Midwater discharge plumes threaten $5.5B Pacific tuna fisheries

Deep-sea mining operations pump a slurry of nodules, sediment, and seawater from the seafloor (4,000-6,000m depth) to a surface vessel, then discharge the processed waste water and sediment back into the ocean at ~1,200m depth (the mesopelagic 'twilight zone'). Research from the University of Hawaii shows that 53% of all zooplankton and 60% of micronekton in this zone would be impacted by discharge plumes, which can spread 200+ km from the discharge point. These small organisms are the primary food source for commercially important tuna species. The CCZ overlaps with fishing grounds that produce 66% of global tuna catches (3.5 million tonnes/year, worth ~$5.5 billion USD). Climate models project this overlap will increase as tuna stocks shift into mining areas under warming scenarios, with skipjack biomass in the CCZ forecasted to increase 30-31%. There is no coordination mechanism between the ISA (which governs mining) and regional fisheries management organizations (IATTC, WCPFC) to manage conflicts. Pacific Island nations that depend on tuna fishing license fees for a major portion of government revenue face an existential economic conflict they have no institutional power to resolve.