There is medium confidence that climate change will reduce global fisheries' productivity , with more significant reductions in tropical and subtropical regions and gains in the poleward areas . Through an ensemble of marine ecosystem models and Earth System Models, mean global animal biomass in the ocean has been estimated to decrease by 5% under the RCP2.6 emissions scenario and 17% under RCP8.5 by 2100, with an average decline of 5% for every 1ºC of warming , affecting food provision, revenue distribution, and potentially hindering the rebuilding of depleted fish stocks . The projected declining rates result in a 5.3-7% estimated global decrease in marine fish catch potential by 2050 , particularly accentuated in tropical marine ecosystems and affecting many low- income countries . Projections indicate that by 2060 the number of exclusive economic zones  with new transboundary stocks will increase to 46 under strong mitigation RCP2.6, and up to 60 EEZs under the RCP8.5 GHG emissions scenario . Similarly, by combining six intercompared marine ecosystem models, Bryndum-Buchholz et al.  projected that under the RCP8.5 scenario a total marine animal biomass decline of 15-30% would occur in the North and South Atlantic and Pacific and the Indian Ocean by 2100. In contrast, polar ocean basins would experience a 20-80% increase. In the eastern Bering Sea, simulations based on RCP8.5 predict declines of pollock  and cod  stocks by the end of the century . Temperate tunas  and the tropical bigeye tuna are expected to decline in the tropics and shift poleward by the end of the century under RCP8.5, while skipjack and yellowfin tunas are projected to increase abundance in tropical areas of the eastern Pacific but decrease in the equatorial western Pacific  . In the western and central Pacific, redistribution of tropical tuna due to climate change is projected to affect license revenues from purse seine fishing and shift more fishing into high seas areas . For the east Atlantic, observational evidence indicates that not only will tuna distribution change with temperature anomalies, but also fishing effort distribution . There is medium confidence that climate change will create new fishing opportunities when exploited fish stocks shift their distribution into new fishing regions in enclosed seas, such as the Mediterranean and the Black Sea . However, in general, where land barriers constrain the latitudinal shifts, the expected impacts of climate change are population declines and reduced productivity  . Besides direct impacts on the abundance of fisheries-targeted species, climate-change-induced proliferation of invasive species could also affect fisheries' productivity  .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report