Oceanic noise pollution is a serious problem that can be easily overlooked, especially in the wake of more physical sources of marine pollution, such as the fabled Great Pacific Garbage Patch. However, anthropogenic sound exposure from ship traffic, sonar, and other means can have detrimental effects on the physiological and social nature of fishes, sea turtles, and marine mammals.
Legislative requirements for the assessment of anthropogenic sound in the ocean are present in different countries, but the criteria to meet them are not so clear for specific sources of sound exposure. ASA S3/SC1.4-2014 – Sound Exposure Guidelines for Fishes and Sea Turtles is a highly informative document that gives organizations the means to make accurate conservation-guided decisions in regards to their oceanic noise creation activities.
Marine animals use sounds to perform many tasks essential to their lives and fitness: to navigate, communicate, find food, locate mates, and avoid predators. The use of and response to these sounds has been developed in the ocean animals throughout their evolutionary path. However, when humans introduce new sound and pressure waves into the sea, they disturb the ambient sound and natural state of the animals.
There are only seven extant species of sea turtle, and all of them face a variety of threats that could potentially drive them towards extinction. While little data is available on the hearing abilities of sea turtles, morphological observations have indicated that the sea turtle has a typical reptilian ear with a few aquatic modifications. Specifically a thick layer of subtympanal fat on the back of the tympanum, the hearing structure makes it difficult to hear in air but easier to detect sound pressure underwater.
Sea turtles hear best between 200 and 750 Hz, so low-frequency noise can harm their hearing and maybe even interfere with their nesting patterns. However, there is not enough available data to understand the full extent of the damages to sea turtles from sound exposure. To fill the gaps in knowledge about sea turtle sound exposure, ASA S3/SC1.4-2014 has extrapolated data on sound exposure for fishes, which is believed to be comparable to that of sea turtles.
Sound exposure in fishes has much more variation, since there are over 32,000 extant fish species. All fishes have ears that convey to them their linear and angular acceleration from sound and pressure, and all bony and cartilaginous fish have a lateral line system that responds to vibrations. The functions of these anatomical features are quickly thrown off from changes in ambient sound.
In addition, many fishes have a gas bladder (swim bladder) that is used for buoyancy control, hearing, sound production, and/or respiration. Species with swim bladders are more likely to suffer from barotrauma (physiological trauma), and sudden pressure changes, often from impulsive sounds, can contribute to this. This not only harms behavior and hearing, but can also cause the animal physical harm, even immediate or delayed mortality.
Since fishes with swim bladders are especially susceptible to changes in sound and pressure, and different fishes respond differently to sound, ASA S3/SC1.4-2014 divides fishes and sea turtles into five groups to better address their potential exposure to sound. These are:
- Fish with no swim bladder
- Fish with swim bladder not involved with hearing
- Fish with swim bladder that is involved with hearing
- Sea Turtles
- Eggs and Larvae
ASA S3/SC1.4-2014 uses these categories to determine the severity of the harm and injury to fishes and sea turtles from sound pollution. The effects that it addresses are mortality and mortal injury, recoverable injury, TTS (short or long term changes in hearing sensitivity that may or may not reduce fitness), masking (impairment of hearing sensitivity from additional sounds), and any behavioral effects (in movement, range, reproduction, etc.).
ASA S3/SC1.4-2014 covers five sources of anthropogenic sound that can lead to these detrimental effects in fishes and sea turtles, labeling their impact as high, low, or moderate. These sources are:
- Explosions used to dismantle in-water structures
- Pile Driving used in the construction of in-water structures
- Seismic Airguns used to extract oil and gas from under the seafloor
- Low- and Mid-Frequency Naval Solar
- Shipping and other continuous noises
Understanding these guidelines on sound exposure impact can help those currently contributing to detrimental sound pollution make better decisions.
While this standard is not intended to assess the hazards of sound exposure for marine animals, it does refer to them. Like fishes and sea turtles, noise pollution is notably dangerous for marine mammals, especially that coming from sonar, since it interferes with the natural sonar abilities of whales, dolphins, and sea lions.
These guidelines were generated with the assistance of a great deal of peer-reviewed literature on the topic. However, those involved with the standard’s publication understood that there is much-more research needed on the subject of marine sound exposure, so the standard comments on research recommendations that could further advance the body of knowledge.