotreta suppression following routine releases of sterile moths in all areas treated, resulting in reduced crop losses and fewer rejections for T. leucotreta in export fruit. The SIT for T. leucotreta was also expanded to the Hex River Valley (Western Cape Province) and the Lower Orange River area (Northern Cape Province) in 2016.

Multivariate analysis of the dominant and sub-dominant epipelic diatoms and water quality data from South African rivers

Data are presented on the distribution of the dominant and sub-dominant epipelic diatoms found in South African rivers from different regions of the country. A multivariate analysis identified 36 diatom species that were associated with different levels ofTDS, PO 4 , NH 4 and SiO 2 . Three groups of rivers were identified. Group I consisted of sites with high PO 4 and SiO 2 which corresponded to Durban Metropolitan Area sites, Kruger National Park rivers, the rivers in the Johannesburg Metropolitan Area and the Orange River. In these rivers 12 diatom species were identified that might indicate those water quality characteristics. Group II included stations where the water quality had high TDS and NH 4 values which were associated with most stations in the Swartkops River in the Eastern Cape. The indicators in this group comprised 12 diatom species. Group III were from sampling stations where the water had low levels of minerals, i.e. the upper reaches of the Gamtoos River and the Swartkops River in the Eastern Cape, the Olifants River in the Northern Cape, rivers sampled in KwaZulu-Natal and the Northern Cape. At these sites, 13 diatom species were found as dominants in this better water quality. Water quality data collected during this study showed that over 50% of the river systems display some degree of eutrophication and thus efforts should be made to reduce inputs of nutrients and pollutants to those rivers.

Historical abiotic events or human-aided dispersal: inferring the evolutionary history of a newly discovered galaxiid fish.

Range expansion of obligate freshwater fishes in the Cape Floristic Region (CFR) of South Africa has mostly been attributed to river capture events and confluence of rivers following sea-level regression. The role of low drainage divides and interbasin water transfers has received less attention. This study analyzed mitochondrial and nuclear DNA sequences to assess the processes that could have influenced the phylogeographic patterns of a newly discovered lineage of Galaxias zebratus (hereafter Galaxias zebratus “Joubertina”) that occurs across two currently isolated river systems close to the Joubertina area in the eastern CFR. Results from both analyses revealed that observed genetic differentiation cannot be explained by isolation between the two river systems. No genetic differentiation was found between the Krom River system and a population from one of the Gamtoos tributaries. Shallow genetic differentiation was found between the Krom and the other Gamtoos populations. Historical river capture events and sea-level changes do not explain the present distribution of Galaxias zebratus “Joubertina” across the Krom and Gamtoos River systems. Interbasin dispersal during pluvial periods, recent river capture, or recent human-mediated translocation seems to be the most plausible explanations.

Aspects of the biology and ecology of the estuarine cirolanid isopod, Cirolana fluviatilis

Trends in the distribution, population dynamics and reproductive biology of the estuarine cirolanid isopod, Cirolana fluviatilis, were investigated over a 12-month period in the warm–temperate Gamtoos River Estuary, by means of baited traps. Tolerance of adult isopods to combinations of salinity and temperature, and sediment preference, were investigated in the laboratory. Isopods were captured in highest numbers in the lower to middle reaches of the estuary, which appears to be related to a preference by C. fluviatilis for sediment with high mud content. Size-frequency distributions tended to be unimodal, becoming slightly bimodal only after manca release, which occurred predominantly during the warm summer months (December–March). Female C. fluviatilis reached sexual maturity at a length of about 6.0 mm, and males at about 5.2 mm. Fecundity was positively correlated to female body length. Brooding females remained inactive, leading to temporal variations in the male to female ratio.

Reproductive co-existence between five Aloe species in the Gamtoos River Valley, Eastern Cape

Reproductive co-existence between five Aloe species in the Gamtoos River Valley, Eastern Cape

Aspects of the biology and ecology of the estuarine cirolanid isopod, Cirolana fluviatilis

Trends in the distribution, population dynamics and reproductive biology of the estuarine cirolanid isopod, Cirolana fluviatilis, were investigated over a 12-month period in the warm–temperate Gamtoos River Estuary, by means of baited traps. Tolerance of adult isopods to combinations of salinity and temperature, and sediment preference, were investigated in the laboratory. Isopods were captured in highest numbers in the lower to middle reaches of the estuary, which appears to be related to a preference by C. fluviatilis for sediment with high mud content. Size-frequency distributions tended to be unimodal, becoming slightly bimodal only after manca release, which occurred predominantly during the warm summer months (December–March). Female C. fluviatilis reached sexual maturity at a length of about 6.0 mm, and males at about 5.2 mm. Fecundity was positively correlated to female body length. Brooding females remained inactive, leading to temporal variations in the male to female ratio.

The Return of Sara Baartman

Return of Sara Baartman. Film by Zola Maseko. New York: First Run Icarus Films, 2003. 53 min., color. $248 purchase, $75.00 rental. Zola Maseko's film focuses on people who engineered return of Sara Baartman's physical remains from Paris to South Africa for burial. In life Baartman was the hottentot Venus in London and Paris in 1800s and 1810s, a famous exhibit. She died young, in France, and French pickled her vagina, and stored her bones in a box. These remains are golden briefcase in this film-the focus of everyone's attention-even though no one can figure out exactly what remains signify. South Africans like to resolve such matters in meetings, and movie is largely a recording of such committee work and of what people were thinking and feeling during hand-over. Maseko's first film, The Life and Times of Sara is excerpted in this one; there are brief monologues, and then scenes of Baartman's burial in Hankey, a nondescript town in Eastern Cape, where President Mbeki gave a suitable speech. movie lasts 53 minutes and is uninspired and often dull: don't expect it to win any Indie cinema award. voice-over begins on a wrong note, by mispronouncing with a non-explosive palatal fricative, g, as goegoe, instead of in usual way, perhaps in order to make a (spurious) claim to specialist knowledge. Khoikhoi were slaughtered in colonial hunting raids and decimated by smallpox, their lands stolen, a fair summation: but it is not clear that Baartman identified herself as a Khoikhoi, or a Christian, or some other ethnic or political name, or, more likely, as a daughter. By time she was born, in 1789, Boers had been acquiring loan farms on far side of Gamtoos River for twenty years. Like so many, she was a resident worker· on such a farm. She happened to have a large and protuberant posterior, for a Khoikhoi or a European, and she caught eye of a lewd impresario. Persuaded to go to Europe (how?), she was displayed in flesh on stage and paid a very small wage. There were always whispered rumors about the hottentot's body, her mythical anatomy and genitalia. Maseko's film, and narration (written and spoken by one Gail Smith), do not explain reference any further. It is to elongated labia minora within folds of a Khoikhoi woman's vagina. A debate still simmers among anthropologists and historians about whether there was such a physical difference, whether it was common, induced by customary practices (pulling), perhaps in some form of masturbation, whether it exists today, etc. Burying Baartman won't stop such talk about different bodies and sexual fetishism. Nineteenth-century audiences had not been shamed into silence and elaborated various discourses around Baartman before and after her death. George Cuvier measured her for anthropometric science, and compared her anatomy to that of apes and dogs. (Discordant music makes it hard to concentrate on what Cuvier was saying. music in this film is awful.) Cuvier made a cast of her after she died, and this model was exhibited at Musee de l'Homme, a veritable part of French history and culture for over 150 years, until 1974. Baartman, narrator Gail Smith tells, us became a symbol of black women's sexuality, which is what Sander oilman has argued.1 This was not case in 1810, when she was considered more of an oddity, but it is certainly true today. No doubt many of people in Maseko's film view Baartman as a symbol of black women's sexuality. Several of her modern partisans, having gained possession of her body in material form, want to use it to proclaim black women's repossession of their own bodies in a transformed South Africa today. Sadly, incidence of rape among black people in South Africa has remained high or even increased in townships since demise of apartheid. For others, Baartman's bones must be buried for spiritual reasons, to repair a trespass on Coloured women's modesty, to assert a form of ownership of her memory, to replace racial typology and exploitation with domestic containment and repose. …

Examining the Genetic Structure among Populations of the Common Cape River Crab Potamonautes Perlatus from River Systems in South Africa Reveals Hydrographic Boundaries

Abstract The genetic structure of the common Cape river crab Potamonautes perlatus (Decapoda: Potamonautidae) was assessed among 21 populations from major drainage systems in South Africa using allozymes and sequence data from two mitochondrial genes (16S rRNA and COI). Protein gel electrophoresis of 15 loci encoding 11 enzyme systems revealed limited genetic variation in the Berg and Olifants drainages. However, in the Gamtoos and Bree river systems, and over all populations, moderate levels of variation were evident from the FST values. Gene-flow estimates revealed high levels of dispersal within and between drainages. In contrast, phylogenetic analysis of the 16S rRNA mtDNA sequence data from 10 representative populations revealed two distinct clades. One consisted of all the rivers that drain the western escarpment, and another consisted of rivers that drain the southern escarpment. The COI mtDNA and a combined sequence data analysis consistently placed the western flowing rivers in a distinct clade. ...

The nutrient status of the agriculturally impacted Gamtoos Estuary, South Africa, with special reference to the river‐estuarine interface region (REI)

Abstract Ecological water reserves are part of the new water management philosophy in South Africa. The estuaries are threatened by excessive water abstraction from their rivers and the consequent reduction in freshwater input. This study was conducted to further improve our understanding of freshwater requirements in terms of nutrients for South African estuaries. The Gamtoos Estuary was sampled between November 1996 and November 1998 to determine its nutrient status and freshwater input rates. Furthermore, the possible existence of a distinct river‐estuarine interface (REI) in terms of nutrients has been investigated. Nutrients analysed included phosphate, nitrate, nitrite, ammonia, dissolved organic nitrogen (DON), dissolved organic carbon (DOC), particulate organic nitrogen (PON) as Kjieldahl nitrogen, total particulate phosphorus and total particulate carbon. The Gamtoos River was found not to be the ultimate source of nutrients to the estuary, but non‐point sources such as the seepage of fertilisers from adjacent agricultural fields determined to a great extent the nutrient status of the estuary. Results showed that it was not possible to identify a defined river‐estuarine interface region for all nutrients. Most were measured in higher concentrations in the lower salinity reaches (<17‰) where we observed the combined effect of inputs from the Gamtoos River, an agricultural drainage pipe, and fertilizer seepage from non‐point sources on nutrient concentration. Prolonged water withdrawal for human use impacts the continuous renewal of the nutrient pool so important to other South African estuaries with relative pristine catchment areas. However, reduced fresh water inputs could enhance eutrophication in polluted estuaries due to a decreased flushing potential of the estuary. In this case the Gamtoos Estuary has a freshwater requirement for freshets and floods to “clean” the estuary of accumulated nutrients and other organic material. This should be a consideration in further freshwater abstraction policies. Conservation issues arise since the Gamtoos Estuary is one of the few permanently open estuaries along the South African coast and serve in this study as an example and as a first attempt to relate freshwater requirements to nutrient dynamics in a South African context. Copyright © 2002 John Wiley & Sons, Ltd.

Effect of River Flow on Estuarine Microalgal Biomass and Distribution

Impoundments and abstraction from rivers have reduced the amount of riverwater flowing into estuaries. This has necessitated research on the riverwater requirements of these important ecosystems. A study was initiated on the structure and biomass of microalgae in the Gamtoos estuary (Eastern Cape Province, South Africa) in order to improve our capability to predict changes and determine the acceptability of reduced riverwater input. The mean annual runoff of the Gamtoos River has been halved by major impoundments. Agriculture in the Gamtoos estuary valley contributes high concentrations of nutrients through groundwater seepage and an extensive sub-surface drainage system. This study determined the responses of microalgae to the volume of river discharge. A strong longitudinal salinity gradient was present at water flow rates ranging from 0·3 to 30·5m3s−1. There was strong vertical stratification at flows above 1m3s−1. Nitrate concentration increased from 1·9±0·2μM (at 0·3m3s−1) to 83·6±13·8μM (at 30·5m3s−1). Phytoplankton biomass was highest in the oligo- and mesohaline reaches of the estuary and was strongly correlated to turbidity. Phytoplankton chlorophylla was highest at flow rates of 0·8 (47·5±4·5μgl−1) and 1·16m3s−1(49·9±7·3μgl−1). Subtidal and intertidal benthic chlorophylla were highest at flow rates of 1·0 (57·7±0·4kg) and 1·16m3s−1(8·7±0·1kg) respectively. A riverwater input rate of ∼1·0m3s−1appears optimal for phytoplankton and benthic microalgal growth. At this flow rate, the estuary acts effectively at removing excess nutrients from the water before it discharges to the sea.

Composition and biogeography of forest patches on the inland mountains of the southern Cape

Patterns in species richness of 23 small, isolated forests on the inland mountains of the southern Cape were studied. Species richness of woody plants and vines of the Kouga-Baviaanskloof Forests was higher than in the western mountain complexes, where species richness in the more southern Rooiberg and Kamanassie Mountains was higher than in the Swartberg range. The Rooiberg, a dry mountain with small forests far away from the coastal source area, had more species than, and contained many species which are absent from, the larger, moister forests of the Kamanassie which are closest to the coastal source areas. Neither altitude nor distance from the source area, the forests south of the coastal mountains, nor long-distance dispersal, adequately explained the variation in species richness. The variations are best explained in terms of dispersal corridors along the Gouritz and Gamtoos River systems which connect the coastal forests with the inland mountains. The distribution patterns of four species groups in relation to the geomorphological history of the two river systems provide relative dates for the expansion and contraction of temperate forest, subtropical forest and subtropical transitional thicket in the southern Cape.

RANGE EXTENSIONS FORGALAXIAS ZEBRATUSCASTELNAU, 1861 (GALAXIIDAE), KROM AND GAMTOOS RIVER SYSTEMS, EASTERN CAPE.

Summary The distribution of the members of the Southern Hemisphere family Galaxiidae has intrigued biogeographers for some time. They are present in South America, Africa, Australia and New Zealand. There is only one species in Africa, the Cape galaxias (Galaxiaszebratus). Galaxias zebratus had previously been recorded from the Keurbooms River in the eastern Cape to the Olifants River in the western Cape. Recently specimens were collected from the source of the Krom River system and the upper Gamtoos River system, which extends the known distribution of this freshwater fish species eastwards. Alien fish, dams and water abstraction threaten what remains of these important populations of Cape galaxias.

The comparative reproductive styles of two closely related African minnows (Pseadobarbus afer andP. asper) inhabiting two different sections of the Gamtoos River system

The comparative reproductive styles of two closely related African minnows (Pseadobarbus afer andP. asper) inhabiting two different sections of the Gamtoos River system

The comparative reproductive styles of two closely related African minnows (Pseadobarbus afer andP. asper) inhabiting two different sections of the Gamtoos River system

The comparative reproductive styles of two closely related African minnows (Pseadobarbus afer andP. asper) inhabiting two different sections of the Gamtoos River system

Effects of turbidity on the neural structures of two closely related redfin minnows,Pseudobarbus aferandP. asper, in the Gamtoos River System, South Africa

The neural structures of the sister species Pseudobarbus afer and P. asper were compared. P. afer, a redfin minnow which inhabits clear, perennial mountain streams, was found to have larger neural structures related to vision than P. asper, which inhabits turbid, intermittent streams of the Gamtoos River system, P. asper did not show any compensation to inhabiting a turbid environment. Overall, P. afer males had the largest neural structures, most notably the optic lobes and cerebella, and P. asper females had the smallest neural structures.

The effects on fish spawning and management implications of impoundment water releases in an intermittent South African river

AbstractThe potamodromous smallscale redfin minnow (Pseudobarbus asper) spawned in the riffle areas of the regulated Groot River, the major tributary of the Gamtoos River system, during controlled releases of water from Beervlei Dam. Water had been released at irregular intervals from this flood control dam solely for irrigating agricultural lands. Flushing flows removed accumulated salts from riverine pools and were followed by reduced flows which initiated spawning of the minnow species. Developing embryos of P. asper were found in the riffle zone of the main river channel during the water releases. Ripe‐running males were located under the boulders in the riffles. Several developing embryos of Labeo umbratus were found with the P. asper eggs. Very little is known about the effects of man‐made alterations to the river flow regime on the reproductive activity of fishes in the majority of South African river systems. The agriculturally based flooding regime at Beervlei may have increased the recruitment of the redfin minnow species. Water management must give cognizance to the biological and environmental requirements within the regulated river systems. Water release strategies from Beervlei Dam should include instream flow decisions based on the requirements of the aquatic environment as well as for agriculture.

Fish Collections Taken from a Small Agricultural Water Withdrawal Site on the Groot River, Gamtoos River System, South Africa

Summary Periodic water releases from Beervlei Dam on the Groot River of the Gamtoos River System were planned to flush the riverine pools of brack water and replace the pools with better quality water which was used to flood irrigate lucerne lands. Fish collections were made in a small irrigation canal situated on the banks of the Groot River. Three fish species were collected. Results indicated that up to a total of 131 smallscale redfin minnows, Pseudobarbus asper, are removed from the system every five minutes at this one small water withdrawal site. Larger minnow specimens and carp, Cyprinus carpio, were entrained during high river flows. When the river flow was reduced there were higher catches of young of the year fish. The fish are carried with the pumped water, which is flood irrigated onto lucerne fields, resulting in stranding and eventual mortality. It is recommended that the use of suitable screens, such as wedge-wire screens, could reduce the number of fish removed from the system during thes...

South-western extension of the known range of two freshwater shrimps,Caridina nilotica(Roux) andMacrobrachium petersi(Hilgendorf), in South Africa

Two freshwater shrimps, Caridina nilotica (Roux) and Macrobrachium petersi (Hilgendorf), were collected in the Gamtoos River in the eastern Cape, representing a southwestern range extension for both. This is the first known record of these species west of Port Elizabeth, and also the first record of an overlap of their distribution ranges with that of the Cape river shrimp, Palaemon capensis (de Man).