752 



Fishery Bulletin 90(4). 1992 



Behavior and 

 movement patterns 



A total of 752 respiration inter- 

 vals were recorded during 53 sei 

 whale sightings (from at least 15 

 different individuals). Inter-respir- 

 ation intervals showed a range of 

 2-928 sec, with a mean of 60.8 

 sec (SD 78.0 sec). The most com- 

 mon respiratory pattern was a 

 single breath followed by a short 

 dive of 45-90 sec. On only four 

 sightings did the whales sub- 

 merge for prolonged dives of 

 6-11 min, and they did so re- 

 peatedly within the observation. 



The regular breath intervals 

 and lack of prolonged dives often 

 appeared associated with near- 

 surface feeding. In the most com- 

 mon feeding behavior, sei whales 

 would take a breath and then roll 

 45-90° around their longitudinal 

 axis while ~3m below the sur- 

 face. The mouth was often slight- 

 ly open as the animal swam for- 

 ward. There were four observa- 

 tions of lunge feeding, when the 

 whale rapidly surfaced with its 

 mouth opened. During lunges, no 

 rolling was observed. On one of 

 four occasions of lunging, the 

 same individual alternated lunges 

 with the more common nearsur- 

 face feeding behavior. 



During feeding and swimming, 

 the whales often remained in an 

 area of ~0.5km2 for over an 

 hour. Whales would either change 

 swimming direction with each 

 breath, or travel in a straight line 

 for 10 min or less before revers- 

 ing, resulting in minimal net 

 movement at the surface. 



Defecations were observed nine 

 times. Feces were bright red and contained chunks of 

 particulate matter. Only mandibles from the copepod 

 Calanus finmarchicus were subsequently identified in 

 fecal material. 



While feeding and traveling comprised most of the 

 behavioral events (both time and number), milling (at 

 least three socializing with one another while moving 

 in apparently random directions, rolling, and remain- 

 ing on the surface continually for over 10 min) was seen 



Figure 2 



Photographic match of sei whale Balaenoptera borealis #22. utilizing both circular scars 

 and dorsal-fin notches as aids in identification. Note the pattern of circular scars below 

 the dorsal fin, particularly the large circular scar below and immediately posterior to 

 the dorsal fin, and the slightly blunted tip of the fin itself. Top photograph was taken 

 10 August 1986, bottom photograph on 22 August 1986. 



four times. This was always associated with one whale 

 leaving the group either during or immediately after 

 the milling period. Breaching was seen once, when a 

 single animal breached twice in rapid succession. 



Social behavior 



Sei whales were seen in groups of 1—6 individuals. 

 Mean group size was 1.8, and was the same on both 



