Startled but not traumatized: the effects of pile-driving on fish behavior

Given the increasing amount of anthropogenic impulsive underwater sound introduced into the marine environment, a wide-ranging coverage of the impact on marine life is needed. Impulsive sound, such as piling sound, can cause mortality, injuries, and hearing loss in the close vicinity of the sound source. The impact on behaviour and physiology of fish can act on a larger scale. Remarkably, little is known about the effects of impulsive sound exposure on fish behaviour and condition. We therefore conducted a laboratory experiment with young European sea bass (Dicentrarchus labrax). During this experiment, fish divided over two sets of treatment tanks were observed for 15 days. The fish in the “sound” treatment were exposed to one hour of impulsive sound on the seventh day. Fish in the “silent” treatment were kept continually in a quiet environment. Behaviour, feeding, growth, respiration, feed conversion efficiency (FCE) and Fulton’s condition index (ΔK) were compared between treatments. The results showed an increase in startle responses and stationary behaviour at the beginning of the sound exposure, and aggression was completely absent during the sound exposure hour. Feeding and respiration were not affected and accordingly, FCE, ΔK, length and weight over 15 days were not different than in the ”silent” treatment. The specific growth rate, however, was significantly different between treatments. The results of this experiment indicate that short-term exposure to impulsive sound can disturb fish behaviour. This disturbance, however, was short-lived and little impact on growth and condition was seen in the current experiments.