Seasonal and interannual variability in wind field and commercial catch rates of austroglossus pectoralis (soleidae)

The impact of deviations in the direction and strength of the wind field on the spatial, seasonal and interannual variability in catch rates of Agulhas sole Austroglossus pectoralis was investigated. Temporal variabilityin the wind cycle on the Agulhas Bank during the period 1981–1996 was deduced mainly from trends in the pressure gradient, measured from south of Cape Agulhas (35°S) to the region of westwind drift (40°S).Because interannual deviations in the catch rates differed between seasons, catch rates were assessed by season. Coastal catch rates of Agulhas sole between Cape Agulhas and Cape Infanta were high in autumn and winter, when offshore north-westerly winds prevailed, and low in spring and late summer, when onshore south-easterly winds dominated. There was often a secondary peak in catch rates in November–December,coincident with a midsummer change in the pressure gradient. Between the period 1982 and 1996, catch rates in autumn and early winter (April–July) were highest during years when the winter north-westerly winds were strongest (r2 = 0.62, p < 0.01). Catch rates usually peaked in May–June. This pattern changed in some years, depending on the timing and rate of change to winter wind conditions. Seasonal and interannual fluctuations in catch rate are associated with deviations in the wind field, but the  mechanism whereby this  effect is mediated remains unknown

Accommodating Dynamic Oceanographic Processes and Pelagic Biodiversity in Marine Conservation Planning

Pelagic ecosystems support a significant and vital component of the ocean's productivity and biodiversity. They are also heavily exploited and, as a result, are the focus of numerous spatial planning initiatives. Over the past decade, there has been increasing enthusiasm for protected areas as a tool for pelagic conservation, however, few have been implemented. Here we demonstrate an approach to plan protected areas that address the physical and biological dynamics typical of the pelagic realm. Specifically, we provide an example of an approach to planning protected areas that integrates pelagic and benthic conservation in the southern Benguela and Agulhas Bank ecosystems off South Africa. Our aim was to represent species of importance to fisheries and species of conservation concern within protected areas. In addition to representation, we ensured that protected areas were designed to consider pelagic dynamics, characterized from time-series data on key oceanographic processes, together with data on the abundance of small pelagic fishes. We found that, to have the highest likelihood of reaching conservation targets, protected area selection should be based on time-specific data rather than data averaged across time. More generally, we argue that innovative methods are needed to conserve ephemeral and dynamic pelagic biodiversity

An upwelling filament North-West of Cape Town, South Africa

Satellite images frequently show a thin filament of water stretching from the Cape Peninsula upwelling cell to beyond the shelf edge north-west of Cape Town. The filament carries nutrients and weakly motile biologicalorganisms from the shelf zone towards the coastal transition zone, where eddies are observed. In order to probe the dynamics of the filament and its generating mechanism, a cruise was undertaken from 7 to10 February 1996. At that time, there appeared to be a filament in retreat, following an upwelling episode. There were two apparent eddies beyond the shelf edge observed in the satellite-derived SST. The southern feature did not have a clear hydrographic structure, but the northern one did, and it appears to be a semi-permanent feature. The region is forced by a number of oceanic and meteorological boundary conditions, none of which is entirely predictable. One is the sporadic advection of warm water from the Agulhas Bank onto the southern shelf. The cruise took place following such an event. The anticipated shelf-edge jet was greatly diminished and forced inshore. The possible effect of barotropic shelf waves on the configuration of the upwelling tongue and the formation of filaments is discussed

Seasonal and interannual changes in Intense Benguela Upwelling (1982-1999)

Monthly maps of remotely sensed sea surface temperatures derived from NOAA/AVHRR thermal images are used to describe changes in 'Intense Benguela Upwelling' during 1982-1999. The coastal area under investigation lies between 9-34degrees S and 8-20degrees E and the total area of cold water between the coast and the course of the 13 degreesC isotherm is considered to be an index of intense, active upwelling. It exhibits a decreasing trend over the study period of 18 years and some evidence for a quasi-cycle of about 27 months. Seasonal cycles are discussed for the total cold water area as well as for its mean alongshore and offshore extents. The main season of cold surface water was found to occur between July and September during the austral winter. It peaks in August with a mean area of about 30x10(3) km(2) and relaxes drastically during the rest of the year. The underlying process of intense coastal upwelling is regionally trapped in two coastal zones. These are centred around 26 and 29degrees S and reach a mean offshore extension of 210 and 130 km, respectively, to form giant upwelling filaments. The area of cold water drastically shrinks, roughly by a factor of two, during weak upwelling years but significantly expands by a factor of about 1.5 during strong years. Associated sea level changes along the south-west African coast were derived from measurements at four coastal stations between 23 and 34degrees S during 1982-1987. The first principal component describes about 63 % of the total sea level variance. The lowest sea levels were found in the prominent Luderitz cell near 26degrees S. On both the annual and interannual time scale, decreasing cold water areas are accompanied by increasing sea levels and vice versa. Mean seasonal cycles reveal that variations in the total cold water area tag behind those in the sea level along the entire south-west African coast by about 1 month.Des cartes mensuelles de température de surface de la mer, obtenues par satellite à partir du capteur NOAA/AVHRR, sont utilisées pour décrire l’épisode intense de la remontée d’eau de Benguela entre 1982 et 1999. La région côtière étudiée s’étend de 9 à 34° S et de 8 à 20° E ; la totalité de la tâche d’eau froide entre la côte et l’isotherme 13 °C est considérée comme le signe d’un upwelling intense. Cet indice décroît durant la période de 18 années et un cycle de 27 mois apparaît. Les cycles saisonniers sont discutés pour l’ensemble de la région « froide ». La saison principale de remontée se situe entre juillet et septembre, durant l’hiver austral. Elle atteint son maximum en août avec une aire moyenne concernée de 30×103 km2 et l’upwelling est particulièrement faible tout le reste de l’année. Deux foyers de remontée existent le long de la côte. Ils sont centrés sur 26° et 29° S et s’étendent au large respectivement jusqu’à 210 et 130 km en formant des filaments géants. L’aire de remontée se réduit de moitié durant les années de faible upwelling et s’étend d’une fois et demi les années d’upwelling intense. Des changements de niveau marin sont associés à ces phénomènes comme le prouvent les mesures effectuées à quatre stations côtières entre 23° et 24° S de 1982 à 1987. La composante principale décrit 63 % de la variance du niveau marin. Les niveaux les plus bas se rencontrent dans la cellule de Lüderitz près de 26° S. Aussi bien à l’échelle annuelle qu’à l’échelle interannuelle, les aires d’eau froide décroissantes sont liées à une montée du niveau marin et vice versa. Les cycles saisonniers moyens montrent que les variations de la surface totale d’eau froide sont décalées d’environ un mois par rapport à celles du niveau marin tout le long de la côte SW d’Afrique

Identification of adult plant resistance to stripe rust in the wheat cultivar Cappelle-Desprez

Following the appearance of stripe rust in South Africa in 1996, efforts have been made to identify new sources of durable resistance. The French cultivar Cappelle-Desprez has long been considered a source of durable, adult plant resistance (APR) to stripe rust. As Cappelle-Desprez contains the seedling resistance genes Yr3a and Yr4a, wheat lines were developed from which Yr3a and Yr4a had been removed, while selecting for Cappelle-Desprez derived APR effective against South African pathotypes of the stripe rust fungus, Puccinia striiformis f. sp. tritici. Line Yr16DH70, adapted to South African wheat growing conditions, was selected and crossed to the stripe rust susceptible cultivar Palmiet to develop a segregating recombinant inbred line mapping population. A major effect QTL, QYr.ufs-2A was identified on the short arm of chromosome 2A derived from Cappelle-Desprez, along with three QTL of smaller effect, QYr.ufs-2D, QYr.ufs-5B and QYr.ufs-6D. QYr.ufs-2D was located within a region on the short arm of chromosome 2D believed to be the location of the stripe rust resistance gene Yr16. An additional minor effect QTL, QYr.ufs-4B, was identified in the cv. Palmiet. An examination of individual RILs carrying single or combinations of each QTL indicated significant resistance effects when QYr.ufs-2A was combined with the three minor QTL from Cappelle-Desprez, and between QYr.ufs-2D and QYr.ufs-5BPeer reviewe