PROBLEM 
Conduct surveys of biological sounds in the ocean. In 
particular, study effects of biological sound on observed 
base ambient noise levels in the San Nicolas Basin near San 
Clemente Island, using hourly recorded samples from two 
widely separated hydrophones resting on the bottom at 60 
and 450 fathoms. 
RESULTS 
1. Of the impressive variety and quantity of biological 
sound in the samples eight types were found to be most 
prevalent. 
2. The sound types were assigned the following 
descriptive names: Click Chorus, Rhythmic Grunt, Motor- 
boating, Barking, Growl, Low-Frequency Groan, 20 c/s 
Long Pulses, and 20 c/s Short Pulses. 
3. The first three types listed were strongly diurnal, 
all showing greatest prevalence at night. 
4, Barking and 20 c/s Long Pulses were present 
during essentially all the 192 hours monitored, both at the 
shallow hydrophone and at the deep hydrophone. 
5. An almost-continuous drone of Rhythmic Grunt 
appeared to be largely responsible for an increased base 
ambient noise level that occurred in the 80 c/s to 300 c/s 
region peaking just before midnight at the deep hydrophone. 
The cause of a high plateau observed in this frequency range 
at the shallow hydrophone from 2100 to 0300 hours was not 
identified. 
OT WME 
0301 0040505 & 
