Fisheries - Enviro Dynamics Namibia

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F I S H E R I E S , M A M M A L S A N D S E A B I R D S S P E C I A L I S T S T U D Y Dr S. Elwen, Namibian Dolphin Project, Mammal Research Institute, University of Pretoria (Marine Mammals) Professor M.J. Gibbons (University of the Western Cape), Dr T. Robertson, Marine Biologist (University of Stellenbosch) Dr Carola Kirchner - Fisheries Consultant, Namibia 1.1 ASSUMPTIONS AND LIMITATIONS This analysis and environmental risk assessment is based on the available literature and the data supplied mostly by the Namibian Ministry of Fisheries and Marine Resources (MFMR), in particular scientific staff of the research branch of MFMR the National Marine Research Centre (NatMIRC), based in Swakopmund. Because of the extent of the environment under consideration assumptions may need to be made based on a broad understanding of the Benguela Ecosystem. Data provided are often limited in extent and may have spatial and temporal bias due to the sampling methods used. The information provided by the fishing industry as well as Interested and Affected Parties is also acknowledged. 2 OVERVIEW OF ICHTHYOFAUNA OF NAMIBIA Supported by the high productivity of the Benguela upwelling ecosystem, abundant fish stocks typify Namibian waters. Fish resources in upwelling systems are typically high in biomass and relatively low in Final Report Namibian Marine Phosphate (Pty) Ltd. Figure 1. Distribution of horse mackerel in the Benguela region Page 12
F I S H E R I E S , M A M M A L S A N D S E A B I R D S S P E C I A L I S T S T U D Y diversity (relative to non-upwelling environments). These stocks have traditionally supported intensive fishing activities. Although varying in importance at different times in history, fisheries have focused on demersal species, small pelagic species, large migratory pelagic fish, linefish (caught both commercially and recreationally) and crustacean resources (e.g. lobster and crabs). The following chapter is a review of the ecologically important species that may be affected by mining of marine phosphate in Namibia. For each species the spatial distribution, recruitment to the commercial fisheries and spawning behaviour are considered. 2.1 PELAGIC FISH SPECIES 2.1.1 Horse mackerel Off Namibia horse mackerel Trachurus trachurus capensis generally occur in waters between 200 – 1000 m depth (Crawford et al. 1987) (Figure 1). Adults are found mostly north of 21°S. Here spawning is highest between October and March in the mixing zone between warm oceanic water and cool coastal waters (O’Toole 1977). Nursery grounds exist adjacent to these spawning grounds but closer to shore. Juveniles migrate south to Walvis Bay especially in winter. Maturing fish then move offshore and migrate north to spawn (Boyer and Hampton 2001a). Horse mackerel of up to two years of age feed predominantly on zooplankton that they consume near the sea surface. Research in the 1980s found that off Namibia 95% of the diet of adult horse mackerel comprised euphausiid shrimps (Konchina 1986 cited in Boyer and Hampton 2001a). This is in contrast to horse mackerel occurring off South Africa which feed opportunistically on euphausiids, polychaete worms, squid, crustaceans and fish such as bearded goby Sufflogobius bibartus (Konchina 1986 cited in Boyer and Hampton 2001a). Since the trophic structure of the northern Benguela system off Namibia has altered substantially in the last two decades (Kirkman 2007, Final Report Namibian Marine Phosphate (Pty) Ltd. Figure 2. Distribution of sardine stocks in the Benguela region Page 13
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10 CONCLUSIONS F I S H E R I E S ,
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12 REFERENCES F I S H E R I E S , M
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Fisheries - Enviro Dynamics Namibia

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