Epipelagic isotherms have recently  deepened at an average of 6.6 + 18.8 m per decade , but there is low agreement on whether species move deeper in pursuit of thermal refuge. Prior studies suggested range shifts to depth , but increasing evidence suggests that fish and planktonic communities across large parts of the North Atlantic, sub-Arctic and northeast Pacific Ocean redistribute horizontally with horizontal climate velocity, except where vertical temperature gradients are particularly steep. There is low confidence for temperature-driven depth shifts in the epipelagic zone . At the same time, decreasing oxygen concentrations and the vertical expansion of OMZs have already decreased suitable habitat of pelagic fishes, including tuna and billfishes, by ~15% primarily due to vertical compression of environmental niches .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report