What do we know about pile driving and fish?
There are growing concerns about the potential effects of in-water pile driving on aquatic organisms. These concerns arise from an increased awareness that high-intensity sounds have the potential to harm both terrestrial and aquatic vertebrates (e.g., Fletcher and Busnel 1978; Kryter 1984; Richardson et al. 1995; Popper 2003; Popper et al. 2004). The result of exposure to intense sounds may extend over a continuum running from little or no effects to the death of the ensonified organism. This paper is a brief review of what is known about the effects of pile driving on fish. It also provides some ideas about the design of future experiments that can be used to test these effects. The conclusions and recommendations presented here are explored in far more detail in a recent review on effects of pile driving on fish (Hastings and Popper 2005). In addition, a broader examination of the general effects of sound on fishes can be found in Popper (2003) and Popper et al. (2004). It is widely believed that fish close to pile-driving activities may be killed by exposure to very intense sounds. There is also some evidence that fish at some greater (but undefined) distance may survive exposure to pile-driving activities. However, experimental data are very limited. Moreover, nothing is known about non-life-threatening effects on fish of some (undefined) distance from the pile-driving operation. Such effects may include (a) non-life threatening damage to body tissues, (b) physiological effects including changes in stress hormones or hearing capabilities, or (c) changes in behavior (discussed in Popper et al. 2004). These effects could be temporary (e.g., a temporary loss of hearing that recovers over time) or of sufficient length to lower long-term survival and/or reproductive potential of individual animals or communities. There are also no data on effects of cumulative exposure to pile-driving sounds. The concerns about currently available pile-driving data arise because there is very little quantification and replication of experiments and because the investigators were not able to control the stimulus to which the fish were exposed. Thus, little is known about the stimulus actually received by fish during experiments. It therefore becomes difficult to evaluate the effects of pile driving on fish that are at different distances from the source. Moreover, there are no studies to date that included observations of the behavior of fish during exposure to pile-driving signals (but see paper by Hawkins in this volume). Because of the dearth of data on effects of pile driving on fish, it has been suggested that data from other types of experiments involving intense signals be extrapolated to pile driving. A problem, however, is that the sounds used in other studies, such as the effects of sonar (Popper et al. 2005a), seismic air guns (Pearson et al. 1992; Engås et al. 1996; Wardle et al. 2001; McCauley et al. 2003; Popper et al. 2005b), and pure tones (Enger 1981; Hastings et al. 1996) differ greatly from sounds produced during pile-driving activities. Moreover, there are also concerns about extrapolating effects between species, and particularly between species that have different life styles, sound-detection capabilities, and responses to adverse stimuli (see Hastings et al. 1996; McCauley et al. 2003; Popper et al. 2005b). Furthermore, there is some evidence to suggest that it may not always be possible to generalize the effects of high-intensity sounds between different age classes of the same species (e.g., Popper et al. 2005b). Since there are issues with the way pile-driving experiments have been done to date, it is worth considering how one might design an experiment that would provide the data needed to understand the effects of pile driving or, for that matter, any intense sound, on fish. One caveat with these suggestions, however, is that they require that fish be kept in a limited locale (e.g., a cage or tank) so that they can be observed before, during, and after the sound exposure, and that the fish can be retrieved for physiological and morphological analysis. Such requirements preclude direct observations on how fishes might behave if they were free from constraints or confinement during the exposure to pile driving, as has been done in one study on the effects of seismic air guns on fishes on a reef (Wardle et al. 2001).