Noise in the ocean comes from different sources. Some are natural (seismic activity, tectonic movements), and some are human-made like sonars, underwater bombs, etc. Deep diving whales rely on echolocation to hunt for their prey. The noise from human activities can affect these whales in quite extreme ways. In this post, we will talk about the impact of human-made noise on deep-diving whales. We will focus on the example of Cuvier’s beaked whales and military exercises
Cuvier’s beaked whales are incredible divers
Cuvier’s beaked whale or Ziphius cavirostris is one of my favorite whales. We had the opportunity to hang out with these elusive little guys when we were working in Italy, on the Ligurian Sea. They can be incredibly challenging to study because they spend most of their time deep underwater. We remember sometimes having to wait 1h15min on the boat for the whales to resurface. They alternate their dives between “short” 15 minute dives and long dives that can last more than two hours! These whales hold the mammalian record for the deepest and longest dive: 2992m (9816 ft) for 2 hours and 17 minutes. UPDATE: These whales have now broken this record: 3 hours and 42 minutes!
Ziphius cavirostris likes to feed on cephalopods they find deep in underwater canyons. To do so, it relies on echolocation, just like other toothed whales.
Here is the problem … Noise affects whales
Sonars from heavy vessel traffic and military exercises impact the survival of Cuvier’s beaked whales. The first mass stranding event reported for Cuvier’s beaked whales was in 1996 in Greece. In May 1996, between twelve and fourteen (depending on the sources), Cuvier’s beaked whales were stranded on the shore, and eight died. The military exercise associated with this mass stranding was conducted the day before the whales died. A NATO oceanographic research center organized the training. It consisted of “shallow water acoustic classification” with an experimental “towed vertically directive source” sonar (TVDS), which produces high levels of low and medium frequency sound to detect diesel and nuclear submarines.
More mass stranding events associated with military exercises occurred over the next years in the world.
There are two types of effects coming from sonar activities.
Short term effects are extreme
- Exposure to loud noise can cause intense short-term responses in the whales’ bodies. Some whales were found beached in the Bahamas after a military exercise, bleeding from their ears and eyes, which is a sign of sound-caused trauma. The crazy loud noise can also cause the whales to panic and push them towards the surface to breathe. Unfortunately, when the whales try to surface too quickly, it can cause decompression sickness or “the bends.” When you emerge too quickly, the nitrogen from the air forms bubbles in your blood and tissues and can cause irreversible damage. British scientists discovered it during a necropsy (post-mortem examination) of Cuvier’s beaked whales stranded in the Canary Islands.
Long term effects can impact a population’s survival
- Long term effects of sonar noise pollution include the decrease in the whales’ fitness. Fitness is the capacity to survive and reproduce healthily. One study found that the whales were moving away from sonar sources and returning to the areas once the sonar activities stopped. Another study found that whales exposed to sonar activities had longer inter-deep dive times. Inter-deep dive time is between the end of the last deep dive and the beginning of the next deep dive. This causes a decrease in the number and duration of deep dives and reduces these whales’ capacity to find food (Falcone 2017). Because whales cannot correctly find food, their long-term fitness decreases, and the impacts on a whole population can be disastrous.
Now let us know what you think. How could we help with the conservation of these whales? What laws should countries implement? Let us know in the comments!