Determination of optimal move-on distance for trawl encounters with vulnerable marine ecosystems

Abstract Regional Fisheries Management Organisations (RFMOs) use ‘move-on’ rules as one way to manage impacts to vulnerable marine ecosystems (VMEs). In response to a proposal to change the move-on distance from 1 to 5 nm for the South Pacific RFMO, we simulated trawl encounters using historical trawl data and information on the modelled size and spatial clustering of VME habitat to determine the optimal move-on distance for meeting conservation objectives while not placing undue burden on fishing operators. Our analyses found that predicted VME habitat patches were typically small, highly clustered, and rarely encountered by the trawl tows. When simulated encounters did occur, move-on distances of 1 nm and 5 nm avoided 73% and 80% of additional encounters with VMEs, respectively. Analysis of the impact on the fishery showed that increasing the move-on distance from 1 to 5 nm would potentially result in up to an additional 53%, 23%, and 9% area reduction of the trawl footprint, seamount, and management area used and accessible to the fishery, respectively. Our analysis demonstrates that, despite typical data limitations for VME indicator bycatch, it is possible using simulation analysis to assess the efficacy of current move-on distances used by RFMOs.