Ecologically or Biologically Significant Areas (EBSAs)
published: 12 Jun 2015
The Walvis Ridge is a significant seamount chain forming a bridge running east to west from the African continental margin to the southern Mid-Atlantic Ridge. It is a unique geomorphological feature likely to be of special importance to vulnerable sessile macrofauna and demersal fish associated with seamounts. Although bottom fisheries occur on the Walvis Ridge, the spatial extent of commercial fishing is limited to a relatively small area. Due to the variation in depths, ranging from slopes to summits and surface waters, it is likely that the area supports a relatively higher biological diversity. The feature supports high diversity of globally threatened seabirds.
The Walvis Ridge is a chain of seamounts, some of which are guyots. The Ridge presents a barrier between North Atlantic Deep Water to the north and Antarctic Bottom Water to the south. The surface oceanographic regime is the South Atlantic Subtropical Gyre bounded by the productive waters of the Benguela Current System and the Subtropical Convergence Zone. The feature as described here is bounded approximately by a 4000 m depth contour and contains significant areas within the likely vertical extent of near-surface zooplankton migration (1000 m). The area supports high diversity of seabirds, some of which are endemic to the Tristan Group in the southwest. Whilst biologically significant data is patchy and variable, the area contains several named seamounts, recognized and endorsed by the General Bathymetric Chart of the Oceans (GEBCO), that are likely to support enhanced primary production, abundance and species richness (e.g. Dobrovol’sky, Ewing, Filippov, Ewing, Valdivia Bank, Wüst).
This feature is entirely outside national jurisdiction, extending obliquely from the Namibia – Angola continental margin (19.3°S) to the Tristan da Cunha island group at the Mid-Atlantic Ridge (37.4°S).
DISCLAIMER: The designations employed and the presentation of material in this map do not imply the expression of any opinion whatsoever on the part of the Secretariat concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.
This is both a benthic and water column feature, essentially a chain of seamounts that individually and collectively constitute an ecologically and biologically significant deep-sea feature. Seamounts and seamount chains are recognized as such by, for example, the Census of Marine Life project CenSeam (http://censeam.niwa.co.nz). Research has been carried out in the past by Russian Federation cruises, and there have been more recent Spanish-Namibian surveys (see summary of knowledge in Perez et al., 2012). Most recently a US Walvis Ridge cruise MV1203 Expedition (March 2012) http://earthref.oth/ERESE/Projects/mv1203 was conducted.
This is primarily recognized as a geological feature but the biota in the area could be vulnerable to fishing (e.g., orange roughy, alfonsino, southern boarfish, deepwater crabs, fragile sessile benthic megafauna) (SEAFO report in FAO Statistical Area 47 and a portion of 34). The fisheries are managed by SEAFO, which has introduced area management, catch quotas, and a suite of bottom-fishing regulations. Concentrations of ferromanganese nodules on the deepest adjacent areas (adjacent Cape Abyssal Plain (Perez et al., 2012)) have been observed, thus in future seabed mining may also be a consideration and would be subject to management by the International Seabed Authority.
BirdLife International (2009) Designing networks of marine protected areas: exploring the linkages between Important Bird Areas and ecologically or biologically significant marine areas. Cambridge, UK: BirdLife International. www.cbd.int/doc/meetings/mar/ewbcsima- 01/other/ewbcsima-01-birdlife-02-en.pdf. BirdLife International (2010) Marine Important Bird Areas toolkit: standardised techniques for identifying priority sites for the conservation of seabirds at-sea. BirdLife International, Cambridge UK. Version 1.1: May 2010. www.birdlife.org/eu/pdfs/Marine_IBA_Toolkit_2010.pdf. Census of Marine Life project CenSeam http://censeam.niwa.co.nz, http://seamounts.sdsc.edu. Clark, M.R., Vinichenko, V.I., Gordon, J.D.M, Beck-Bulat, G.Z., Kukharev, N.N. and Kakora 2007. Large scale distant water trawl fisheries on seamounts. Pp. 361-412 in Seamounts: Ecology, Fisheries and Conservation. Fish and Aquatic Resources Series 12, T.J. Pitcher, T. Morato, P.J.B. Hart, M.R. Clark, N. Haggan and R.S. Santos, eds, Blackwell Publishing, Oxford. Durán Muñoz, P., M. Sayago-Gil, F.J. Murillo, J.L. Del Río, L.J. López-Abellán, M. Sacau, and R. Serralde. 2012. Actions taken by fishing nations towards identification and protection of vulnerable marine ecosystems in the high seas: The Spanish case (Atlantic Ocean). MarinePolicy 36:536–543, http://dx.doi.org/10.1016/j.marpol.2011.09.005. FAO FIRMS (Fishery Resources Monitoring System) firms.fao.org. GEBCO (General Bathymetric Chart of the Oceans) Available at http://www.gebco.net/data_and_poducts/gridded_bathymetry_data/. Jacobs, C.L. and Bett, B.J (2010) Preparation of a bathymetric map and GIS of the South Atlantic Ocean: a review of available biologically relevant South Atlantic Seamount data for the SEAFO Scientific Committee. National Oceanographic Centre Southampton, Research and consultancy Report No. 71 (unpublished manuscript). Perez, J.A.A, E. dos Santos Alves, M.R. Clark, O. A. Bergstad, A. Gebruk, I. Azevedo Cardoso, and A. Rogacheva. 2012. Patterns of life on the southern Mid-Atlantic Ridge: Compiling what is known and addressing future research. Oceanography 25(4):16-31, http://dx.doi.org/10.5670/oceanog.2012.102. Reid T, Ronconi R, Cuthbert R, and Ryan PG (2013) – unpublished data on Spectacled Petrel distribution. Rogers, A.D and Gianni, M. (2010) The implementation of UNGA Resolutions 61/105 and 64/72 in the Management of Deep-Sea Fisheries on the High Seas. Report prepared for the Deep Sea Conservation Coalition, International Programme on the State of the Ocean, London UK. 97 pp. Sanchez, P. and J.A. Alvarez 1988 Scaeurgus unicirrhus (Orbigny, 1840) (Cephalopoda Octopodidae): First record from the South-east Atlantic. South African Journal of Marine Science 7: 69-74. Zibrowius, H. and Gili, J.M. (1990) Deep-water Scleractinia (Cnidaria Anthozoa) from Namibia, South Africa and Walvis Ridge, southeastern Atlantic. Scientia Marina 54(1): 19-46.
Areas described as meeting EBSA criteria that were considered by the Conference of the Parties
C1: Uniqueness or rarity High
As the only extensive seamount chain off of the Mid-Atlantic Ridge in the Southeast Atlantic, the Walvis Ridge is a unique geomorphological feature. It is continuous in a transversal direction rather than latitudinal. The series of seamounts provides a potential stepping stone feature for organisms from coast to mid ocean (e.g., dispersion of the benthic octopod (Scaeurgus unicirrhus) (Sanchez and Alvarez, 1988).
C2: Special importance for life-history stages of species High
Seamount chains may facilitate connectivity between individual seamounts over extensive distances. The varied topography and geomorphology support demersal fish resources (based on demersal fisheries records in locations shallower than 2000 m). The varied bathymetry dictates distribution area and provides significant habitat for bentho-pelagic species (e.g., hotspots for orange roughy) and is likely to do so also for epipelagics (Clark et al., 2007, Rogers and Gianni, 2010). These seamounts are significant habitats for coldwater corals and sponges. Nine species of scleractinian coldwater coral have been recorded on the summit, upper and lower flanks of Walvis Ridge seamounts (Zibrowius and Gili, 1990). Thus the Ridge is of special importance for sessile macrofauna and for demeral fish associated with seamounts (FAO FIRMS species distribution maps) (http://firms.fao.org). The feature is also an important post-breeding area for Spectacled Petrel Procellaria conspicillata, an Atlantic Ocean endemic species breeding only on an island within the Tristan group and recorded as foraging along the Walvis Ridge (Unpublished information: Reid et al. 2013). It includes parts of foraging areas of globally threatened seabirds, including Tristan Albatross (Diomedea dabbenena), Wandering Albatross (Diomedea exulans) and Atlantic Yellow-nosed Albatross (www.seabirdtracking.org).
C3: Importance for threatened, endangered or declining species and/or habitats Medium
Bluefin and big-eye tuna occur in the area (e.g., FishBase), and orange roughy hotspots are known (SEAFO information). The far south EEZ of Tristan da Cunha is a foraging area for albatross, penguins, shearwaters and petrels (www.seabirdtracking.org). Historic whale capture data in the mid-ocean portion of the feature (Right Whale and Sperm Whales) indicate former concentrations (maps derived from OBIS presented at workshop), and an opportunistic survey within the area in 2009 as part of the South Atlantic MAR-ECO project recorded 23 sightings of cetaceans (Perez et al. 2012).
C4: Vulnerability, fragility, sensitivity, or slow recovery Medium
Habitat-forming sessile megafauna are fragile and vulnerable to bottom contact fishing gears and slow to recover from damage. Habitat prediction models (maps available at workshop) and some observational data (Durán Muñoz et al. 2012, Perez et al. 2012 and papers cited therein) indicate presence of cold-water corals. Based upon limited empirical evidence (e.g. observations from Spanish/Namibian cruises on the Valdivia Bank) it is likely that seamounts along the Walvis Ridge have sensitive habitats, biotopes and species, justifying a medium (bordering on high) criterion ranking.
C5: Biological productivity No information
Lack of information precludes a ranking on this criterion; however, several seamounts extend into the photic zone and may have enhanced primary production. Significant areas are within the likely vertical range of epipelagic zooplankton migration (Jacobs and Bett, 2010).
C6: Biological diversity Medium
Apart from seabirds and some benthic megafauna and fish studies (see Perez et al. 2012 for review), data on biological diversity is limited. The south-west end of the feature has high seabird diversity, including Spectacled Petrel, Atlantic Yellow-nosed Albatross, Sooty Albatross and Atlantic Petrel. Observations and the range of habitats created by the seamount complex and immediately adjacent abyssal area suggest comparatively higher diversity of ecosystems, habitats, communities and species. Foraging range extrapolations and satellite tracking work have highlighted the south-west part of the feature as important for the following seabird species (status on IUCN Red List 2012 is given for all): Tristan Albatross (Diomedea dabbenena) - Critically Endangered Atlantic Yellow-nosed Albatross (Thalassarche chlororhynchos) – Endangered Sooty Albatross (Phoebetria fusca) – Endangered Grey Petrel (Procellaria cinerea) – Near Threatened Atlantic Petrel (Pterodroma inerta) – Endangered Black-browed Albatross (Thalassarche melanophrys) – Endangered Cory’s Shearwater – Least Concern Great Shearwater (Puffinus gravis) – Least Concern Grey-headed Albatross (Thalassarche chrysostoma) – Vulnerable Northern Royal Albatross (Diomedea sanfordi) – Endangered Southern Giant-petrel (Macronectes giganteus) – Least Concern Wandering Albatross (Diomedea exulans) – Vulnerable
C7: Naturalness Medium
Human influence is largely historic, and fisheries were and are mainly confined to seamount summits (SEAFO information, Clark et al. 2007, and relevant papers cited in Perez et. al. (2012)). Whaling has ceased in this area for several decades. Apart from seamounts that are likely to have been impacted by bottom-fishing, the remainder of the area is considered to have a high degree of naturalness.
Additional criteria BirdLife Important Bird Areas Criteria (BirdLife 2009, 2010) A1 Regular presence of threatened species A4ii >1% of the global population of a seabird