Harbor seals respond with aversion to 69-kHz pings: Implications for weighting procedures for marine mammal noise metrics.

Abstract

Author Shane tracked cultured white seabass (Atractoscion nobilis) instrumented with 69-kHz ultrasonic coded transmitters (UCTs) in the vicinity of harbor seals (Phoca vitulina), later finding the bones of fish associated with UCTs. This led the authors to suspect that seals had targeted and eaten instrumented fish. To determine whether seals could detect pings, four harbor seals and a ringed seal at SeaWorld San Diego were exposed to pings from two 69-kHz and one 83-kHz UCTs and their spontaneous responses observed. The seals were not expected to respond strongly because most of the energy in the pings was close to the upper limit of hearing, but three of the four harbor seals reacted with aversion to the 69-kHz pinger with the highest source level (147 dB re 1 μPa), swimming into a refuge pool or jumping out of the water. The received level at the closest point of approach was estimated at 20 dB above sensation level or less. The results suggest that seals may be especially responsive to high-frequency tonal signals, and that broadband weighting functions may not consistently yield efficient exposure metrics. [Funded by NOAA; in-kind support from SeaWorld San Diego.]