Abstract
Underwater breathing apparatus (UBA) has played a vital role in the study of aquatic environments, and is commonly used in visual census of mobile aquatic animals. The possibility of artifacts arising from diver presence and from the noise produced by UBA have long been recognised but not systematically studied. Here we analyse the noise produced by the three types of UBA used for research; self-contained underwater breathing apparatus (SCUBA), semi-enclosed circuit re-breather (SECR), and fully enclosed circuit re-breather (FECR) systems. There were significant differences in the source levels (SL) produced by the different UBA for both mean SL (p < 0.001) and mean peak SL (p < 0.001). SCUBA produced the most noise followed by SECR and FECR (161 ± 1, 131 ± 2, and 108 ± 1 dB re 1 μPa at 1 m, ±S.E.). Much of the sound produced by all three UBA was at low frequencies (<200 Hz), the range in which the hearing organs of fish and decapod crustaceans are most sensitive. Calculations indicated that the UBA are likely to be detectable by fishes at considerable distances depending on natural ambient noise levels.
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