Impact on the fishing sector and aquaculture

Climate change affects the physical and chemical properties of the oceans. In addition to warming, the increased uptake of CO₂ leads to ocean acidification. This has direct consequences for fish, shellfish and other marine organisms. Ocean acidification affects coral growth and represents a threat to the survival of endangered reefs. Coral bleaching events are likely to increase. Additionally, calcareous shells of mollusks, such as mussels and oysters, become thinner. Since the beginning of industrialization, the average pH of the oceans has already fallen 0.1. This change means that seawater has become acidic by about 30%. By 2100, a further decrease of 0.3 to 0.4 is expected; the pH of seawater was not so low for at least 50 million years. When water is warmed, it can absorb less oxygen, having as possible consequences: The maximum length that large fishes can reach decreases; the number of coastal regions with low-oxygen waters increases; regions in the ocean where oxygen content is depleted for natural reasons spread.

For the fishing industry, the impact of climate change worldwide is considered to be most likely negative. Fish stocks will shift regionally. Corresponding changes have already an impact on the composition of fish catches. With further global warming, many species will keep migrating polewards. Some forecasts indicate that biodiversity and fishing catch potential will increase on average in mid and high latitudes and will decrease in tropical latitudes. Such changes are likely to affect the means of existence in tropical developing countries (for instance, of artisanal fishermen). In the inter-tidal zones of the North Pacific and the North Atlantic, the habitats of many species have shifted as much as 50 km per decade. This can be a major threat to marine food webs. Changes in resources in coastal regions and the resulting food insecurity for the people living there can cause more illegal, unreported and unregulated fishing (IUU).

Aquaculture could be affected if not enough feed for fish can be caught. Mortality of aquaculture shellfish will increase because of ocean acidification. Brackish and freshwater aquaculture farms that keep their animals in ponds and lagoons are particularly at risk in low-latitude tropical coastal areas. Risks include storm surges, intrusion of salty sea water due to rising sea levels and flooding caused by stronger rains. However, climate change may also have positive aspects for aquaculture: These include rapid growth of the breeding animals, more efficient utilization of feed, longer breeding periods, larger areas of distribution of species or an expansion of farming areas due to sea-ice decline.