38 
have reported barking from California sea lions submerged 
in a laboratory pool. 
From the foregoing observations and from the fact 
that the pinniped signal levels in the July 1963 San Clemente 
tests at the 450-fathom hydrophone were well above the 
background noise, it seems reasonable to assume that the 
pinniped sound sources were submerged and possibly 
deeply submerged. 
Finally, mention must be made of the fine listening 
conditions which resulted in such good S/N for the biological 
sound. In 69 percent of the hours sampled there was no 
noticeable propulsion sound at either hydrophone, and 
other man-made sounds such as sonar pinging were even 
more rare. Such conditions are remarkable for a coastal 
area so close to shipping lanes and show it to be a good 
site for further study of ambient noise phenomena. 
