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Orange Shelf Edge

The Orange Shelf Edge is a transboundary EBSA shared between Namibia and South Africa on their western continental margins. In Namibia, it includes Tripp Seamount and a shelf-indenting canyon; in South African, it includes portions of three threatened shelf and shelf edge habitat types (one of which is Critically Endangered) that are in relatively natural/pristine condition. This EBSA is a persistent hotspot of demersal fish biodiversity, which may be a result of the local habitat heterogeneity. The pelagic environment has medium productivity, cold to moderate Atlantic temperatures (SST mean=18.3°C) and moderate chlorophyll levels related to the eastern limit of the Benguela upwelling on the outer shelf.

EBSA Description: Orange Shelf Edge

General Information

Summary

The Orange Shelf Edge, occurs at the western continental margin of South Africa and Namibia, spanning the border between the two countries. On the Namibian side, it includes Tripp Seamount and a shelf-indenting canyon. The EBSA comprises shelf and shelf-edge habitat with hard and unconsolidated substrates, including at least eleven offshore benthic habitat types. According to recent threat status assessments of coastal and marine habitat in South Africa and Namibia, four habitat types represented in the EBSA are threatened, one of which is Critically Endangered and another which is Endangered. However, the area is one of few places where these threatened habitat types are in relatively natural/pristine condition. Based on an analysis of long-term trawl-survey data, the Orange Shelf Edge is a persistent hotspot of demersal fish biodiversity, which may be a result of the local habitat heterogeneity. In summary, this area is highly relevant in terms of the following EBSA criteria: ‘Importance for threatened, endangered or declining species and/or habitats’, ‘biological diversity’ and ‘naturalness’. 

MARISMA updates

The site description has been updated; the EBSA boundaries have been refined.

Introduction of the area

The area occurs at the outer shelf and shelf edge of the western continental margin of South Africa and Namibia, spanning the border between the two countries. It includes hard and unconsolidated (sand) shelf and shelf edge benthic habitat at depths of approximately 350-1200 m on the South African side (Sink et al., 2012). On the Namibian side, it includes Tripp seamount and a shelf-indenting submarine canyon, providing a heterogeneous habitat (Holness et al., 2014). The pelagic environment in the area is characterized by medium productivity, cold to moderate Atlantic temperatures (SST mean = 18.3 °C) and moderate chlorophyll levels related to the eastern limit of the Benguela upwelling on the outer shelf (Lagabrielle 2009).

Description of location

 

The area occurs at the outer shelf and shelf edge of the western continental margin of South Africa and Namibia, spanning the border between the two countries. It is entirely within the national jurisdiction of the two countries.

 

Area details

Feature description of the area

The area includes a high diversity of shelf and shelf-edge habitat with hard or unconsolidated (sand) substrates (Sink et al., 2012; Holness et al., 2014). It includes at least eleven offshore benthic habitat types that have been identified for South Africa and Namibia: Namaqua Shelf Edge, Southern Benguela Hard Outer Shelf, Southern Benguela Sandy Shelf Edge, Namaqua Outer Shelf, Namib Lower Slope, Namib Seamount, Namib Upper Slope, South Atlantic Lower Bathyal, South Atlantic Upper Bathyal and Southern Benguela Sandy Outer Shelf (Sink et al., 2012; Holness et al., 2014). On the Namibian side, it includes Tripp seamount and a shelf-indenting canyon. The pelagic environment of the area is characterized by medium productivity, cold to moderate temperatures, and moderate chlorophyll levels related to the eastern limit of the Benguela upwelling on the outer shelf (Lagabrielle 2009).

The area has been subjected to annual demersal fish trawl surveys conducted by the Department of Agriculture, Forestry and Fisheries of South Africa (see Atkinson et al., 2011 for details), and under the Nansen Programme in Namibia (see Jonsen and Kathena 2012 for details). Based on spatial modeling of nearly 30 years of distribution and abundance data from these surveys, Kirkman et al., (2013) identified a persistent hotspot of species richness for demersal fish species that coincides with part of the area. This may be related to the local habitat heterogeneity, including the presence of a shelf-indenting submarine canyon and the close proximity of a seamount. Generally, however, seamounts and canyons in the region have been poorly studied (Sink et al., 2011).

Feature conditions and future outlook of the proposed area

Sink et al., (2012) estimated the threat status of coastal and marine habitats in South Africa by assessing the cumulative impacts of various pressures (e.g., extractive resource use, pollution and others) on each habitat type. This analysis was extended to Namibia by Holness et al. (2014). Of the benthic habitat types in the area, one (Southern Benguela Hard Shelf Edge) is Critically Endangered, indicating that very little (<20 %) of the total area of this habitat is in good (natural or pristine) condition. One is Endangered (Namaqua Shelf Edge) and two other habitats (Southern Benguela Hard Outer Shelf and Southern Benguela Sandy Shelf Edge) are Vulnerable, implying that although there are sufficient areas of intact biodiversity of this type to meet the biodiversity target, there has been habitat degradation and some loss of ecosystem processes. However, the Orange Shelf Edge is one of the few areas where these threatened habitats are in good condition, largely because it has been subjected to relatively little extractive resource use (e.g., fishing, mining) pressure, and is relatively remote from sources of pollution. Overall the assessments of Sink et al. (2012) and Holness et al. (2014) classify 78 % of the Orange Cone area as being in good condition, with an additional 13 % being in fair condition.

Previously, the Orange Shelf area was identified by Majiedt et al. (2013) as one of six marine ‘primary focus areas’ for spatial protection in South Africa, with the good condition of threatened habitats and the relative absence of anthropogenic pressures as the major drivers of this selection. Similarly, the assessment of Holness et al. (2014) identified the Namibian portions of the EBSA as being of high priority for place-based conservation measures. Tripp seamount on the Namibian side of the border is the location of a productive pelagic pole-and-line tuna fishery (FAO 2007).

 

Assessment of the area against CBD EBSA criteria

 Uniqueness or rarity

 

Rank: Low

Neither the benthic nor pelagic habitat types that are known to occur in the area are unique to the area (Sink et al., 2011).

 Special importance for life-history stages of species

 

Rank: Medium

Elsewhere it has been shown that seamounts, shelf breaks and submarine canyons (all of which occur in the area) constitute important foraging habitats for pelagic-feeding vertebrates such as seabirds, cetaceans and large fish species, including migratory species, which exploit elevated primary production and high standing stocks of zooplankton, fish, and other organisms at these features (Dearden and Topelko 2005, Sydeman et al., 2006, Morato et al., 2008). Generally, however, seamounts and canyons in the region have been poorly studied (Sink et al., 2011).

 Importance for threatened, endangered or declining species and/or habitats

 

Rank: High

Habitat threat status assessments by Sink et al. (2012) and Holness et al., (2014) highlighted a number of threatened habitat types that are represented in the EBSA. The threat status of one of the benthic habitats that is most prominent in the area, Southern Benguela Hard Shelf Edge, is Critically Endangered (Sink et al., 2012), indicating that very little (< 20 %) of the remaining area of this habitat is in good (natural or pristine) condition. Another habitat type, Namaqua Shelf Edge, is Endangered (Holness et al., 2014), while two other prominent benthic habitat types in the area, Southern Benguela Hard Outer Shelf and Southern Benguela Sandy Shelf Edge, are Vulnerable (Sink et al., 2012). This implies that, although there are sufficient areas of intact biodiversity of these habitats to meet the conservation targets, there has been habitat degradation and some loss of ecosystem processes. The importance of the area for the conservation of the threatened habitat types represented in the Orange Shelf Edge was emphasized by Majiedt et al. (2013) and Holness et al. (2014).

 Vulnerability, fragility, sensitivity, or slow recovery

 

Rank:  Medium

The threatened status of the three habitat types that occur on the South African side of the border (Sink et al., 2012), implies that degradation and some loss of ecosystem processes has been associated with these habitat types in other areas, and therefore that they are vulnerable to the effects of human activities. Seamounts, submarine canyons and the shelf break, all of which occur in the area, are all potentially vulnerable marine ecosystems (FAO 2009). Seamount communities are particularly vulnerable to human activities (e.g. trawling) due to intrinsic biological factors that are characteristic of seamount-associated species (e.g. slow growth rate, late maturation), with the likelihood of very long time scales of recovery if damaged (Gjerde & Breide, 2003, Clark et al., 2006).

 Biological productivity

 

Rank: Medium

The area is at the eastern limit of the Benguela upwelling region (Hutchings et al., 2009), where the pelagic environment is characterized by medium productivity, and moderate chlorophyll levels (Lagabrielle 2009). However, shelf edge environments (e.g. Springer et al., 1996, Piatt et al., 2006, Coleman et al., 2011), seamounts (e.g. Moore et al., 2002, Pitcher et al., 2011) and submarine canyons (e.g. de Leo et al., 2010, McClain and Barry 2010), all of which occur in the proposed area, are associated with elevated productivity and biomass levels, spanning several trophic levels. Tripp seamount on the Namibian side of the border supports a productive pole-and-line tuna fishery (FAO 2007).

 

 Biological diversity

 

Rank: High

Based on spatial modelling of 20-30 years of distribution and abundance data from demersal trawl surveys in Namibian and South African waters, Kirkman et al. (2013) identified the area as a persistent hotspot of species richness for demersal fish species. This may be linked to the habitat heterogeneity of the area, including the shelf edge, the presence of a shelf-indenting submarine canyon and the close proximity of a seamount. Further, 487 species have been recorded in the area (OBIS 2017). Diversity of habitat types is also high, with 11 habitat types occurring in the area (Sink et al., 2012; Holness et al., 2014).

 

 Naturalness

 

Rank: High

The area on the South African side is one of the few areas where the threatened habitat types are in good condition (relatively natural/pristine), largely because it has been subjected to relatively low levels of anthropogenic pressures (Sink et al., 2011). The importance of the area for the conservation of the threatened habitat types represented there has therefore been emphasized by Majiedt et al., (2013). Although there are impacted areas, much of the Namibian portion of the area is also in good condition (Holness et al., 2014). 

 

References

Atkinson L.J., Leslie, R.W., Field, J.G., Jarre, A. 2011. Changes in demersal fish assemblages on the west coast of South Africa, 1986–2009. African Journal of Marine Science, 33: 157–170

Clark, M.R., Tittensor, D., Rogers, A.D., Brewin, P., Schlacher, T., Rowden, A., Stocks, K., Consalvey, M. 2006. Seamounts, deep-sea corals and fisheries: vulnerability of deep-sea corals to fishing on seamounts beyond areas of national jurisdiction. UNEP-WCMC, Cambridge, UK.

Coleman, F.C., Scanlon, K.M., Koenig, C.C. 2011. Groupers on the edge: Shelf edge spawning habitat in and around marine reserves of the northeastern Gulf of Mexico. Professional Geographer, 63: 456-474.

Dearden, P., Topelko, K.N. 2005. Establishing criteria for the identification of ecologically and biologically significant areas on the high seas. Background paper prepared for Fisheries and Oceans Canada. Marine protected Areas Research Group, 50 pp.

De Leo, F.C., Smith, C.R., Rowden, A.A., Bowden, D.A., Clark, M.R. 2010. Submarine canyons: hotspots of benthic biomass and productivity in the deep sea. Proceedings of the Royal Society B, 277: 2783-2792.

FAO. 2007. Namibia: Country Profiles. Food and Agricultural Organisation (FAO) Country Profiles. http://www.fao.org/fi/website/FIRetrieveAction.do?dom=countrysector&xml=FICP_NA.xml&lang=en. (accessed 17 April 2012).

FAO. 2009. Appendix F: International Guidelines for the Management of Deep-sea Fisheries in the High Seas. In: Report of the Technical Consultation on International Guidelines for the Management of Deepsea Fisheries in the High Seas. Rome, 4–8 February and 25-29 August 2008. FAO Fisheries and Aquaculture Report No. 881. Rome, Italy: Food and Agriculture Organization of the United Nations. pp. 39-51.

Gjerde, K.M., Breide, C. 2003. Towards a Strategy for High Seas Marine Protected Areas: Proceedings of the IUCN, WCPA and WWF Experts Workshop on High Seas Marine Protected Areas, 15-17 January 2003, Malaga, Spain.

Holness S., Kirkman S., Samaai T., Wolf T., Sink K., Majiedt P., Nsiangango S., Kainge P., Kilongo K., Kathena J., Harris L., Lagabrielle E., Kirchner C., Chalmers R., Lombard M. 2014. Spatial Biodiversity Assessment and Spatial Management, including Marine Protected Areas. Final report for the Benguela Current Commission project BEH 09-01.

Hutchings, L., van der Lingen, C.D. Shannon, L.J., Crawford, R.J.M., Verheye, H.M.S., Bartholomae, C.H., van der Plas, A.K., Louw, D., Kreiner, A., Ostrowski, M., Fidel, Q., Barlow, R.G., Lamont, T., Cotzee, J., Shillington, F., Veitch, J., Currie, J.C., Monteiro, P.P.S. 2009. The Benguela Current: An ecosystem of four components. Progress in Oceanography, 83: 15 – 32.

Johnsen, E., Kathena, J. 2012. A robust method for generating separate catch time-series for each of the hake species caught in the Namibian trawl fishery. African Journal of Marine Science, 34: 43–53.

Kirkman, S.P., Yemane, D., Kathena, J., Mafwila, S., Nsiangango, S., Samaai, T., Axelsen, B., Singh, L. 2013. Identifying and characterizing demersal biodiversity hotspots in the BCLME: Relevance in the light of global changes. ICES Journal of Marine Science, 70: 943–954.

Lagabrielle E. 2009. Preliminary report: National Pelagic Bioregionalisation of South Africa. Cape Town: South African National Biodiversity Institute.

Majiedt, P., Holness, S., Sink, K., Oosthuizen, A., Chadwick, P. 2013. Systematic Marine Biodiversity Plan for the West Coast of South Africa. South African National Biodiversity Institute, Cape Town.

McClain, C.R. Barry, J.P. 2010. Habitat heterogeneity, disturbance, and productivity work in concert to regulate biodiversity in deep submarine canyons. Ecology, 91: 964-76.

Moore, S.E., Watkins, W.A., Daher, M.A., Davies, J.R., Dahlheim, M.E., 2002. Blue whale habitat associations in the Northwest Pacific: analysis of remotely sensed data using a Geographic Information System. Oceanography, 15:, 20–25.

Morato, T., Varkey, D.A., Damaso, C., Machete, M., Santos, M., Prieto, R., Santos, R.S. and Pitcher, T.J. 2008. Evidence of a seamount effect on aggregating visitors. Marine Ecology Progress Series, 357: 23-32.

OBIS. 2017. Summary statistics of biodiversity records in the Orange Shelf EBSA. (Available: Ocean Biogeographic Information System. Intergovernmental Oceanographic Commission of UNESCO. www.iobis.org. Accessed: 2017-07-27).

Piatt, J.F., Wetzel, J., Bell, K., DeGange, A.R., Balogh, G.R., Drew, G.S., Geernaert, T., Ladd, C., Byrd G.V. 2006. Predictable hotspots and foraging habitat of the endangered shorttailed albatross (Phoebastria albatrus) in the North Pacific: Implications for conservation. Deep-Sea Research II, 53: 387-398.

Pitcher, T.J., Morato, T., Hart, P.J.B., Clark, M.R., Haggan, N., Santos, R.S. (Eds.). 2007. Seamounts: Ecology, Fisheries & Conservation. Blackwell Publishing, Oxford, UK.

Sink KJ, Attwood CG, Lombard AT, Grantham H, Leslie R, Samaai T, Kerwath S, Majiedt P, Fairweather T, Hutchings L, van der Lingen C, Atkinson LJ, Wilkinson S, Holness S, Wolf T. 2011. Spatial planning to identify focus areas for offshore biodiversity protection in South Africa. Unpublished Report. Cape Town: South African National Biodiversity Institute.

Sink, K., Holness, S., Harris, L., Majiedt, P., Atkinson, L., Robinson, T., Kirkman, S., Hutchings, L., Leslie, R., Lamberth, S., Kerwath, S., von der Heyden, S., Lombard, A., Attwood, C., Branch, G., Fairweather, T., Taljaard, S., Weerts, S., Cowley, P., Awad, A., Halpern, B., Grantham, H., Wolf T. 2012. National Biodiversity Assessment 2012: Technical Report. Volume 4: Marine and Coastal Component. South African National Biodiversity Institute, Pretoria.

Springer, A.M., McRoy, C.P., Flint, M.V. 1996. The Bering Sea green belt: shelf-edge processes and ecosystem production. Fisheries Oceanography, 5: 205-223.

Sydeman, W.J., Brodeur, R.D., Grimes, C.B., Bychkov, A.S., McKinnell, S. 2006. Marine habitat “hotspots” and their use by migratory species and top predators in the North Pacific Ocean: Introduction. Deep-Sea Research Part II, 53: 247-249. 

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OrangeShelfEdge

EBSA criteria met at a high (red), medium (orange) or low (yellow) rank. 

 

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