Ship noise in an urban estuary extends to frequencies used for echolocation by endangered killer whales
- Published
- Accepted
- Subject Areas
- Conservation Biology, Environmental Sciences, Marine Biology, Coupled Natural and Human Systems
- Keywords
- noise, hydrophone, killer whale, orca, odontocete, marine mammal, ship, pollution, acoustics, bioacoustics
- Copyright
- © 2015 Veirs et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ PrePrints) and either DOI or URL of the article must be cited.
- Cite this article
- 2015. Ship noise in an urban estuary extends to frequencies used for echolocation by endangered killer whales. PeerJ PrePrints 3:e955v3 https://doi.org/10.7287/peerj.preprints.955v3
Abstract
Combining calibrated hydrophone measurements with vessel location data from the Automatic Identification System, we estimate underwater sound pressure levels for 1,582 unique ships that transited the core critical habitat of the endangered Southern Resident killer whales during 28 months between March, 2011, and October, 2013. Median received spectrum levels of noise from 2,812 isolated transits are elevated relative to median background levels not only at low frequencies (20-30 dB re 1 μPa2/Hz from 100-1000 Hz), but also at high frequencies (5-13 dB re 1 μPa2/Hz from 10,000-96,000 Hz). Thus, noise received from ships at ranges less than 3 km extends to frequencies used by odontocetes like the southern resident killer whales for communication and echolocation. Broadband received levels (11.5-40,000 Hz) near the shoreline in Haro Strait (WA, USA) for the entire ship population were 111 ± 6 dB re 1 μPa on average. Mean ship speed was 14.4 ± 4.1 knots. Most ship classes show a linear relationship between received level and speed with a slope near +1 dB/knot. Assuming near-spherical spreading based on a transmission loss experiment we compute mean broadband source levels for the ship population of 173 ± 7 dB re 1 μPa @ 1 m without accounting for frequency-dependent absorption. Spectrum, 1/12- octave, and 1/3-octave source levels for the whole population have median values that are comparable to previous measurements and models at most frequencies, but for select studies may be relatively low below 200 Hz and high above 20,000 Hz. Median source spectrum levels peak near 50 Hz for all 12 ship classes, have a maximum of 159 dB re 1 μPa2/Hz @ 1 m for container ships, and vary between classes by about 25 dB re 1 μPa2/Hz @ 1 m at low frequencies (50 Hz), 13 dB re 1 μPa2/Hz @ 1 m at mid-frequencies (1,000 Hz), and 5 dB re 1 μPa2/Hz @ 1 m at high frequencies (10,000 Hz). Below 200 Hz, the class-specific median spectrum levels bifurcate with large commercial ships grouping as higher power noise sources. Within all ship classes spectrum levels vary more at low frequencies than at high frequencies, and the degree of variability is almost halved for classes that have smaller speed standard deviations.
Author Comment
Frequency range reduced from 96 - 40 kHz on some figures and in some results. Minor additions and changes to the text, as well as some reference additions, primarily related to comments regarding possibility of shallow water attenuation and extrapolation of transmission loss study to frequencies beyond the pure tones tested.
Supplemental Information
R files: processed data and plotting script
These related files should allow readers to re-create our plots and/or access the processed data underlying our plots.