Recovery from exposure to pile driving signals by Chinook salmon.

Abstract

Juvenile Chinook salmon exposed to pile driving sounds showed a variety of barotrauma injuries immediately post‐exposure, with number and severity of injuries increasing with increased cumulative sound exposure levels (SELcum). Important remaining questions pertain to the severity of these injuries over time post‐exposure including whether (a) injuries are eventually mortal, (b) new injuries show up, or (c) there is recovery over time. Juvenile Chinook salmon were exposed to either high or low SELcum pile driving stimuli. Fish were assessed for barotrauma injuries immediately following exposure and at 2, 5, or 10 days post‐exposure. No fish died during recovery and all fish exhibited normal feeding behavior within hours of exposure. The injuries observed at day zero were comparable to those found in the previous pile driving studies at the same SELcum. However, beginning with day 2, the frequency of appearance of injuries began to decrease, with fish at day 10 showing few remaining injuries. These results suggest that Chinook salmon exposed to pile driving stimuli have the potential to recover from barotrauma injuries, and that new injuries did not show up post‐exposure. These are important findings that need to be considered when establishing exposure criteria for pile driving projects.