GASKIN and WATSON: HARH( )K fOKPOISE 



100 



Figure 4. -Distributions of 669 harbor 

 porpoises in Fish Harbour 1973-75 over 

 subsurface topographic features, by eight 

 subphases of the tide: Slack low water (SL), 

 slow flood 1 (SFi), fast flood (FF), slow 

 flood 2 (SF2), slack high water (SH), slow 

 ebb 1 (SEj), fast ebb (FE), and slow ebb 2 

 (SE2). Solid line shows percentage over 

 shallow shelf, scarps, and slopes; dotted 

 line, percentage over basins and channels. 



20 



10- 



SFi FFi SF2 SH SEi FE SE2 



Subphases of tide 



SL 



seen on the two above occasions during simultaneous 

 surveys outside the present study area. 



Only in the case of this particularly distinctive 

 animal were we able to obtain enough observations 

 to map some of her patterns of movement over ex- 

 tended periods. On 17 August 1973, for example, we 

 tracked her for 2 h 12 min (57 position fixes. Fig. 9), 

 noting that she tended to stay close to the slopes of 

 the main basin-channel, with one foray around the 

 small basin in Lords Cove. This kind of point-to-point 

 travelling interspersed with short periods of 

 submergences in one location is quite typical of this 

 species. This animal repeated almost identical range 

 movements on 13 and 29 August 1974. On 1 and 30 

 August 1974 (1 h 4 min and 3 h 3 min respectively) 

 this animal spent far longer periods in relatively 

 restricted locations (Fig. 10). Submergences were 

 again of the "pattern B" type, and no surface resting 

 was recorded. On 1 August many herring were seen 

 jumping at the surface immediately after each 

 submergence by the female. Her calf was often left 

 at the surface during these bouts. 



"Systematic patrolling" of small areas, often in the 

 lee of ledges or small islets was also recorded (Fig. 



10). The movements illustrated were carried out by a 

 school of three medium-sized animals accompanied 

 by one small one on 2 August 1974. The group 

 sychronously dove repeatedly while moving back and 

 forth in one restricted scarp location, then abruptly 

 travelled to the second location shown and repeated 

 the pattern. 



DISCUSSION 



The distribution of some small odontocetes is 

 known to be correlated with sea surface tempera- 

 tures (Gaskin 1968; Wiirsig and Wiirsig 1980), but 

 the relationship is almost certainly indirect, the 

 result of influences exerted one or more levels fur- 

 ther down the food chain. The entry of the main sum- 

 mer population of harbor porpoises into the study 

 area not only coincides with 9°-10°C surface 

 temperatures, but also with the arrival of large 

 numbers of juvenile herring which feed in the Quod- 

 dy region during the summer months (Battle et al. 

 1936; Jovellanos and Gaskin 1983). Although trans- 

 port of relatively small fish into the study area might 

 be expected to be at a maximum during spring tides, 



435 



