Effects of spatial variability on the exposure of fish to hypoxia: a modeling analysis for the Gulf of Mexico

Abstract. The hypoxic zone in the northern Gulf of Mexico varies spatially (area, location) and temporally (onset, duration) on multiple scales. Exposure fish to dissolved oxygen (DO) concentrations (< 2 mg L?1) is often lethal avoided, while exposure 4 L?1 occurs readily causes sublethal effects decreased growth fecundity for individuals many species. We simulated movement individual within a high-resolution 3-D coupled hydrodynamic water quality model (FVCOM-WASP) configured examine how spatial variability DO would affect concentrations. Eight static snapshots (spatial maps) were selected from 10 d FVCOM-WASP simulation that showed range variation (degree clumpiness) when total area was moderate (four high maps). An additional case allowing vary time (dynamic DO) also included. All simulations performed 2-D (bottom layer only) (allows vertical fish) sets maps. Fish every 15 min with each switching among three algorithms: tactical avoidance imminent, strategic had occurred recent past, default (independent not invoked. Cumulative hypoxia higher under compared but little effect exposure. In contrast, relatively exposures all simulations. Spatial opposite between maps: percentage exposed 2–3 increasing increased area. There wide simulation. These results suggest averaging over cells steps can result underestimation effects. Our methods inform larger models are critical assessing management actions reduce nutrient loadings will populations.