Exploring mechanisms of change in a Southern Ocean fishery with a co-produced network model

Abstract A key challenge in planning long-term fisheries sustainability is overcoming uncertainties around predicted changes in target populations and catch rates in response to climate change and fishery trends. We combine transdisciplinary knowledge co-production and qualitative network modelling to advance system understanding and elucidate likely responses of a Patagonian toothfish fishery to future change. We co-developed a model of the Kerguelen Plateau biophysical-socioeconomic system with knowledge holders from industry and science; the first whole-of-system qualitative network model of intermediate complexity for this region. We present new approaches for dealing with uncertainty in network structure, and for investigating how perturbations propagate through a network. Using these tools, we found multiple potential pathways of decline for toothfish population and catch, including via increases in water temperature at the surface and at depth, downwelling scavenging benthos (e.g. sea lice), bycatch, localised depletion or changes in fishing tactics. However, the likelihood of outcomes depended on interaction strengths and assumptions, and in some cases we observed possible mechanisms of increase conditional on certain effects, including how fishery responses to change affect their interactions with the system, and the magnitude of temperature effects on prey and benthic scavengers. Our results highlight critical information gaps, including the potential role of scavenging benthos in fishery-ecosystem interactions and likely changes in the prey field in response to warmer water, that require filling to improve predictions for toothfish populations and catch and forward planning for the fishery.