What Is the Spawning Potential for Shortnose Sturgeon (Acipenser brevirostrum) in the Penobscot River after Dam Removal? An Acoustic Telemetry and Habitat Suitability Study

Recently the two lowermost dams were removed from the Penobscot River, Maine, restoring 14 km of diadromous fish habitat. Shortnose sturgeon have been documented foraging and wintering in the Penobscot River but there has been no indication of spawning since monitoring began in 2007. During the first spring after the dam removals, 16 sturgeon with active acoustic tags were tracked and 29 icthyoplankton net samples were conducted. Fish were not observed upstream of the lowermost removal site and no early life stage sturgeon were captured. Previous field assessment and modeling studies indicate suitable spawning habitat above the removed dams: water depths of 1.2-10.4 m, velocities from 0.4-1.8 m/s, and bottom substrates with large interstitial spaces. In the reach above the lowermost removal site, gravel (40%) and cobble (31%) dominate along the shore where spring discharge levels create suitable water depths for spawning. Water velocity, depth, and bottom substrate will be incorporated into a spawning habitat suitability model for newly available habitat. Weighted usable area estimates will be used to compare suitable habitat availability under various river conditions, including the conditions prior to the dam removals. Habitat suitability maps will allow more efficient acoustic telemetry and aid future restoration efforts.