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Dr. Fridtjof Nansen
"Dr. Fridtjof Nansen"
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RV Dr Fridtjof Nansen explores seamounts of the Southeast Atlantic

The UN General Assembly has listed seamounts among marine habitat that may have particularly vulnerable benthic communities and fisheries resources. The recent cruise of the RV “Dr. Fridtjof Nansen”, from the 15. Jan to the 12. Feb 2015 aimed at mapping the occurrence and abundance of benthopelagic fish and sessile epibenthos in the southeast Atlantic.

This included indicators of vulnerable marine ecosystems (VMEs sensu FAO Guidelines for Deep-sea Fisheries in the High Seas), in selected ‘existing fishing areas’ and areas closed to fishing within the convention area of the Southeast Atlantic Fisheries Organisation (SEAFO). Using towed video systems and other samplers, the international scientific party enhanced information of both fish and VME-indicators such as corals, on the seamounts known as Schmitt-Ott, Wüst, Vema, Valdivia, and Ewing.

The cruise was a contribution to the Southeast Atlantic Fisheries Organization (SEAFO) resulting from a co-operation between SEAFO, the EAF-Nansen project, and the FAO. The aim is to facilitate activities in support of the efforts by SEAFO to meet objectives in relation to the United Nations General Assembly (UNGA) resolution 61/105 and the associated FAO Guidelines on Deep-sea Fisheries in the High Seas. The south eastern Atlantic was selected by the recently initiated GEF-sponsored FAO ABNJ programme (“Common Oceans”) as an area of particular attention.

Despite a shortage of data on the occurrence of ‘vulnerable marine ecosystems’ (VMEs, as defined in the FAO Guidelines), SEAFO has introduced comprehensive measures to protect such ecosystems from significant adverse impacts within the convention area. SEAFO has closed 10 subareas of the convention area to all fishing activity, a regulation most recently revised in 2011. Best available bathymetry data were compiled to locate subareas recognised in the FAO guidelines as VME features, essentially primarily seamounts. Fishing was assumed restricted to the upper 2000m of any feature, hence an updated map of areas shallower than 2000m was the basis of further selection (Fig. 1). In SEAFO such areas are seamounts or seamount complexes of various sizes and shapes.

The spatial distribution of VME indicators such as corals and sponges (i.e. as given in FAO guidelines) is however not well known in SEAFO, hence a need for further information from scientific investigations at sea has been recognised. Also, there is a pronounced shortage of fisheries-independent data for assessing the status and providing advice on targeted fisheries resources such as Patagonian toothfish, pelagic armourhead, alfonsino and deep-water crabs.

The international scientific party comprised competent scientists from SEAFO Contracting Parties supplemented by invited experts to strengthen the competence on benthos and fish taxonomy and identification. Five of seven SEAFO CPs were represented on the cruise, i.e. Namibia. Angola, the European Union, South Africa and Norway.

Koraller på et av undervannsfjellene

Extensive bathymetry mapping was conducted in all seamounts that had never been mapped and in those that had been insufficiently mapped. New maps were generated for Schmitt-Ott, two locations at Wüst, and the shallower parts of Vema. Several video transects up the hill from around 1000m to the summit was conducted in all locations and provided new documentation of the occurrence of coral and other benthic taxa, as well as crab and benthopelagic fishes.

Further analyses of the data and assessment of the results are pending. A few initial inferences were reported in the initial cruise report to be followed in the autumn of 2015 by a full report:

Bathymetry and substrate:

  • Many seamounts were significantly deeper than given by authoritative sources. In most areas, the potential fishing areas are smaller than earlier estimated.
  • Ancient coral framework is the dominant hard substrate (except at Schmitt-Ott), and soft sediments are biogenic, including foraminiferan deposits, pteropod shells, and coral rubble.

VME indicators:

  • Most seamounts visited have VME indicators, i.e. mainly live corals.
  • At Schmitt-Ott there was a pronounced dominance of gorgonians. In all other seamounts the diversity was greater, and more scleractinians occurred.
  • Notably, in Valdivia and Ewing, scleractinians (dead or alive) seem to be restricted to slopes and knolls within a limited depth range.

Human footprint

  • Frequent video observations of lost pots and rope were made in Vema and some in Valdivia. These could not be aged, but may well have been abandoned/lost many years ago. In Ewing, lost trawl gear was observed in one of the summit dives.
  • On the main Valdivia Bank and a western shallow bank, what was suspected to be trawl door skid marks were observed. These areas have flat rocky surfaces.
  • No evidence of impacts of trawling or pot fishing was observed in areas of soft sediments, including the extensive areas with coral rubble and ancient coral framework.
  • In areas with high densities of live (and dead) coral that may be regarded as candidate VMEs, the first impression from the video records is that the benthic communities are intact and not impacted by fishing. However, the widespread occurrence of dead scleractinian coral, probably ancient, makes a full evaluation difficult and this phenomenon deserves further attention.