Biological monitoring for environmental compliance before, during, and after underwater blasting events in tidal freshwater of the Columbia River, USA

Underwater explosives were detonated to fracture basalt rock to deepen the Columbia River navigation channel.  We performed biological monitoring to meet compliance requirements for the project.  For each blast, biological monitoring objectives were to: 1) notify the Corps of the presence of marine mammals inside a 500-ft zone around the blast site prior to blast detonation, 2) estimate the take of juvenile and adult chum salmon, and 3) count and report the probable cause of death of listed salmonids, sturgeon, and eulachon collected during post-blast surveys.  Monitoring methods included visual observations during pre- and post-blast surveys.  Take was estimated using a dose-response model with measured fish flux and blast pressures among the inputs.  Monitoring data were compiled and reported to the Corps within 6-h of the last blast each day.  During the four-month study period, nearly 100 blasts occurred.  The estimated take of juvenile and adult salmon was zero fish.  A total of three dead sturgeon and no dead marine mammals, salmon, or eulachon were observed during post-blast surveys.  Conducting the project during the winter when biological activity in the river is minimal helped the project comply with federal and state requirements to not adversely impact marine mammals and fishes.