EXPEDITION "WALTERS SHOAL"
32°30’S / 44°E
©David SHALE - Faune des monts sous-marins
The number of seamounts in the western part of the Indian Ocean is estimated at 268, in what is referred to as a "fishing zone", being summits at less than 2000 m depth. The study of the composition of benthic communities, and in particular the connectivity between coastal and offshore areas, is crucial to the way in which these resources are managed and conserved. The work on the "water column" will allow us to better understand the pelagic communities and their dynamics and to understand the physical processes resulting from the interactions between current and topography that are at the origin of the high biological productivity around the Walters Shoal compared to surrounding areas. By advancing scientific knowledge, the project seeks to determine among the resources, what may be the ''natural wealth'', what should be considered as "common heritage of mankind", thus helping to the identification of priority protection areas in the high seas.
Seamount characteristics
The term "seamount" is generally used for a submarine topographical elevations of more than 1000 m. The seamounts do not emerge. They are mostly of volcanic origin, but can sometimes be formed by tectonic uplift or by accumulation of serpentine mud. This habitat is one of the largest oceanic environment (28 million km2), with an estimated 25,000 to 200,000 mounts for large formations, and up to 25 million for small mounts or domes of more than 100 m.
Seamounts are known to be aggregators of biological resources, in particular because of the current-topography interactions they induce. They influence, for example, local oceanic circulation, vertical mixing of water bodies, summit formation of retention cells
(Taylor's Column). Thus, according to their characteristics (size, diameter, distance to the surface, etc.) the force and the effect of the physical processes vary and can accentuate the biological processes. In particular, primary production can be promoted by deep nutrient-rich upwelling, thereby increasing the biomass of lower and upper trophic compartments, improving the food supply of wildlife visiting these seamounts.
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Vulnerability of seamount resources
The isolation of seamounts makes the evolutionary and ecological mechanisms very different from those operating in the deep ocean around them. Some of the benthic fauna they contain is composed, inter alia, of endemic species and species with very slow development. As a result, these ecosystems are highly vulnerable. The restoration of these once degraded environments will depend in large part on the ability of the larvae of structuring species to recolonize the area
(Proximity of source populations, connectivity and phenomenon of hypersedimentation). These ecosystems are important in terms of biodiversity and genetic heritage. They also have areas favored by large pelagic predators, marine mammals and seabirds.
Situated for the most part outside national jurisdictions, seamounts are at the heart of a twofold challenge: the exploitation of fisheries resources by the fishing industry and the exploitation of offshore mining.
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Walters Shoal
32°30’S / 44°E
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Discovered in 1963 by the South African frigate SAS Natal led by Commander Walters, the Walters Shoal is a group of submarine mounts located near the southern end of the Madagascar Ridge (700 km south of Madagascar, 1000 km to the east of the coasts of South Africa). It is distinguished by shallow areas that reach 18 to 15 m below the surface of the sea and by an important biodiversity.
Its isolation and position in subtropical waters, relatively cold (19 ° C), suggests a particular benthic biodiversity composed of endemic species on the one hand and species with long larval lives and vast distributions on the other. Regarding the visiting migratory fauna of the site, SIODFA indicated that the site was notorious for whale sightings. However, in general, the fauna is almost unknown.
The Walters Shoal is considered a productive and active fishing place, but it is difficult to obtain data from fisheries statistics for reasons of industrial confidentiality.
The shoal is known to have been the target of bottom fishing in the past, and the latter is decayed by deep-sea lobster fishing (Palinurus barbarae - IUCN Red List) and lobster (Palinurus delagoa). Thark fishery, using gill nets, has also been reported.
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