Using platforms of opportunity such as whale-watching
vessels is common for cetacean research, not least owing
to the high cost of conducting dedicated surveys at sea.
Imperfect sampling design that frequently characterises
such research, including restricted spatial and temporal
coverage, bias towards one or more particular species, and
time limitations set by the length of trips, can profoundly
influence results. However, as long as adequate spatial and
temporal coverage is achieved and a range of habitats are
included in surveys, bias in the results can be minimised
(Evans and Hammond 2004). The effects of areal restriction
of the whale-watching vessels could potentially have been
confounding in this study, especially considering that they
preferentially targeted southern right whales in the shallow
waters during winter.