Fish provide essential nutrition for 3 billion people. For at least 400 million people in the world’s poorest countries, they supply half or more of the animal protein and minerals in the diet. Warming oceans are now reshuffling where those fish live.
Climate change is expected to shift fish distributions and change how much fish is available and traded. The biggest drops in maximum catch potential are projected for the tropics, mostly in the South Pacific. One widely cited model projects that global fish community biomass could fall by as much as 30% by 2100. Another projection puts the decline in global ocean catch at 6 percent by 2100 and 11 percent in tropical zones.
Fish on the move
Skipjack and bigeye tuna are expected to be pushed further east as temperatures and currents change. That would move fishing grounds toward the Pacific islands and away from Melanesia, which now holds most of the stock. Western Pacific canneries would be disrupted, tuna production would shift elsewhere, and the effect on food security is uncertain.
In the North Atlantic, the problem starts lower in the food chain. Cool-water copepods have moved north as the water warmed. Warm-water species with less biomass have taken their place. Atlantic cod need large copepods, and with those moving poleward, cod mortality is high and recruitment has dropped sharply. Overfished cod are more exposed still, because depleted populations are smaller, younger and less genetically diverse. Baltic cod, already near their upper temperature limits, face changes in average size and growth.
Freshwater fish are moving too. In the Volga-Kama basin, southern Ponto-Caspian species are spreading north into new reservoirs, while cold-adapted vendace and European smelt are losing range.
Who pays
Models for 2050 suggest total global catch potential may change by less than 10 percent, depending on emissions. The averages hide a lot. In almost 85 percent of the coastal countries analysed, marine and terrestrial food production are predicted to fall, and countries differ widely in how well they can adapt.
Poor and rural people take the hardest hit, because they lack the money and labor to change quickly. In Bangladesh, Cambodia, Gambia, Ghana, Sierra Leone and Sri Lanka, fish supply over 50% of protein intake. More than 500 million people in developing countries depend directly or indirectly on fisheries and aquaculture for a living. Over 37% of world fish production by volume is traded across borders.
The local pictures vary. Low-lying nations such as the Maldives and Tuvalu are especially vulnerable, and whole communities there may become among the first climate refugees. Fishing communities in Bangladesh face sea-level rise, flooding and more typhoons. Along the Mekong, which produces over 1 million tons of basa a year, saltwater intrusion from rising seas and dams threatens livelihoods. In rural Alaska, residents of Noatak and Selawik cope with erratic weather, changes in where fish are and when, and altered boat access.
Fishing itself is a small part of the emissions problem. Fishing vessels caused about 0.5 percent of global CO2 emissions in 2012, or 172.3 million tonnes.
