Studies on the effects of offshore wind farm construction on marine life have focused on behavioral reactions in porpoises and seals (Thomsen et al. 2006). The effects on fish have only very recently come into the focus of scientists, regulators, and stakeholders (Popper and Hastings 2009). Pile-driving noise during construction is of particular concern because the very high sound pressure levels (see Thomsen et al. 2006) could potentially prevent fish from reaching breeding or spawning sites, finding food, and acoustically locating mates that could result in long-term effects on reproduction and population parameters. There is also the possibility that avoidance reactions might displace fish away from potential fishing grounds that could lead to reduced catches (see, e.g., Engås et al. 1996). However, the nature and extent of behavioral reactions of marine fish due to pile driving have not been studied in controlled experiments. Therefore, the impacts of pile driving on marine fish remain unknown.