Scientific rambling
Imagine diving into the sea with your scuba gear on, and you might see the pitch-black deep sea below, the open waters above, and the dense ...... of fish surrounding you
Most of what you use to perceive the world around you in the sea comes from the vision that is limited by a narrow pair of diving goggles, and the little touch that is isolated from the wetsuit. Have you ever wondered if the world perceived by dolphins in the same space is completely different? After all, they have electrical sensing, magnetic sensing, and strong echolocation capabilities.
In 1981, magnetic sensing was first confirmed in dolphins: American researchers found magnetic fragments closely related to neuronal connections from the brains of four stranded dolphins. Scientists were surprised by the discovery, suggesting that it may have a sensory function or a role in nautical navigation.
In 1985, another group of researchers discovered the relationship between cetacean stranding locations and the Earth's geomagnetic field: several species of whales and dolphins actually tend to run aground in places with lower magnetic field strength. If cetaceans use the Earth's magnetic field to find their bearings, one hypothesis is that areas with weaker magnetic fields increase the likelihood of stranding due to confusion in bearing recognition.
In 2014, a team of scientists from the University of Rennes conducted a behavioral study that allowed us to demonstrate that dolphins have magnetic perception. They tested the spontaneous response of six captive dolphins to two objects of the same shape and density: the first contained a magnetically charged piece of neodymium (a metal), while the second device was completely demagnetized. When the device contained a piece of strongly magnetized neodymium, the dolphin approached it faster. This can lead to the conclusion that dolphins are able to distinguish between these two stimuli based on their magnetic properties.
The data supports the hypothesis that cetaceans can use the Earth's magnetic field to determine their own position, so when the magnetic field is weak, there is a greater chance of stranding.
When prey moves their muscles and bones, it emits a faint electric field. Some marine predators, such as dolphins, are able to sense prey through these electric fields, especially in areas of the seafloor where visibility is reduced.
In 2012, scientists first discovered electrical sensing in dolphins – structures known as tentacle crypts that act as electrical receptors. In this study, the researchers noted that the tentacle crypt has a well-innervated ampullary structure, which is reminiscent of the ampullary electrical receptors of other species, such as bluegils (sharks and rays). These tentacle crypts are thought to be electrical sensing receptors that are capable of receiving small electric fields emitted by prey in aquatic environments.
The same study also found behavioral evidence of electrical perception. A male Guiana dolphin was trained to respond to electrical stimuli produced by small and medium-sized fish by orders of magnitude. For example, a goldfish 5 to 6 centimeters long produces an electric field of 90 microvolts per centimeter and a peak energy of 3 Hz.
Experiments have shown that dolphins can sense weak electric fields, and their sensitivity is comparable to that of platypus's electrical receptors. In 1985, a German-Australian team made the first definitive demonstration of the electrical reception of the platypus, which was able to find the battery under pitch black water, in Canberra. In 2023, a team of researchers found similar detection thresholds in bottlenose dolphins using the same behavioral tests.
Echolocation is a more sensitive sense than receiving an electric or magnetic field, and it involves dolphins making a series of clicking sounds. The vibrations produced are highly oriented and move forward. When a sound wave touches the surface of an object, it returns and is perceived through the dolphin's jaws. In this way, they can perceive sound waves very well without the need for an outer ear.
Thanks to this information, dolphins can not only know the location of the target, but also deduce the density of the target: the dolphin can tell from a distance of 75 meters whether a sphere with an inch in diameter is made of solid steel or filled with water.
The dolphin's impressive ability to "see with its ears" doesn't stop there. Dolphins can hear the sound waves emitted by their fellow dolphins, and in this way, they can "share" the information they detect with team members and coordinate their actions.
To sum up, we know that dolphins can determine their position in the ocean through magnetic perception, can search for prey in the sea through electrical perception, and can also sense the distance, shape and even density of surrounding objects through echolocation.