Reaching New Depths
A number of marine mammals have been known to dive deeper than is standard for their family. Weddell seals have been recorded at depths of 600m, southern elephant seals at depths of 1500m, and the famous Sperm whale can dive dive to depths of 1200m for over an hour. However, the title for deepest diving marine mammal goes to the Cuvier’s Beaked Whale (Ziphius cavirostris), which has been recorded at depths of 2992m – over 500m deeper than the height of Ben Nevis and Snowdon combined! After the initial recording of 2,992m, Gregory S. Shaw and his team tested the tags again to ensure they weren’t malfunctioning.
Experts have considered the record breaking dive to be unusually deep, but Cuvier’s Beaked Whale is still known to regularly dive to depths of 2000m. This whale, despite the depth of the dive, is much smaller than the Sperm whale (males can be up to 6.9m, and females up to 5.5m), so scientists are interested in how Cuvier’s have adapted to dive to such deep depths multiple times a day. Depth of dive isn’t the only record that this whale has broken for marine mammals. The longest recorded dive for Cuvier’s was 137 minutes.
Considering the size of Cuvier’s whale, scientists like Dr Sascha Hooker have been studying the diving behaviour of these mammals. The two major issues that these whales face in their repeated dives are withstanding the pressure and maintaining enough oxygen for the duration of the dive. The Cuvier’s beaked whale will, prior to diving, exhale the contents of its lungs by up to 90%, reducing it’s buoyancy (effectively sink, rather than swim to the deep). As the whale dives, its lungs collapse due to an increase in pressure. The whales ribs are not completely connected to the central sternum, and have the ability to fold towards the tail (acting like a hinge) which helps prevent damage from compression.
After the lungs have collapsed, the whale has to utilise oxygen stored in its muscles and blood rather than the lungs. As well as having particularly effective gas exchange in the lungs (using up to 90% of the air in the lungs, as opposed to 15% in humans), whales have large amounts of haemoglobin (storing oxygen in their blood) and myoglobin in their muscles. Deep diving mammals have a high blood-to-body-volume ratio, and amounts of muscle myoglobin which supply the whale with large amounts of oxygen, up to ten times more concentrated than myoglobin in human muscles. To prevent unnecessary oxygen consumption during dives, the whale reduces the flow of blood to parts of its body, including the kidneys and liver, and reduce their heart rate.
Like many marine mammals, the body shape of the Cuvier’c beaked whale is torpedo-like for hydrodynamic efficiency. To improve this profile, the beaked whale has ‘flipper pockets‘ (also found with Sperm Whales), which the flippers can fold into during dives to reduce water resistance, allowing the whale to glide through the water (and make stores of oxygen last longer).
SciShow – A quick summary of how marine mammals can hold their breath for so long.
In recent years, scientists have been looking into the potentially harmful impacts that anthropogenic activities could have on this species. A study in 2006 focused on the potential impacts intense shipping activity could have on the foraging behaviour and hearing of Cuvier’s whales. Articles about the potential effect humans have on strandings are being published with increasing frequency, attributing the stranding to collisions, entanglements in fishing gear and military activity.
Cuvier’s beaked whales use echolocation while hunting, which can be affected by anthropogenic noise pollution, and this can reduce foraging efficiency. Military activities have been associated with stranding events, and can result decompression sickness in individuals (after rapidly surfacing following deep dives) in response to sonar activities. The most serious impact these have are gas bubbles, which have been observed in stranded whales. Trauma to the auditory system has also been observed. As there is currently limited information on the sound of these whales, naval vessels are unable to detect the Cuvier’s beaked whale prior to starting military activities.
Due to the elusive behaviour of this whale, not much is known about its life history or the abundance of the species. Most of the information learned about this species comes from strandings.
It is only recently that scientists have been able to track the dives of Cuvier’s beaked whales using satellite tags. Despite gaining some knowledge about these whales, and how they have adapted to such dives, it is still unknown how the whales avoid high-pressure nervous syndrome. Long-term studies are currently focusing on the impacts sonar have on whale behaviour and their recovery.