Orca Diving Activity Raises Questions
Diurnal variations in the diving behaviour of British Columbia killer whales raises questions regarding the possible effects of boat traffic, distribution patterns of salmon, and whether whales rely on vision for capturing prey.
Killer whales foraging on salmon in BC's inland coastal waters are most active during the day. They swim faster, dive more frequently and to deeper depths than at night.
Movement of boats and salmon may also explain the ten-year trend for whales to perform fewer deep dives during the day. Although these orcas mainly remain close to the surface, the study recorded whales diving up to 140 metres on average, and as deep as 264 metres.
The same diving patterns were found amongst four pods of southern resident orcas and with both sexes, aged 3 to 60 years. The one exception is that adult males make deep dives significantly more often during daylight hours than do adult females.
Robin W. Baird, M. Bradley Hanson and Lawrence M. Dill. 2005. Factors influencing the diving behaviour of fish-eating killer whales: sex differences and diel and interannual variation in diving rates. Canadian Journal of Zoology. 83: 257-267.