Hypoxia (dissolved oxygen concentrations < 1.4 ml/L) is common in bottom waters across the continental shelf off Oregon and Washington during the summer months (Figure HYP-01). The presence of hypoxic waters can be lethal to benthic invertebrates and may displace demersal fish species (Grantham et al. 2004).
Along the Newport Hydrographic (NH) Line, hypoxic waters tend to occupy the lower 10 - 30 m of the water column (Figure HYP-01). Spatially, hypoxic bottom waters can cover the entire width of the shelf (Figure HYP-02), but is less common in shallower areas (< 30 m depth) where wind and wave action helps to aerate the water column.
Juvenile salmon tend to reside in the upper layer of the water column and are likely not directly influenced by hypoxia.
The greatest extent of hypoxic bottom waters typically occurs in August and September. Based on regional surveys conducted since 2006, hypoxic bottom waters can cover up to 62% of the shelf north of the Newport Hydrographic line (Figures HYP-02 and HYP-03).