The frequency histogram for PTT #840 (Figure 75) demonstrates a compact range for 

 the percentage of time spent submerged and may suggest a limited repertoire of behaviors. 

 The frequency histograms for PTT #823 and PTT #839 (with their large sample sizes) 

 indicate animals with much wider ranges of values but substantially different distributions. 

 PTT #823 spent from 56% to 95% of summary periods submerged, while PTT #839 spent 

 81% or more of its time submerged during most periods (45% of the periods in the 86% to 

 95% range). 



A common time base was used in Figures 76 and 77 to determine whether 

 fluctuations in submergence time varied synchronously, perhaps in association with weather. 

 This did not appear to be the case for the three animals with significant overlap (PTT #833, 

 PTT #839 and PTT #823). 



Surface Resting Behavior 



In 1990,of 988 error-free transmissions, 361(37%) reported a discrete dive duration 

 of "zero." This meant that the transmitter did not go underwater for more than six seconds 

 between transmissions (from 42 s - 54 s) and, thus, constituted what we term "surface 

 resting." Table 15 summarizes, by period, the number of zero duration dives (ZDD) as a 

 percentage of total error-free dives for each tagged whale. Zero duration dives accounted 

 for 0-69% of all dive messages for individual whales although the time spent at the surface 

 (from %TSUB calculations) varied from 13-33%. There was no trend between duration 

 of operation and percentage of zero duration dives. If there were, it might be interpreted 

 as an affect of tagging. We do not know if prolonged surface time is resting, recovering 

 from oxygen debt or swimming at the surface. However, we believe whales could only swim 

 at very slow speeds without submerging the transmitter, so we assume this activity is 

 primarily surface resting. 



The abundance of zero duration dives for animals with large sample sizes suggest that 

 they are a normal function of whale activity and a greater proportion of their activity than 

 previously suspected. While surface resting has been seen by many observers, there have 

 been no studies published on this behavior in free-ranging whales which cover multiple 24- 

 hour periods. This is the first study of large whales to document the frequency of surface 

 resting. It is not known to what extent boat proximity may disturb or preclude this behavior. 

 Conversely, if right whales are not disturbed easily, it may explain why they are struck by 

 vessels so often. 



"Stripe" (PTT #840) had the highest overall average percentage of ZDDs (69%), 

 spent the most time (33%) at the surface (TSUB = 67) and also had the fastest swimming 

 speed. PTT #839, the longest-ranging female with calf, showed 31% of her "dive" messages 

 as surface resting activity (ZDDs) but averaged only 17% of her time at the surface. The 

 long-range movements of the adult male (PTT #823) showed 25% of its messages in this 



114 



