Detecting acoustically tagged green sturgeon in the Northeast Pacific Ocean

Identifying critical habitats is challenging for a relatively rare species like green sturgeon ( Acipenser medirostris ), which spends most of its life at sea. We used a fixed array and an autonomous underwater vehicle (Slocum glider) as monitoring platforms to detect acoustically tagged green sturgeon in the coastal ocean. For 1 month in 2018 during spring (May) and again in fall (September–October), both methods were used simultaneously to detect sturgeon bearing uniquely coded transmitters. For the fixed array, nine acoustic receivers were interspersed with three sentinel transmitters along a single line of latitude off Winchester Bay, OR. For the glider, two 3-week deployments were completed along the coast of Oregon from nearshore to the 200-m depth contour. For both deployments, the glider flew a zig-zag course southward as it profiled the water column and collected water quality information. Tagged green sturgeon and sentinel transmitters were successfully detected by both the fixed array and the glider. The fixed array provided indications of onshore and offshore movement, while the glider indicated along-shore movement. Although more green sturgeon were detected by the fixed array, the glider provided information on potential sturgeon aggregation areas. In addition, this application of the underwater glider may provide a unique opportunity for public engagement, teaching, and outreach.