The Application of the FIT Model to Sustained Noise

Drilling, fracking (hydraulic-fracturing) and dredging occurs in coastal and offshore waters of the US and internationally. In recent years, the potential impact of underwater sounds associated with drilling and dredging operations are under scrutiny by regulatory agencies. National Marine Fisheries Service has impulsive sound interim criteria for fish and marine mammals. Intense, whether peak sound or sustained sound, underwater noise has the potential to cause sublethal and lethal injury to fish and marine mammals. The critical issues are the generated sound levels relative to ambient noise, duration, and how to assess sound effects on fish. Peer-reviewed studies involving pile-driving and confined blasting activities have documented types of tissue injuries caused from impulsive sounds exposure. From these activities, assessment methods and FIT model (Fish Index of Trauma) were developed to rank fish sub-lethal and lethal injuries. Source levels of drilling sounds can range from 130 to 220 dB re 1 µPa. To investigate sound-induced tissue injury from drilling noise, we use a case study from underwater pile-driving activities. This presentation focuses on the development of this model system in relation to underwater drilling noise.