Vessel noise effects on delphinid communication

Abstract

Increasing numbers and speeds of vessels in areas with populations of cetaceans may have the cumulative effect of reducing habitat quality by increasing the underwater noise level. Here, we first use digital acoustic tags to demonstrate that free-ranging delphinids in a coastal deepwater habitat are subjected to varying and occasionally intense levels of vessel noise. Vessel noise and sound propagation measurements from a shallow-water habitat are then used to model the potential impact of high sound levels from small vessels on delphinid communication in both shallow and deep habitats, with bottlenose dolphins Tursiops sp. and short-finned pilot whales Globicephala macrorhynchus as model organisms. We find that small vessels travelling at 5 knots in shallow water can reduce the communication range of bottlenose dolphins within 50 m by 26%. Pilot whales in a quieter deep-water habitat could suffer a reduction in their communication range of 58% caused by a vessel at similar range and speed. Increased cavitation noise at higher speeds drastically increases the impact on the communication range. Gear shifts generate high-level transient sounds (peakpeak source levels of up to 200 dB re 1 µPa) that may be audible over many kilometres and may disturb close-range animals. We conclude that noise from small vessels can significantly mask acoustically mediated communication in delphinids and contribute to the documented negative impacts on animal fitness.

Changes in bottlenose dolphin whistle parameters related to vessel presence, surface behaviour and group composition

“…Such changes can have longer lasting impacts resulting in seasonal (Rako et al, 2013) Relative to observable changes in surface behaviour, the impacts of boats on the acoustic behaviour of cetaceans has received less attention. Changes in the production or parameters of vocalizations may be related to elevated levels of anthropogenic noise associated with vessel engines (Jensen et al, 2009;Parks, Johnson, Nowacek, & Tyack, 2011;Pirotta et al, 2012), the physical presence of boats (Pirotta, Merchant, Thompson, Barton, & Lusseau, 2015), boat type (La Manna, Manghi, Pavan, Lo Mascolo, & Sarà, 2013) or vessel behaviour 3 during encounters, and the interplay between these factors can be difficult to disentangle (see Ellison, Southall, Clarke, & Frankel, 2011).As cetaceans are highly acoustically oriented and rely on acoustic signals throughout their daily lives, they are particularly sensitive to elevated noise levels. Sound generated through outboard engines, which are typically used by small-scale cetacean watching boats, can be loud (149-152 dB re 1µPa root mean square at 1 m) and broadband, extending between 0.2 and 40 kHz and result in significant reduction of communication range (Jensen et al, 2009).…”

“…Although excessive noise can cause hearing damage, and even strandings in cetaceans (Weilgart, 2007), the more relevant impacts of boat noise generated through marine tourism activities are likely to be the masking of calls (Jensen et al, 2009) In bottlenose dolphins (Tursiops spp.) long-range communication relies on whistles, defined as narrow-band, frequency-modulated signals, ranging between 0.8 and 28.5 kHz in frequency (May-Collado & Wartzok, 2008;Schultz & Corkeron, 1994).…”

“…Sound generated through outboard engines, which are typically used by small-scale cetacean watching boats, can be loud (149-152 dB re 1µPa root mean square at 1 m) and broadband, extending between 0.2 and 40 kHz and result in significant reduction of communication range (Jensen et al, 2009). Although excessive noise can cause hearing damage, and even strandings in cetaceans (Weilgart, 2007), the more relevant impacts of boat noise generated through marine tourism activities are likely to be the masking of calls (Jensen et al, 2009) In bottlenose dolphins (Tursiops spp.) long-range communication relies on whistles, defined as narrow-band, frequency-modulated signals, ranging between 0.8 and 28.5 kHz in frequency (May-Collado & Wartzok, 2008;Schultz & Corkeron, 1994).…”

“…Sound generated through outboard engines, which are typically used by small-scale cetacean watching boats, can be loud (149-152 dB re 1µPa root mean square at 1 m) and broadband, extending between 0.2 and 40 kHz and result in significant reduction of communication range (Jensen et al, 2009). …”

Whale Watching as Ecotourism: How Sustainable is it?

“…There are many advantages of this kind of ecotourism.If conducted properly this activity is relatively benign (Blewitt 2008;Jensen et al 2009;Noren, Johnson, Rehder & Larson 2009). Through proper management, whale watching has proven to be profitable and sustainable.This approach provides a resource for ongoing cetacean research as well as a context in which to promote an appreciation of the marine environment and to explore conservation issues in the public discourse (Greenpeace 2010).…”