Riverine dominance of a nearshore marine demersal food web: evidence from stable isotope and C/N ratio analysis

The Thukela Bank, KwaZulu-Natal, supports a diverse ecosystem and South Africa’s only prawn fishery. Oceanographic studies suggest riverine input is not important for the biology of this system, whereas biological studies suggest the contrary, with prawn catches increasing with increased fluvial run-off. The aim of this study was to determine (i) the importance of riverine and marine organic matter for the Thukela Bank food web; and (ii) whether there are seasonal changes in the Thukela River stable isotope values, and, if so, whether these are reflected in the isotope values of demersal organisms. Estuarine organic matter, sediments and demersal organisms were collected from several sites across the bank in the wet and dry seasons of 2008, 2009 and 2010. Marine particulate organic matter was also collected in 2010 and analysed for δ13C and δ15N, as well as C/N ratios. There were strong seasonal changes in isotopic values of organic matter and fauna, especially faunal δ13C. There was an apparent time-lag in organisms assimilating riverine organic matter isotopic values, with the isotopic signature of demersal organisms reflecting that of riverine organic matter from the previous season, which is likely the result of tissue turnover time. In 2010, Thukela Bank sediment organic matter was of riverine origin and this maintained the demersal food web. We conclude that Thukela River organic matter is an important input to the food web of the Thukela Bank, indicating that any future damming of the catchment area could have serious consequences for this ecosystem.DHE

The mammals of Angola

Scientific investigations on the mammals of Angola started over 150 years ago, but information remains scarce and scattered, with only one recent published account. Here we provide a synthesis of the mammals of Angola based on a thorough survey of primary and grey literature, as well as recent unpublished records. We present a short history of mammal research, and provide brief information on each species known to occur in the country. Particular attention is given to endemic and near endemic species. We also provide a zoogeographic outline and information on the conservation of Angolan mammals. We found confirmed records for 291 native species, most of which from the orders Rodentia (85), Chiroptera (73), Carnivora (39), and Cetartiodactyla (33). There is a large number of endemic and near endemic species, most of which are rodents or bats. The large diversity of species is favoured by the wide range of habitats with contrasting environmental conditions, while endemism tends to be associated with unique physiographic settings such as the Angolan Escarpment. The mammal fauna of Angola includes 2 Critically Endangered, 2 Endangered, 11 Vulnerable, and 14 Near-Threatened species at the global scale. There are also 12 data deficient species, most of which are endemics or near endemics to the countryinfo:eu-repo/semantics/publishedVersio

Reproductive biology and growth of the yellowbelly rockcod Epinepheluse marginatus (Serranidae) from South-East Africa

Investigation of the reproductive biology and growth of the yellowbelly rockcod Epinephelus marginatus from South-East Africa confirms that the species is a monandric protogynous hermaphrodite, i.e. males are derived from females, probably as a result of environmental or social cues. Spawning occurred during summer, female size-at-50% maturity was 622mm TL and the smallest male recorded was 800mm TL. Sex ratios of mature fish were female biased (1:0.18). Tetracycline marking revealed that deposition of growth bands is annual, and the von Bertalanffy growth parameters determined by means of otoliths were L&#8734 = 1 249mm TL, k = 0.09 year–1 and t0 = –1.43 years. The species is therefore long-lived, slowgrowing and matures late. Other studies indicate that E. marginatus aggregate for spawning, and tagging work has shown that they exhibit high site fidelity. The life history of the species indicates that it is vulnerable to overexploitation.Keywords: grouper, growth, hermaphroditism, protogyny, SerranidaeAfrican Journal of Marine Science 2006, 28(1): 1–1

Subtropical demersal fish communities on soft sediments in the KwaZulu-Natal Bight, South Africa

<p>The project entitled Ecosystem Processes in the KwaZulu-Natal Bight, part of the African Coelacanth Ecosystem Programme (ACEP), enabled the description of demersal fish communities over soft sediments, including from some areas that have rarely been explored in the subtropical waters of the east coast of South Africa. A total of 165 fish taxa from 78 families were caught, and were dominated by the Sparidae (five species), Triglidae (four species), Acropomatidae (three species), Macrouridae (eight species), Chlorophthalmidae (one species), Paralichthyidae (three species) and Sciaenidae (six species), which together contributed 75% and almost 60% to numbers and weight, respectively. The most ubiquitous species were <i>Chlorophthalmus punctatus</i> and <i>Pagellus natalensis</i>. Species composition was structured mainly by depth, and proximity to the Thukela River, the latter being particularly influential on the adjacent Thukela Bank that harbours a unique community. There are close affinities between KZN Bight soft-sediment fish communities and those off Western Australia, and particularly with communities from East Africa. The unique nature of fish communities off the Thukela River is part-motivation towards the establishment of a large marine protected area in the northern part of the KZN Bight, which is increasingly the focus of disruptions such as impoundments and mining.</p

Can bycatch reduction devices be implemented successfully on prawn trawlers in the Western Indian Ocean?

Bycatch reduction devices (BRDs) are increasingly being used in prawn trawl fisheries worldwide. This paper describes an experiment with a Nordmøre grid and a square-mesh panel on a prawn trawler off Moçambique. Although numbers of hauls that caught elasmobranchs were low, 75% of hauls with grids caught fewer large rays than those without grids; hauls using grids caught no large sharks at all. In its final configuration, the grid respectively reduced prawn, discard and retained fish catches by 5%, 25% and 32% relative to control hauls; the square-mesh panel increased prawn catches by 3% and respectively reduced discard and retained fish catches by 23% and 18% relative to control hauls. Changes in prawn catches were not statistically significant; however, when the grid and the square-mesh panel were used together, they reduced prawn, discard and retained fish catches by 25%, 47% and 26% respectively relative to control hauls (all significant except for retained fish catches). Overall, the Nordmøre grid successfully released large elasmobranchs, and the grid and the square-mesh panel individually reduced bycatch without reducing prawn catches. In combination, the two BRDs also reduced bycatch, but at the cost of substantially reduced prawn catches. The results indicate that there is scope for the wider use of BRDs on prawn trawlers in the Western Indian Ocean region, although this would require increased support from management agencies and industry. Keywords: bycatch, bycatch reduction device, prawn trawlingAfrican Journal of Marine Science 2007, 29(3): 453–46

Reproductive biology of a diandric protogynous hermaphrodite, the serranid Epinephelus andersoni

Epinephelus andersoni is a serranid endemic to south-eastern Africa. An investigation of the reproductive biology of this species from two areas along the east coast of South Africa revealed that E. andersoni exhibits several features that differ from the hermaphroditism found in most other epinepheline serranids. Among sexually mature fish, there is a complete overlap of male and female sizes and significantly more males than females. Males can develop directly from the juvenile phase as well as by sex change from functional females, although testicular morphology does not vary according to developmental pathway. Hence, the species is classified as a diandric protogynous hermaphrodite, a sexual pattern hitherto unconfirmed for the genus Epinephelus. The morphology of the gonads also differs from that of congeners, with male and female tissues being spatially distinct. A substantial part of the mature-sized component is not reproductively active, possibly because of edge-of-range effects and/or because not all individuals spawn each year. Reproduction occurs between November and January, and female total length at 50% maturity is 492 mm.link_to_subscribed_fulltex

A retrospective assessment of the stock status of Otolithes ruber (Pisces:Sciaenidae) as bycatch on prawn trawlers from KwaZulu-Natal, South Africa

No Abstract.African Journal of Marine Science Vol.29(2) 2007: pp. 247-25

Synthesis An editorial synthesis of the ACEP project: Ecosystem Processes in the KwaZulu-Natal Bight

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A brief overview of the ACEP project: Ecosystem Processes in the KwaZulu-Natal Bight

This introductory paper lays the basis for this supplementary issue by briefly presenting the state of knowledge on the KwaZulu-Natal (KZN) Bight at the start of this multi-disciplinary, multi-institutional, ship-based research project that ran from 2009 to 2013. The rationale and aims of the project are also described. The project was a major component of the South African Department of Science and Technology’s African Coelacanth Ecosystem Programme (ACEP), which has been prominent in supporting research on the east coast of South Africa and the wider South-West Indian Ocean. Pivotal to this was the RS Algoa, which was made available for two 30-day surveys (winter and summer) in the KZN Bight by the Department of Environmental Affairs. Although some aspects of the bight ecology are known, much of the research is dated and fragmented, and required refreshing and consolidation in order to produce a platform upon which the understanding of the region’s ecosystem functioning could be established. Much of the oceanographic knowledge is also dated, with no dedicated surveys and significant measurements undertaken since 1989. The overarching theme of the KZN Bight project was to examine the relative importance of sources of nutrients to the central KZN coast and how these are taken up and recycled in the ecosystem, and to describe aspects of the benthic biodiversity, which is poorly described in much of this region. An ambitious project, its accessibility to a ship-based research platform and the diverse scientific skills of the participating scientists allowed considerable success, as reflected in the papers that follow.Keywords: benthic, community, demersal, fluvial, models, nutrients, oceanography, pelagic, sedimen

Influence of the sardine run on selected nearshore predatory teleosts in KwaZulu-Natal

The relationships between shore-angling catch rates of nearshore predatory teleosts in KwaZulu-Natal, South Africa, and the timing of the sardine run were examined using a multiple regression model. Results showed that catch rates of five (elf Pomatomus saltatrix, garrick Lichia amia, king mackerel Scomberomorus commerson, blacktip kingfish Caranx heberi and kingfish Caranx spp.) of the nine teleost predators selected for their predatory habits on sardine Sardinops sagax were significantly higher during the months of the sardine run (June–July/August). This corroborates anecdotal and scientific reports of close associations between these predatory fish and the run. It is not clear whether these relationships can be ascribed to a feeding migration by the predators, a reproductive migration by the predators or an extension of suitable habitat for both prey and predators during these months. It is possible that the misidentification of some predatory species may have confounded the results for some species, or that these species are not as strongly influenced by the sardine run as previously thought. Keywords: CPUE, feeding, linefish, migration, recreational fishing, sardine, spawningAfrican Journal of Marine Science 2010, 32(2): 375–38