The Omani shelf hypoxia and the warming Arabian Sea

Interdecadal changes in oxygen depletion, with a special reference to artisanal landings of large pelagic fishes, were analysed. Data from 53 expeditions incorporating 29,043 vertical profiles of temperature and 2114 of dissolved oxygen implied an increase in temperature of 1.2 °C over the past 50 years in the upper 30 m layer of sea water during the south-west (summer) monsoon. The thermal stratification of the water column increased and the oxycline shoaled from 153 m in the 1960s to 80 m in the 2000s. Concentration of dissolved oxygen <3.5 mL L⁻¹ is known to induce symptoms of stress for many tropical pelagic fishes, compressing them within upper layers and exposing them to fishery. The habitat compression by the Oman shelf hypoxia has two components: a seasonal oxycline shoaling and an interdecadal trend.