Divergent responses of pelagic and benthic fish body-size structure to remoteness and protection from humans

Abstract

Animal body-size variation influences multiple processes in marine ecosystems, but habitat heterogeneity has prevented a comprehensive assessment of size across pelagic (midwater) and benthic (seabed) systems along anthropic gradients. In this work, we derive fish size indicators from 17,411 stereo baited-video deployments to test for differences between pelagic and benthic responses to remoteness from human pressures and effectiveness of marine protected areas (MPAs). From records of 823,849 individual fish, we report divergent responses between systems, with pelagic size structure more profoundly eroded near human markets than benthic size structure, signifying greater vulnerability of pelagic systems to human pressure. Effective protection of benthic size structure can be achieved through MPAs placed near markets, thereby contributing to benthic habitat restoration and the recovery of associated fishes. By contrast, recovery of the world’s largest and most endangered fishes in pelagic systems requires the creation of highly protected areas in remote locations, including on the High Seas, where protection efforts lag.

Editor’s summary

Marine megafauna are increasingly threatened and are difficult to protect. Understanding the influence of humans on body size in fishes is also challenging given that data on marine species often come from fishery-based activities. Letessier et al . deployed more than 17,000 remotely operated baited devices to collect data on fish size and abundance as related to habitat (pelagic or benthic), human activities, and marine protected areas. Pelagic species were strongly influenced by human pressures and protection. The authors concluded that benthic species could be effectively protected even near markets, whereas only more remote protected areas will effectively safeguard large pelagic species. —Sacha Vignieri

Abstract

Fish size structure is more affected by human pressure in midwater than in seabed ecosystems.