Tolerance by ringed seals ( Phoca hispida ) to impact pipe-driving and construction sounds at an oil production island

During June and July 2000, impact pipe-driving sounds at Northstar Island (Prudhoe Bay, Alaska) were recorded underwater and in air at distances 63-3000 m from the source. Simultaneously, reactions of nearby ringed seals (in water or on ice) were documented. Pipe-driving pulses were analyzed to determine unweighted peak and rms sound-pressure levels (SPLs) and sound-exposure levels (SELs). Underwater, mean levels for these parameters reached 157 and 151 dB re: 1 microPa and 145 dB re: 1 microPa2 x s, respectively, at 63 m. The corresponding values in air were 112 and 96 dB re: 20 microPa and 90 dB re: (20 microPa)2 x s, respectively. Underwater SPLs were <180 dB re: 1 microPa at all distances. During 55 h of observation, 23 observed seals exhibited little or no reaction to any industrial noise except approaching Bell 212 helicopters. Ringed seals swam in open water near the island throughout construction activities and as close as 46 m from the pipe-driving operation. Based on current audiometric data for seals, these sounds are expected to be audible to less than 3 km underwater and at least 0.5 km in air. Most likely the seals around Northstar Island were habituated to industrial sounds.