An opportunistic boat-based survey to the Mauritania upwelling zone in July 2005 discovered an unprecedented concentration of Wilson’s Storm-petrels Oceanites oceanicus. Flocks of up to 600 birds were concentrated along the boundary between warm surface waters and cooler upwelled waters. These flocks formed an aggregation of at least 5,000 birds, which is an unprecedented total for this species in Western Palearctic waters.

The Mauritania upwelling zone lies just within the Western Palearctic boundary and is an important feeding area for both resident and migratory seabirds (e.g. Wynn & Knefelkamp 2004; Camphuysen & van der Meer 2005). Upwelling in this region is driven by northeast-flowing Trade Winds pushing surface waters offshore. These surface waters are replaced by cold, deep, upwelled waters, which are rich in nutrients and able to support elevated levels of primary productivity. This in turn supports concentrations of higher trophic levels, including fish and seabirds (Wynn & Knefelkamp 2004).

IntroduPrevious pelagic trips to the region in winter and spring have revealed important concentrations of species such as Cory’s Shearwater Calonectris diomedea, Northern Gannet Morus bassanus, Pomarine Skua Stercorarius pomarinus, Long- tailed Skua Stercorarius longicaudus, Sabine’s Gull Xema sabini, Black Tern Chlidonias niger and Common Tern Sterna hirundo (Brown 1979; Leopold 1993; Burton & Camphuysen 2003; Camphuysen 2003; Wynn & Knefelkamp 2004; Camphuysen & van der Meer 2005).ction

From 4–26 July 2005, a research expedition to the Mauritanian continental shelf and upper slope (Figure 1) enabled the seabird assemblage in mid summer to be assessed for the first time. The purpose of this short article is to document an unprecedented Western Palearctic concentration of Wilson’s Storm-petrels Oceanites oceanicus recorded in the Mauritania upwelling zone between 15 and 17 July 2005, and to briefly discuss the controls on their spatial distribution.

We are grateful to Kees Camphuysen and Andy Webb for providing useful comments that helped to improve the manuscript. We thank the Captain, officers and crew of RV Meteor for their assistance with data collection.

Brereton, T. 2011. Cape Verde to Madeira - the seabirds and cetaceans of Macaronesia. Naturetrek Tour Report 2–10 May 2011. Naturetrek, England.

Brown, R. G. B. 1979. Seabirds of the Senegal upwelling and adjacent waters. Ibis 121: 283–292. [Crossref]

Burton, C. & Camphuysen, C. J. 2003. Seabird and cetacean surveys in the vicinity of the Chinguetti oil field, offshore Mauritania, March 2003. EIA report by Bowman Bishaw Gorham for Woodside Energy Ltd.

Camphuysen, C. J. 2003. Seabirds and marine mammals off West Africa. Responses 2000 Cruise Report. NIOZ, Texel.

Camphuysen, C. J. & van der Meer, J. 2005. Wintering seabirds in West Africa: foraging hotspots off Western Sahara and Mauritania driven by upwelling and fisheries. African Journal of Marine Science 27: 427–437. [Crossref]

Halley, A. & Noeske, A. 2007. Travel Special: Wilson’s Storm-Petrel Oceanites oceanicus off Europe. http://www.club300.de/articles/008_wilsons/index.html

Krastel, S., Wynn, R. B., Hanebuth, T. J. J., Henrich, R., Holz, C., Meggers, H., Kuhlmann, H., Georgiopoulou, A. & Schulz, H.D. 2006. Mapping of seabed morphology and shallow sediment structure of the Mauritania continental margin, Northwest Africa: some implications for geohazard potential. Norwegian Journal of Geology 86: 163–176.

Leopold, M. F. 1993. Seabirds in the shelf edge waters bordering the Banc d’Arguin, Mauritania, in May. Hydrobiologia 258: 197–210. [Crossref]

Marr, T. & Porter, R. 1992. Spring seabird passage off Senegal. Birding World 5: 391–394.

Wynn, R. B. & Knefelkamp, B. 2004. Seabird distribution and oceanic upwelling off northwest Africa. British Birds 97: 323–335.