There is a growing concern in the United States and throughout the world that in-water pile driving used in construction of wind farms, bridges, and other projects has the potential to affect the health and survival of fishes. However, very little is known about such effects. Earlier studies, while examining the impacts on fishes at actual pile driving construction sites, suffered from the inability of the investigators to control the pile driving activities and the immense
difficulties of working in the field in order to quantify effects. In order to start to quantify such effects, this study was designed to provide quantitative data to define the levels of impulsive sound that could result in the onset tissue damage resulting from rapid changes in pressure that directly affect the body gasses and thus affect body tissues (referred to as Barotrauma). Such rapid changes in pressure are generated by impulsive sound signals.
In order to examine barotrauma effects, a High Intensity Controlled Impedance Fluid-filled wave Tube (HICI-FT) was developed that enabled laboratory simulation of high-energy impulsive sounds that were characteristic of aquatic far-field, plane-wave acoustic conditions. The sounds used were based upon the impulsive sounds generated by an impact hammer striking a steel shell pile.
In the first study juvenile Chinook salmon (Oncorhynchus tshawytscha), a species with a physostomous swim bladder, were exposed to impulsive sounds and subsequently evaluated for physical barotrauma injuries (Chapter 3; Halvorsen et al. 2012a). Observed injuries ranged from mild hematomas at the lowest sound exposure levels to organ hemorrhage at the highest sound
exposure levels. Frequencies of observed injuries were used to compute a biological response weighted index (RWI) to evaluate the physiological impact of injuries at the different exposure levels. As single strike and cumulative sound exposure levels (SELss, SELcum respectively) increased, RWI values increased. Based on the results, tissue damage associated with adverse physiological costs occurred when the RWI was greater than 2. In terms of sound exposure levels, an RWI of 2 was achieved for 1920 strikes by 177 dB re 1 µPa2 ∙s SELss yielding a SELcum of 210 dB re 1 µPa2 ∙s, and for 960 strikes by 180 dB re 1 µPa2 ∙s SELss yielding a SELcum of 210 dB re 1 µPa2
∙s. These metrics define thresholds for onset of injury in juvenile Chinook salmon.
While the first study showed that there was little immediate mortality resulting from exposure to pile driving, it was realized that fishes may succumb to their barotrauma injuries at a later time. The question arose as to whether fish show increased injuries post exposure, and/or whether they could recover from injuries. To explore this, juvenile Chinook salmon were exposed to simulated
high intensity pile driving signals to evaluate their ability to recover from barotrauma injuries (Chapter 4; Casper et al. 2012). 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 assessment of injuries
immediately 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.
Another issue was whether the effects of pile driving found in juvenile Chinook salmon are applicable to other species. To test this, the study was extended to a comparative analysis of response to pile driving stimuli in the lake sturgeon (Acipenser fulvecens, Acipenseridae), a species with a physostomous swim bladder; the Nile tilapia (Oreochromis niloticus, Cichlidae), a species with a physoclistous swim bladder; and the hogchoker (Trinectes maculates, Achiridae) a flatfish without a swim bladder (Chapter 5; Halvorsen et al. 2012b).
Results for the hogchoker demonstrated no observable barotrauma at the maximum sound exposure used (the same level that resulted in mortal injuries in the other tested species). The lake sturgeon and Nile tilapia showed a range of injuries. At the maximum sound exposure, Nile tilapia had the highest number and most severe injuries overall as compared to the lake sturgeon. Decreases in the exposure levels were correlated with a decrease in the number and severity of injuries for each species. Moreover, as exposure levels came nearer to the onset of injury threshold found in juvenile Chinook salmon, Nile tilapia, lake sturgeon, and Chinook salmon showed similar injury responses. Furthermore, the observed injuries became more similar between lake sturgeon, Nile tilapia, and Chinook salmon. These results imply that the presence and type of swim bladder correspond with barotrauma injuries at the higher sound exposure
levels. Therefore, physoclistous fish are more sensitive to the higher sound exposure levels than physostomous fish.
The results from these studies are the first to quantify the effects of impulsive sounds on fishes. They are also the first that can provide science-based data useful for developing criteria for impulsive sources. The results also define an onset of injury in Chinook salmon at an SELcum of over 210 dB re 1µPa2
∙s derived from 960 strikes and SELss of 180 dB re 1µPa2 ∙s. At these
levels, most of the other species were still showing moderate to mortal injuries. It wasn’t until the SELcum was 207 re 1µPa2 ∙s that the other species had comparable injury scores to the Chinook salmon, suggesting other species may be a small amount more sensitive and might have a lower threshold. It is important to note the metrics used to define threshold include the number
of strikes and the SELss levels that yield the SELcum values.
Major conclusions of this study are that: (a) For all species studied, onset of barotrauma effects did not occur until the SELcum was substantially above the current interim regulations. (b) Barotrauma injuries were not observed in a species without a swim bladder (hogchoker). (c) There were differences in the sound exposure level at which barotrauma appeared in fish. In the most sensitive tested species barotrauma was seen at an SELcum of 207 dB re 1 µPa2 ·s yielded from SELss 177 dB re 1 µPa2 ·s and 960 strikes. (d) The important metrics used to define the impulsive exposure incorporate how the energy accumulated. Three recommended metrics are: SELcum, SELss and the number of strikes. (e) Effects from exposure to pile driving sounds appear
to be consistent across species, even when there are substantial differences in fish morphology, including in both physostomous and physoclistous fishes.