| Summary: | 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.
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