Abstract
The High Seas, lying beyond the boundaries of nations’ Exclusive
Economic Zones, cover the majority of the ocean surface and host roughly
two thirds of marine primary production. Yet, only a small fraction of
global wild fish catch comes from the High Seas, despite intensifying
industrial fishing efforts. The surprisingly small fish catch could
reflect economic features of the High Seas - such as the difficulty and
cost of fishing in remote parts of the ocean surface - or ecological
features resulting in a small biomass of fish relative to primary
production. We use the coupled biological-economic model BOATS to
estimate contributing factors, comparing observed catches with
simulations where: (i) fishing cost depends on distance from shore and
seafloor depth; (ii) catchability depends on seafloor depth or vertical
habitat extent; (iii) regions with micronutrient limitation have reduced
biomass production; (iv) the trophic transfer of energy from primary
production to demersal food webs depends on depth; and (v) High Seas
biomass migrates to coastal regions. Our results suggest that the most
important features are ecological: demersal fish communities receive a
large proportion of primary production in shallow waters, but very
little in deep waters due to respiration by small organisms throughout
the water column. Other factors play a secondary role, with migrations
having a potentially large but uncertain role, and economic factors
having the smallest effects. Our results stress the importance of
properly representing the High Seas biomass in future fisheries
projections, and clarify their limited role in global food provision.