Benguela Current large marine ecosystem

August 19, 2011, 9:30 pm
Source: NOAA

Introduction

caption Benguela Current. (Source: NOAA)

This large marine ecosystem (LME), which borders the Atlantic Ocean, is characterized by its temperate climate. It is a western boundary ecosystem, and the strongest wind-driven coastal upwelling system known. The LME is defined by the Benguela Current. It is a complex and highly variable system for which there is evidence of system change and fragmentary but important evidence pointing to increasing instability and variability. Climate is the primary force driving the LME, with intensive fishing as the secondary driving force. The Global Environmental Facility (GEF) is supporting an ecosystem-based project that was requested by the governments of Angola, Namibia and South Africa. It aims at integrated management, sustainable development and environmental protection. The countries have addressed transboundary issues by preparing a Transboundary Diagnostic Analysis (TDA) and implementing a Strategic Action Programme (SAP). The Strategic Action Programme (SAP) and the Transboundary Diagnostic Analysis documents are available on-line (see above). LME book chapters and articles pertaining to this LME include Crawford, Shannon and Shelton (1989), Bakun, 1993, and Shannon and O’Toole, 2003.

Productivity

The Benguela Current LME is one of the most strongly wind driven coastal upwelling systems known. (For a map of bathymetric features and surface currents for this LME, see Shannon and O’Toole, 2003). The principal upwelling center is situated off of southern Namibia. The upwelling system is bounded at both northern and southern ends by warm water systems, the tropical/equatorial Eastern Atlantic and the Indian Ocean’s Agulhas Current. Sharp horizontal gradients (fronts) exist at these boundaries, but these display substantial variability in time and space—at times pulsating in phase and at others not. Interaction between the LME and the adjacent ocean systems occurs over thousands of kilometers (km) (see Benguela Current Large Marine Ecosystem Transboundary Diagnostic Analysis, 1999). There are also teleconnections between the Benguela and processes in the North Atlantic and Indo-Pacific oceans (e.g. El Niño). The Current is believed to play a significant role in global ocean and climate processes. For seasonal and inter-annual variability, decadal changes and regime shifts, see Shannon and O’Toole, 2003, and see also the paper by Shannon and O'Toole (1999) which describes the oceanography and environmental variability of the Benguela Current. The LME is an important center of marine biodiversity and is one of the most productive ocean areas in the world. It is considered a Class I, highly productive (>300 grams of Carbon per square meter per year (gC/m2-yr)), ecosystem based on SeaWiFS global primary productivity estimates. It supports a large biomass of fish, crustaceans, sea birds and marine mammals. It presents favorable conditions for a rich production of small pelagics, herrings, sardines and anchovies. The LME’s considerable environmental variability can severely impact the ecosystem and lead to a marked decline in fish abundance and availability. There is still a limited understanding of this highly variable and complex system of physical, chemical and biological interactions and processes.

Fish and Fisheries

caption (Source: NOAA)

Harvests are characterized by stock fluctuations according to the variations in the primary and secondary level productivity. The Food and Agriculture Organization (FAO) 10-year trend shows decreasing catches of hakes, herrings, sardines, anchovies and miscellaneous pelagic fishes (see FAO, 1999, Figure 12). Cods, hakes and haddocks represent about 21% of the catch. Herrings, sardines and anchovies represent about 38% of the catch. Miscellaneous pelagic fishes represent about 32% of the catch. The total catch decreased from 1.3 million tons in 1990 to 900,000 in 1996 and then rose to 1.2 million tons in 1999. Anchovies and sardines are key links in the local trophic system (see Shannon et al., 1988). For more information on sardines, anchovies, sardinellas, hakes and rock lobster, and for transboundary considerations, see Shannon and O’Toole, 2003. This LME is extremely rich in fishery resources. The confluence of warm and cooler waters provides a protected spawning area for the northern sardine and anchovy populations (see Shelton and Hutchings, 1990). But the status and yield of the ecosystem as a whole is difficult to predict. There are major changes in the abundance, composition, distribution and availability of marine species. The over exploitation of the commercial fish stocks and some unsustainable harvesting of the living resources continue to be a cause of concern. The Transboundary Diagnostic Analysis (TDA) identifies overharvesting and wastage through the dumping of bycatch and undersize fish (see TDA, 1999). It also identifies a loss of biotic integrity (changes in community composition, species and diversity). Mariculture is underdeveloped. The role of non harvested species in the ecosystem is unknown. The Global International Waters Assessment (GIWA) has issued a matrix that ranks LMEs according to the destruction and degradation of ecosystems, habitat and community modification, pollution and global change. GIWA characterizes the Benguela Current LME as severely impacted in the area of overexploitation of fisheries, and biological and genetic diversity. These impacts and other indicators of unsustainable exploitation of fisheries are increasing. There is heavy exploitation of resources by foreign fleets, resulting in severe depletion and the collapse of several fish stocks. Superimposed on this fishing pressure is the impact of the inherent natural environmental ecosystem variability and change. Global climate change could intensify coastal winds and disrupt the balance of upwelling, sheltered areas and mixing that is so favorable to the anchovy and sardine fisheries (see Bakun, 1993). This poses difficulties in the sustainable use and management of the LME’s living resources. The governments of Angola, Namibia and South Africa have agreed to try to improve predictability, harmonize the management of shared stocks, assess non-exploited species and develop a regional mariculture policy. They have agreed to conduct joint surveys and assessments of shared fish stocks over a 5-year period beginning in 2002. They have committed to a compliance with the FAO Code of Conduct for responsible fisheries. Three new programs and initiatives (ENVIFISH--Environmental conditions and fluctuations in distribution of small pelagic fish stocks, VIBES, a program focussing on the variability of pelagic fisheries resource in the Benguela Current, and BENEFIT--Benguela environment fisheries interaction training program) focus on fish resource dynamics. The University of British Columbia Fisheries Center has detailed fish catch statistics for this LME (Click on the figure source below for more information). The Benguela Current LME Website has more details on the Integrated overview of fisheries of the Benguela Current region .

Pollution and Ecosystem Health

caption Benguela Current coastline. (Source: NOAA)

Health concerns in this LME focus on endangered and vulnerable species, altered food webs (changes in community composition, species and diversity), and the disruption of fish, bird and mammal migrations due to El Niño events. Top predators such as marine mammals and coastal birds (e.g. African penguins) are now threatened or endangered. Alien species such as the Mediterranean blue mussel have been introduced through ballast water, bilge water and mariculture operations. There is habitat destruction and modification (wetlands, mangroves, lagoons), and loss or modification of ecotones, The Global International Waters Assessment (GIWA) has issued a matrix that ranks LMEs according to the destruction and degradation of ecosystems, habitat and community modification, pollution and global change. GIWA characterizes the Benguela Current LME as severely impacted in the area of chemical pollution, solid wastes, radionuclides, spills and economic impacts. These impacts and other pollution indicators are increasing. The Transboundary Diagnostic Analysis (TDA) identifies chronic and catastrophic deterioration in water quality. Harmful algal blooms (HABs) occur of the coasts of all three countries. There is high pollution risk associated with ongoing seabed mining and petroleum exploration and production. A substantial volume of oil is transported through this LME. Pollution from industries and poorly planned and managed coastal developments and near shore activities is resulting in a rapid degradation of vulnerable coastal habitats. The rapid expansion of coastal cities has created pollution “hot spots” in all three countries, with resultant deterioration in water quality. The problem is aggravated by an increase in marine litter from land and shipping activities. The increased nutrient loading of coastal waters is caused by sewage discharge from aging water treatment infrastructure, and by industry. Other issues are the disposal of illegal hazardous waste, and lack of public awareness. There is inadequate human and infrastructure capacity to assess the health of the ecosystem as a whole.

Socio-economic Conditions

Near shore and offshore sediments hold rich deposits of minerals (diamonds, phosphorite, diatomite), as well as oil and gas reserves. Extensive diamond mining is being conducted by dredging along the coasts and continental shelves of Namibia and South Africa. Capped abandoned wellheads hamper fishing, while drill cuttings and hydrocarbon spills impact on the environment. Due to the natural beauty of the coastal regions, their biodiversity and their culture, significant tourism has developed in some areas. Marine life that is not harvested, such as whales, dolphins and seabirds, is increasingly recognized as a valuable resource for nature-based tourism. However, pollution in some coastal environments will lead to a loss of tourism and employment. Fur seals were harvested in the early 17th century. This was followed by extensive whaling operations in the 18th and 19th centuries. Commercial trawling started around 1900. Commercial guano production from penguins, gannets and cormorants began in the early 20th century (see Cooper et al., 1982). Commercial purse seine fishing for sardine was initiated in the 1950s (see Benguela Current Large Marine Ecosystem, 1999, p. 3). Unpredictable fisheries yields have sometimes resulted in the closure of fish canning factories. Artisanal fishermen experience loss of income and unemployment and many of the coastal communities are poor. The civil war in Angola led to the migration of part of the affected populations to the coastal areas. The Transboundary Diagnostic Analysis (TDA) examines the socioeconomic consequences of non-optimal harvesting of living resources, mining and drilling impacts, a hampered mariculture industry, harmful algal blooms, and the variability of the LME. The 3 countries bordering the LME are making efforts to develop a viable mariculture policy, and to solve conflicts between fisheries and coastal and offshore diamond, gold, oil and gas production. They are cooperatively analyzing the socioeconomic consequences of harvesting methods, in order to improve the sustainable use of the living resources, in compliance with the FAO Code of Conduct for Responsible Fishing. They are phasing out subsidies that encourage the continuation of non-environmentally friendly technologies. Reports have been prepared on the socio-economics of some key maritime industries, off-shore oil and gas exploration and production, and diamond mining. An Overview of the socio-economics of some key maritime industries in the Benguela Current region is available at the BCLME website.

Governance

caption Benguela Current coastal development. (Source: NOAA)

The fragmented nature of coastal and marine resource management is a legacy of the colonial past and of subsequent political turmoil in Namibia, Angola and South Africa (liberation struggles, civil wars, military conflict, the apartheid regime in South Africa). The languages and cultures of the foreign occupiers were different, as were the management systems and laws they bequeathed to the now independent and democratic countries of the region. There was a relative absence of inter-agency (or inter-ministerial) frameworks for management of the marine environment and its resources and scant regard for sustainability. For more information on this legacy, see Benguela Current Large Marine Ecosystem, 1999, and Shannon and O’Toole, 2003. The three countries expressed a will to address this fragmented legacy and to ensure an integrated and sustainable approach to the management of their marine and coastal resources (see O’Toole et al., 2001). In 1998, the Global Environmental Facility (GEF) approved support for an ecosystem-based project, with a focus on sustainable management. The 3 countries prepared a TDA and SAP (see Benguela Current Large Marine Ecosystem, 2002), which reviewed the existing knowledge of the status of the LME and identified the threats to the LME. They are establishing an Interim Benguela Current Commission (IBCC) to strengthen regional cooperation and address the gaps in current knowledge. The priorities addressed are increased fishing pressure, toxic algal blooms and pollution from ongoing seabed mining and petroleum production. For information on the successes of BENEFIT (The Benguela-Environment-Fisheries-Interaction & Training), launched in 1997, see Benguela Current Large Marine Ecosystem, 1999, p. 6. The 3 countries are attempting to harmonize the management of shared stocks, and to improve the predictability of extreme events. They are developing a ballast water policy. Obstacles are lack of capacity (equipment, vessels, expertise), and limited funding for marine monitoring.


References

Articles and LME Volumes

  • Bakun, Andrew. 1993. "The California Current, Benguela Current, and Southwestern Atlantic Shelf Ecosystems: A Comparative Approach to Identifying Factors Regulating Biomass Yields." in Kenneth Sherman, Lewis M. Alexander, and Barry D. Gold (eds), Large Marine Ecosystems, Stress, Mitigation and Sustainability. American Association for the Advancement of Science. Washington, D.C. Benguela Current Large Marine Ecosystem, 1999. Transboundary Diagnostic analysis. 52 pages. Benguela Current Large Marine Ecosystem, 2002. Strategic Action Programme. 24 pages. ISBN: 087168506X.
  • Crawford, Robert J.M., Shannon, L.V., and P.A. Shelton. 1989. "Characteristics and Management of the Benguela as a Large Marine Ecosystem," in Kenneth Sherman and Lewis M. Alexander (eds.), Biomass Yields and Geography of Large Marine Ecosystems (Boulder: Westview). AAAS Selected Symposium 111. ISBN: 1402031580.
  • FAO, 2003. Trends in oceanic captures and clustering of large marine ecosystems—2 studies based on the FAO capture database. FAO fisheries technical paper 435. 71 pages.
  • Shannon, L.V. and M.J. O’Toole, 2003. Sustainability of the Benguela: ex Africa semper aliquid novi. In: K. Sherman and G. Hempel, Large Marine Ecosystems of the World – Trends in Exploitation, Protection and Research. ISBN: 0444510273.

Other References


  • Bakun, A. and Nelson, C.S. 1991. Wind stress curl in subtropical eastern boundary current regions. J. Phys. Oceanogr. 21:1815-1834.
  • Borchers, P., and Hutchings, L. 1986. Starvation tolerance, development time, and egg production of Calanoides carinatus in the southern Benguela Current. J. Plank. Res. 8(5):855-874.
  • Boyd, A.J. 1979. A relationship between sea-surface temperature variability and anchovy Engraulis capensis recruitment off southwestern Africa. Fish. Bull. S. Afr. 12:80-84.
  • Carter, R.A., McMurray, H.F., and Largier, J.L. 1987. Thermocline characteristics and phytoplankton dynamics in Agulhas Bank waters. In "Benguela comparative ecosystems." pp. 327-336. ed. by A.I.L. Payne, J.A. Gulland, and K.H. Brink. Special volume of the South African Journal of Marine Science, Vol. 5. Sea Fisheries Research Institute. Capetown, South Africa.
  • Cooper, J., Brooke, R.I., Shelton, P.A. and Crawford, R.J.M. 1982. Distribution, population size, and conservation of the Cape cormorant (Phalacrocorax capensis). Fish. Bull. S. Afr. 16:121-143.
  • Crawford, R.J.M., and Shannon, L.V. 1986. Longterm changes in the distributions of fish catches in the Benguela. in Proceedings of the international symposium on long term changes in marine fish populations. Vigo. November,1986.
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  • Maze, R., Camus, Y., and Le Tareau, J.-Y 1986. Formation de gradient thermiques a la surface de l'ocean, au-dessuss d'un talus, par interaction entre les ondes et le melange du au vent. J. Cons. Int. Explor. Mer. 42:221-240.
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Citation

(2011). Benguela Current large marine ecosystem. Retrieved from http://www.eoearth.org/view/article/51cbed0e7896bb431f68f621

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