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Location Namibia, Karas
Central coordinates 14o 50.00' East  25o 43.00' South
IBA criteria A1, A4i, A4ii, A4iii
Area 3 ha
Altitude 0 - 40m
Year of IBA assessment 2001

Site description Located 800 m offshore, the precipitous Mercury Island lies within Spencer Bay, about 110 km north of Lüderitz. The island is within a zone of intense oceanic upwelling that is responsible for the elevated nutrient levels and high fish biomass around these near-shore islands. Somewhat elongate, this steep-sided island reaches 40 m, is 500 m long and 100 m wide. It is the smallest of the three guano islands at 3 ha. Known as the island that shakes (hence the name Mercury), the interior of the island is hollow, and large swells, common in this region, thunder inside the coves under the island, causing it to reverberate ominously. The island is unvegetated and was first exploited for guano in the 1840s when thousands of tons of ‘white gold’ were stripped from its flanks. It is the northernmost of the 18 near-shore islands of the Diamond Coast used by breeding seabirds.

Key Biodiversity See Box for key species. Mercury Island is one of three very important coastal seabird-breeding islands along the Diamond Coast of south-western Namibia; the other two are Ichaboe (IBA NA016) and Possession (NA018). Mercury regularly supports over 15,000 seabirds, including Spheniscus demersus, Morus capensis, Phalacrocorax neglectus, and small numbers of P. coronatus. The island’s breeding population of Phalacrocorax neglectus has decreased by about 50% in the last 15 years. The seabirds cover virtually the entire surface area of the island, leaving no space for other species.

Non-bird biodiversity: Several whale species migrate through these waters, including Megaptera novaeangliae (VU) and Eubalaena australis (LR/cd). The cetaceans Cephalorhynchus heavisidii (DD), Lagenorhynchos obscurus (DD) and Tursiops truncatus (DD) occur in these waters.

Populations of IBA trigger species

Species Season Period Population estimate Quality of estimate IBA Criteria IUCN Category
African Penguin Spheniscus demersus resident  1,000-3,000 breeding pairs  A1, A4ii  Endangered 
African Penguin Spheniscus demersus winter  4,000-10,000 individuals  A1, A4ii  Endangered 
Cape Gannet Morus capensis resident  1,300 breeding pairs  A1, A4ii  Vulnerable 
Cape Gannet Morus capensis winter  10,000 individuals  A1, A4ii  Vulnerable 
Bank Cormorant Phalacrocorax neglectus resident  679 breeding pairs  A1, A4i  Endangered 
Bank Cormorant Phalacrocorax neglectus winter  2,000 individuals  A1, A4i  Endangered 
African Oystercatcher Haematopus moquini winter  present  A1  Near Threatened 
A4iii Species group - seabirds winter  10,000-19,999 individuals  unknown  A4iii   
A4iii Species group - seabirds resident  10,000 individuals  unknown  A4iii   

Protected areas

Protected area Designation Area (ha) Relationship with IBA Overlap with IBA (ha)  
Namibia Islands Marine Protected Area 955,525 protected area contains site 3  

Land use

Land-use Extent (% of site)
nature conservation and research -

References Cooper et al. (1980), Crawford et al. (1982, 1989), Hockey (1982), Kemper et al. (in press), Pallet (1995), Rand (1963), Swart (1987, 1988), Williams (1993).

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Recommended citation  BirdLife International (2016) Important Bird and Biodiversity Area factsheet: Mercury Island. Downloaded from on 27/10/2016

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