10 
Sound 2, the Rhythmic Grunt (fig. 2), is similar to a 
frog croak and is very probably made by swim-bladder 
muscles, which are among the most important producers of 
sound in the fish world. The number of pulses in a grunt 
varied from one to five, and the number of pulses in a grunt 
from an individual source showed a tendency to repeat from 
one grunt to the next. Individual pulses were triangular in 
shape with a duration that varied between 100 and 300 msec. 
The grunt repeated at intervals that ranged between 4 and 
6 seconds. The Rhythmic Grunt sound was present at both 
hydrophones, mainly during the night hours. 
Sound 3, Motorboating (fig. 3) resembles the noise of 
a one-cylinder engine running slowly. Similar sounds 
emanate from ride vehicles in amusement parks. Charac- 
teristically, the start of the Motorboating pulse train was 
not noticed because it was masked by background noise, 
but the sound gradually increased in intensity over its 
typical 4-second duration and then abruptly terminated. 
The pulse repetition rate was approximately 13 pulses per 
second. Motorboating was mainly prevalent at night in 
shallow water in groups of two or more pulse trains, 
usually in train pairs. The interval between the terminations 
of the first and second members of a pair was generally 7 
or 8 seconds. This sound also is probably generated ina 
swim-bladder muscle system. 
Sound 4, Barking (fig. 4),is very similar to a dog's 
barking, and most people familiar with seals or sea lions 
would without hesitation identify it as originating in this 
type of animal. The Sonagram in figure 4 shows one com- 
bination of Barking (yelps and snorts, alternately one and 
then the other, the yelps being the patterns that are higher 
and more extensive in frequency). Actually, this figure 
represents just one vocalization combination. On other 
occasions the sounds could be described as chuckling, 
chattering, gargling, moaning, etc. For the purpose of 
this report all these sounds will be considered as Barking. 
Sound 5, the Growl (fig. 5), is another sound that can 
almost certainly be attributed to the sea lion, because it 
