Nunkoo I.,University of Cape Town |
Reed C.,University of Cape Town |
Kerwath S.,University of Cape Town |
Kerwath S.,Fisheries Research and Development
African Zoology | Year: 2015
The presence of Southeast Asian walking catfish, Clarias batrachus, in Mauritian freshwater systems has been confirmed. Three female Clarias batrachus were caught in Rivière Sèche, close to the town of Phoenix, Mauritius (20°17′ S, 57°33′ E). This constitutes the first record of the introduction of this species into the wild on the island of Mauritius. © 2015 Zoological Society of Southern Africa.
Kerwath S.E.,Fisheries Research and Development |
Kerwath S.E.,University of Cape Town |
Winker H.,University of Cape Town |
Gotz A.,South African Environmental Observation Network |
Attwood C.G.,University of Cape Town
Nature Communications | Year: 2013
Potential fishery benefits of Marine Protected Areas (MPAs) are widely acknowledged, yet seldom demonstrated, as fishery data series that straddle MPA establishment are seldom available. Here we postulate, based on a 15-year time series of nation-wide, spatially referenced catch and effort data, that the establishment of the Goukamma MPA (18 km alongshore; 40 km 2) benefited the adjacent fishery for roman (Chrysoblephus laticeps), a South African endemic seabream. Roman-directed catch-per-unit-effort (CPUE) in the vicinity of the new MPA immediately increased, contradicting trends across this species' distribution. The increase continued after 5 years, the time lag expected for larval export, effectively doubling the pre-MPA CPUE after 10 years. We find no indication that establishing the MPA caused a systematic drop in total catch or increased travel distances for the fleet. Our results provide rare empirical evidence of rapidly increasing catch rates after MPA implementation without measurable disadvantages for fishers. © 2013 Macmillan Publishers Limited.
Hubbart B.,University of Cape Town |
Pitcher G.C.,University of Cape Town |
Pitcher G.C.,Fisheries Research and Development |
Krock B.,Alfred Wegener Institute for Polar and Marine Research |
Cembella A.D.,Alfred Wegener Institute for Polar and Marine Research
Harmful Algae | Year: 2012
The variability of toxigenic phytoplankton and the consequent uptake and loss of toxins by the mussel Choromytilus meridionalis was investigated in the southern Benguela at the event scale (3-10 days) in response to the upwelling-downwelling cycle. Phytoplankton and mussel samples were collected daily (20 March-11 April 2007) from a mooring station (32.04°S; 18.26°E) located 3.5km offshore of Lambert's Bay, within the St Helena Bay region. Rapid changes in phytoplankton assemblages incorporated three groups of toxigenic phytoplankton: (1) the dinoflagellate Alexandrium catenella; (2) several species of Dinophysis, including Dinophysis acuminata, Dinophysis fortii, Dinophysis hastata and Dinophysis rotundata; and (3) members of the diatom genus Pseudo-nitzschia. Analysis of phytoplankton concentrates by LC-MS/MS or LC-FD provided information on the toxin composition and calculated toxicity of each group. Several additional in vitro assays were used for the analysis of toxins in mussels (ELISA, RBA, MBA for PSP toxins; and ELISA for DSP toxins). Good correspondence was observed between methods except for the MBA, which provided significantly lower (approximately 2-fold) estimates of PSP toxins. PSP and DSP toxins both exceeded the regulatory limits in Choromytilis meridionalis, but ASP toxins were undetected. Differences were observed in the composition of both PSP and DSP toxins in C. meridionalis from that of the ingested dinoflagellates (PSP toxins showed an increase in STX, C1,2, and traces of dcSTX and GTX1,4 and a decrease in NEO; DSP toxins showed an increased in DTX1, and traces of PTX2sa, and a decrease in OA). The rate of loss of PSP toxins following dispersal of the A. catenella boom was 0.12d-1. Variation in the loss rates of different PSP toxins contributed to the change in toxin profile in C. meridionalis. Prediction of net toxicity in shellfish of the nearshore environment in the southern Benguela is limited due to rapid phytoplankton community changes, high variability in cellular toxicity, and the selective uptake and loss of toxins, and/or transformation of toxins. © 2012 Elsevier B.V.
Pitcher G.C.,Fisheries Research and Development |
Pitcher G.C.,University of Cape Town |
Probyn T.A.,Fisheries Research and Development
Harmful Algae | Year: 2011
Oxygen deficiency in the southern Benguela has a pronounced negative impact on living marine resources and within the greater St Helena Bay anoxia is the cause of large episodic mortalities of the rock lobster Jasus lalandii. These impacts have motivated further investigation, specifically of the role of high biomass dinoflagellate blooms, commonly known as red tides, in the development of anoxic conditions. A high resolution time series of dissolved oxygen concentrations obtained from a bottom mooring off Elands Bay, located within the greater St Helena Bay region, is examined in relation to the development of an exceptional bloom of the dinoflagellate Ceratium balechii and an anoxia-induced mass mortality. A clear seasonal trend is evident in bottom dissolved oxygen concentrations, initiated in spring by upwelling events that advect low oxygen waters across the shelf. Increased deposition of organic carbon derived from primary production maxima in summer and autumn, together with the development of an increasingly stratified environment exacerbate dissolved oxygen deficits leading to a progressive decline in dissolved oxygen concentrations in the cold bottom layer. Within this seasonal timeframe episodic anoxia may occur throughout the water column of shallow inshore regions following the decay of red tides accumulated within these environments under conditions of persistent downwelling. Anoxia within these shallow non-stratified nearshore regions is dependent on exceptional organic loading of the water column as afforded by the decay of red tide and to the absence of wind-induced mixing or wave action. These requirements contribute to the local and transient character of these events of anoxia. With the onset of winter strong mixing results in reduced primary production and increased ventilation of bottom waters causing an increase in dissolved oxygen concentrations. © 2011 Elsevier B.V.
Pieterse A.,Stellenbosch University |
Pitcher G.,Fisheries Research and Development |
Pitcher G.,University of Cape Town |
Naidoo P.,Institute for Animal Production |
Jackson S.,Stellenbosch University
Journal of Shellfish Research | Year: 2012
The Pacific oyster Crassostrea gigas is cultured at 8 commercial farms in South Africa. Worldwide, environmental-specific intensive selection on the species optimizes commercially beneficial traits, but its performance has not been studied in South Africa. From May 2010 to March 2011, we compared 2-mo measurements of growth rate, condition, and survival of 3 cohorts of different origin in longline culture at 3 different South African environments: 2 sea-based farms located in Saldanha Bay (Western Cape) and Algoa Bay (Eastern Cape) and a land-based farm at Kleinzee (Northern Cape). Overall, Saldanha Bay was cooler (mean sea surface temperature of 16.0°C; CV, 16.2%) than the other 2 localities, which did not differ significantly from one another (Kleinzee: 18.6°C; CV, 20.4%; Algoa Bay: 17.8°C; CV, 8.9%). The high variability at Kleinzee reflected stronger summer warming than at the other 2 farms. Saldanha Bay had higher phytoplankton biomass (mean, 14.3 mg chlorophyll a/m3; CV, 54.2%; May 2010 to March 2011) than did Algoa Bay (mean, 5.3 mg chlorophyll a/m3; CV, 81.0%; September 2010 to March 2011). The 3 cohorts showed similar trends in growth and condition. Growth rates, expressed as live or dry mass gains, were 2-10 times those reported elsewhere in the world, and dry weight condition indices were also high. High live mass growth rates in Algoa Bay, despite its relatively low phytoplankton biomass, seem to reflect a similar phenomenon to that reported in other relatively phytoplankton-poor grow-out environments, such as the Mediterranean Thau Lagoon in France. Dry meat mass gain and condition were highest for oysters in Saldanha Bay, with high food availability offsetting the thermal advantages of the warmer Algoa Bay site. Oysters in the bottom layers of the cages grew significantly faster than those in the top layers, particularly in Saldanha Bay, possibly reflecting fine-scale vertical differences in phytoplankton biomass. Saldanha Bay is the best of the 3 locations to produce market-ready oysters. Algoa Bay yields faster growth but leaner oysters and is a good nursery location, as is Kleinzee, which yields overall slow growth but good shell quality in winter and early spring. Copyright © 2013 BioOne.