FISHERY BULLETIN: VOL. 80, NO. 2 



seen on a relatively few occasions, approximately 

 8% of our observations. Our clearest observations 

 have been from aircraft, particularly on 23 April 



1979 when several sequences of bubble net for- 

 mation were photographed (Fig. 4). The whale, 

 maintaining its longitudinal body axis on a 

 nearly horizontal plane, swims some 3-5 m (esti- 

 mated) below the surface in a circular pattern. 

 The dorsal surface (and blowhole) of the whale is 

 rotated toward the center of the circle so that the 

 flippers are oriented nearly in the vertical plane. 

 As the whale swims in this manner, approxi- 

 mately 15 bubble bursts are released, which rise 

 to the surface as columns and appear to form an 

 effective corral. As the circle or net nears com- 

 pletion, the whale appears to pivot on the axis of 

 the flippers. The flukes are thrust to the outside, 

 and a stream of underwater turbulence is seen 

 trailing from the region of the dorsal fin. The 

 whale then banks to the inside and turns sharply 

 into and through the center of the net — all below 

 the surface of the water. The aerial photographs 

 show apparent feeding, i.e., the mouth is agape 

 and the lower jaw region is greatly distended. 

 Only after this stage does the whale rise to the 

 surface, pause, and blow one or more times be- 

 fore exiting the area of the bubble net. Measure- 

 ments show the circle to be approximately equal 

 in diameter to the whale's length— about 13-15 

 m. While bubble nets constructed in both the 

 clockwise and counterclockwise directions have 

 been observed, the clockwise direction appears 

 to be more common. 



There are several variations to the behavior 

 described above. Shipboard observations in May 



1980 showed that bubble nets are not restricted 

 to 360° circles, but instead may include from V/ 4 - 

 2 complete revolutions as the whale swims in a 

 spiral of decreasing radius. Often, smaller 

 bursts of smaller bubbles made up the greater 

 portion of the outer ring, with the bursts and 

 bubbles both increasing in size within the inner 

 ring. Additionally, a line of bubbles 10-30 m in 

 length would often directly precede the forma- 

 tion of the circular portion of the bubble net. This 

 gave the overall structure the shape of a "6" or a 

 "9." Finally, surface lunge feeding (gradual rise 

 type), rather than underwater feeding, was re- 

 ported from this series of shipboard observa- 

 tions. 



BUBBLE CLOUDS.-Bubble clouds form the 

 second major category of bubbling behaviors 

 associated with feeding. There are several 



marked differences to the bubble columns de- 

 scribed above. In this case, a single underwater 

 exhalation forms a single, relatively large (4-7 m 

 diameter), dome-shaped "cloud" made up of 

 small (estimated to be <2 cm), uniformly sized 

 individual bubbles (Fig. 5). In a few observations 

 where we were able to see the early stages of bub- 

 ble cloud formation, the cloud appeared quite 

 narrow initially, about 2-3 m in diameter, but ex- 

 panded as it rose toward the surface. In many 

 observations, schools of American sand lance, 

 Ammodytes americanus, were visible over wide 

 areas in patches at the surface in the general 

 area of feeding activity, but prior to the onset of 

 any bubbling behavior in their immediate vicin- 

 ity. In all observations, the whale dove out of 

 sight to produce the bubble cloud which rose 

 gradually toward the surface. The prey, appear- 

 ing as a disturbance at the surface, would at 

 times leap vigorously into the air when the bub- 

 ble cloud surfaced into the school. 



The subsequent appearance of the whale rela- 

 tive to the bubble cloud displayed a good deal of 

 variation. Observations to date suggest five pos- 

 sible variations, as illustrated in Figure 6. When 

 lunge feeding through the cloud's center was 

 seen (Fig. 6A), the speed of the lunge was slower 

 than lunge feeding observed in the absence of 

 clouds. In the second type of behavioral sequence 

 (Fig. 6B, the slow, horizontal appearance of the 

 whale in the surfaced cloud), over 70 bubble 

 cloud observations recorded from shipboard in 

 1978-79 suggest a repetitive, rigidly patterned 

 activity composed of the following: 



1) The whale sounds, usually with flukes in the 

 air. 



2) A cloud of bubbles appears beneath the sea 

 surface up to 2 1 / 4-3% min after sounding. 



3) The whale, not obviously swimming, rises 

 slowly to the surface. Its back first appears in the 

 center of the spent cloud of bubbles 5-9 s after the 

 first bubbles in the cloud reach the surface. 



4) Three to ten blows and slow, shallow diving 

 precede the sounding dive which begins the next 

 sequence. 



In this common activity, the actual feeding prob- 

 ably takes place in the cloud and below the sur- 

 face, with the whale's appearance marking the 

 conclusion of the episode. Although no feeding is 

 visible at the surface, the presence of a number of 

 important elements (prey abundant in bubble 

 clouds, similarity of structure to those in known 



264 



