Gas Bubble Trauma Incidence in Adult Salmonids in the Columbia River Basin

Very few studies have focused on the health threat to adult salmonids from gas bubble trauma (GBT) caused by water spill at hydroelectric dams in the Columbia River basin. From 1995 to 1999, 4,667 adult chinook salmon Oncorhynchus tshawytscha, 1,878 sockeye salmon O. nerka, and 1,431 steelhead O. mykiss at Bonneville Dam were examined to determine the incidence of GBT relative to total dissolved gas supersaturation (TDGS) levels. Polynomial regression models were constructed to determine whether an association existed between increasing levels of TDGS and the incidence of GBT. For sockeye salmon and steelhead, we found a significant positive association between TDGS and the incidence of GBT. However, no statistically significant relationship between TDGS and GBT was found for chinook salmon. Most symptoms of GBT were minor (26% fin occlusion) being observed in sockeye salmon (15 fish) and steelhead (2 fish) only when TDGS exceeded 126%. Chinook salmon were rarely observed with GBT, despite the sampling of large numbers when TDGS exceeded 130%.