Underwater blast pressure effects on caged juvenile fish from confined rock removal during the Columbia River channel improvement project

The Columbia River Channel Improvement Project lead by the U.S. Army Corps of Engineers was initiated to improve conditions for commercial traffic between Portland, OR and the Pacific Ocean, and complete restoration projects in the Columbia River estuary. During November 2009 through February 2010, underwater explosives were used to lift the basalt bottom between river miles 87 and 88. We performed biological monitoring to meet compliance requirements for the project. The presence of marine mammals, diving birds, and dead/moribund salmonids (Oncorhynchus spp.), sturgeon (Acipenser transmontanus), and eulachon (Thaleichthys pacificus) were monitored for each blast. Specially designed cages for high water flow conditions were placed 100 to 300 ft from the blasting location with autonomous blast sensors that recorded pressure associated with the blasts. Depth-acclimated neutrally buoyant fry and juvenile salmonids were examined for impulsive-sound-related physical damage at 0, 24, and 48 hrs. Injuries ranged from no damage to petechial hemorrhages and perforated swimbladders even though sound exposure levels rarely exceeded 30 peak psi. Injuries were identified for an impulsive sound-injury model. Also, exposure of fishes transiting the impacted area was estimated using sound fields, hydrodynamics, and fish movements resulting in a distribution of stressor “dose” model.