ACOUSTIC ECOLOGY | Ocean Issues: Ship traffic

Boats of all kinds make noise in the ocean. The overall ambient background noise in the waters off the California coast has roughly doubled each decade since the 1960's, primarily due to increased shipping; it is likely that similar increases are taking place across the northern hemisphere. Supertankers cause the most extreme effects, with cruise ships also significant in some areas, especially when visiting otherwise pristine locations. Noise is generated by engines, bearings, and other incidental mechanical parts, though surprisingly, the loudest sounds are made by the ceaseless popping of bubbles created by spinning propellors. Acoustic "hot spots" exist near major shipping centers, an undersea parallel to the density of sound in cities or near highways.

Most research suggests that fish and cetaceans exhibit avoidance behavior in response to engine noise. However, it iis nearly impossible to separate the effects of noise disturbance from other modern stresses (polution, overfishing, etc). Over the past five years, shippping noise has spurred more serious consideration as a key human-generated noise impacts that has significant effects on ocean life. In 2008, the US, Australia, and European countries joined to initiate a process at the International Maritime Organization aimed at establishing voluntary ship-quieting guidelines.

Recreational, whale-watching, and fishing boats also can trigger reactions in whales and dolphins; there are increasingly troubling indications that boat traffic can cause significant disruption in foraging activity. For a glimpse of this, see an AEI summary of foraging disruptions, presented to a Canadian Science Advisory Secretariat meeting in May 2009 [PDF OF THE FULL PAPER] or [PDF OF A POWERPOINT PRESENTATION], and visit our ongoing coverage of new research studies.

You can get a good sense of the current thinking about shipping noise by reading the relevant sections of AEI's annual Ocean Noise recap:

Ocean Noise: What We Learned in 2007
Summary of new research, policy developments in ocean noise during 2007, along with a look ahead at developing stories for 2008.

Ocean Noise: What We Learned in 2006
Summary of new research, policy developments in ocean noise during 2006, along with a look ahead at developing stories for 2007.

NOAA Symposium on Shipping Noise and Marine Mammals - A 2004 symposium; the website includes a wealth of research papers and Powerpoint presentations available for download. [WEBSITE]

Glacier Bay Acoustic Monitoring Program - Glacier Bay National Park is home to a dazzling array of wildlife, including humpback whales, which attracts cruise ships and private boaters. The Park has instituted a 500m buffer from all animals, and is engaged in long-term acoustic monitoring, aimed at creating "noise goals" for the future. [WEBSITE] [RESEARCH REPORTS FROM GLACIER BAY]

Effect of Noise on Fish - A collection of research papers gathered by a Navy researcher on the topic. Includes research sponsored by the International Council for the Exploration of the Sea in 1995 stating that "overwhelming evidence has been presented that show an avoidance reaction to vessels when the radiated noise levels exceed their threshold of hearing by 30dB or more." [WEBSITE]

Herring "panic fleeing" behavior - EVS, a State of Washington consultanting firm seeking reasons for the preciptious drop in herring stocks found that herring schools break into "panic fleeing" when ships pass over them, and avoid spawning in areas of heavy ship traffic. Given the widespread pollution and climatic changes also effecting the fish, it's not clear how crucial the behavioral disruptions are to the declining stocks of this important link in the oceanic food chain. Source: Seattle Post-Intelligencer, 11/21/01 [FULL STORY]

Belugas and icebreakers - Researchers in Canada are trying to discover whether decreases in beluga populations may be tied to increased icebreaker traffic. Their work, based on computer models that suggest behavioral changes may be induced up to 14km away from the vessels, is profiled in a recent issue of New Scientist. [READ ARTICLE]

Manatee hearing limits usefulness of "slow idling" rules aimed to prevent collisions - One of the first bioacoustics studies to investigate the hearing of manatees and their environment indicates that manatees are often unable to determine the location of slow idling boats, thus remaining in their path, resulting in injury or death. Among the new findings are that manatee hearing systems are not well-tuned to the low frequency sounds of boats, and that acoustic masking can make locating the sound difficult. The researchers suggest a design for a directional acoustic warning device that could be more effective at preventing collisions. Source: American Scientist, Vol90, March-April 2002 [READ ARTICLE]

Ship Traffic