Trophic relationships and oceanography on and around a small offshore bank

• Published in: Marine ecology. Progress series (Halstenbek) 2008-07, Vol.363, p.15-28
• Main Authors: Stevick, Peter T., Incze, Lewis S., Kraus, Scott D., Rosen, Shale, Wolff, Nicholas, Baukus, Adam
• Format: Article
• Language: English
• Subjects: Animal fins; Biomass; Cetacea; Cetaceans; Foraging; Herring; Internal waves; Marine; Predators; Sea birds; Waves; Whales
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps07475

Small offshore banks may be sites of intense feeding by upper trophic level predators. We studied the distribution of cetaceans, seabirds, pelagic fish, euphausiids and zooplankton over a 9 × 15 km bank to determine the conditions and processes that concentrated prey there and to examine the relative importance of bottom-up or top-down controls. Euphausiids were the primary prey during most foraging activity. While these were widespread in subsurface waters, foraging was concentrated on dense surface swarms that formed during daylight hours over 2 small crests. Internal wave passage resulted in upward movement and concentration of euphausiids in these areas through a coupling of physical processes and euphausiid behavior, resulting in surface swarms. Thus, internal waves appear to provide a critical mechanism enhancing trophic energy transfer. The formation of dense, localized and accessible prey concentrations was more important to foraging than was the overall available prey biomass. The estimated maximum daily consumption of euphausiids by cetaceans, seabirds and herring combined was