Mesopelagic fish biomass and trophic efficiency of the open ocean

Abstract

With a current estimate of about 1000 million tons, mesopelagic fish dominate the world total fish biomass. However, recent acoustic observations show that mesopelagic fish biomass could be significantly larger than the current estimate. We combined modeling and a sensitivity analysis of the acoustic observations from the Malaspina2010 Circumnavigation Expedition to show that the previous estimate needs to be revised to at least one order of magnitude higher biomass. We show that there is a close relationship between the open ocean fish biomass and primary production, and that the energy transfer efficiency from phytoplankton to mesopelagic fish in the open ocean is higher than what is typically assumed. Our results indicate that the role of mesopelagic fish on the oceanic ecosystems and global ocean biogeochemical cycles needs to be revised as they may be respiring in deep waters around 10 % of the primary production.