The potential impact of deep-sea mineral extraction and polymetallic nodule collection on whales, dolphins and other marine life must be carefully considered and managed.
Noise
It is known that noise created by ocean industries such as shipping, drilling and tidal turbines can affect whales, dolphins and other marine life. Impacts range from increased stress levels and behavioural changes to injury and strandings. It is not surprising, then, that concerns have been raised about the potential noise effects of polymetallic nodule collection.
Technology trials conducted in the deep ocean show that surface vessels will be the main source of noise associated with polymetallic nodule collection. This is because no cutting or drilling is required to lift polymetallic nodules from the seafloor.
We know from other ocean industries that there are several methods that can be deployed to avoid or minimize the impact of vessel noise on marine life. These include noise abatement systems, the use of specialist Marine Mammal Observers who are trained to monitor for the presence of marine mammals before potentially disruptive activity begins, and the use of underwater microphones and specialized software to detect and identify marine mammal vocalizations in real-time.
Another important impact mitigation strategy entails avoiding noise in the SOFAR (Sound Fixing and Ranging) channel, which is a zone of the ocean where sound travels further than in other parts. Many marine animals, such as whales and dolphins, rely on low-frequency sounds to communicate over long distances using this channel. Thus, it is important to avoid operating noisy equipment (such as pumps) in the SOFAR channel, which in the Clarion Clipperton Zone typically occurs at 800 to 1500 meters water depth.
Sediment plumes
Cetaceans spend most of their time in the upper part of the ocean as this is where their food is, and most species are found in the top 1000 meters of the water column. Of the species that have been observed in the Clarion Clipperton Zone, there is only one species (Ziphius cavirostris) that dives below 1250 meters, with a deepest known diving depth of 3000 meters. The shallowest seafloor depth of the Clarion Clipperton Zone, on the other hand, is 4200 meters, meaning there is at least 1200 meters of separation between seafloor activities such as deep-sea mineral extraction and the deepest diving whale. Importantly, extraction systems can and should be designed to avoid discharges at depths where cetaceans occur.
Ship Strikes
Ship strikes are a major cause of mortality for larger cetaceans. As shipping traffic increases, so too does the risk of collisions, particularly in busy marine regions where cetaceans and shipping routes overlap.
When it comes to deep-sea mineral extraction, the Clarion Clipperton Zone (for example) is not a major shipping route and there’s room for cetaceans to move away from a noise they don’t like.
The use of specialist Marine Mammal Observers who are trained to monitor the presence of marine mammals will also help ensure ship strikes do not occur.
Future work
Cetacean surveys are an important part of environmental baseline research required for deep-sea mining and other ocean activities. What we know so far is that much of the cetacean activity in the CCZ is likely migratory in nature and cetaceans are unlikely using the CCZ as a breeding ground.
Where applicable, the appropriate mitigation methods will need to be incorporated into Environmental Impact Assessments, Environmental Impact Statements, and Environmental Management and Monitoring Plans to ensure that cetacean populations remain safe.