Behavioural responses of killer whales to whale-watching : opportunistic observations and experimental approaches

• Main Author: Williams, Robert Michael
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/9146

Johnstone Strait provides important summer habitat for British Columbia's northern resident killer whales (Orcinus orca). The site is also an active whale-watching area. A voluntary code of conduct recommends that boaters do not approach whales closer than 100 m to address perceived, rather than demonstrated, effects of boat traffic on killer whales. The purpose of my study was to test the relevance of this guideline. Relationships between boat traffic and whale behaviour were studied in 1995 and 1996 by shore-based theodolite tracking of 25 identifiable focal animals from the population of 209 whales. Individual killer whales were repeatedly tracked in the absence of boats and during approaches by a 5.2 m motorboat that paralleled each whale at 100 m. In addition, whales were tracked opportunistically, when no effort was made to manipulate boat traffic. Dive times, swim speeds, and surface active behaviours such as breaching and spyhopping were recorded. Male killer whales swam significantly faster than females. Whales responded to experimental approaches by adopting a less predictable path than observed during the preceding, no-boat period, although males and females employed subtly different avoidance tactics. Females responded by swimming faster and increasing the angle between successive dives, whereas males maintained their speed and chose a smooth, but less direct, path. Canonical correlations between whale behaviour and vessel proximity are consistent with these conclusions, which suggests that weakening whale-watching guidelines, or not enforcing them, would result in higher levels of disturbance. High variability in whale behaviour underscores the importance of experimental studies when assessing behavioural impacts of human activity on killer whales.