The operational phase will result in noise from operational vessel movements.

Transcription

1 13B Port Study Area Underwater Noise Scoping Report 13B.1 Introduction Direct impacts to fish and marine mammals may occur as a result of construction noise and vibration. Noise and vibration will occur during dredging of the approach channel, turning circle and quay location as well as during the piling required for construction quay and associated structures. Dredging and piling generates a certain amount of underwater noise and vibration, which can impact fish distributions and marine mammal behaviour. A description of noise levels in air can be found in Chapter 8: Noise and Vibration. Underwater noise is considered below. The operational phase will result in noise from operational vessel movements. Noise assessment involves a number of technical terms. These are described in the box below. Underwater Noise Measurements Since there is a range of ways in which underwater noise can be quantified, a variety of noise metrics are often referred to in literature. Underwater noise levels are commonly referred to in terms of decibels (db). The decibels are based on a ratio of the underwater sound pressure to a common reference of 1 micropascal (db re μpa). The acoustic pressure referred to above can be expressed as either the peak to peak (p-p), peak (peak) or root mean square (rms). The type of pressure measurement used is an important consideration when comparing noise levels and criteria and the type of pressure measurement should be stated when quoting noise levels. The peak pressure is the maximum absolute pressure for an instantaneous signal. However, acoustic pressure varies from positive to negative to form the pressure fluctuations that can be heard by fauna. Therefore, it is also possible to refer to the peak to peak value (p-p), which is the algebraic difference between the highest (positive) point to the lowest (negative) point of a sound pressure signal. The peak to peak value is higher for a given signal than the peak value. These measures do not reflect average values of sound and an additional quantity is used to reflect this, which is referred to as the root mean squared (or rms) value. This quantity is the square root of the mean of the instantaneous pressures squared. With a continuous signal a measurement of the root mean square (rms) sound pressure is an appropriate metric. With a sound impulse (ie in impact piling), however, a metric must be chosen which adequately describes the potential for damage to fauna of pulses of different lengths and energy distribution; that is, which measures the acoustic energy in the transient event. The sound exposure level (SEL) is one such metric. The SEL is defined as that level which, normalised to 1 second, has the same acoustic energy as the transient event and is expressed as db re 1μPa 2 s. For a discussion of piling impacts, a cumulative SEL value is derived that considers the SEL of a single-strike value and the number of strikes required to place a pile at its final depth. 13B.2 Baseline 13B.2.1 Fish There are several species of fish which likely to pass through the survey area. Priority species identified during surveys in 2008 include the Blackchin guitarfish (Rhinobatos cemiculus) and Daisy stingray (Dasyatis margarita). These are both members of the group including all rays and skates, and are listed as Endangered by the IUCN. The Bonga shad (Ethmalosa finmbriata) is both abundant and widespread. Fish diversity and abundance in the study area is concentrated in coastal waters less than 20 m deep, especially around the mouths of estuaries. The fish population is dominated by demersal species, preferring to live close to the seabed. 13B-1

2 Sound Detection in Fish Fish have differing sensitivities to noise depending on various anatomical and physiological structures. Two sound detection mechanisms are present in those marine fish species that have the ability to hear: the inner ear system of otolithic bones, and a lateral line system comprising a series of sensory cells that run from the gills to the tail fin. These cells allow the fish to detect relative motion and sound in the aquatic environment. Many species also use the gas-filled swim bladder in the abdominal cavity for detecting sound. Underwater noise causes the swim bladder gas to vibrate and links between the swim bladder and the ear allow the sound wave energy to be re-directed to the ear. The use of the swim bladder allows fish to detect sounds with hearing sensitivity increased in species where the ear and swim bladder are more closely connected. Sharks and rays do not have swim bladders. Hearing specialists such as herring-like species, including sardinella (Sardinella sp), bonga shad (Ethmalosa fimbriata) and West African ilisha (Ilisha africana), are characterised by high auditory sensitivity and bandwidth. The majority of fish species possess a swimbladder but no special connections to the inner ear. Their sensitivity is moderate and the bandwidth of frequencies that they are able to hear tends to be narrow. These are commonly referred to as hearing generalists and are likely to include most species found in the study area. Sciaenid fishes, which make up the majority of the fish population in the area in terms of biomass, are considered to be hearing generalists (1). 13B.2.2 Marine Mammals Different cetaceans (including the Atlantic humpbacked dolphin) are likely present in the study area. The West African manatee may also occasionally enter the area but is likely a rare visitor. Most cetacean species will be located in offshore waters, and are unlikely to be found near to the port site. Atlantic Humpbacked Dolphin inhabit coastal and estuarine waters, and have been known to swim up into rivers. West African manatee may be found in mangrove channels, or occasionally in coastal and estuarine waters when moving between areas. 13B.2.3 Turtles There are five species of marine turtle that are likely to be within the survey area. These include Green sea turtle (Chelonia mydas) and Hawksbill turtle (Eretmochelys imbricata). These species predominantly inhabit offshore, coastal and estuarine waters, where they feed. There is the possibility that some species use sandy beaches in the area for nesting, but this is likely to involve only occasional individuals. 13B.2.4 Measured Baseline A survey of baseline underwater noise levels was carried out in the offshore area off the coast of Guinea, south of Conakry in the autumn of 2011 (2). The goals of the acoustic monitoring program were to document baseline ambient noise conditions, and identify sources of underwater noise off the south coast of Guinea. The acquired acoustic data were analysed to quantify ambient sound levels and the presence of anthropogenic activity (shipping noise) in the area. Ambient sound off Île Kaback was recorded from 24 September 2011 to 3 November The sound levels were unusually quiet. The mean level for the band of Hz was 95.2 db with a standard deviation of 10.8 db. A very small amount of boating and shipping activity was present. (1) Cruz, A. & Lombarte A. (2004). Otolith size and its relationship with colour patterns and sound production. Journal of Fish Biology 65: (2) Simandou Project Port Component Baseline Environmental Report for Underwater Noise Conditions off Kaback Island Area (Ginea) Preliminary Version, JASCO Applied Sciences. Environnement Illimité inc., March B-2

3 The dominant sound sources were wind, waves, and biological sources, especially daily fish choruses and snapping shrimp. This location as being unusually quiet in comparison with typical subsea ambient noise levels in other parts of the world. The levels at 50 and 100 Hz are 2-7 db below the minimum usual traffic levels for shallow water shipping noise. At frequencies above 500 Hz, localized anthropogenic activity, wind, waves, rain, and biological activity become the dominant sound sources. For the period of late September-early November 2011, the area off Île Kaback the acoustic data indicates very low average sea states, and that fish and snapping shrimp are the dominant noise sources. There is some acoustic detection that may be from cetaceans, however, they are intermittent. The recording period occurred during the wet season, but there is little evidence of strong precipitation in the acoustic data. Heavy rain typically appears as a band of energy from Hz, depending on the drop size. Closer to shore and in the Morebaya River estuary, ambient noise levels are likely affected by breaking waves. 13B.3 Methodology for Predicting Potential Impacts from Underwater Noise 13B.3.1 Sound Propagation This assessment has been carried out considering the potential noise source, the propagation path of the sound underwater and suitable criteria for the receptors. At this stage using approximate sound propagation spreading characteristics has been assumed. This does not include the effects of the sound speed profile and bathymetry in the area. For long range propagation calculations an assumption of 15xlog(R/R0) provides a good estimate of spreading where R is the distance from the source at which predictions are required and R0 is the distance at which the source measurement was made. This is the empirical prediction approach currently endorsed by a multiagency Fisheries Hydroacoustic Working Group for the California Department of Transportation (2009) (1) and its use has currently been re-endorsed by the NMFS Northwest Region as a practical way of assessing the potential effect of piling projects (2). 13B.3.2 Noise Source For the purposes of this assessment the main source of noise has been assumed to be the noise from driven piling during construction and predicted noise levels have been carried out for this noise source. The piles that are to be used in this project are expected to have a diameter of 1.2 m. However, options are being considered for large piles with diameters of 1.5 m and 1.6 m. Noise data for various ranges of pile diameters are included in the FHWG guidance document and data is presented for a 66 diameter (1.7 m) pile from piling at the Richmond-San Rafael bridge. The data are presented in Table 13B.1 below. The data are based on measurements of 1.7 m diameter CIDH Trestle piles that were driven using a diesel impact hammer. Reported driving energies were about 270 kilojoules. Note that the SEL value was found to be 11 to 12 db lower than the rms value, and is quoted conservatively as 10 db below the rms in this assessment. Table 13B.1 Single Strike Noise from Pile Driving (Measured at 10 m) Pile Peak Pressure Level db re 1 μpa RMS Sound Pressure Level db re 1 μpa Sound Exposure Level (db re 1μPa 2 s) CIDH (66 inch) impact (at 10 m) Source: California Department of Transportation (2009) (1) ICF Jones and Stokes, (2009). Technical Guidance for Assessment and Mitigation of the Hydroacoustic Effects of Pile Driving on Fish, ICF Jones and Stokes for the California Department of Transportation, February 2009, 298 pp. (2) Memorandum from NMFS Northwest Region and Northwest Fisheries Science Center: Guidance Document: Sound Propagation Modeling to Characterize Pile Driving Sounds Relevant to Marine Mammals, January 31, B-3

4 Piling source levels vary depending on the diameter of the pile and the method of pile driving (impact or vibropiling). The piling methodology has not been developed at this stage and the highest noise levels (from driven piling) are used in this assessment. The frequency spectrum for piling ranges from less than 20 Hz to more than 20 khz with most energy around Hz (1). In order to calculate the accumulated SEL exposure level the number of pile strikes per day must be estimated. The number of strikes per pile is not available at this stage, and an example value from the FHWG document of strikes per pile has been used. The maximum piling rate is one pile per rig per day for piles that are simply driven into place, and less from those that required toe drilling. The maximum number of rigs that could practically operate together is four, giving a maximum number of piles driven of four in a day. This would result in a total of pile strikes in a 24 hour period. The noise from vessels in the area has also been considered. Dredging vessels are likely to be the most significant of these and their noise emissions are typically equivalent to a noisy merchant vessel underway. They also affect an area for longer than a passing vessel, and therefore the potential effect has been assumed to be larger. Dredging emits continuous broadband sound during operations, mostly in the lower frequencies. Source levels range from 160 to 180 db re 1 μpa at 1 m (maximum ~ 100 Hz) (2). Most energy has been found to be below 500 Hz. Dredging has also been measured for a variety of vessels in the UK (3) (4) which confirmed the conclusions that dredging was within the range of general shipping noise but suggested that total noise levels could be up to 190 db re 1 μpa at 1 m rms. This higher source term has been used to assess potential dredging and vessel noise. 13B.4 Predicted Impact Zones 13B B Fish Criteria The potentially lethal effects on fish have been considered rather than the effects of sub-lethal hearing damage in this assessment. Work has been done by the Fisheries Hydroacoustic Working Group (5) (FHWG) to try to address this knowledge gap. Interim criteria of 206 db re 1 μpa (peak) have been set with accumulated sound exposure level (SEL) of 187 db and 183 db re 1 μpa 2 -sec. The SEL criteria are intended to take into account the likely noise exposure over time, which would require more detailed knowledge of likely timings of activities than is available at this stage of the project. However, these parameters have been estimated based on current knowledge to enable an estimate to be made, assuming a worst case based on the assumption that fish might not move when the piling starts. The SEL is measured over the duration of the seismic pulse, and then an accumulated value is calculated over all of the noise events in one day. The 183 db exposure criterion above is intended to apply to fish weighing less than 2 g. There are insufficient peer reviewed reliable data available for the onset of behavioural disturbance in fish as noted by the Fisheries Hydro Acoustic Working Group (FHWG). However, it is noted that as a conservative measure, NOAA Fisheries and USFWS generally have used 150 db rms as the threshold for behavioural effects to fish species of particular concern (salmon and bull trout) for most biological opinions evaluating pile driving, citing that sound pressure levels in excess of 150 db rms can cause temporary behavioural changes (startle and stress) that could decrease a fish s ability to avoid predators. Relatively little justification is given to support this statement, but in the absence of other criteria this value was used to indicate where behavioural effects might be likely. It should be noted that those agencies that support this approach have indicated that mitigation would not be expected in the situation that this level was exceeded. (1) Götz et al, (2009). Overview of the impacts of anthropogenic underwater sound in the marine environment. OSPAR Commission. (2) Götz et al, (2009). Overview of the impacts of anthropogenic underwater sound in the marine environment. OSPAR Commission. (3) Robinson, et al (2011) (4) Measurement of Underwater Noise Arising from Marine Aggregate Dredging Operations, MALSF, Feb (5) ICF Jones and Stokes, (2009). Technical Guidance for Assessment and Mitigation of the Hydroacoustic Effects of Pile Driving on Fish. ICF Jones and Stokes for the California Department of Transportation, February 2009, 298 pp. 13B-4

5 Compared to pelagic elasmobranchs (sharks and rays), the little skate (Raja erinacea) and another bottom dwelling shark (the horn shark, Heterodontus francisi) have less sensitive hearing (1). It is suggested that this less sensitive hearing is linked to feeding on benthic prey. However, in order to conduct a conservative assessment the same criterion has been applied to all fish. Noise from dredging and vessel movements is not expected to result in injury to fish and it is only considered in terms of behavioural response using the criterion above. 13B Predicted Zones of Impact Fish are not expected to experience injury as a result of the piling work beyond approximately 18 m from the source due to individual pile strikes, and 6.8 km in terms of cumulative exposure for fish with mass greater than 2 g. For smaller fish the zone for cumulative noise exposure damage would extend to approximately 10 km. The noise level would reduce to about 150 db re 1 μpa (rms) at approximately 10 km. This zone would be expected to result in behavioural reactions in fish according to the NOAA and USFWS approach. As noted above noise from dredging and vessel movements is not expected to result in injury to fish and it is only considered in terms of behavioural response. Noise levels will meet 150 db re 1 μpa (rms) at 465 m. 13B B Marine Mammals Criteria The criteria in Southall et al (2007) (2) suggest that in order to cause instantaneous injury to cetaceans (including porpoise) resulting in a permanent loss in hearing ability (referred to as permanent threshold shift, PTS), the sound level must exceed 230 decibels (db) re 1 micropascal (μpa) (peak). A thorough review of data relating to studies from pulsed sound was undertaken to support the successful application for a recent (2010) seismic survey project by the United States Geological Survey (USGS) (3). This review considered some of the studies that are considered in the Southall et al study discussed above, and considered the level at which a significant effect was likely. This review noted that the US National Marine Fisheries Service (NMFS) guidance for cetaceans states that they should not be exposed to pulsed underwater noise at received levels >180 db re 1 μpa (rms). The 180 re 1 μpa (rms) level has not been considered to be the level above which Temporary Threshold Shift (TTS) might occur, but rather that it could not be ruled out. TTS is considered to be auditory fatigue that results in a short term loss of hearing sensitivity rather than permanent hearing damage. The review of published studies suggested that these were appropriate for assessing the significant effects that are likely (rather than the onset of effects). In order to be conservative, a cautious assessment criterion of 180 db re 1 μpa (rms) has been assumed for all Cetacean species in this assessment. The USGS review of literature also concluded that the many studies of criterion for Level B Harassment (ie behavioural responses that are significant enough to result in a change in the animal s natural behaviour rather than purely short term reactions to noise) support the NMFS view that disturbance is generally likely to occur at 160 db re 1 μpa (rms). (1) B M Casper, P S Lobell, HY Yan (2003). The hearing sensitivity of the little skate, Raja erinacea: A comparison of two methods, (2) Southall, B.L., A.E. Bowles, W.T. Ellison, J.J. Finneran, R.L. Gentry, C.R. Greene Jr., D. Kastak, D.R. Ketten, J.H. Miller, P.E. Nachtigall, W.J. Richardson, J.A. Thomas and P.L. Tyack. (2007). Marine mammal noise exposure criteria: initial scientific recommendations. Aquatic Mammals 33(4): (3) Haley, B., Ireland, D., and Childs, J.R., (2010). Environmental Assessment for a Marine Geophysical Survey of Parts of the Arctic Ocean, August September 2010, U.S. Geological Survey Open-File Report , version B-5

6 For non-pulsed sounds such as dredging a noise assessment criterion of 120 db re 1 μpa (rms). This has also been applied to vessel movements, but it is expected that these will only generate noise over a limited period of time so that the effect will be lower than for dredging. Information on the hearing sensitivity of the West African manatee Trichechus senegalensis is not available, however, West Indian manatees have a reported hearing ability of between 15 Hz and 46 khz with the best sensitivity at 6-20 khz (1) (2). Other data suggest West Indian manatees are most sensitive around khz but are less sensitive at 4 khz and even 8 khz, although there was some sensitivity up to 35 khz (3). Research has indicated that elevated sound levels affect the behavioural patterns of the Florida manatee (a subspecies of the West Indian manatee) (4). In the absence of more specific data it has been assumed that they are no more sensitive than other marine mammals in this assessment. 13B Predicted Zones of Impact Marine mammals are not expected to experience injury as a result of single impulses from piling even at 10 m according to Southall et al criterion (230 db re 1 μpa (peak)). NMFS criteria at which temporary threshold shift cannot be ruled out (180 db re 1 μpa (rms) are expected to be exceeded at 100 m from the source. However, temporary threshold shifts will not result in a long term effect. Behavioural disturbance is expected above 160 db re 1 μpa (rms) and this is predicted to occur at m. As noted above noise from dredging and vessel movements is not expected to result in injury to marine mammals and it is only considered in terms of behavioural response. Noise levels will meet 120 db re 1 μpa rms) at m. Marine mammal populations have been noted close to shipping lanes and ports and these results should be considered in this context. Prediction at large distances is also subject to a large degree of uncertainty, and simple calculations tend to ignore site specific factors that will affect noise propagation in river environments. These factors include attenuation as noise travels around bends or over shallower water. The predictions presented here are expected to be worst case estimations of the impact zones. 13B B Turtles Criteria There are no reliable data in the scientific literature for the assessment of temporary or permanent hearing damage for turtles. Criteria for behavioural reactions to pulsed sounds ie piling noise have been based on the work by (McCauley), which suggests that behavioural reactions on caged turtles would be expected 166 (beginning of behavioural response) to 175 db re 1 μpa (rms) (likely avoidance reaction level). A study by Weir (5) argues that an assessment of turtle behaviour in relation to seismic surveys is hindered by the apparent reaction of individuals to the ship and towed equipment rather than specifically to airgun sound. These reactions occurred at close range (usually <10 m) to approaching objects and appeared to be based principally on visual detection. On this basis a quantitative criterion has not been adopted for dredging or vessels. (1) Richardson, JW., Greene, CR., Malme, CI. and Thomson, DH. (1995). Marine Mammals and Noise. Academic Press. 576 pages. (2) Gerstein, ER., Gerstein, L., Forsythe, SE. and Blue, JE. (1999). The underwater audiogram of the West Indian manatee (Trichechus manatus). Journal of the Acoustical Society of America, Volume 105, Issue 6, pp (3) Gerstein, ER., Gerstein, L., Forsythe, SE. and Blue, JE. (1999). The underwater audiogram of the West Indian manatee (Trichechus manatus). Journal of the Acoustical Society of America, Volume 105, Issue 6, pp (4) Miksis-Olds, J.L. and Wagner, T. (2011). Behavioral response of manatees to variations in environmental sound levels. Marine Mammal Science Volume 27, Issue 1, pages (5) Observations of Marine Turtles in Relation to Seismic Airgun Sound off Angola, Marine Turtle Newsletter 116:17-20, B-6

7 13B Predicted Zones of Impact The predictions of piling noise show that noise levels would exceed the impact criteria for behavioural reactions between approximately 215 m and 858 m. However, the predicted ranges based on these criteria need to be seen in the context of Marine Mammal Observer (MMO) studies during other activities such as seismic surveys, where turtles were observed close to the vessel. It would not have been possible to determine subtle behavioural reactions from the vessel based observations, but the presence on a regular basis suggested that noise from the vessel would not deter turtles from using the area. Table 13B.2 Summary of Impact Zone Sizes Species Effect Criterion Distance to Meet Criterion (m) Effects of Piling Noise Fish Potentially lethal effect 206 db re 1 μpa (peak) 18 Fish at least 2g Potentially lethal effect Accumulated SEL of 187 db re 1 μpa 2 -sec Fish <2g Potentially lethal effect Accumulated SEL of 183 db re 1 μpa 2 -sec Fish Behavioural effects 150 db re 1 μpa (rms) Marine Mammals Injury 230 db re 1 μpa (peak) Not exceeded for this source Marine Mammals Potential Temporary Threshold Shift 180 db re 1 μpa (rms) 100 Marine Mammals Behavioural effects 160 db re 1 μpa (rms) Turtles Injury and hearing damage No criteria available Not applicable Turtles Behavioural effects 166 to 175 db re 1 μpa (rms) 215 to 858 m Effects of Vessels / Dredging Fish Behavioural effects 150 db re 1 μpa (rms) 464 Marine Mammals Behavioural effects 120 db re 1 μpa (rms) Turtles Behavioural effects None available May not react until within a few metres 13B-7