Effects of marine vessel management on the underwater acoustic environment of Glacier Bay National Park, AK

Abstract

To protect the underwater acoustic environment and the marine mammals that depend upon it, Glacier Bay National Park implements marine vessel quotas, speed regulations, and routing restrictions in biologically important areas. Here, we characterize the underwater acoustic environment to quantify changes in conditions related to vessel management actions. Analysis of hourly 30-second acoustic samples obtained from a seafloor hydrophone included manual (aural and visual) identification of physical, biological, and human-made acoustic sources and measuring received sound pressure levels. A total of 10,659 30-second acoustic samples collected in 2000, 2001, 2007 and 2008 were analyzed. By quantifying the sources, occurrence, and characteristics of underwater sound we gained a new understanding of how the underwater acoustic environment relates to vessel management. For example, the occurrence of noise from large marine vessels (e.g. cruise ships) decreased despite an increase in the vessel quotas and use-days, likely due to changes in the timing of cruise ship entries. Our work documented the occurrence of biologically important humpback whale and harbor seal vocalizations; the frequency of occurrence of these vocalizations gives an indication of Glacier Bay's importance for these species and seasonality of calls documents the times of year at which a pristine acoustic environment would most benefit each species. These first descriptions of acoustic conditions in a protected coastal habitat indicate that both regulations and vessel behavior independent of regulations have discernible effects on the acoustic environment. Quantitatively describing these changes is a crucial first step toward protection of this important underwater habitat.