Browsing by Author "Malauene, Bernardino Sergio"

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    Environmental influences on banana shrimps of the Sofala Bank, Mozambique Channel
    (2015) Malauene, Bernardino Sergio; Moloney, Coleen L; Roberts, Michael J; Marsac, Francis; Penven, Pierrick; Lett, Christophe
    The Sofala Bank in the western Mozambique Channel is an essential habitat for shallow-water penaeid shrimps. It supports an important multi-sector and -species fishery, with Fenneropenaeus indicus and Metapenaeus monoceros (banana shrimp) being the two main target species. Over the past decade this valuable resource has been declining, which has been attributed to environmental changes, but no conclusive evidence has been found. This PhD thesis aims to understand the interactive roles of biophysical processes on recruitment of banana shrimps, par ticularly their larvae on the Sofala Bank. It is hypothesized that shrimp larvae can be advected offshore by passing mesoscale eddies to regions where they are unable to survive and are thus lost. In the absence of both physical and biological observations, a modelling approach is used. A high-resolution, nested, coastal, Regional Ocean Modeling System (ROMS) of the Sofala Bank is developed. In general, the model agrees well with available observations and literature. The ROMS outputs and self-organizing map analysis indicate that the shelf circulation, structure and river plumes are strongly influenced by the highly energetic o_shore eddy activity. A biophysical, individual-based model (IBM) coupled to the ROMS was developed for early life stages of banana shrimps on the Sofala Bank. The IBM uses spawning patterns identified from analyses of both commercial and research survey data. Simulations indicate that shrimp larvae are lost offshore by entrainment in mesoscale eddies at inter- and intra-annual scales and eddies therefore are unlikely to produce a continuous declining in the catch. In contrast, these eddies induce onshore transport of larvae, promoting coastal settlement, compared with periods without eddies. Locations for simulated larval coastal settlement are identified: northern, central and southern. The roles of tides and larval diel vertical migration in influencing simulated larval settlement success was not conclusive; further research considering a selective tidal stream is needed. Simulated larvae were sensitive to low lethal temperature and river plumes. A conceptual model for the Sofala Bank circulation and another for the banana shrimps, early life history dynamics are proposed based on the results of this thesis.
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    Shelf edge upwelling off Northern Mozambique
    (2010) Malauene, Bernardino Sergio; Shillington, Frank; Moloney, Coleen; Roberts, Mike
    A combination of satellite and in situ data were used to infer the occurrence and temporalspatial variability of upwelling near Angoche. The data were derived from MODIS SST and Chl-a between 2003 and 2007, in situ moored underwater temperature recorder at a depth of 18 m for the period 2003ô2007 and two shipboard surveys providing CTD and XBT data in December 2008 and in August 2009 in the northern Mozambique region. The results con rm that shelf edge upwelling occurs along the northern coast of Mozambique near Angoche between 15 and 18oS, covering an area of approximately 68 000 km2. The upwelling signature was not strong at the surface. Two upwelling core regions were identi ed: (1) the shelf core region and (2) the slope core region. At the shelf core region upwelling was more persistent than at the slope core upwelling. The upwelling displayed seasonal variation between persistent downwelling (warm water) between AprilôJuly and intermittent upwelling (cool water) events between AugustôMarch. Generally the upwelling lasted for a period of about two months but, shorter periods between 8 and 30 days were also observed. The driving mechanism for the shelf edge upwelling o northern Mozambique was determined from satellite observations (NOAA/NCDC) of blended sea surface wind data, and by multi-satellite (AVISO) altimeter sea surface anomaly data between 2003 and 2007 and also during the two cruise surveys in December 2008 and August 2009. These data showed upwelling is in part wind-driven in response to the northôeasterly (NE) monsoon weak-wind velocities between AugustôMarch in the austral spring-summer. The intermittent nature of the upwelling season is also partly due to uctuations in wind direction during the NE monsoon winds. Eddies appear to play a limited role in driving the upwelling.