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.
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.
BirdLife International (2019) Important Bird Areas factsheet: Mercury Island. Downloaded from http://www.birdlife.org on 15/10/2019.