Submergence Time 



Using summary data, the average dive duration was multiplied by the number of dives 

 in each period to obtain the time (seconds) spent submerged during a summary period 

 (average duration x number of dives — TSUB). This is expressed as a percentage of the 

 entire summary period (21,600 s) in 1990 and 14,400 in 1989. 



1989 



Figure 65 shows the chronological progression of percentage time submerged and 

 locations of PTT #843. The time spent submerged was more consistent in the Bay of Fundy 

 and on Brown's Bank than during the transit into the Gulf of Maine and around Jeffrey's 

 Ledge, when some summary periods suggest significant periods at the surface (low % 

 TSUB). 



Figure 66 shows the average percent time submerged by time of day (in GMT). This 

 figure shows some variation throughout the day. The largest sample occurred in the early 

 afternoon from 1600 - 2000 GMT (1200 - 1600 EST; see Figure 6 for relationships of GMT, 

 EST and daily light cycle) and has the highest percentage of time submerged and least 

 standard deviation. This is a time field biologists often refer to as the "mid-day lull" when 

 whales are less frequently observed. This may be explained in part by the high TSUB values 

 for that time of day. 



1990 



A total of 294 calculations for time submerged are summarized in Tables 13 and 14. 

 The seven whales spent a combined average of 78% (range: 86% - 97%) of their time 

 submerged, while individuals spent an average of 67% (PTT #840) to 87% (PTT #827) of 

 their time submerged. Individual whales were reasonably consistent. Six whales had 

 differences between their high and low period averages of 4% - 12%. The mean for each 

 animal is depicted (with standard deviation) in Figure 67. There are significant differences 

 between individual animals. A frequency histogram of the percent time submerged for all 

 1990 whales combined is shown in Figure 68 with details on individual whales shown in 

 Figures 69-75. Animals most commonly spent 86% -90% of their 6-hour summary periods 

 submerged. For four of the 1990 whales, the highest average percentage of time spent 

 submerged occurred between dawn and noon (Period 3), compared to noon to 1800 local 

 time for PTT #843 in 1989. The lowest average time submerged occurred for three whales 

 between dusk and midnight (Period 1) and another three whales between midnight to sunrise 

 (Period 2). PTT #825, PTT #827 and PTT #840 had the same periods for their high and 

 low averages, although all had low sample sizes. "Wart" and "Willie" (PTT #823 and PTT 

 #839) had large sample sizes, had different periods for their high and low average TSUB, 

 and also differed from all other whales. 



100 



