Oceans of noise - Whale and Dolphin Conservation Society

7.6. Methods of protection
Compliance monitoring is undertaken to meet conditions of legislation or voluntary guidelines
(Gisiner 1998) and, in fact, monitoring is essential to assess whether required mitigation measures
are effective (Gisiner 1998, HESS 1997).
Dotinga and Oude Elferink (2000) and Richardson (1995) noted that there are four types of
mitigation measures. Each of these is considered in turn:
1. Construction, design and equipment standards: Where more ‘environmental friendly’
options are available, these should be considered, as should investigation into developing such
technologies. A reasonable assumption would be that lower noise levels are always to be
preferred. Seismic surveys are considered an extreme noise source of concern for cetaceans. A
marine vibrator – another method for seabed survey – has been developed and has a lower peak
amplitude, slower rise time and significantly less energy above 100Hz (Deffenbaugh 2001) and
may be a realistic alternative to the airgun arrays that are currently used worldwide in seismic
activities.
A nearby ship is likely to produce substantially higher sound levels locally than distant shipping
noise (Cato 2000), yet the impact may be over a short time period. Should a population use an
area in or near a shipping lane however, there are long term implications for these individuals.
Vessels used for whale watching can produce high levels of underwater sound in close proximity
to the animals. The factors most affecting the noise levels are the distance from the whale and
vessel speed, and to a lesser extent, vessel type (McCauley et al. 1996). Thus, whilst benign
observation and study of whales is to be encouraged, the expanding cetacean watching industry
clearly benefits from regulation to ensure that it does not become harmful to cetaceans (ANZECC
2000). Various whale watching guidelines are available and practised widely as a mitigation
measure (see for example Annex 2). Harassment and noise from whale watching boats is an
increasing concern in areas such as Puget Sound where whale watching has become popular in
recent years (Erbe, 2000).
A variety of concerns have been raised about the potential of whale watching to harm O. orca
(Kruse, 1991; Osborne, 1991; Duffus and Dearden 1993; Phillips and Baird 1993; Williams et al.,
1998). The vessels used for whale watching can produce high levels of underwater sound in close
proximity to the animals. The factors most affecting the noise levels are the distance from the
cetacean and vessel speed and, to a lesser extent, vessel type (McCauley et al. 1996).
Bain (2002) states that a shift from primarily large, low RPM vessels to small, high RPM vessels
that may have resulted in an increase in the average noise exposure experienced by whales in the
southern resident population.
The noise level of boats circling O. orca is already considered to be very close to the critical level
assumed to cause permanent hearing loss over prolonged exposure (Erbe, 2000). Masking of O.
orca calls has been recorded over 14km (Erbe, 2001). This could reduce detectability of prey
(Trites and Bain, 2000).
Bain and Dahlheim (1994) found that noise could mask echolocation and impair communication
required for cooperative foraging. Bain (2002) calculated that above ambient noise levels, noise
from whale watching vessels above this level will increase masking and reduce echolocation
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