| Summary: | Anthropogenic noise in the sea has increased during the past decades as a consequence of increased shipping traffic, oil and gas exploitation, and underwater construction work (Southall et al., 2007; Slabbekoorn et al., 2010). Such anthropogenic noise may affect marine animals by causing hearing injuries (Smith et al., 2004; Popper et al., 2007), masking of biological sounds (Richardson et al., 1995), or behavioural responses such as avoidance of the exposed habitat (e.g. Engås et al., 1996; Morton and Symons, 2002). In 2006, the Norwegian Navy began to operate a new class of frigates, equipped with high-power sonars transmitting at frequencies overlapping with the hearing range of several species of fish and marine mammals found in Norwegian waters (Enger, 1967; Richardson et al., 1995). As naval sonar operations often coincide with the geographic distribution of these species, an examination of potentially negative effects was needed. My PhD work includes three papers on the effect of such sonars have on herring (Clupea harengus), and one paper concerning the effect of sonars on the diving behaviour of three species of cetaceans; killer whales (Orcinus orca), pilot whales (Globicephala melas) and sperm whales (Physeter macrocephalus). In paper 1, herring were exposed to sonar signals at 1-2 kHz (Low Frequency Active Sonar, LFAS) and 6-7 kHz (Mid frequency Active Sonar, MFAS), and playbacks of recorded sounds produced by killer whales while feeding, during herring overwintering in the Lofoten area. Herring behaviour was monitored by two upward-looking echosounders, located 400 m apart, as the sonar source approached and passed the fish. No significant horizontal or vertical avoidance reactions were detected in response to the sonar transmissions, however, the killer whale feeding sounds induced both vertical and horizontal movements. The results indicate that sonar transmissions at 1-2 kHz and 6-7 kHz have negligible influence on herring at the source levels tested (197 and 209 dB re 1 Pa, for LFAS and MFAS, ...
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