Scott R. Veirs1, Val R. Veirs2, Rob
Williams3, Michael Jasny4, Jason D.
Wood5
1Beam Reach Marine Science & Sustainability, Seattle,
WA, U.S.
2Colorado College Physics Department, Colorado
Springs, CO, U.S.
3Pew Fellow in Marine Conservation, Vancouver, BC,
Canada
4Natural Resources Defense Council, Vancouver, BC,
Canada
5SMRU Consulting, Friday Harbor, WA, U.S.
Corresponding author:
Scott Veirs1
Email address:
scott@beamreach.org
Abstract
\label{abstract}
Underwater noise pollution from ships is a chronic, global stressor
impacting a wide range of marine species. Ambient ocean noise levels
nearly doubled each decade from 1963-2007 in low-frequency bands
attributed to shipping, inspiring a pledge from the International
Maritime Organization to reduce ship noise and a call from the
International Whaling Commission for member nations to halve ship noise
within a decade. Our analysis of data from 1,582 ships reveals that half
of the total power radiated by a modern fleet comes from just 15% of
the ships, namely those with source levels above 179 dB re 1 μPa @ 1 m.
We present a range of management options for reducing ship noise
efficiently, including incentive-based programs, without necessarily
regulating the entire fleet.
Introduction
\label{introduction}
At its June 2016 meeting, the Scientific Committee of the International
Whaling Commission (IWC) agreed that chronic ocean noise is increasing
in many regions and adversely affecting populations of whales and other
cetaceans (IWC Scientific
Committee, 2016). Emerging evidence links chronic ocean noise to
negative effects not only on marine mammals
(Rolland et al., 2012;
Williams et al., 2015) but also fish
(Popper & Hawkins, 2015)
and invertebrates (Wale,
Simpson & Radford, 2013). Ships are a major source of chronic ocean
noise, responsible for doubling low-frequency levels every decade
throughout the second half of the 20th century
(McDonald, Hildebrand &
Wiggins, 2006; Andrew, Howe & Mercer, 2011). In some coastal and other
high-traffic areas, ship noise has reached levels that degrade habitat
for endangered species of whales and other marine wildlife (Van Parijs
et al., 2012; Erbe et al., 2014).
These developments have inspired a number of recent policy initiatives
to reduce noise pollution from ships. Prominently, the International
Maritime Organization issued voluntary guidelines in 2014, building on
earlier targets (Wright,
2008) and encouraging industry to reduce underwater radiated ship noise
in the 10-300 Hz band
(Dekeling et al., 2014;
IMO/MEPC, 2014). The U.S. National Oceanic and Atmospheric
Administration last year launched an agency-wide
Ocean Noise Strategy to
better integrate risk assessment and mitigation of chronic ambient noise
pollution into federal planning actions. European legislation treats
ocean noise as a pollutant, and requires member states ultimately to
attain “good environmental status” with respect to noise across
multiple marine regions
(URN, 2014;
Audoly et al., 2015; Garrett et al., 2016; Merchant et al., 2016). In
some jurisdictions, most recently Canada, governments have committed
themselves to regulate shipping noise, but none have yet devised a
management system to meet a ship noise reduction target.
In addition to aspirational targets to improve global ocean health,
efforts to reduce ship noise also have immediate, real-world
implications for economic development and endangered species
conservation. The southern resident killer whale (SRKW) is a critically
endangered population whose critical habitat spans the international
(Canada-U.S.) border and shipping lanes serving the ports of Vancouver
(British Columbia, Canada) and Seattle-Tacoma (WA, U.S.). Both Canada
and the U.S. have recognized ocean noise as a threat to SRKW recovery
(NMFS, 2008; DFO Canada,
2011). There are a number of large-scale industrial development
proposals pending for this region
(Gaydos, Thixton & Donatuto,
2015) that could increase ship traffic and raise ocean noise levels.
Both countries must consider ocean noise in SRKW critical habitat when
assessing environmental impacts of proposed developments, and balance
economic growth with conservation of endangered species. All of SRKW
summertime critical habitat is ensonified already at levels exceeding
one European threshold defining good environmental status
(Erbe, MacGillivray &
Williams, 2012), so it could be argued that noise reduction has become
a necessary precursor to additional industrial development in this
region.
What would be required of industry to substantially reduce noise from
commercial ships? To understand what would be necessary, we considered
the quantitative noise reduction target reaffirmed last summer by the
IWC’s Scientific Committee, namely reducing the contributions of
shipping to ocean ambient noise in the 10-300 Hz frequency band by 3 dB
(halving the total radiated power) within 10 years, and by 10 dB within
30 years (IWC Scientific
Committee, 2016). We explored various mechanisms to attain this -3
dB/decade target, including reducing the number, acoustic source level,
or speed of individual ships.
Methods
\label{methods}
We assessed four distinct management options by analyzing 2,800 source
level measurements of 1,582 unique, isolated ships recorded as they
transited northbound in Haro Strait, a shipping channel within the
Salish Sea (Veirs, Veirs &
Wood, 2016). For ships in the data set with multiple transits we
averaged the source spectrum levels (power spectral density) over all
available transits.
To assess the relative noise contributions of different ships in the
population of 1,582 ships in 12 ship classes, we integrated the source
spectrum levels for each unique ship to acquire the total power (watts)
radiated by each ship in a frequency band (10-40,000 Hz). This band is
wider than the 10-300 Hz band stipulated in the noise reduction target
endorsed by the IWC. We chose to broaden the band because ship noise at
ranges less than ~3 km extends beyond 300 Hz to
frequencies where SRKW hearing is most sensitive
(Veirs, Veirs & Wood, 2016)
and because ship noise has been identified by regulatory agencies in
Canada and the U.S. as a chronic, habitat-level stressor threatening the
recovery of the endangered killer whale population in this region
(Williams et al., 2016).
After integration, we sorted the total radiated power levels, ranking
them from lowest to highest. Then we summed the power from each ship,
yielding the cumulative total radiated power – a distribution we used
to assess quantitatively a range of management options that would
accomplish a 3 dB reduction in the total noise radiated by this
population of ships. (A 3 dB reduction is equivalent to halving the
total radiated power.) Finally, we converted individual ship source
levels from watts to dB re 1 μPa @ 1m. (Note, however, that we
abbreviate the resulting broadband (10-40,000 Hz) source levels as
“dB” in this paper for brevity.)
We used an iterative method to understand the first two management
options: removal of gross polluters; and reduction of gross polluter
source levels to a threshold that achieves the desired halving of power
overall. For the first option, we removed the loudest ship from the
population and re-calculated the total radiated power. If the initial
total power was not yet halved, then we repeated the process. For the
second option, we also calculated the reduction threshold iteratively.
We lowered the source level of the loudest ship to the level of the
next-loudest ship in each iteration until the total power radiated by
the population was halved.
To help managers more deeply understand the practical implications of
these two management options, we tabulated the number of ships affected
(Table 1). To allow easy extrapolation to the global fleet or other
regional subpopulations of it, we also tabulated the number of affected
ships as a percentage of both our population and, where applicable, the
total number of ships in each class.
The third noise management option was based on the observation that for
many ships a 1 knot reduction in speed leads to 1 dB reduction in
broadband underwater source level
(Veirs, Veirs & Wood,
2016). We found the speed limit needed to achieve the 3 dB reduction
iteratively by: reducing the speed of each loudest ship to the selected
speed limit; making a proportional reduction in the source levels;
re-integrating the new source level distribution; and checking to see if
the reduced total power equaled half of the initial total power.
The fourth management option was requiring a 3 dB reduction of every
ship in the fleet. Assessing this option required no new computation.
For all options, we assumed that the distribution of source levels in
our data set was statistically representative of the noise output from
the global fleet, or other regional subsets of it. This assumption
underpins our assertion that our regional data set can be used to assess
options for managing oceanic noise beyond our study area.
Results and discussion
\label{results-and-discussion}
The cumulative distribution of source levels (Figure 1) in our dataset
ranges from 141-186 dB and has two inflection points, with
~80% of the population having intermediate source
levels of 165-180 dB. Importantly, half the total power is radiated by
just 15% of the ships in the fleet (i.e., those with source levels
greater than 179.0 dB). More than two-thirds of these gross polluters
are cargo and container ships, with each class containing
~90 such vessels in our population (Table 1, Figure 2).
About 43% of container ships are gross polluters, by far the highest
proportion of any ship class in our dataset.
Management options could focus on gross polluters by targeting fleet
size or operations. In the region where our data originated, for
example, managers could halve the total power radiated by this ship
population by removing the loudest 15% of the fleet
(n=~240 ships) or by reducing the source levels of the
loudest 42.8% of the fleet (n=~677 ships) to 175.4 dB
(Table 1). These results confirm empirically the idea
(Leaper, Renilson & Ryan,
2014) of dramatically reducing acoustic pollution by targeting the
noisiest ships for quieting. The maximum reduction required by the 175.4
dB threshold, about 10 dB, should be attainable with existing quieting
technologies (Southall &
Scholik-Schlomer, 2008) and techniques
(Audoly et al., 2015), or
for many types of new ships with only a 1% increase in design/build
costs (Spence & Fischer,
2016).
Because container ships had the highest average source levels (178+/-4
dB) of the 12 ship classes we analyzed
(Veirs, Veirs & Wood,
2016), they would be most affected by policies that target gross
polluters (Table 1). In our population of container ships, 43% would be
affected by the removal option, while almost 90% would be affected by
the noise reduction option. By contrast, some ship classes would be
completely unaffected by any management option that limits source
levels. No fishery, pleasure, or military ships in our population had
source levels exceeding 175 dB, possibly due to military, fishery, and
research classes having already adopted ship-quieting technologies
(Southall &
Scholik-Schlomer, 2008).
Of the management options considered, speed limits appear most likely to
reduce noise quickly – by making an operational change, rather than
undertaking replacements, retrofits, or maintenance. Because most ships
can reduce their broadband source level by ~1 dB by
slowing down by 1 knot
(Veirs, Veirs & Wood,
2016), in our study area the 3 dB noise reduction target could be met
by enforcing a speed limit of 11.8 knots (6.1 m/s) which would affect
83% of the ship population. For comparison, the mean and standard
deviation of the speed distribution is 14.1 ± 3.9 knots for the ship
population and 19 ± 2 knots for the fastest class, container ships
(Veirs, Veirs & Wood,
2016). While the compliance burden would fall more broadly across the
fleet than with the removal or reduction options (Figure 2),
faster-moving ships would be required to reduce speed more than other
ships, and slow-moving classes would be unaffected. If a uniform speed
limit of 11.8 knots conflicts with the “bare steerage” speed required
for safe navigation of ships in a particular class, the 3 dB reduction
could also be achieved by having all ships in the fleet decrease their
speed by 3 knots (Figure 2).
Any noise reduction achieved by decreasing ship speed will increase the
time that species are exposed to the lower noise levels. Behavioral
response and masking are driven not only by the noise level, but also by
a temporal overlap between the noise and the animal. A reduction of 3 dB
in the total radiated power of ships does not address this temporal
overlap, but in our study area, it would likely increase the functional
acoustic space of SRKWs substantially and lower the maximum ship noise
exposures that could cause behavioral responses or masking in the
species (Holt,
2008; Williams, R Clark, C W Ponirakis, D Ashe, E, 2013; Williams et
al., 2014, 2016). Such benefits should be weighed against the increase
in temporal overlap that may result from speed reduction. At the same
time, other environmental effects of a speed limit should be considered,
including altered fuel efficiency (air pollution) and risk of collisions
(oil spills and ships striking baleen whales).
Proven technologies (Southall
(Audoly et al., 2015) exist
for reducing ship noise. Combinations of them, without necessarily
altering speed, could be used to reduce source levels by 3 dB in each
ship across the entire fleet, or just in gross-polluting ships. To date,
however, minimal mitigation has been undertaken by the commercial
shipping industry, either due to lack of regulation or incentives to
adopt them.
Management vehicles include, at least: regulated vessel speed limits in
biologically important habitat, like those mandated off the U.S. East
Coast to reduce ship strike mortality in North Atlantic right whales;
tax incentives or subsidies to retrofit or replace noisy ships with
quieter ones, for which designs already exist
(Leaper, Renilson & Ryan,
2014); regulated noise emission standards for all or some ships
entering into a state’s internal waters; or port-based incentives and
other measures. As an example of the latter, the Port of Vancouver, one
of the largest ports in SRKW critical habitat, is reducing berthing fees
through its EcoAction program to reward ships that are accredited as
quiet by ship-classification societies.
Conclusions
\label{conclusions}
If our analysis and inferences hold true for other regions,
identification of gross acoustic polluters could help guide the creation
of regional or port-devised incentives or regulatory requirements to
reduce underwater noise pollution. Although our sample is drawn from one
site in the northeastern Pacific Ocean, it represents one of the largest
archives of calibrated source characteristics for ships anywhere in the
world. Compared with solutions proposed for thornier environmental
problems like climate change
(Barrett, 2003; Obama,
2017), managing ship noise may be more tractable in part because even a
relatively low compliance rate (e.g., 15-42.8 % of the fleet) could
yield major environmental improvements. Despite projections of ship
noise rising through 2030
(Frisk, 2012), optimal
management of the global fleet could begin to reduce the current
detrimental levels of noise without necessarily regulating the entire
fleet.
Acknowledgements
\label{acknowledgements}
We thank Liam Reese for his graphic design of Figure 2. R.W. thanks the
Pew Fellowship in Marine Conservation program for support of his work on
ocean noise. The authors declare no competing financial interests.
Source spectrum level data are available in the R data file,
data_1_3_BB_100.Rdata at
https://doi.org/10.7717/peerj.1657/supp-1.
S.V., V.V., and J.W. provided the ship source level data set. V.V.
processed the data to assess noise management options that were
developed in consultation with S.V. R.W., M.J., and J.W. provided policy
context and strategy prioritization. S.V. coordinated data product
generation. All authors contributed to the writing of the manuscript.
References
\label{references}
Andrew RK., Howe BM., Mercer
JA. 2011. Long-time trends in ship traffic noise for four sites off the
North American West Coast. The Journal of the Acoustical Society
of America 129:642–651.
Audoly C., Flikeema M., Baudin
E., Mumm H. 2015. Guidelines for Regulation on Underwater Noise
from Commercial Shipping. AQUO/SONIC.
Barrett S. 2003.
Environment and Statecraft : The Strategy of Environmental
Treaty-Making: The Strategy of Environmental Treaty-Making . OUP
Oxford.
Dekeling R., Tasker M., Graaf
SVD., Ainslie M., Andersson M., André M., Borsani JF., Brensing K.,
Castellote M., Cronin D., Dalen J., Folegot J., Leaper R., Pajala J.,
Redman P., Robinson SP., Sigray P., Sutton G., Thomsen F., Werner S.,
Wittekind D., Young JV. 2014. Monitoring Guidance for Underwater
Noise in European Seas-Part I: Executive Summary. Luxembourg:
Publications Office of the European Union.
DFO Canada. 2011.
Recovery Strategy for the Northern and Southern Resident Killer
Whales (Orcinus orca) in Canada . Fisheries and Oceans Canada.
Erbe C., MacGillivray A.,
Williams R. 2012. Mapping cumulative noise from shipping to inform
marine spatial planning. The Journal of the Acoustical Society of
America 132:EL423–EL428.
Erbe C., Williams R.,
Sandilands D., Ashe E. 2014. Identifying Modeled Ship Noise Hotspots for
Marine Mammals of Canada’s Pacific Region. PloS one 9:e89820.
Frisk GV. 2012. Noiseonomics:
The relationship between ambient noise levels in the sea and global
economic trends. Scientific reports 2:437.
Garrett JK., Blondel P.,
Godley BJ., Pikesley SK., Witt MJ., Johanning L. 2016. Long-term
underwater sound measurements in the shipping noise indicator bands 63
Hz and 125 Hz from the port of Falmouth Bay, UK. Marine pollution
bulletin 110:438–448.
Gaydos JK., Thixton S.,
Donatuto J. 2015. Evaluating Threats in Multinational Marine Ecosystems:
A Coast Salish First Nations and Tribal Perspective. PloS one
10:e0144861.
Holt MM. 2008. Sound
Exposure and Southern Resident Killer Whales: A review of current
knowledge and data gaps. NMFS-NWFSC.
IMO/MEPC. 2014.
Guidelines for the reduction of underwater noise from commercial
shipping to address adverse impacts on marine life . International
Maritime Organization, Marine Environmental Protection Commission.
IWC Scientific Committee.
2016. Report of the Workshop on Acoustic Masking and Whale
Population Dynamics. Bled, Slovenia: International Whaling Commission.
Leaper R., Renilson M., Ryan
C. 2014. Reducing underwater noise from large commercial ships: current
status and future directions. Journal of Atmospheric and Oceanic
Technology 9.
McDonald MA., Hildebrand JA.,
Wiggins SM. 2006. Increases in deep ocean ambient noise in the Northeast
Pacific west of San Nicolas Island, California. The Journal of the
Acoustical Society of America 120:711–718.
Merchant ND., Brookes KL.,
Faulkner RC., Bicknell AWJ., Godley BJ., Witt MJ. 2016. Underwater noise
levels in UK waters. Scientific reports 6:36942.
NMFS. 2008. Recovery
Plan for Southern Resident Killer Whales (Orcinus orca). Seattle,
Washington: National Marine Fisheries Service, Northwest Region.
Obama B. 2017. The
irreversible momentum of clean energy. Science 355:126–129.
Popper AN., Hawkins A. 2015.
The Effects of Noise on Aquatic Life II . Springer.
Rolland RM., Parks SE., Hunt
KE., Castellote M., Corkeron PJ., Nowacek DP., Wasser SK., Kraus SD.
2012. Evidence that ship noise increases stress in right whales.
Proceedings of the Royal Society B: Biological Sciences . DOI:
10.1098/rspb.2011.2429.
Southall BL., Scholik-Schlomer
A. 2008. Potential application of vessel-quieting technology on large
commercial vessels. In: Final Report of the National Oceanic and
Atmospheric Administration (NOAA) International Conference. 1-2 May,
2007, NOAA Fisheries, Silver Spring, MD.
Spence JH., Fischer RW. 2016.
Requirements for Reducing Underwater Noise From Ships. IEEE
Journal of Oceanic Engineering PP:1–11.
URN. 2014. Underwater
Radiated Noise (URN). Bureau Veritas.
Van Parijs SM., Frankel AS.,
Ponirakis DW., Hatch LT., Clark CW. 2012. Quantifying loss of acoustic
communication space for right whales in and around a U.S. National
Marine Sanctuary. Conservation biology: the journal of the Society
for Conservation Biology. DOI:
10.1111/j.1523-1739.2012.01908.x.
Veirs S., Veirs V., Wood JD.
2016. Ship noise extends to frequencies used for echolocation by
endangered killer whales. PeerJ 4:e1657.
Wale MA., Simpson SD., Radford
AN. 2013. Noise negatively affects foraging and antipredator behaviour
in shore crabs. Animal behaviour.
Williams R., Erbe C., Ashe E.,
Beerman A., Smith J. 2014. Severity of killer whale behavioral responses
to ship noise: A dose–response study. Marine pollution bulletin
79:254–260.
Williams, R Clark, C W
Ponirakis, D Ashe, E. 2013. Acoustic quality of critical habitats for
three threatened whale populations. Animal conservation.
Williams R., Thomas L., Ashe
E., Clark CW., Hammond PS. 2016. Gauging allowable harm limits to
cumulative, sub-lethal effects of human activities on wildlife: A
case-study approach using two whale populations. Marine Policy
70:58–64.
Williams R., Wright AJ., Ashe
E., Blight LK., Bruintjes R., Canessa R., Clark CW., Cullis-Suzuki S.,
Dakin DT., Erbe C., Hammond PS., Merchant ND., O’Hara PD., Purser J.,
Radford AN., Simpson SD., Thomas L., Wale MA. 2015. Impacts of
anthropogenic noise on marine life: Publication patterns, new
discoveries, and future directions in research and management.
Ocean & coastal management 115:17–24.
Wright AJ. 2008.
International Workshop on Shipping Noise and Marine Mammals .
Hamburg, Germany: Okeanos - Foundation for the Sea.