Human life is noise.
Cars and buses rumble down streets, sirens blare day and night, machines bleep and whir whilst the sky is filled with metallic birds, and even in the most remote places, someone will probably be blasting music out of a speaker. We may be aware that silence is golden, but rarely do we consider the effect our noise has on other species, particularly those deep beneath the ocean surface.
Sonar is used by military bases to detect submarines, and by oil and gas companies to determine the best spots to drill the sea bed to exploit the rich resources there. Since the development of this technology, whale strandings across the world have sharply increased in number.
When scuba diving, humans are constantly warned not to ascend too quickly for fear of getting ‘the bends’, the lighthearted nickname for decompression sickness, a potentially highly debilitating disorder that occurs when nitrogen dissolved in the blood and cerebrospinal fluid forms bubbles as water pressure decreases. Divers are strictly instructed to ascend at a uniform pace with set times and depths at which to pause to allow accumulated nitrogen bubbles to dissipate. The tissues most likely to be affected are those with a high fat content, including the brain and spinal cord. Unfortunately, other animals do not have such strict rules based on experimental results, much less have recompression chambers or oxygen masks to prevent long term effects of decompression sickness.
For beaked whales, a species that swims at great depths for extended periods of time, sonar in oceans causes activation of the stress response. In these gentle giants, this prolonged activation causes their heartbeats to increase, contrary to the adaptation required for deep diving which reduces oxygen consumption and prevents the accumulation of nitrogen bubbles in blood vessels. This alone can cause decompression sickness in the whales, but additionally the fear they experience causes them to rapidly rise towards the ocean surface, allowing nitrogen bubbles to build up. The incapacitated whales then are unable to swim efficiently and often end up beaching themselves as a reponse. The introduction of midfrequency active sonar in US naval bases in the late 1950s, operating at 4.5-5.5 kHz, has been linked to 121 mass strandings between 1960 and 2004 of Cuvier’s beaked whales.
Necropsies of beached whales have produced disturbing results, and show just how severe the physiological response to sonar can be. Studies on beached beaked whales in Greece and Almeria between 2002 and 2014 found gas bubbles in their veins, organ blood clots and haemorrhages of ‘varying severity’ in multiple tissues throughout the bodies. A study by the same researchers found the stress responses were increased in whale populations that were infrequently exposed to navy sonar, whereas populations residing in areas where sonar techniques were more commonly used became less distressed. Changes in behaviour of beaked whales has been observed in such areas, including a technique named ‘evasive maneuvering’, even at very low levels of navy sonar activity. It is unsurprising that at higher levels, there is simply a response of fear rather than one of adaption, as the flight response of the whales is immediately activated.
After banning sonar in waters around the Canary Islands in 2004, previously a hotspot for mass strandings, no further strandings have occurred. However, it is clear that current policies are not worldwide and do not do enough to protect marine wildlife, particularly when it comes to monitoring ocean sound pollution. In 2008, the Military of Defence claimed it was ‘extremely unlikely’ that sonar from Royal Navy military operations on the Cornish coast was linked to the stranding of 26 dolphins, yet post mortems showed no signs of prior disease, and the MoD had previously denied the presence of military activity in those waters. Clearly, there is an unwillingness for governmental organisations to take responsibility for ensuring such activities have minimal effect on vulnerable wildlife.
Organisations should use well-monitored locations and implement mitigation policies. The problem is that each species may respond differently to sonar, and therefore any policy making must take this into consideration. Perhaps the most simple action would be to restrict operations and training to areas of the ocean that are not home to myriad species of whale or dolphin, rather than attempting to find sonar frequencies that have a less extreme effect on cetaceans. In 2008, a US survey (restricted to Washington DC) found that 75.2% of respondents believed the military should be made to adhere to environmental regulations during peacetime; 75.8% of respondents also believed that “sonar use should be moderated if it impacts cetaceans”. This demonstrates a public interest in the preservation of marine wildlife, which governmental organisations should consider.
Since it is unlikely that governmental departments of defense will simply ban all military activity in the range of whales and dolphins, a balance must be struck in terms of ensuring that mass strandings linked to sonar exploits cease to occur, but allowing military operations to proceed, provided there is just cause for them to. Methods for such measures include controlled exposure experiments that assess behavioural responses to characterised sound sources, which may allow identification of exposure levels that warrant action to avoid disastrous future impacts on wildlife.
For beaked whales, it is possible to detect the presence of the animal, then modify the sonar accordingly or avoid the animals completely. Such technology includes use of boats or aircraft for visual surveys of migration patterns and location of beaked whales, passive acoustic detection to locate whales by listening to their calls, as well as commercially available active sonar detection. Using sonar to detect animals to prevent them being affected by sonar seems, however, slightly contradictory to the cause. It has been shown that whilst this is the most efficient detection method, it is certainly able to be heard by various species, including those being tracked, and therefore may alter their behaviour. Thus, any results may potentially be unreliable and wholly unhelpful for producing accurate location and movement profiles to be used in military or even policy making.
The question therefore remains: what is the best plan of action?
It is clear that military operations with such disastrous environmental effects cannot continue without alteration. A compromise must be reached whereby operations can occur, but there are measures to ensure that they are carried out in areas of the ocean that are not home to creatures sensitive to sonar; furthermore, frequencies that do not cause physiological and acoustic distress should be used. Undoubtedly this is a complex challenge, but one that is essential to prevent future beaching events and potential changes to aquatic wildlife behaviour, which could wreak havoc on marine biodiversity.
In a world where the effects of human activity on the marine environment are becoming increasingly more obvious and destructive, focus on prevention and mitigation is key, and should be at the forefront of any political agenda. Sonar may be silent to humans above the sea, but its effect on aquatic species is deafening.