ESR prepress abstract  -  DOI: https://doi.org/10.3354/esr00857

Predicting the acoustic exposure of humpback whales from cruise and tour vessel noise in Glacier Bay, Alaska, under different management strategies

Adam S. Frankel*, Christine M. Gabriele

*Email: adam.frankel@marineacoustics.com

ABSTRACT: Vessel traffic management regimes intended to protect baleen whales can have unexpected consequences on whale exposure to underwater noise. Using the Acoustic Integration Model, we simulated whale and vessel movement in Glacier Bay National Park (GBNP) to estimate vessel noise exposures to humpback whales Megaptera novaeangliae while varying the number, speed (13 vs. 20 knots), and timing of cruise ships while keeping a constant number, speed, and timing of smaller tour vessels. Using calibrated noise signatures for each vessel and the known sound velocity profile and bathymetry of Glacier Bay, we estimated received sound levels for each simulated whale every 15 s in a 24 h period. Simulations with fast ships produced the highest maximal sound pressure level (MSPL) and cumulative sound exposure levels (CSEL). Thirteen-knot ships produced CSEL levels 3 times lower than those traveling at 20 knots. We demonstrated that even in cases where a ship is only a few dB quieter at a slower speed, CSEL is lower although the ship’s transit may take substantially longer. Synchronizing ship arrival times had little effect on CSEL or MSPL but appreciably decreased Cumulative Sound Exposure Time (CSET). Overall, our results suggest that the most effective way to reduce humpback whale acoustic exposure in GBNP is to reduce cruise ship speed or numbers, although adjusting ship schedules may also be beneficial. Marine protected area managers may find these results illustrative or adapt these methods to better understand the acoustic effects of specific vessel management circumstances.