Quantifying and Communicating the Impacts of Groundfish Bottom Trawling on Deoxygenation and Nutrient Fluxes off Oregon

Working with collaborators from the Oregon Department of Fish and Wildlife, we are in the midst of an extremely rare and short-lived opportunity to collect meaningful information on the role that spatial fishery management approaches may play in determining ecological and biogeochemical characteristics of the seafloor in an important area along Oregon’s shelf break. In 2002, the National Marine Fisheries Service (NMFS) introduced substantial restrictions to groundfish bottom trawling along the U.S. west coast when they implemented the Rockfish Conservation Area (RCA), a large-scale spatial closure designed to reduce the catch of overfished groundfishes in the bottom trawl fishery. In 2020, in response to rebuilding of key groundfish stocks after 18 years of closure, NMFS re-opened the RCA to bottom trawling with Amendment 28 to the West Coast Groundfish Fishery Management Plan, which also made adjustments to several of the existing Essential Fish Habitat (EFH) Conservation Areas.

With support from Oregon Sea Grant and the Oregon State Research Vessel Program we have ongoing work to assess progressive changes in habitat characteristics, abundance and diversity of benthic invertebrates and fishes, biogeochemical fluxes, and carbon burial within areas newly opened to bottom trawling at depths to 300 m along the continental shelf break near Heceta Bank, Oregon. Our goal is to transition from assessing short-term effects of individual, or a few trawl passes, to assessment of long-term effects of varying intensities of sustained trawling that is quantified using both Vessel Monitoring System (VMS) records and trawl logbook data.

Map of study area showing RCA boundaries and 2019 ROV transect locations on the OR margin
Map of study area showing RCA boundaries and 2019 ROV transect locations on the OR margin.

ODFW and OSU researchers initiated an ROV-based video sampling program in the RCA, north and adjacent to Heceta Bank, in the fall of 2019 prior to the closure, establishing a baseline of data on representative habitats and associated biota. S. Marion, W. Wakefield and coworkers collected high-definition stereo video footage along 38 Remote Operated Vehicle (ROV) 1-km transects between 44° 2’ and 44° 32’ N latitude in the RCA, bounded by the 100 fm (183 m) RCA shoreward boundary and a 300 m depth offshore limit (the ROV’s working depth limit). In collaboration, our group initiated collection of sediment cores at sites corresponding to three latitudinally-separated RCA transects to document substrate types and textures, associated organisms, pore water chemistry, carbon burial and disturbance indicators based on 210Pb profiles. We also have made eddy covariance lander measurements of oxygen fluxes and deployed a new benthic lander to yield biogeochemical fluxes from near-bottom solute concentration gradients and velocity profiles. We intend to continue seeking external support from a variety of sources for this initiative.