Environmental Impacts
HOW ARE THE MARINE ANIMALS AFFECTED BY SEISMIC SURVEYS?
Up to now, in South Africa, there has been virtually no concern or scientific research on the effects of seismic surveys on marine animals. Conversely, on a global scale, the environmental impacts and effects of seismic surveys are well documented.
Why are seismic surveys allowed in South Africa if there are impacts to marine life?
The main rationale why marine seismic surveys are allowed in South African waters, according to the Department of Environmental Affairs, is that species will move away from the sound source during soft starts1 A soft start, is a slow increase in noise or sound level used to warn and drive larger species, such as dolphins and whales, away from the area before the main airgun blasts begin, thus attempting to minimize the negative effects of the sound and pressure in the water. This assumption is grossly incorrect and has been scientifically disproven 2,3,4 but there is also a growing concern for animals which are unable to avoid the airguns, such as juvenile animals and invertebrates.
Why is sound so important in the ocean?
Contrary to oceanographer Jacques-Yves Cousteau’s description of the sea as a silent world, the ocean is actually a noisy place, where animals rely on sound to survive. However, man-made sound in the ocean is on the increase and scientific studies have demonstrated that marine animals, including whales, dolphins, turtles, seals, birds and even the smaller animals such as the crabs, squid and shellfish are negatively affected, in different ways5 by this additional man-made noise.
Animals’ use of sound is crucial to their life cycles6. Two ways in which animals use sound is by i) actively producing sound, such as whales who advertise their reproductive status with a song7
and those who ii) by listening to sounds emitted by other living organisms, such as their prey or predators, and to sounds produced by non-living factors, such as wave action on shorelines for acoustic cues, which aid in orientation and navigation8,9.
Marine animals, both large mammals and small invertebrates, produce sound for communication, reproduction, aggression, defence mechanisms, antagonistic interactions, courtship, group coordination, orientation, navigation and the identification of prey10. They rely on being able to produce sound which is heard and being able to hear sound and interpret sound for their own survival.
How do marine animals react to man-made sound in the water?
A number of responses have been reported. Physical responses include soft tissue damage11, embolisms12, damage to organs used in balance13, concussions in penguins14 , haemorrhaging15 and decompression sickness16. Hearing impairment has also been reported to cause Temporary Threshold Shift (TTS) or Permanent Threshold Shift (PTS). Threshold shift, or simply a type of deafness, refers to an increase in the minimum sound level required for an animal to hear a sound17. A TTS is followed by successful recovery to normal hearing thresholds after a given period of time in the absence of that sound. PTS, is when the sensory hair cells in the inner ear are permanently damaged and lost making recovery impossible18.
Stress is associated with the change in body chemistry19 and can be equally disruptive as physical damage, as it can have implications on sexual maturation, growth, reproduction and general ability to survive20,21,22. Perceptual effects can occur when there is an interference to sounds of interest which are drowned out or masked by man-made noise. The effects of this in the long term could have implications on breeding populations and thus population success23. Most animals may have the ability to counteract this and make minor changes to their vocalisations and behaviour, however, these modifications may be at a huge cost in terms of energy24 and associated life history strategies such as reproduction.
Behavioural responses to noise are dependent on various factors, including age, sex, presence of offspring, location and an individual animals’ previous encounter with a specific sound or noise. Behavioural responses include modification of vocal behaviour, displacement from important habitats, and other subtle responses including increased breathing rates, change in dive duration, time spent at the surface, rapid or erratic movements25,26,27,28,29,30, all with high energy costs31,32.
In South Africa, there is only a single study on the impact of seismic surveys, which was undertaken off Port Elizabeth within the feeding area of an African Penguin (Spheniscus demersus)33 colony. The study showed that penguins avoided their preferred feeding areas during seismic surveys and feeding further from the survey vessel when in operation. Upon termination of seismic surveys, the penguins reverted to their normal behaviour34, a behaviour which was also observed in Gray whales (Eschrichtius robustus) off Sakhalin Island in Russia35.
Why are mitigation measures used globally and in South Africa flawed?
Most scientific research on the impacts of seismic surveys has been conducted on whales and dolphins and as a result, most mitigation measures are to protect these animals, including in South Africa. Globally, it is becoming more evident that mitigation measures are not adequate36. It was recorded that ~250 male fin whales (Balaenoptera physalus) appeared to stop singing for several weeks to months during a seismic survey in the Gulf of Mexico. These animals resumed singing within hours or days after the survey ended37. Given male fin whales use vocalisations for reproduction by finding and attracting mates38, it can only be assumed that such an effect would be biologically significant39. In addition to this a blue whales (Balaenoptera musculus) ceased calling in the presence of a seismic survey at 10km away40. Conversely, a different group of blue whales appeared to have the opposite reaction and they changed their vocalizations41 by calling consistently more on days when the seismic surveys were actively ongoing, suggesting that seismic survey noise interfered with important signals used in their social interactions and feeding42. Marine mammals have also been recorded to avoid seismic noise by vacating the area43,44,45. Current mitigation measures have little or no effect on changes in mammal vocalizations and associated changes in behaviour.
What marine animals are affected by seismic surveys and how?
Whales and dolphins
Globally, it is accepted that seismic surveys are a probable cause of whale strandings and deaths46. In a study of stranded/entangled animals, it was found that between 36-57 % of bottlenose dolphins and rough-toothed whales had profound hearing loss, implying that impaired hearing could have led to their stranding / entanglement47.
The first recorded mass stranding in KwaZulu-Natal occurred on the coast of the iSimangaliso Wetland Park, a case of barotrauma in a Trues Beaked whale (Mesoplodont mirus) and a number of unusual strandings occurred during 2016, which also coincidently was the highest number of whale strandings in the history of the east coast of South Africa ever recorded48.
While no causal link between the seismic surveys and the increased incidences of whale strandings have been established in South Africa, it remains difficult to discount the coincidence given the absence of any other reported offshore activities that may have resulted in this, such as severe weather events. It must also be recognized that South Africa does not have the expertise, funding or manpower to undertake autopsies of freshly stranded whales and dolphins at a moment’s notice.
Since South Africa only banned commercial whaling in 1979, many of the whale populations are still recovering49, but as one significant pressure to whales was banned, another was introduced. It is imperative that the Department of Environmental Affairs take the history of the populations into account when creating acceptable mitigation measures.
Seals
Globally, other animals have shown to be affected by seismic surveys. Grey seals (Halichoerus grypus) and harbor seals (Phoca vitulina) displayed strong avoidance behavior, converted from a feeding behavior to a transiting behavior, stopped feeding, had slower heart rates and were hauling out onto land to possibly to escape the noise50,51.
Sea Turtles
Sea turtles only have a moderate ability to move from an area being surveyed52,53 but they are prone to TTS54. Loggerhead turtles (Caretta caretta) and green turtles (Chelonia mydas) have shown different responses including swimming to the surface and remaining there or staying slightly submerged55 and increased their swimming speed56. It is acknowledged that turtle behaviour is difficult to interpret57 and some studies have reported that turtles do not display signs of distress58.
Apart from the impacts of sound, adult turtles are known to becoming entangled in the seismic survey gear. In response to this, turtle guards were developed and built onto the tail buoys to prevent turtle mortality. This is not a legislative requirement in South Africa.
The nesting grounds of the Southern African loggerhead (Caretta caretta) and leatherback turtle (Dermochelys coriacea) populations are located on the northern east coast. Each year tens of thousands of turtle hatchlings enter the sea from the east coast and live their life on the surface of the sea at the mercy of the Agulhas current. Unlike their adult counterparts, hatchlings cannot swim fast enough out of the high levels of sound around a seismic survey vessel which is known to cause hearing loss.
Fish and fisheries
The implications of seismic surveys to the fishing industry are in two ways, the impacts on the fish themselves and the impacts on their behaviour. Fish have various body parts which are affected and respond to sound, they include their skeleton, reproductive maturity, swim bladder and ear bones59.
Many fish studies have recorded several effects including death60, physical damage to ear bones61, damage to swim bladders62,63, internal bleeding64, blindness65 and hearing loss66. Conversely, some studies have recorded no physical damage67,68,69,70,71,72, no hearing loss73, or changes in behaviour74,75,76, when certain species have been subjected to seismic survey noise.
Changes in catch rates and behaviour of rockfish77, cod78,79,80, haddock81, blue whiting82 and herring83, have been recorded which is of concern to the fishing industry. Conversely, an increase in catch during seismic surveys in water deeper than 200m has been reported84, while in the Faroe Islands, no impact to catch has been recorded85, however, based on interviews with fishermen, 75% believed they observed a reduction in catch as a result of seismic surveys86.
Invertebrates
Impacts of seismic surveys and ocean noise are not confined to vertebrates. Impacts have been recorded in squid87, shellfish88,89,90 and crustaceans91,92,93.
Zooplankton
In 2017 ground-breaking research showed that marine seismic survey air gun operations can kill large swathes of plankton, the basis of the marine food chain94. Furthermore, all larval krill, the primary food source of whales, were killed. Considering the enormity of these survey areas (PGS Survey 2018 = ~238 611 km2), the Agulhas current which can move at four meters per second, and the increase in biomass distribution in this area, it is imperative that research and a critical review on mitigation measures on organisms at the lower levels of the food chain are considered for mitigation95.
The jury is still out on the cumulative effects of ocean noise96 but it is accepted that it may have ecosystem-scale effects97, as well as consequences of the “knock-on” effects on animals, their prey and their predators within the food chain98. An understanding of ecosystem-scale effects of man-made ocean noise necessitates further research on lower trophic levels, involving a variety of marine taxa99.
The lack of consideration and blatant disregard for the principles of the National Environmental Management Act (NEMA, Act of 1998), which states that the precautionary principle or risk adverse approach should be applied in such cases where information is lacking, demands critical review of all suspected risk by the relevant government departments and organisations.
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