5.4. Injury and Disturbance to Fish

  1. For fish, the most relevant criteria for injury effects are considered to be those contained in the Noise Exposure Guidelines for Fishes and Sea Turtles (Popper et al., 2014). These guidelines broadly group fish into the following categories based on their anatomy and the available information on hearing of other fish species with comparable anatomies:
  • Group 1: fishes with no swim bladder or other gas chamber (e.g. elasmobranchs, flatfishes and lampreys). These species are less susceptible to barotrauma and are only sensitive to particle motion, not sound pressure. Basking shark Cetorhinus maximus, which do not have a swim bladder, also fall into this hearing group.
  • Group 2: fishes with swim bladders but the swim bladder does not play a role in hearing (e.g. salmonids). These species are susceptible to barotrauma, although hearing only involves particle motion, not sound pressure.
  • Group 3: fishes with swim bladders that are close, but not connected, to the ear (e.g. gadoids and eels). These fishes are sensitive to both particle motion and sound pressure and show a more extended frequency range than Groups 1 and 2, extending to about 500 Hz.
  • Group 4: fishes that have special structures mechanically linking the swim bladder to the ear (e.g. clupeids such as herring, sprat and shads). These fishes are sensitive primarily to sound pressure, although they also detect particle motion. These species have a wider frequency range, extending to several kHz and generally show higher sensitivity to sound pressure than fishes in Groups 1, 2 and 3.
  • Fish eggs and larvae: separated due to greater vulnerability and reduced mobility. Very few peer-reviewed studies report on the response of eggs and larvae to anthropogenic noise.
  1. The guidelines set out criteria for injury effects due to different sources of noise. Those relevant to the Array are considered to be those for impulsive piling sources only, as non-impulsive sources were not considered to be a key potential impact and therefore were screened out of the guidance[9]. The criteria include a range of indices including SEL, rms and peak SPLs. Where insufficient data exist to determine a quantitative guideline value, the risk is categorised in relative terms as “high”, “moderate” or “low” at three distances from the source: “near” (i.e. in the tens of metres), “intermediate” (i.e. in the hundreds of metres) or “far” (i.e. in the thousands of metres). It should be noted that these qualitative criteria cannot differentiate between exposures to different noise levels and therefore all sources of noise, no matter how loud, would theoretically elicit the same assessment result. However, because the qualitative risks are generally qualified as “low”, with the exception of a moderate risk at “near” range (i.e. within tens of metres) for some types of hearing groups and impairment effects, this is not considered to be a significant issue with respect to determining the potential effect of noise on fish.
  2. The injury threshold criteria used in this underwater noise assessment for impulsive piling are given in Table 5.4   Open ▸ . In the table, both peak and SEL criteria are unweighted. Physiological effects relating to injury criteria are described below (Popper et al., 2014; Popper and Hawkins, 2016):
  • Mortality and potential mortal injury: either immediate mortality or tissue and/or physiological damage that is sufficiently severe (e.g. a barotrauma) that death occurs sometime later due to decreased fitness. Mortality has a direct effect upon animal populations, especially if it affects individuals close to maturity.
  • Recoverable injury: Tissue and other physical damage or physiological effects, that are recoverable, but which may place animals at lower levels of fitness, may render them more open to predation, impaired feeding and growth, or lack of breeding success, until recovery takes place.
  • TTS: Short term changes in hearing sensitivity may, or may not, reduce fitness and survival. Impairment of hearing may affect the ability of animals to capture prey and avoid predators, and also cause deterioration in communication between individuals affecting growth, survival, and reproductive success. After termination of a noise that causes TTS, normal hearing ability returns over a period that is variable, depending on many factors, including the intensity and duration of noise exposure.

Table 5.4:
Criteria for Onset of Injury to Fish Due to Impulsive Piling (Popper et al., 2014)

Table 5.4: Criteria for Onset of Injury to Fish Due to Impulsive Piling (Popper et al., 2014)

 

  1. The criteria used in this underwater noise assessment for non-impulsive piling and other continuous noise sources, such as vessels, are given in Table 5.5   Open ▸ . The only numerical criteria for these sources are for recoverable injury and TTS for Groups 3 and 4 Fish.


Table 5.5:
Criteria for Onset of Injury to Fish Due to Non-Impulsive Noise (Popper et al., 2014)

Table 5.5: Criteria for Onset of Injury to Fish Due to Non-Impulsive Noise (Popper et al., 2014)

 

  1. The criteria used in this underwater noise assessment for explosives are given in Table 5.6   Open ▸ . It should be noted that there are no thresholds in Popper et al. (2014) in relation to eggs and larvae in terms of sound pressure.

 

Table 5.6:
Criteria for Injury to Fish Due to Explosives (Popper et al., 2014)

Table 5.6: Criteria for Injury to Fish Due to Explosives (Popper et al., 2014)

 

  1. It should be noted that there are no thresholds in Popper et al. (2014) in relation to noise from high frequency sonar (>10 kHz). This is because the hearing range of fish species falls well below the frequency range of high frequency sonar systems. Consequently, the effects of noise from high frequency sonar surveys on fish has not been conducted as part of this study, due to the frequency of the source being beyond the range of hearing and also due to the lack of any suitable thresholds.
  2. Behavioural reaction of fish to noise has been found to vary between species based on their hearing sensitivity. Typically, fish sense noise via particle motion in the inner ear which is detected from noise-induced motions in the fish’s body (refer to section 9 for further details on particle motion). The detection of sound pressure is restricted to those fish which have air filled swim bladders; however, particle motion (induced by noise) can be detected by fish without swim bladders[10].
  3. Highly sensitive species such as herring have elaborate specialisations of their auditory apparatus, known as an otic bulla – a gas filled sphere, connected to the swim bladder, which enhances hearing ability. The gas filled swim bladder in species groups such as cod and salmon may be involved in their hearing capabilities, so although there is no direct link to the inner ear, these species are able to detect lower noise frequencies and as such are considered to be of medium sensitivity to noise. Flat fish and elasmobranchs have no swim bladders and as such are considered to be relatively less sensitive to sound pressure.
  4. The most recent criteria for disturbance are considered to be those contained in Popper et al. (2014) which set out qualitative criteria for disturbance due to different sources of noise. The risk of behavioural effects is categorised in relative terms as “high”, “moderate” or “low” at three distances from the source: “near” (i.e. in the tens of metres), “intermediate” (i.e. in the hundreds of metres) or “far” (i.e. in the thousands of metres), as shown in Table 5.7   Open ▸ .
Table 5.7:
Criteria for Onset of Behavioural Effects in Fish for Impulsive and Non-Impulsive Noise (Popper et al., 2014)

Table 5.7: Criteria for Onset of Behavioural Effects in Fish for Impulsive and Non-Impulsive Noise (Popper et al., 2014)

 

  1. It is important to note that the Popper et al. (2014) criteria for disturbance due to noise are qualitative rather than quantitative. Consequently, a source of noise of a particular type (e.g. piling) would be predicted to result in the same potential impact, no matter the level of noise produced or the propagation characteristics.
  2. Therefore, the criteria presented in the Washington State Department of Transport (WSDOT) Biological Assessment Preparation for Transport Projects Advanced Training Manual (WSDOT, 2011) are also used in this assessment for predicting the distances at which behavioural effects may occur due to noise from impulsive piling. The manual suggests an unweighted sound pressure level of 150 dB re 1 μPa (rms) as the criterion for onset of behavioural effects, based on work by (Hastings, 2002). Sound pressure levels in excess of 150 dB re 1 μPa (rms) are expected to cause temporary behavioural changes, such as elicitation of a startle response, disruption of feeding, or avoidance of an area. The document notes that levels exceeding this threshold are not expected to cause direct permanent injury but may indirectly affect the individual fish (such as by impairing predator detection). It is important to note that this threshold is for onset of potential effects, and not necessarily an ‘adverse effect’ threshold.