Dolphins are marine mammals, and just like land-dwelling mammals, they require air to breathe. Unlike fish, which are non-mammalian animals, dolphins do not possess gills (gills allow fish to extract oxygen from the water), so they must come to the surface of the water to breathe. While dolphins breathe air like other mammals, they also breathe uniquely to most mammal species.
For dolphins to inhale and exhale, they must breathe through their blowhole, not their mouth. This is because there is a major difference between dolphins and land mammals, which is that dolphins live exclusively in the ocean. To maximize their survival and make life easier, they have developed separate holes for breathing and eating.
So while humans (and most land mammals) can both breathe and eat through their mouth, dolphins can only breathe through their blowhole and are incapable of breathing through their mouth; in fact, dolphins don’t even possess vocal cords. This is very important for several reasons.
First, when a dolphin dives underwater, it is actually holding its breath. To prevent the dolphin from accidentally sucking up the water when hunting for and consuming prey, the dolphin’s esophagus (food passage) remains separate from its nostrils and lungs (air passage), connected to its blowhole.
If a dolphins air passage was connected to its mouth and it accidentally inhaled water while hunting for food underwater, there is a good chance the dolphin would get water in its lungs and possibly drown, so in theory, the dolphin’s air passage mustn’t be connected to the dolphin’s mouth.
Second, by having a blowhole on the top of its head, a dolphin can rest at the surface of the water without having to lift its head all the way up to breathe. This can be extremely important when dolphins are at rest near the water’s surface as it makes it much easier for these marine mammals to acquire the oxygen they need with as little effort as possible.
Dolphins are known as conscious breathers, meaning they never fall completely asleep because if they did, they might drown, so when they go into a resting state, half of their brain remains alert to allow them to obtain oxygen when necessary easily. Note: Remaining semi-awake can also help the dolphin react quickly to potential threats or predators by maintaining awareness of its surroundings.
When a dolphin is seen spouting water from its blowhole, it is actually water collected around the blowhole when the dolphin was submerged; it is not water that has entered the dolphin’s blowhole and/or lungs which could cause the dolphin to drown or panic.
For a dolphin to dive into the water without worrying about inhaling water when it is submerged, the muscles surrounding the dolphin’s blowhole contract prevent the dolphin from accidentally taking in any unwanted water.
As far as how long a dolphin can hold its breath varies depending on the species. Some dolphins can only hold their breath for a few minutes (3 – 7 minutes) while underwater, while other species have been known to hold their breath for over 20 minutes during deep dives.
Most of what is known about a dolphin’s ability to hold its breath is from observations of their lives. Their ability to hold their breath may be a result of their physiology.
Some dolphins may possess better lungs, organ systems, and breathing control than other species, or it could be the fact that some dolphins hunt for food at deeper depths, so they generally take longer dives than other species.
Threats that can cause drowning
For dolphins being able to hold their breath for extended lengths of time has been an evolutionary transition. Before inhibiting the ocean, these marine mammals’ ancestors were believed to be land-dwelling animals once. Over the course of millions of years, they evolved into fully aquatic ocean living dolphins.
Despite huge advances in evolution, dolphins are still very limited in their ability to dive for extended periods of time. Compared to other land mammals such as humans, the length of time a dolphin can hold its breath seems quite amazing; however, because they are mammals, they face the same threats all mammals do when it comes to long drives/or an inability to rise for air.
The first major issue dolphins face underwater is drowning. If a dolphin gets caught underwater and is unable to resurface, it can easily drown and die.
This can occur if a dolphin gets caught in a fishing net or other fishing hazard, gets harmed or stuck in an area where constriction is being performed, becomes injured or unconscious from a hard impact, or gets trapped underwater by an object.
In many cases, dolphins are excellent swimmers and can avoid getting trapped by the most common underwater objects. However, they can still be at risk of becoming trapped in fishing equipment that’s intended to capture fish, as this is one of the most common ways dolphins are known to drown.
In these instances, a dolphin may lunge at a condensed group of fish, thinking that they are easy prey only to get trapped by the net, or they can swim into the net as it may appear fairly transparent and invisible. Being unable to rise back to the surface, they drown as all mammals would.
The second major but less common threat dolphins face when diving underwater is decompression sickness. Decompression sickness occurs when a mammal (particularly humans) dives deep underwater and then rise to the surface too quickly.
The quick rise and release of pressure on the body cause bubbles to develop in the body and bloodstream, leading to significant medical conditions and even death.
Although dolphins have developed ways to help prevent decompression sickness from happening in extreme cases, it has been observed that dolphins may also get decompression sickness (aka the bends).
Observations of beached dolphins have found occurrences of developing gases and bubbles in the bloodstreams of several dolphins that have been beached.
It is believed that dolphins may rise to the surface too quickly due to loud ambient noises that can interfere with their echolocation or sense of direction. Loud explosions, jet engines, and sonar have all been thought of as possible causes of dolphin decompression.
Solving the problem
To solve the problems of fishing hazards and noise pollution, organizations and governments may set up policies to minimize the usage of certain objects, materials, or noises that can potentially harm dolphins.
Depending on where these marine mammals live, several policies have already been put into place to minimize whales and/or dolphins’ chances of being harmed.
Individuals and companies operating boats may be required to maintain a certain distance from known cetacean habitats, especially boats/ships that perform regular whale watching activities.
Commercial fishing boats may also be required to follow strict policies regarding the use of their nets, where they fish, and how they monitor and/or dispose of their materials.
In addition to setting policies, research is also being performed on the activities that are thought to cause unnatural dolphin deaths to determine if such activities are causing an issue and, if so, how to best resolve the issue.
Issues found to harm marine mammals such as dolphins may be sent to specific governing bodies or organizations such as the International Whaling Commission to be reviewed and weighed regarding possible interventions.