8.2 The significance of ocean deoxygenation for open ocean tunas and billfishes Shirley Leung,K. A. S. Mislan, Barbara Muhling and Richard Brill 8.2 The significance of ocean deoxygenation for open ocean tunas and billfishes Shirley Leung1,*, K. A. S. Mislan1,2, Barbara Muhling3,4 and Richard Brill5 1 School of Oceanography, University of Washington, USA. Email :
[email protected] 2 eScience Institute, University of Washington, USA 3 University of California Santa Cruz, Santa Cruz, CA, USA 4 National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southwest Fisheries Science Center, La Jolla, CA, USA 5 Virginia Institute of Marine Science, Gloucester Point, VA, USA Summary • Tunas and billfishes should be especially sensitive to low ambient oxygen conditions given their high metabolic rates as well as the large differences between their resting and maximum metabolic rates. Although there are many behavioural similarities among the different species, there are also clear and demonstrable differences in growth rates, maximum adult size, physiological abilities, low-oxygen tolerances, and preferred environmental conditions. • Climate change is projected to alter oxygen concentrations throughout the open ocean, with most regions undergoing decreases due to a slowdown in ocean ventilation and a decline in surface oxygen solubility. Between 200 and 700 m depth (a vertical range including depths to which tunas and billfishes commonly descend to forage), the greatest and most certain decreases in oxygen concentrations are projected to occur in the North Pacific and much of the Southern Ocean, while the smallest and least certain changes are projected to occur within the tropical Pacific Ocean.