Green Sturgeon Physical Habitat Use in the Coastal Pacific Ocean

The green sturgeon’s (Acipenser medirostris) complex life history makes it vulnerable to species-wide threats in both freshwater and at sea. It is a highly migratory, oceanic, anadromous species captured as bycatch in both commercial and sport fisheries. Green sturgeon marine habitat is poorly understood, yet population declines have preceded legal protection and curtailment of activities in marine environments deemed to increase its extinction risk. We utilized data from a coastal tracking array that recorded the passage of 37 acoustically tagged green sturgeon located along the Siletz Reef near Newport, Oregon, USA to characterize green sturgeon marine habitat use. First, we classified seafloor physical habitat features with high-resolution bathymetric and backscatter data. We then described the distribution of habitat variables and their relationship to green sturgeon detections using an ordination, and used generalized linear models to describe green sturgeon habitat preferences. Finally, we summarized depth and temperature recordings from seven additional green sturgeon present off the Oregon coast that were fitted with pop-off archival geolocation tags. Our analyses indicated that green sturgeon spent a longer duration in areas with high seafloor complexity, especially where a greater proportion of the substrate consists of boulders. Green sturgeon in marine habitats are primarily found at depths of 20-60 meters and from 9.5-16.0° C. Many sturgeon in this study were likely migrating in a northward direction and may have been using complex seafloor habitat because it coincides with the distribution of benthic prey taxa or provides refuge from predators. Identifying important green sturgeon marine habitat is an essential step towards accurately defining the conditions that are important for its survival and will eventually yield range-wide, spatially explicit predictions of sturgeon distributions.