Models predict climate-driven ocean warming and reduced ventilation of the deep ocean will lower levels of dissolved oxygen (DO) in the ocean by 1–7% by 2100, with in situ observations suggesting reductions of >2% since 1960. Globally distributed, open-ocean oxygen minimum zones (OMZ) and ‘dead zones’ are increasing in area and volume as a result, with unknown consequences for ecosystems and biodiversity. Potential impacts may be particularly significant for large, fast-swimming oceanic predators with high oxygen demands, such as sharks and tunas, by reducing available habitats and concentrating them further in surface waters where they are more vulnerable to fisheries. A major concern is how ocean warming, deoxygenation and fisheries exploitation may interact to impact future sustainability of apex predator populations. However, increased vulnerability of oceanic predators from surface fisheries due to expanding OMZs has not been quantified because direct measurements in OMZ habitats have not been made; new approaches and data are needed.
This proposal addresses major unknowns in oceanic fish behaviour and ecology in oxygen poor environments that will predict responses to future warming and ocean deoxygenation and the effects on species vulnerability to fishing. We apply individual-based tracking studies and movement analysis and develop new technologies to understand from direct measurements how oceanic fish actually respond to hypoxic regions. Modelling studies establish the effects of future warming and deoxygenation on predator niches, shifting distributions and altered susceptibility to fishing exploitation.
Specific objectives are to (1) determine broad-scale space use and fine-scale physiological and behavioural responses of oceanic fishes to OMZs to quantify biophysical habitat preferences and test the habitat compression hypothesis directly; (2) quantify oceanic fish metabolism and predator-prey interactions directly to determine the ecological importance of waters around OMZs to oceanic fishes for testing the habitat trap hypothesis; (3) quantify spatial overlap between remotely tracked fish and fishing vessels to determine the impact of biophysical habitat changes on susceptibility to fisheries above OMZs and adjacent areas; and (4) develop and test spatially explicit models based on empirical fish-habitat-vessel relationships to predict future habitat availability under climate-driven OMZ expansion and fisheries exploitation.
