Larval fish abundance, composition and distribution at Senghor Seamount (Cape Verde Islands)

Abstract

The Cape Verdean Senghor-Seamount rises up to 93 m below the surface, and lies within the Cape Verde Frontal Zone (CVFZ), and within the southwestward North Equatorial Current. The seamount and its oceanic surroundings were surveyed with Multiple-Opening-Closing Net (MCN) fish larval catches, Issacs-Kidd midwater trawl (IKMT) micronekton hauls and an analysis of some conductivity–temperature–depth data (RV Poseidon cruise no. POS 320/2). The thermal and saline stratifications showed widely symmetrical uplifts near the summit. The larval fish community was diverse (H′ = 2.656) and composed mainly of larvae of meso- to bathypelagic species (91.5%). In IKMT, 44.1% of the specimens originated from demersal parents (H′ = 3.296), and mostly, albeit not entirely, from West African coastal waters, after advection along the CVFZ to and across this potential “stepping stone”. Gross larval fish abundance (median 35.5 specimens/1 m2) and composition agreed well with historical literature data from adjacent waters and seamounts north of the CVFZ, whereas south of the CVFZ and towards NW-Africa reported abundances were higher. Vertical distributions of larvae which generally live at greater depths showed a rise above the seamount, following the hydrographic uplift, accompanied by “thinning-out effects” through bathymetric disturbance. The extent to which findings at Senghor Seamount are representative for small, shallow and steep seamounts in the tropical NE-Atlantic is discussed.