[MARMAM] Todd et al 2014: A review of impacts of marine dredging activities on marine mammals. ICES J. Mar. Sci. first published online November 4, 2014 doi: 10.1093/icesjms/fsu187

Victoria Todd v.todd at oceanscienceconsulting.com
Tue Nov 11 02:53:21 PST 2014

Dear MARMAMers,

We are pleased to announce publication (including supplementary on-line 
data) of the following article:

Victoria L. G. Todd, Ian B. Todd, Jane C. Gardiner, Erica C. N. Morrin, 
Nicola A. MacPherson, Nancy A. DiMarzio, and Frank Thomsen 2014: A 
review of impacts of marine dredging activities on marine mammals. /ICES 
Journal of Marine Science/, doi: 10.1093/icesjms/fsu187.

Marine dredging is an excavation activity carried out worldwide by many 
industries. Concern about the impact dredging has on marine life, 
including marine mammals (cetaceans, pinnipeds, and sirenians) exists, 
but effects are largely unknown. Through consulting available 
literature, this review aims to expand on existing knowledge of the 
direct and indirect, negative and positive impacts on marine mammals. In 
terms of direct effects, collisions are possible, but unlikely, given 
the slow speed of dredgers. Noise emitted is broadband, with most energy 
below 1 kHz and unlikely to cause damage to marine mammal auditory 
systems, but masking and behavioural changes are possible. Sediment 
plumes are generally localized, and marine mammals reside often in 
turbid waters, so significant impacts from turbidity are improbable. 
Entrainment, habitat degradation, noise, contaminant remobilization, 
suspended sediments, and sedimentation can affect benthic, epibenthic, 
and infaunal communities, which may impact marine mammals indirectly 
through changes to prey. Eggs and larvae are at highest risk from 
entrainment, so dredging in spawning areas can be detrimental, but 
effects are minimized through the use of environmental windows. 
Sensitive environments such as seagrass beds are at risk from 
smothering, removal, or damage, but careful planning can reduce 
degradation. Assessing impacts of contaminant remobilization is 
difficult, but as long as contaminated sediments are disposed of 
correctly, remobilization is limited in space and time. Effects of 
suspended sediments and sedimentation are species-specific, but 
invertebrates, eggs, and larvae are most vulnerable. Positive effects, 
including an increase in food, result from greater nutrient loads, but 
are often short term. Dredging has the potential to impact marine 
mammals, but effects are species and location-specific, varying also 
with dredging equipment type. In general, evidence suggests that if 
management procedures are implemented, effects are most likely to be 
masking and short-term behavioural alterations and changes to prey 

*Supplementary data*
The supplementary data feature a world map of regional boundaries used 
to compose distributions of marine mammals, and a referenced world-wide 
review table, that lists family, scientific names, common name, range of 
best hearing (10 dB from max; kHz), frequency of minimum hearing 
threshold (kHz), minimum hearing threshold (dB re 1 µPa), methodology, 
diet, region, habitat, documented effects of dredging, and potential 
effects of dredging. The table was created to assist stakeholders in 
developing mitigation plans for dredging activities that have  potential 
to impact marine mammals.

If you subscribe to /ICES J. Mar. Sci./ the article and supplementary 
are available at 
or you can download the PDF and supplementary material on 


Dr. Victoria Todd
Managing Director
OSC Ltd.
Ocean House, 4 Brewery Lane
Belhaven, Dunbar, East Lothian
Scotland, EH42 1PD
T: +44 (0)1368 865 722
M: +44 (0)7719 489 415
F: +44 (0)1368 865 729
W: www.osc.co.uk
E: vt at osc.co.uk

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