NORRIS ET Al. BEHAVIOR OF CALIFORNIA GRAY WHALE 



the animals dove to or near the bottom during this 

 traverse (maximum recorded depth 110 ±10 m). 

 The impression given by the track at this point is 

 that the animals were navigating to some extent 

 by diving to the bottom and when the water 

 deepened they turned for shallower inshore water. 

 This is similar to the findings of Evans (1974b) for 

 the instrumented whale Gigi released off San 

 Diego which also dove to near the bottom and 

 reached a maximum depth of 170 m. 



Once near shore they skirted Punta Tosco at the 

 southern tip of Santa Margarita Island, moving 

 directly up the Rehusa Channel to a point off the 

 middle of Isla Cresciente in quite shallow water at 

 1400 h. The animals remained there for 2 h and 

 stayed almost constantly at the surface. Much 

 rolling and throwing of pectoral flippers and flukes 

 could be seen. We speculate that this interlude 

 could have included a nursing sequence following 

 the concerted swimming effort immediately after 

 capture (Figure 2). After milling in the general 

 area of Isla Cresciente at 0900 h, the pair began to 

 move southward again, staying close inshore. At 

 0200 h the following night, the radio signal 

 changed from the intermittent signal typical of a 

 swimming and periodically surfacing animal to a 

 constant signal, indicative of harness release. The 

 harness was retrieved successfully at 0930 h. The 



track had covered 213 km in 63 h, for a traverse 

 rate of 3.4 km/h, or 1.8 knots (2.1 knots excluding 

 20 ± h of quiescence) and had travelled 159 km 

 southeast directly past the last calving lagoon on 

 the Baja California coast. 



One may speculate why the two instrumented 

 animals that left the calving lagoon went south 

 rather than in the expected northerly direction. 

 The normal path at the beginning of northerly 

 movement is not known. First, it seems possible 

 that initial movement from the lagoon may in- 

 corporate some milling or nondirectional 

 movement before migration begins. Second, the 

 driving force which motivates and directs the 

 northern migration may be involved. Is it 

 hormonally stimulated, and timed by parturition 

 and nursing? If so, what is the equivalent change 

 in the male and how are these hypothetically 

 related hormonal events related to path direction 

 as well as to initiation of the migration itself? That 

 is, does an animal have a general southward 

 tendency of movement at one period that changes 

 to north before normal migration back to Arctic 

 latitudes? Third, could the attachment of in- 

 struments produce an initial direction aberration 

 in path? In view of our observations of instru- 

 mented mother-young behavior within the lagoon 

 itself, this appears unlikely, but further study of 



3 4 



Time (minutes) 



_JU_ 



I 

 



J 



J_JL 



I 

 2 



I I 



3 4 



Time (minutes) 



i 

 5 



i 

 6 



J_ 



FIGURE 2.— Respiratory patterns of (a) a quiescent and (b) a swimming calf. The record in (a) was recorded off Isla Cresciente at the 

 entrance to Almejas Bay, Baja California Sur, Mexico. This is the southernmost calving lagoon on the peninsula. The mother-calf pair 

 lay at or near the surface in shallow water for 2 h. The repeated bouts of surface activity may represent nursing sequences. Each spike 

 represents a radio transmission from the calf. These transmissions were given every second when the antenna broke the surface, and 

 indicate an average of 16 s/min surface time. Amplitude of spikes varies with transmission efficiency. Time is in minutes. The record in 

 (b) is for the same pair during normal swimming and indicates an average surface time of 3 s/min. 



163 



