Pelagic fish more impacted by human pressures and protections than benthic species

Pelagic fish – species that occupy the water column of the open ocean, neither near the bottom nor near the shore – are more impacted by both human pressure and protection than bottom-dwelling benthic species, researchers report. The findings highlight the need for increased marine protection in remote pelagic locations. Body size is a universal biological property that influences a range of ecological processes in marine ecosystems. Measuring body-size-structured variation can be a useful framework for understanding and predicting the impacts of overfishing or the success of fisheries regulations and marine conservation policies. However, such assessments across marine habitats and marine protected areas (MPAs) are particularly challenging because most data on marine species are derived from fisheries-based activities. Moreover, different survey methodologies are used in pelagic (midwater) and benthic (seabed) systems, making intersystem comparisons difficult. To address this, Tom Letessier and colleagues deployed more than 17,000 stereo baited remote underwater video stations (BRUVS) across the Atlantic, Indian, and Pacific Oceans to conduct a global size- and abundance-based assessment of marine pelagic and benthic fishes. The remotely operated observation systems enabled the authors to collect standardized, fisheries-independent data on fish size and abundance in virtually any marine habitat or region. Combined, the data encompassed more than 820,000 observations of pelagic and benthic fishes, spanning six orders of magnitude in body size, from zooplankton size classes to large oceanic predators. Letessier et al. evaluated how fish size and abundance related to habitat system, human activities, and MPAs. The authors found that the size structure of pelagic species was more strongly impacted by human pressure than their benthic counterparts. However, pelagic species were also more influenced by the protections of MPAs. Although the size structure of benthic species could be effectively protected in both MPAs and near markets, the findings suggest that only increased protection in remote regions will effectively protect the world’s largest and most endangered pelagic fishes.