Pile-driving and other impulsive sound sources have the potential to injure or kill fishes. One mechanism that produces injuries is the rapid motion of the walls of the swim bladder as it repeatedly contacts nearby tissues. To further understand the involvement of the swim bladder in tissue damage, a specially designed wave tube was used to expose three species to pile-driving sounds. Species included lake sturgeon (Acipenser fulvescens)-with an open (physostomous) swim bladder, Nile tilapia (Oreochromis niloticus)-with a closed (physoclistous) swim bladder and the hogchoker (Trinectes maculatus)-a flatfish without a swim bladder. There were no visible injuries in any of the exposed hogchokers, whereas a variety of injuries were observed in the lake sturgeon and Nile tilapia. At the loudest cumulative and single-strike sound exposure levels (SEL cum and SEL ss respectively), the Nile tilapia had the highest total injuries and the most severe injuries per fish. As exposure levels decreased, the number and severity of injuries were more similar between the two species. These results suggest that the presence and type of swim bladder correlated with injury at higher sound levels, while the extent of injury at lower sound levels was similar for both kinds of swim bladders.

Juvenile Chinook salmon, Oncorhynchus tshawytscha, were exposed to simulated high intensity pile driving signals to evaluate their ability to recover from barotrauma injuries. Fish were exposed to one of two cumulative sound exposure levels for 960 pile strikes (217 or 210 dB re 1 µPa2·s SELcum; single strike sound exposure levels of 187 or 180 dB re 1 µPa2⋅s SELss respectively). This was followed by an immediate assessment of injuries, or assessment 2, 5, or 10 days post-exposure. There were no observed mortalities from the pile driving sound exposure. Fish exposed to 217 dB re 1 µPa2·s SELcum displayed evidence of healing from injuries as post-exposure time increased. Fish exposed to 210 dB re 1 µPa2·s SELcum sustained minimal injuries that were not significantly different from control fish at days 0, 2, and 10. The exposure to 210 dB re 1 µPa2·s SELcum replicated the findings in a previous study that defined this level as the threshold for onset of injury. Furthermore, these data support the hypothesis that one or two Mild injuries resulting from pile driving exposure are unlikely to affect the survival of the exposed animals, at least in a laboratory environment.

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.