Time filter

Source Type

Malauene B.S.,University of Cape Town | Malauene B.S.,Instituto Nacional Of Investigacao Pesqueira | Shillington F.A.,University of Cape Town | Roberts M.J.,Oceans and Coasts Research | Moloney C.L.,University of Cape Town
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2014

Direct in-situ observations from a shallow underwater temperature recorder on the continental shelf and from a shipboard oceanographic survey, were combined with MODIS satellite data (sea surface temperature and chlorophyll-. a) to assess the temporal and spatial variability of temperature and chlorophyll-. a in the Mozambique Channel near the coastal town of Angoche, 16°S. Intermittent, relatively cool surface water and elevated chlorophyll-. a signatures were found, indicating upwelling near Angoche over an area between 15°S and 18°S. A 5-year (2002-2007) analysis of temperature (from both in-situ and satellite) revealed two distinct periods: (1) the August-March period with highly variable intermittent "cool water" events and (2) the April-July period with little temperature variability. Generally, periods of cooling occurred at about 2 months intervals, but shorter period occurrences (8-30 days) of cool coastal events were also observed. Two possible forcing mechanisms are discussed: (1) wind derived coastal upwelling (using satellite blended sea surface wind derived from NOAA/NCDC) and (2) the effect of passing transient southward moving eddies (using sea level anomalies from AVISO altimetry). It is suggested that the cool surface, elevated chlorophyll-. a waters are primed and formed by favourable wind-driven Ekman-type coastal upwelling, responding to alongshore northeasterly monsoon winds prevailing between August and March. These waters are then enhanced in chlorophyll-. a and advected further offshore by anti-cyclonic/cyclonic eddy pairs interacting with the shelf. © 2013 Elsevier Ltd.

Kirkman S.P.,Branch Oceans and Coasts | Kirkman S.P.,University of Cape Town | Yemane D.,University of Cape Town | Atkinson L.J.,University of Cape Town | And 8 more authors.
Fisheries Oceanography | Year: 2015

Using long-term survey data, changes in demersal faunal communities in the Benguela Current Large Marine Ecosystem were analysed at community and population levels to provide a comparative overview of the occurrence and timing of regime shifts. For South Africa, the timing of a community-level shift observed in the early 1990s, and of a lesser shift observed in the mid-2000s, corresponded well with the results of other studies that showed environmental, community-level or population-level changes at similar times, suggesting that environmental forcing had played a role. Several population-level shifts were detected for Namibia; these and a regime shift in the overall community identified for this country corresponded well to the timing of severe environmental perturbations and an extensive regime shift in the pelagic ecosystem of this area. However, the interpretation of these shifts was confounded by changes in sampling gear; closer scrutiny of the types of species affected and the direction of shifts (increase/decrease) in relation to the timing and nature of sampling gear modifications, revealed that the observed shifts were potentially an artefact of gear changes. This highlighted the importance of accounting for changes in sampling protocols during the analysis and interpretation of long-term data. For Angola, a community level shift in the mid-2000s and population-level changes for a few species (mainly positive), could not have been influenced by gear changes which took place mainly before the onset of the time series under consideration. However, no clear environmental or anthropogenic changes that could have influenced these shifts were obvious. © 2015 John Wiley & Sons Ltd.

Livramento F.,Agostinho Neto University | Rangel I.M.,Instituto Nacional Of Investigacao Pesqueira
Toxicon | Year: 2010

The presence of ASP toxins in Luanda Bay, an area 2700 km apart from the closest record of this type of toxicity and with a different hydrographic regime, was studied. Two outbreaks were confirmed by LC/MS/MS with presence of domoic acid and some isomers both, in plankton and in three of the most important bivalve species from the area. Domoic acid levels in the studied bivalves were below the regulatory limits for most countries and the first estimations indicate that they depurated the toxin quickly. It is, therefore, unlikely that any intoxication would have taken place by consumption of these bivalve species. Notwithstanding, the relatively high annual frequency of the blooms together with possibility that other bivalve species could retain this compound more strongly, suggest that this kind of intoxication might pose a significant risk in Angola. © 2009 Elsevier Ltd. All rights reserved.

Yemane D.,Fisheries Management | Yemane D.,University of Cape Town | Kirkman S.P.,Branch Oceans and Coasts | Kirkman S.P.,University of Cape Town | And 4 more authors.
Reviews in Fish Biology and Fisheries | Year: 2014

Distributional change, expressed as range expansion or contraction, has been observed in many marine populations and related to changes in the environment. The extent of such distributional changes is also expected to increase in response to future climate change. The Benguela Current Large Marine Ecosystem (BCLME) which adjoins the south-western coast of Africa is a global marine hotspot with long-term warming occurring over a large area. The area is also an important centre of marine food production for three countries-South Africa, Namibia and Angola and is considered to be vulnerable to future climate change or increased climate variability. In this study we analysed change in distribution and range size of several demersal fish species in the BCLME over the period 1985-2010, including both commercial and non-commercial fish populations. Some of the observed changes in distribution and range size correspond to what is expected with increased warming whereas others appear to the contrary. Overall the results of the study highlight the complex nature of the response of fish population to climate change. © 2014 Springer International Publishing Switzerland.

Vardaro M.F.,Oregon State University | Bagley P.M.,Aker Solutions | Bailey D.M.,University of Glasgow | Bett B.J.,UK National Oceanography Center | And 10 more authors.
Limnology and Oceanography: Methods | Year: 2013

The DELOS (Deep-ocean Environmental Long-term Observatory System) project is a long-term research program focused on understanding the impacts of oil and gas extraction on deep-sea ecosystems. We have installed two seafloor observation platforms, populated with ROV-serviced sensor modules, at 1400 m water depth in the Southeast Atlantic off the coast of Angola. The 'impact' Near-Field platform is located 50 m from subsea oil production facilities. The 'control' Far-Field platform is 16 km distant from any industry seafloor activity. Each platform includes oceanographic, acoustic, and camera sensor modules. The latter carries two still cameras providing close-up and wide-angle views of the seabed. The Far-Field platform is also equipped with a sediment trap that deploys to 100 m above the seafloor. The instrumented platforms were installed in Feb 2009, and the sensor modules subsequently serviced in Aug 2009, Feb 2010, and Aug 2010. Here, we report on our first experiences of operating the observatories and present some of the first data. The oceanographic data (temperature, salinity, oxygen concentration) and biological observations (demersal fish and benthic invertebrates) suggest that the two study sites have near identical environmental characteristics. We, therefore, believe that these sites are appropriate as control and impact locations for long-term monitoring of potential anthropogenic effects referenced to natural background environmental variation. We suggest that DELOS-type observatories, particularly operated as pairs (or in networks), are a highly effective means of appropriately monitoring deep-water resource exploitation-both hydrocarbon extraction and mineral mining ©2013, by the American Society of Limnology and Oceanography, Inc.

Discover hidden collaborations