Underwater noise from maritime sources and impact on marine life Cato C. ten Hallers-Tjabbes

Perceiving stimuli (signals) from the environment is vital for animal behaviour In a marine environment vision is limited Acoustic sense and chemoreception instead Vision can perceive many signals together in a space (overview) Acoustic sense can perceive one signal at a time; the stronger one is heard

Acoustic signals from the environment for animal behaviour and communication Sounds generated in the physical environment: Sounds from conspecifics: Sounds from other species: Predator/prey Symbionths Echolocation: self-generated signals Navigation / orientation

Human activities that generate sound Shipping Fisheries Benthic trawling Sonar Mineral extraction Military activities Shooting / explosions Dredging Construction work Sequestration of carbon dioxide

Impact of man-made sound on marine life Temporary or permanent threshold shift = Deafening Damage to hearing and other vital organs: Excess sound disturbs the natural diving pattern. Lethal if severe Avoidance of favourable areas for Feeding, Reproduction, Shelter, a.o. Inhibition of sensory-mediated behaviour

How do marine animals detect sound The level of background noise influences the potential of detection Verboom, 2006

Man-made noise may affect animal acoustic perception when: The frequency range of man-made noise overlaps with the animal’s acoustic perception window and Man-made noise is louder than the sounds animals are naturally perceiving The acoustic window to the outside world also offers an opportunity to enter [or intrude] Verboom, 2006

Examples of fish and marine mammal audiograms Porpoise = guideline Verboom Seal = guideline Verboom Cod = Chapman & Hawkins (1973), Hawkins (1993) Herring = estimate Enger (1967) < resulting auditory filters Porpoise and seal audiograms = based on several measurements (combination of results). Cod = measured audiogram. Herring = estimated, based on evoked potential measurement. Hearing filter = reversed shape of the audiogram Verboom, 2006

Man-made sound and animal acoustic perception Weighted levels of pile driving noise Each species hears a different spectrum of the same sound. Crosses = Broadband peak level of one hit during pile driving. The red part of the spectrum is the spectrum a herring hears; level = 237 dB (assuming the audiogram of picture 2). The green part is the spectrum a porpoise hears; level = 207 dB. So, the herring hears the low-frequency part, the porpoise the high-frequency part. Pile driving has more influence on herring and cod than on porpoise. A weighted level is the level of a certain sound spectrum filtered by the hearing filter of a certain species. Verboom, 2006 Red = Herring hearing spectrum Green = Porpoise hearing spectrum

Animal perception of human-generated sound levels calculated weighted source levels Broadband (free-field) source level and weighted levels per species (dB re 1 microPa at 1 m)   broadband cod h. seal porpoise herring wind turbine pile driving 256 228 225 207 237 Airgun – seismic exploration 220 184 161 224 LFAS – military sonar 218 213 185 shipping noise upper limit 199 193 179 173 197 wind turbine in operation 162 148 135 176 shipping noise lower limit 160 144 138 122

man-made sound sources and marine animal acoustic windows Verboom, 2006 Free-field source level of some man-made underwater noises. Broadband levels are indicated in the legend. Free-field = level of which the influence of local conditions (i.e. bottom and water surface effect on propagation) is eliminated. Upper and lower limit of shipping noise = spreading of 25 ships, length between 25-100m, speed between 8-16 knots, noise reduction measures on board = between ‘none’ and ‘pretty good’. Pile driving level is the peak level of one hit. Airgun is the level of one small airgun. Hearing range = frequency range between max sensitivity (0 dB) and minus 15 dB of the relevant audiogram. Dotted line = no audiogram available.

Dose-response relationship Porpoises Verboom, 2006 Dose-response relationship is the relationship between a certain sound level and a certain effect on the behaviour of an animal. For habour porpoises this relationship has been estimated by TNO, partly based on Dutch research results (Seamarco). It was found that the ‘discomfort threshold’ for certain sound types was around 105 dB re 1 micropascal. The discomfort threshold is the level that an animal usually does not exceed when approaching a sound source. Shipping sound is between 122 and 173 dB at 1m distance from the ship (weighted free-field source level). When an approaching porpoise does not exceed a weighted level of 105 dB, the porpoise stays between 560 m (upper limit) and 0 m (lower limit) away from the ship. Radius of Shipping Noise for Porpoises is ~0 – 560 m, based on a Discomfort Threshold of 105 dB

Avoidance of man-made sound hampered in crowded shipping areas Netherlands Government, 1995 Shipping density = 45 Ships/Day

Migratory Routes Fish and invertebrates Migrate too Few migratory (Shirihai & Jarett, 2006. Whales, Dolphins and Seals) Few migratory routes are known Grey Whale Killer Whale Fish and invertebrates Migrate too Global shipping densities as reported to AMVER (Source: AMVER 2002)

Frequencies and Sound Levels Evaluating the impact of man-made sound on marine life: Frequencies and Sound Levels Hearing properties Masking of pure tone Irregular sound propagation - Frequency ->

Conclusions Shipping and other man-made sound sources in the ocean are likely to increase Shipping routes coincide with migratory routes of marine animals The role of acoustic impact on ecosystem functioning may be much larger than currently understood Sound levels of ships may be higher than necessary due to imperfectly moving mechanical parts, Improving mechanical performance reduces excess sound levels and reduces operational costs IMO may be the appropriate International Organisation to take a lead in developing a strategy to reduce the impact of man-made sound in the marine environment