Echoing porpoise clicks as an alert

The PPD alerts porpoises to the presence of fishing nets using resonant acoustic reflectors that increase the net’s “acoustic visibility”, and do so in a less complicated way than the currently used pingers.

When a porpoise emits a click, the reflectors transmit back a stronger echo, making the reflectors appear to the porpoise to be much larger objects than they are, and thus alerting them to danger.


Marine Mammal Bibliography Web Site

Marine Mammal Bibliography web site - scientific articles:

NRDC.org Protecting Whales from Dangerous Sonar

This page has links to NRDC's pdf file and a movie narrated by Pierce Brosnan.

High-intensity military sonar, which generates sound at levels in the range of 235 dB, has been proven to disturb, injure and even kill marine mammals. The Navy’s mid-frequency sonar devices are in widespread use and have been definitively connected to mass strandings of whales. The Navy’s Low Frequency Active Sonar, in the early stage of deployment around the world, carries for hundreds of miles. Even 100 miles from the source sound levels can approach 160 decibels. During tests near Alaska, the Navy calculated sound levels of 140 decibels 300 miles from the source ship -- an intensity level approximately 100 times more intense than the noise aversion threshold for gray whales.
Great and rare images of Beaked Whales from the Washington Post

Time Mag. Writes About Japanese Dolphin Hunt

The Time magazine published and article about the horrible dolphin hunt in Japan.