Seafood is a vital source of protein for more than 3.3 billion people. The UN Food and Agriculture Organization (FAO) projects the need for a 15% increase in global fish consumption by 2030; its director-general, QU Dongyu, calls the growth of fisheries and aquaculture “vital in our efforts to end global hunger and malnutrition”. There’s one big problem: the growth rate of the global wild-fish catch peaked in 1963 and plateaued in the 1990s. It has been in slow decline the past few years. When it comes to the wild-fish catch, we are most likely past “peak fish”. Virtually all of the oceans are overfished, or at their maximum capacity. An assessment of 1,439 wild-fish populations found that 10% are on the brink of collapse. Another 45% are overfished and there isn’t enough information about the rest to know if the current fishing levels are sustainable, according to 2021 Global Fishing Index, which states: “Over the past 50 years, the world has witnessed a massive decline in the health of its fisheries. Quite simply, we are removing fish from the ocean at a far greater rate than they can naturally replenish.” There are several reasons why ocean life faces such a serious health crisis, including marine pollution, especially hundreds of millions of tons of plastics; global heating affecting water temperature; and emissions of CO2 making the oceans 26% more acidic. But overfishing, particularly bottom trawling, which destroys corals and other habitat, is a major culprit. So is aquaculture the solution to the looming seafood shortage? As it turns out, the answer is no. Aquaculture’s growth rate has been in decline since 1996. While the industry did experience rapid growth decades ago, its five-year moving-average annual growth rate peaked at 14.1% in 1996 and is now at about 2%, according to a new study in Frontiers in Marine Science. As well as peak fish, “peak aquaculture” might be just around the corner. There are constraints on good places to site fish farms, a lack of high-quality water, struggles with cost and availability of food for the farmed species, disease and pest pressure, and the impact of the climate crisis and resulting weather variability. There is another, surprising reason: increasing human opposition to ocean-based fish farms. On Canada’s west coast, years of protests by the local fishing community, Indigenous groups and environmentalists has led to more than 100 salmon fish-farms being scheduled to be phased out by 2025. Properly managed, the oceans could provide far more wild fish than today, according to many marine scientists. In fact, studies have found that global fisheries catches could generate 16m more tons annually than current production levels. That would require sound management, such as the agreement to protect 30% of oceans under the recent Convention on Biological Diversity (Cop 15), the WTO’s agreement to ban the estimated annual $15.4bn of harmful fisheries subsidies (primarily from China, Japan and the EU), stronger governance of the high seas and a binding global treaty to end plastic pollution. But I’d like to highlight the importance of marine protected areas (MPAs). MPAs are no-fish or limited fishing zones that become a refuge for fish and give protection to the overall marine ecosystem. It is particularly important to protect larger, older fish because they can produce hundreds or thousands more offspring over their lifetime, which go on to disperse into unprotected waters. (In 2005, I wrote one of the first articles about this for New Scientist.) Study after study shows that a protected ecosystem becomes healthier and fish numbers soar. For example, the biomass (the number of fish) in fully protected MPAs may be 670% greater than in adjacent unprotected areas. Eventually, the fish in an MPA spill over into other areas where they can be caught. Rashid Sumaila, a fisheries economist at the Institute for the Oceans and Fisheries, in Canada, says: “We’ve got to rebuild and take good care of our wild fish – and then when we do sustainable aquaculture, together hopefully we’ll be able to meet our demand for fish.” Protecting 30% of the oceans in full MPAs could go a long way to returning them to their former health and abundance. That would be a very good thing, not just for those 3.3 billion people who depend on the protein that lives in them, but for all of us. A version of this article first appeared on Stephen Leahy’s newsletter Need to Know