Abundance of pelagic decapods in the northern Benguela upwelling system during AFR258, D356 and MSM17/3

Pelagic decapods were collected in the northern Benguela upwelling system off the coast of Namibia on three cruises: FRS Africana (December 2009), RRS Discovery (September/October 2010) and RV Maria S. Merian (February 2011). Three transects along 17°S, 19°S and 23°S were sampled during each cruise. Decapods were collected with a 1 m**2 single (December 2009) and double (September/October 2010, February 2011) MOCNESS (Multiple Opening and Closing Net and Environmental Sensing System; Wiebe et al., 1985). The single MOCNESS was equipped with 9 and the double MOCNESS with 18 nets of 333 µm mesh size. The towing speed of the vessel was 2 knots and the heaving speed of the winch was 0.5 m s-1. Maximum sampling depth was close to the seafloor at the shallow stations (shelf and shelf break) or down to 750 m (2009), 2600 m (2010) and 3000 m (2011) at the deeper slope and oceanic stations. Discrete depths intervals (0-25, 25-50, 50-100, 100-200, 200-400, 400-600, 600-800, 800-1000 m) were sampled at most stations. At stations deeper than 1000 m, 250 m intervals were performed to a maximum depth of 3000 m. The volume filtered ranged from 181 to 368 m3 for narrow depth intervals of 50 m and from 645 to 975 m**3 for 200 m intervals. The samples were preserved in 4% buffered formaldehyde-seawater solution. In the laboratory of the Institute for Hydrobiology and Fisheries Science (IHF) at the University of Hamburg, preserved samples were sieved in size fractions of <0.5, 0.5-1, 1-2, 2-5 and >5 mm and for taxonomic analysis stored in Steedman-solution (Steedman, 1976). The size class of >5 mm was used for the recording of decapods. Decapod species were identified according to Crosnier & Forest (1968; 1969), Kensley (1971a; 1971b) and Pérez Farfante & Kensley (1997) and enumerated and measured separately (total length from the anterior margin of the eye to the end of telson). Abundance is expressed as both, numbers of individuals per m**2 and per m**3.