Effects of Pile Driving on Fish
Popperlab research papers on pile driving effects on fishes
Pile driving in the aquatic environment is being a major issue in the U.S. and around the world. Pile driving is required for a wide range of construction activities including building bridges, piers, off-shore wind farms, etc. The concern, as discussed in our comprehensive review () is that very little is known about the effects of pile driving on fish or other aquatic life. While there have been past studies, most of these have been difficult to design and, in many cases, poorly executed. It is, in particular, very hard to control the sounds to which fish are exposed from pile driving operations since they are often very large and very expensive, and (understandably), people doing construction need to work as quickly as possible and they cannot easily mange the rate of their pile driving activities to fit an experimetnal protocol.
In order to undertstand effects of pile driving on fish, we (Arthur Popper and Michele Halvorsen) teamed with Tom Carlson at the Pacific Northwest National Laboratory (PNNL) to develop a lab-based systemt that would enable us to expose fish to simulated pile driving sounds in the lab, at sound intensities equivalent to those fish would encounter in the wild. Moreover, we wanted to be able to control all sound parameters, including sound intensity, number of strikes, inter-spike interval, etc.
To do this, we developed a device called the HICI-FT (Figure below). In this figure, the HICI-FT is seen in the vertical position (left) and the chamber is open as it would be when we were putting in fish. Dr. Michele Halvorsen is seen by the control system for the experiments. The two black boxes above Dr. Halvorsen, and the silver tubes, are all part of the cooling system required to run the HICI-FT. The large gray cylinder above the opening of the HICI-FT is one of the two transducers.
In the following figure, the HICI-FT is seen in the operational position, with our colleague Dr. Brandon Casper standing beside it. After fish are placed in the device, the chamber is turned to the horizontal position and the fish exposed to sounds. After the exposure is completed, the HICI-FT is turned vertically, opened, and the fish removed for study.
In the intial study, we examined effects of exposure to 960 or 1920 pile driving strikes on Chinook salmon. The results of this study can be found in Halvorsen et al. (2011) and in Halvorsen et al. (2012). as well as in the other publications listed on the top of this page. We discovered that juvenile Chinook salmon start to show onset of physiological effects from pile driving sounds when the cummulartive Sound Exposure Level (SELcum ) exceeds about 210 dB re 1 µPa2·s. We also found that onset of physiological effects are better "predicted" by knowing about the single strike sound exposure level (SELss) and the number of strikes. In other words, the onset of physiological effects depends on the single strike level and the number of strikes. Thus, if there are to be more strikes, the single strike level should be lower to prevent reaching onset of physiological effects than if there are to be fewer strikes.
We also found, as discussed in the paper, that the kinds of effects we encountered at the onset level for physiological effects (SELcum 210 dB re 1 µPa2·s) were highly likely to be recoverable (minor bleeding at the base of fins, for example) and it was only when one reached a higher cummulative sound level were any effects that we thing might be potentially affecting survival take place.
Some of our ther findings, as highlighted in our publications, show that:
Effects found in Chinook salmon are also found in other species that have a swim bladder.
A species of fish without a swim bladder (hogchocker) does not show barotrauma injury, even with at very high sound exposure levels.
Effects on the ear (hair cell damage, and presumably hearing) do not start to show up until sound exposure levels are substantially higher than those that induce other non-auditory injuries.
A very important conclusion from our studies is that onset of injries as a result of exposure to pile driving sounds only occurs at sound exposure levels that are at least 20 dB above the levels that are part of the current interim guidelines used on the U.S. west coast and in other parts of the world.