Dive Duration 



In both 1989 and 1990, two types of dive durations were measured: discrete dives and 

 averages during summary periods. Discrete dive information was collected on 1770 dives 

 plus an additional 914 submergences counted between transmissions. Due to time 

 constraints, we did not analyze discrete dives for the 1990 whales in detail. 



Discrete Data 



In 1989, PTT #843 reported 304 discrete dive durations with a range of 6 to 

 848 s (0.1 - 14.1 min.). After considering surfacings between transmissions, the overall 

 average was 73.5 s. The skewed distribution of discrete dive durations was typical of other 

 species studied in detail to date (Gray whales: Harvey and Mate, 1984; Bowheads: Wursig, 

 et al., 1984; and Humpbacks: Dolphin, 1987), where most dives were less than 30 seconds 

 (Figure 52). Because discrete dives proved to be a subsample reflecting the summary data 

 (see below), we concentrated our 1990 analyses on zero duration dives (see "Surface 

 resting"). 



In 1990, the three longest maximum duration dives from the 1990 discrete information 

 were 40.07,28.23 and 17.47 minutes. All were for PTT #839. We believe the 17.47 min. 

 (1049 s) dive is feasible but are skeptical of the two longer dives. It may have been possible 

 for the whale to breathe in a spy-hop position without the PTT surfacing to result in such 

 long dives. It is also possible that these were transmission errors, in which case they would 

 not have adversely affected the average dive duration calculated for the summary period. 



Summary Data 



1989 



The mean dive duration of PTT #843 for 4-hour periods was 74 s ± 18, lower than 

 for all 1990 whales except PTT #823 (the male). Figure 53 shows the frequency distribution 

 of average dive durations for all 4-hour summary periods in 1989. 



1990 



Average dive durations for the 6-hour summary periods are shown in Tables 1 1 and 

 12 and are presented graphically in Figure 54. The overall average dive duration for all 

 animals in all periods was 86 s ±48 with less than a 10% difference between periods when 

 the data for all animals were pooled. There was considerable variation between animals 

 (with a range of 54 s - 162 s) and between periods for individual animals. There was only 

 a 10% difference between period averages for "Wart" (PTT #839) with a range of 95 s - 105 

 s compared to 90% for another female, "Stripe" (PTT #840) with a range of 113 s - 212 s. 

 Of the seven animals analyzed, four showed their longest average dive duration between 



83 



