Recent Submissions

  • Rebuilding the Namibian hake fishery: a case for collaboration between scientists and fishermen

    Paterson, Barbara; Kainge, Paulus (2014)
    One of the most important fisheries in the northern Benguela is the Namibian hake fishery, which targets both Merluccius capensis and Merluccius paradoxus. In spite of attempts to rebuild the hake stocks that were severely depleted by distant-water fleets before Namibia's independence in 1990, stocks have failed to recover. Because the ecological goal of stock rebuilding competes with social and economic objectives on the political stage, the ability to make accurate abundance estimates is important. However, the precision of abundance estimates is impeded by lack of understanding of hake behavior and of the effects of environmental factors. Furthermore, at present both species of hake are assessed and managed as one Namibian stock. We present qualitative information derived from interviews that we conducted with Namibian hake trawl and longline fishers during the 2009 and 2010 fishing seasons, and information gleaned from analyzing logbook data. We contextualize both types of data within the scientific literature on Namibian hakes and the Namibian hake fishery. Fishers monitor sea surface and bottom temperature, water quality, currents, and weather, and they have detailed knowledge about the behavior and habitat of hakes. Fishers differentiate between three different types of M. capensis, which they associate with different fishing areas. They also describe innovations that have taken place over the past 20 years, which are of relevance to the assessment of fishing efficiency and effort, but have not been taken into account in the stock assessments. Our analysis of logbook data supports the increase in efficiency. The results show that closer collaboration between scientists and fishers has the potential to improve the accuracy of survey estimates and stock assessments, and thus is important for rebuilding of hake stocks and the hake fishery.
  • The community structure of demersal fish species from bottom-trawls off Namibia and the West coast of South Africa.

    Mwafila, Samuel Kakambi (2017)
    Changes in the structure and composition of the demersal fish assemblages are assessed using a variety of ecosystem indicators known to capture such changes, which may be induced by bottom-trawling. The aim of this study was to investigate whether there are any structural changes in demersal fish assemblages by way of latitudinal variation. The study was conducted from the Kunene River to Agulhas Bank during the 2007 demersal surveys. Abundance and biomass data was analysed using cluster analysis, non-metric multidimensional scaling, abundance biomass comparison curves, and similarity profiles in PRIMER v6 software. The dendrogram identified three main groups, two in northern Benguela, separated into shelf and slope assemblages and one in the southern Benguela, without any distinction between shelf and slope at 19% similarity. Identified assemblages are spatially distinct. The average similarities on the continental shelf in northern Benguela were driven by the following top three species: M. capensis, Sufflogobius bibarbatus and Trachurus trachurus capensis; on the continental slope they were driven by M. paradoxus, Nezumia micronychodon and Helicolenus dactylopterus; while the similarities in southern Benguela assemblages were driven by M. paradoxus, H. dactylopterus and Lophius vomerinus, in order of % contribution.
  • Characterizing and Comparing the Spawning Habitats of Sardine (Sardinops sagax) and Anchovy (Engraulis encrasicolus) in the Northern Benguela Region

    Tjizoo,Mbeurora Beau (2008)
    Spawning habitats of sardine and anchovy in eastern boundary current systems are characterized in an attempt to understand the fluctuations observed in their abundance. The northern Benguela, as an eastern boundary current system, is characterized by turbulent conditions that seem to govern the variability observed in the abundance of these species. Sardine and anchovy have developed mechanisms that enable them to maximize productivity. In the northern Benguela, spawning intensity is historically known to be high in periods and vicinities where turbulence is reduced. However, it is believed that selection of conditions for spawning by these species may change withfluctuations in abundance of fish.
  • A transboundary study of the pelagic fish stocks of southern

    Krakstad, Jens-Otto; Amaro, Aristóteles P. da S.; Shigwedha, Vaino (Bueguela Current ComissionBergen, 2012)
    The main objectives of the survey were the following: • To map the distribution and estimate the abundance of the most commercially important pelagic species in the Namibia-Angola transboundary area (15°50-19°00’), following the survey design utilized in Angolan waters (6 n.mi spacing between transect lines), with special emphasis on the two horse mackerel Cunene horse mackerel (Trachurus trecae) and Cape horse mackerel (Trachurus capensis), sardine “Pilchard” (Sardinops sagax) and other small pelagic species, including anchovy (Engraulis capensis) and round herring (Etrumeus whiteheadi). • To map the distributions and estimate the abundance of the same species in central Namibia south to Dune Point (20°15’ S), following the established survey design with 10 n.mi spacing between the transect lines. • To study and analyse the biological state of the main species, including length frequencies, length-weight relationships, reproductive stages and length-at-maturity. • To map the meteorological and hydrographical conditions in the survey area by means of continuous recordings of weather data such as Sea-surface temperature (SST), Seasurface salinity (SSS), wind
  • Evaluation of the Status of the Namibian Hake Resource (Merluccius spp.) Using Statistical Catch-at-Age Analysis

    Kirchner, Carola; Kainge, Paul; Kathena, Johannes (University of Cape TownCapetown, South Africa, 2012)
    Namibian hake is the most important fish resource in Namibia. This monograph is a compilation of all the hake data, historic and recent, that has been used to inform stock assessment and management since the late 1970s. It presents the statistical catch-at-age analysis used to evaluate the state of the Namibian hake resource under different assumptions. This analysis treats the two hakes, Merluccius paradoxus and M. capensis, as a single stock. The data and modeling show that the stock has not as yet recovered to its maximum sustainable yield level, despite foreign fishing effort having been removed in 1990. Best estimates suggest the current stock to be roughly 20% of pre-exploitation levels; however this figure is sensitive to model assumptions. Signs indicate that the stock is slowly recovering from its all-time low in 2002-2004. Because the two hake species are pooled for assessment, the resource is currently managed on a relatively simple adaptive basis; 80% of the estimated replacement yield is reserved for fishing, the remainder being left for rebuilding.
  • Towards the development of environmental indices for the Namibian shelf, with particular reference to fisheries management.

    Bartholomae, Ch.; Van der Plas, A. (2007)
    The Namibian Ministry of Fisheries and Marine Resources has the task of collecting and providing relevant oceanographic information for management of their fisheries. However, quality information is difficult to provide because of the complexity of the processes involved in the Namibian marine ecosystem. Nonetheless, there are oceanographic data available that can contribute to fisheries management by improving the general understanding of important oceanographic processes related to fisheries. The focus of this paper is on the development of simple environmental indices that can serve as a measurement or proxy of the state or intensity of certain important oceanographic processes or variables for temporal comparison. These indices relate to oceanographic processes such as upwelling, frontal movements, anoxic bottom conditions and biological indicators, which can be updated on a regular basis to provide a long-term perspective of the particular processes to management and marine scientists.
  • Oceanographic and faunistic structures across an Angola Current intrusion into northern Namibia waters.

    John, H.C.H.; Mohrholz, V.; Lutjeharms, J.R.E. (2004)
    It is thought that the penetration of Angolan waters through the Angola–Benguela Frontal Zone (ABFZ) into the much cooler Benguela regime may come about by a poleward slope undercurrent as well as by cross-frontal filaments. To test this hypothesis, two zonal transects off the northern Namibian coast were surveyed by CTD casts, current measurements and ichthyoplankton samples during April 1999. Simultaneous sea-surface temperature (SST), chlorophyll-a concentration, and wind data were obtained from satellite. The multidisciplinary results are described.An intense intrusion of the Angola Current into northern Namibian waters occurred with distinct signals of high temperatures and salinities, low chlorophyll-a concentration, and Angolan fish larvae of both the neritic and oceanic communities. This intrusion was temporarily displaced offshore by strong southeasterly winds, which also caused coastal upwelling and enhanced productivity. The expected slope undercurrent was not found. The Benguela Upwelling Front coincided with a sharp boundary between equatorward flow inshore, and generally southward flow offshore, whilst the offshore component of the Angola– Benguela Frontal Zone was located much farther south than anticipated, and showed only weak temperature gradients. Inshore of the Benguela Upwelling Front temperate Benguela fauna had characteristics of anomalously warm conditions. Tropical fish larvae offshore were clearly related to advection in Angola Current water, but not to recent spawning of their parents in it. Inconsistencies were observed in some cross slope boundaries between oceanic versus neritic fish larvae that can only partly be explained by Ekman drift of the surface layer, indicating that both the hydrographic and faunistic structures resulted from opposing meridional flows over time scales as different as 6 days to 4 weeks, intense mixing in the friction zone between them, and the westward displacement of a mesoscale gyre contributing its own anticyclonic flowfield. A conceptual transport model is presented.
  • Use of environmental parameters to explain the variability in spawnerrecruitment

    Kirchner, C. H.; Bartholomae, C. H.; Kreiner, A. (2009)
    This study attempts to explain the variability in recruitment of sardine in the northern Benguela and to develop potential models by including environmental information to predict recruitment. Two different recruitment and spawner number datasets were available: a VPA-developed dataset, for the period 1952–1987, and data from a simple age-structured model for 1992–2007. In all, four environmental indices were used: the degree of the intrusion of the warm Angola Current into northern Namibia, termed the Angola–Benguela front index; the extent of the upwelling area off central Namibia; average sea surface temperature (SST) over the northern and central Namibian shelf; and wind stress anomalies at Lüderitz as an indicator of upwelling strength. Contrary to general belief, it was found that extremely high recruitment can happen at low spawner levels. This occurred in years in which a large upwelling area existed in association with the minimum southward intrusion of the Angola Current. These effects override the normal negative linear relationships with SST and the positive linear relationship with wind. However, when the area of upwelling is average or small, the effects of spawner biomass, SST and wind become important factors in the variability of recruitment. To estimate exceptional recruitment, the upwelling and front indices were included in the model. To measure medium and weak recruitment, spawner numbers and the SST and wind anomaly formed part of the model. These models can be used simultaneously to predict recruitment before annual acoustic surveys take place and thus aid management decisions.
  • Assessment of an environmental barrier to transport of ichthyoplankton from the southern to

    Lett, Christophe; Veitch, Jennifer; Van der Lingen, Carl D.; Hutchings, Larry (2007)
    The Lüderitz upwelling cell and Orange River cone (LUCORC) area, a transboundary region between South Africa and Namibia, is considered to be an environmental barrier to transport of ichthyoplankton from the southern to the northern Benguela upwelling ecosystems. We use environmental data and modelling to assess the potential mechanisms responsible for this barrier: environmental data were extracted from the 1 × 1° World Ocean Atlas 2001 database and used to build maps of annual mean salinity, temperature, chlorophyll, dissolved oxygen and nutrient concentrations; outputs of a regional circulation model were used in an individual-based model to assess the transport of passive particles from the southern to the northern Benguela. The data show no clear environmental barrier at sea surface, but the model results suggest that particles released there would be largely transported offshore. The model also shows that particles released below the surface could be transported alongshore from the southern to the northern Benguela, but low subsurface temperatures would increase ichthyoplankton mortality and hence be a strong limiting factor to northward transport. We conclude that the combination of a surface hydrodynamic and a subsurface thermal barrier could limit the possibility for ichthyoplankton of epipelagic species to be transported from the southern to the northern Benguela, but that ichthyoplankton of mesopelagic species, having a wider tolerance to low temperatures, would be less affected.
  • The selection of spawning location of sardine (Sardinops sagax) in the northern Benguela after changes in stock structure and environmental conditions

    Kreiner, Anja; Yemane, Dawit; Stenevik, Erling K.; Moroff, Nadine E. (2011)
    Most reports on the distribution of spawning areas of sardine (Sardinops sagax) in the northern Benguela originate from the 1970s and 1980s. The northern Benguela system was in a high upwelling regime during those decades. Since the early 1990s upwelling favourable winds have decreased and a trend of increasing sea surface temperature (SST) has been observed. Changes in the structure of sardine stock in the northern Benguela have been observed and it has been suggested that a reduced biomass and changes in stock structure has led to decreased spawning in the favourable southern locations, thus preventing a recovery of the sardine stock. The present paper on the contrary shows that there has been a shift in spawning location from the less favourable northern areas in the early 1980s to spawning areas further south in the 2000s. Thus, the failure of the northern Benguela sardine stock to recover since its collapse in the late 1960s cannot be explained by spawning in less favourable areas. The shift in preferred spawning location to more southern areas since the 1980s was to be expected with a general warming of the northern Benguela system. Alternative explanations for the failure of the sardine stock to recover such as a reduction in average length as well as length at 50% maturity, leading to a reduction in reproductive output, increased predation pressure, and increased low oxygen waters are proposed.
  • Marine Resources Act, no 27 of 2000.

    Office of the Prime Minister (Office of the Prime Minister, 2001-08-01)
    Fishing for recreational purposes; forms and procedures for granting rights or exploratory rights,allocating quotas and issuing licences
  • Cross-shelf biogeochemical characteristics of sediments in the central Benguela and their relationship to overlying water column hypoxia

    Monteiro, P.M.S.; Van Der Plas, Anja; Pascall, A. (Nisc, 2007)
    Data from two cross-shelf sediment sampling cruises were used to explain reasons for the sediment biogeochemical variability in respect of carbon, nitrogen and sulphur, and how the cycling of these elements governs the biogeochemistry of the overlying water through their control of the redox conditions. The spatial extent of this benthic–pelagic flux link is limited to the innershelf mud belt system on the Namibian shelf. The inshore mud belt is the primary deposition area of the carbon and nitrogen new production export flux. The offshore organic-rich zones are thought to be relict particulate organic matter originating from the inshore mud belt rather than from an overlying pelagic source. These data were used to set up a multi-layer sediment model that was used through sensitivity analyses to elucidate the input characteristics that result in the most significant feedbacks on hypoxia in the overlying water. The analyses showed that, although the new production flux is a requirement to drive an oxygen demand in the sediments, the onset and persistence of anoxia may depend critically on a low-oxygen boundary condition threshold. This is thought to be a key differentiating factor between systems that, despite comparable carbon export fluxes, are characterised by a persistent hypoxia/anoxia signal and those that are characterised by episodic hypoxia events. It was concluded that sediment oxygen demand and methane and ‘sulphide’ emissions from the central Benguela sediments are responses to external hypoxia boundary conditions rather than the local drivers of oxygen variability.
  • A Comparison Of Condition Factor And Gonadosomatic Index Of Sardine Sardinops Sagax Stocks In The Northern And Southern Benguela Upwelling Ecosystems, 1984–1999

    Van der Lingen, C.D.; Kreiner, A.; Fréon, P. (Department of Environmental Affairs and Tourism, 2001)
    Time-series of condition factor (CF) and gonadosomatic index (GSI) were generated using general linear models (GLM) for sardine Sardinops sagax stocks in the northern and southern Benguela ecosystems over the period 1984–1999. During this period the biomass of sardine in the northern Benguela remained at relatively low levels of <500 000 tons, whereas that of southern Benguela sardine increased 40-fold to 1.3 million tons. The GLMs explained 27 and 45% of the observed variation in CF, and 32 and 28% of the observed variation in GSI, for sardine in the northern and southern Benguela subsystems respectively. Whereas the sardine CF in the northern Benguela remained stable over time, that for the southern Benguela stock declined steadily during the study period. Sardine CF showed a seasonal cycle in the southern but not in the northern Benguela. Time-series of GSI showed high interannual variability but no trends in either subsystem, and the seasonal pattern was similar for both stocks. The lack of coherence between the CF time-series for sardine in the two subsystems further suggests that sardine stocks in the northern and southern Benguela subsystems are independent.
  • Namibia Ministry of Fisheries and Marine Resources Annual Report 2004.

    Anon. (Namibia Ministry of Fisheries and Marine Resources, 2004)
    Economic and operational challenges for Namibia's marine fishing and processing sectors
  • An introduction to the Zooplankton of the Benguella current Region

    Gibbons, M.J. (1997)
    The Benguella Current Large Marine Ecosystem (BCLME) is situated off the west coast of southern Africa and is one of the four eastern boundry upwelling systems in the world. It's high level of primary productivity supports an important global resevoir of biodiversity and biomass of zooplankton, fish, seabirds,....