NREL - National Renewable Energy Laboratory

Evaluation of the Effect of Noise from Offshore Pile-Driving on Marine Fish

Publication TypeReport
Year of Publication2002
Document Number1980-1-03-1- rev. 2.UK
Pagination23 pp.
CityÅbyhøj, DK

The purpose of this memo is to evaluate the possible effects of noise from offshore piledriving activity on fish.

As part of a plan to establish offshore wind turbines in Denmark, the Ministry of the Environment and Energy introduced a government order asking the electricity companies to set up five large-scale offshore wind farms with a total output of 750 MW.

Rødsand in the Femer Belt was selected as the location for one demonstration project with an output of 150 MW. The project was approved on the condition that an EIA (Environmental Impact Assessment) study was conducted in accordance with the guidelines of the Ministry of the Environment and Energy (May 1999). Permission was also given to carry out the necessary preliminary studies.

The construction of an offshore wind farm at Rødsand may potentially affect the fish population in the area during construction and operation. Technical background reports are prepared to form the basis for the actual EIA study.

As part of this work, a report on underwater and above-water noise measurements and analysis during offshore pile-driving at a wind-turbine park under construction in Sweden was conducted (Ødegaard & Danneskoild-Samsøe, 2000). This paper attempts to estimate the effect that noise from the offshore pile-driving will have on the behaviour and physiology of the fish present in the area of the proposed wind farm. According to information given by SEAS, the piledriving of one monopile at Rødsand will last four hours. There will most probably be 72 mills in the demonstration project at Rødsand.

The hearing ability and avoidance of sound by fish species present in the area of the proposed wind farm (Bio/consult, 2000a, b) is taken into consideration.

Different species of fish have different hearing abilities and the reason for this is mainly differences in the physiology. Thus, in order to make a meaningful evaluation of the possible effects of noise on fish, it is essential to have an understanding of the hearing capability of fish, the physiology behind it, and how it influences the behaviour of the fish. A short description of the hearing abilities of fish is given. This includes a description of audible thresholds and the differences between different fish species.

On the basis of the scientific knowledge gathered, the possible hearing ability of the fish found at Rødsand is described and the possible impact that noise will have upon the fish is evaluated.

Even though the noise from pile-driving might seem tremendous to the human ear, this is not the case for all species of fish.Bottom living fish in which the swimbladder has degenerated and hearing is not specialised generally have high auditory threshold levels and will probably hardly hear the noise frequencies above 250 Hz. At frequencies below 250 Hz the lowest auditory thresholds is app. 90-110 dB. This group of fish includes flounder, plaice, dab, turbot, sea scorpions, eelpout, sandeels and gobies that are all present in the proposed construction area at Rødsand.

Cod, whiting and silver eel, that are also present in the proposed construction area at Rødsand has a swimbladder and can probably hear frequencies up to 300-500 Hz. At frequencies below 300-500 Hz. the lowest auditory thresholds is app. 75-100 dB.

Although the reported avoidance reaction of fish at low frequencies is not completely clear it is possible, that low sound frequencies from pile-driving could elicit some avoidance from species without specialised hearing, especially those with a swimbladder (cod, whiting and silver eel). Avoidance reactions would be most plausible at short distances (less than 30 meter) from the sound source.

It is not likely, that the hearing of flounder, plaice, dab, turbot, sea scorpions, eelpout, sandeels and gobies, cod, whiting and silver eel will be harmed by the noise. Some degree of habituation of the same fish species to the noise from pile-driving is also plausible. Herring and sprat (brisling), that are also found at Rødsand has a specialised hearing with low auditory threshold levels and a broad hearing bandwidth (50-75 dB at 200-3000Hz), which is probably reflected in the avoidance threshold.

Some damage to the sensory cells of the ear has been reported from clupeid fish (like herring and sprat) to occur at sound pressures of 153-170 dB. These noise levels occur at frequencies from 100 Hz to 2500 Hz at the four distances investigated from the piledriving (Ødegaard & Danneskiold-Samsøe, 2000). Therefore herring and sprat will probably show escape response as a result of pile-driving. The noise from pile-driving could harm the hearing ability of these two fish species. Some studies have provided evidence, that hearing ability can be regenerated after damage.

It is not likely, that the noise from pile-driving will produce any other physical injuries to any of the fish species.

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TagsSweden; Offshore Wind; Fish (general); 2002; Report