Movement Patterns and Distributional Shifts of Dungeness Crab (Cancer magister) in Response to Hypoxia

Hypoxia (dissolved oxygen < 2 mg/l) has emerged as a widespread threat to estuaries, coasts and semi-enclosed seas worldwide. Regionally, hypoxia has been identified as a key threat to the Puget Sound ecosystem, particularly in southern Puget Sound and Hood Canal. Hood Canal is subject to seasonal hypoxia in its southern reaches, and prior work has demonstrated short-term reductions in densities of demersal fish and macro-invertebrates in hypoxia-impacted areas. We interpreted these findings as an indication of distributional shifts that reduce mobile organisms’ exposure to hypoxic conditions, potentially resulting in secondary ecological effects (e.g., enhanced vulnerability to predators, increased competition). We evaluated the nature and extent of these distributional shifts through a combination of acoustic telemetry and visual surveys in shallow habitats. We deployed an acoustic receiver array in two regions of Hood Canal, a southern highly impacted region and a northern reference region, and tagged 30 dungeness crab with pressure sensing acoustic transmitters. Weekly monitoring of water quality revealed strong gradients in dissolved oxygen over time and space, with the vertical extent of low (<1 mg/l) waters increasing markedly at the end of summer in the Southern site. Analysis of movement, depth preferences, and shallow water densities will be used to link animal behaviors to these differences in water quality.