Minerals Report - International Seabed Authority

3.1.2 Changes to the seabed and resident communities
The mining process, treatment and the overboard discharge of
tailings comprehensively mixes the sediment horizons overlying the
footwall directly beneath the ore body. This alters the natural habitat of
the infaunal communities. The process also destroys the organisms in the
mined sediments, and others are smothered by resedimentation of the
coarser-grained material discharged overboard as it settles on the seabed.
Recolonisation of the mined areas (termed “chronically artificially
disturbed”) [15] by benthic organisms requires time, and the structure of
the communities is altered – benthic community structure is commonly
considered to be an important indicator of environmental conditions.
Researchers identified some 233 infaunal species, including at least
one species that is new to science. The organisms range in size between
worms of 20 cm in length to minute snails millimetres in diameter
[16,17,18,19].
The spatial extent of this impact is restricted to the area in which
mining occurs and most likely to a couple of hundred metres beyond due
to the resedimentation of sediment put into suspension during the mining
process. The analysis of the communities based on grab sampling from
mined and unmined areas shows that recovery to a stable biological
community may take from 4 to 8 years [19,20,21].
3.1.3 Effects on fish and dolphins
The initial study showed that within the mining area there are
relatively few species, no fish spawning grounds and currently no
commercial fishing activity. Rock lobster is the basis for an important
fishery in Namibia, but DBM’s operations do not overlap with the optimal
habitat or any rock lobster fishing activities. Consequently, potential for
conflict between the deep-water diamond mining operations and the
fishing industry is avoided.
The potential for noise from vessels and/or from the mining
process to impact on fish and marine mammals was considered.
Measurements of noise levels established that the frequencies generated
are lower than those used by marine mammals for communication
[22,23,24].
INTERNATIONAL SEABED AUTHORITY 631