Peter L. Tyack Terrance Howald
Woods Hole Oceanogr. Inst., Woods Hole, MA 02543
Underwater biological sounds are transient events. Durations range from microseconds to tens of seconds, frequencies from <10 Hz to >100 kHz, and source pressure levels up to >220 dB re : 1 (mu)Pa at 1 m. While each sound is produced by one individual, many sounds occur in choruses that may involve thousands of simultaneous sources. Some crustaceans produce loud impulsive noise in the 2--20 kHz range. These animals are common enough in many shallow areas to dominate the ambient near 10 kHz. Evening fish choruses seasonally dominate the ambient in many shallow waters in the 100--1000 Hz frequency range. While whales and dolphins are less numerous than the animals listed above, many species produce sounds of sufficient intensity to affect the ambient. For example, during their winter breeding season fin whales produce series of 20-Hz pulses lasting 1 s at source levels of 180 dB re : 1 (mu)Pa at 1 m. Dolphin echolocation clicks may reach source pressure levels >220 dB with spectral peaks 50--150 kHz. Dolphins are also skilled mimics of manmade sounds, which may lead to unpredicted interference.