Cumulative ecosystem pressures exerted by demersal fisheries in the Brazilian Meridional Margin: Hotspots and refuges

Abstract

Demersal fishing operations exert, cumulatively, at least three forms of pressures over the benthic environment: mortality of megafauna (landed and discarded), discards of carrion back to the marine environment (also referred to as Predictable Anthropogenic Food Subsidies - PAFS) and disturbance of the seabed, by contact with bottom gear. This study presents a spatial synthesis of these forms of pressure on the Brazilian Meridional Margin (BMM, SW Atlantic) and their accumulated effect, in contribution to the development of effective space-based fishing management strategies. We analyzed landed catch, discards and effort of 2,125 fishing trips of industrial vessels operating double-rig trawlers, pair trawlers, stern trawlers, bottom longline and gillnets, monitored during 2018 in the main fishing harbors of Southern and Southeastern Brazil. All forms of pressure and the Accumulated Pressure Index (API) were represented spatially in a 20 × 20 nautical mile quads mesh grid. We demonstrated that nearly half of the BMM area was under high pressure. We also delimited fishing pressure hotspots in coastal and shelf areas mostly within the ‘Brazilian Bight’ region, between São Paulo and Santa Catarina states (24–29°S). Conversely, slope regions were found to be less demanded by demersal fishing, with both benthic ecosystems and demersal populations being barely disturbed. These were regarded as the main refuge areas for benthic and benthopelagic megafauna. Double-rig trawling was a major driver of pressure accumulating over half of total number of demersal fishing trips in 2018. Individual double-rig trawling operations also disturbed a seabed area far greater than the areas disturbed by the other fishing gear, and discarded the largest fraction (∼48%) of the produced mortality. Reducing the demersal fishing pressure on the BMM seems to be primarily concerned with abating the intensity of double-rig trawling, and/or diluting their effect through spatial management measures.