Dolphins are some of the most intelligent creatures on our planet, yet we still don’t know a lot about them. One of the questions many biologists, or just average marine enthusiasts, have is whether or not dolphins can smell. This blog post aims to answer this question and provide a deeper understanding of these majestic sea creatures to readers and scientists alike.
Sensory Adaptations for Marine Animals and their Use
Marine animals have many types of sensory systems that vary between species and are crucial to their survival success. Some sensory receptors present in marine animals include passive listening, haptosence, and the lateral line system. Echolocation is also a significant sensory adaptation in odontocete cetaceans.
Variability in Sensory Adaptations Across Habitats
The degree to which each species will rely on each sensory adaptation depends on their general life strategies. Additionally, the habitat they tend to live in, such as open ocean versus coastal waters, plays a significant role. The difference between shallow versus deep water, and clear versus turbid water, also influences their sensory adaptations.
Sensory perception helps an individual detect objects in their physical environment, including food, prey, and predators. It also aids in identifying communication signals and discerning social partners. For example, auditory senses are quite well-developed in dolphins and whales so that they
can listen for signals from other members of their pod or potential mates, as well as potential prey. Further, seals and sea lions have a very well-developed haptosence. This is inferred via long, sensitive “whiskers” on their face and allows them to detect disturbances in the water.
Echolocation is also a well-known and widely appreciated adaptation that many citations rely on for the detection of prey and navigating their environment. This form of sensory reception is extremely fascinating. It demonstrates one of the many inconceivable evolutionary adaptations mammals have undergone over the millions of years since they have re-entered the aquatic environments. Echolocation involves the emitting of brief sound pulses, or clicks, and then listening for the echoes that bounce back to create an auditory map of their environment.
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Olfactory of Marine Mammals
So, how do marine animals smell? Well, it is a bit different for aquatic animals than it is for terrestrial organisms. In terrestrial organisms, airborne odors dissolve across the mucus covering the nasal cavity and bind to special proteins that send signals to the brain through Cranial Nerve I (CN I)). This allows for the ability to smell. However, CN I also appear to be active in response to waterborne stimuli as well, demonstrating the sensation of smell is possible underwater for some species. Since water is more dense than air, it can carry chemicals in the water further than the air can, which allows for chemical stimuli (smells) to travel over great distances.
Some examples of marine animals capable of smell include porpoises, mysticetes, cartilaginous fishes, and many other organisms we may have not even discovered yet! However, mysticetes are interested in that they can only detect smell in the air, not the water. This means their olfactory systems are not of much use while they are going about their daily activities and must surface if they wish to smell.
And of course, sharks have a very acute sense of smell, enabling them to track down prey from hundreds of meters away. The chemicals released from decomposing whale carcasses or from fish chum can therefore be sensed by sharks and let them know there is a meal waiting for them. Cartilaginous fish have two special organs on their head that can sense chemicals in the water, where water flows into the fish’s nose.
As the fish moves forward, the water passing through its nose creates a difference in pressure,
which helps it detect smells in the water.
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Chemo sensory in Dolphins: Do Dolphins Actually Smell?
Cetaceans have lost a significant number of their olfactory receptors over the course of evolution, and odontocetes in particular have seen the greatest loss of these sense organs including the olfactory tract, bulb, and CN I. So, to put it simply, dolphins can’t smell in the same capacity that cartilaginous fish can smell waterborne odors, but they do have their own mechanism for interpreting these smells.
Gustation in Dolphins: How Dolphins Taste
Dolphins have a third chemical sense known as the vomeronasal organ, which is located at the base of the nose. Although its ducts open behind the incisors in the mouth, the organ is able to sense stimuli on the palate and essentially “taste” these smells through impulses transmitted via CN V from the oral cavity to the brain. This perception is now referred to as quasi-olfaction, and may offer the missing link that researchers have been looking for regarding dolphin chemo sensory reception.
Research has shown that dolphins can interpret (or taste) sour, bitter, and salty flavors, allowing them to detect different chemicals in the water that may be released from their prey, predators, or companions
(such as urine and feces). Further, dolphins have shown to be capable of discriminating between different flavors, going towards a food source that they know they prefer – another example of “tasting the smells”. It is also probable that dolphins are only capable of detecting such chemicals and flavors at a short distance, making it only useful in close-range circumstances rather than longer-range distances.
Conclusion
In conclusion, the answer to whether or not dolphins can smell is not a clear-cut, definitive line of yes or no. Rather, it is an extremely complicated and not well-understood area of marine research that requires further investigation to obtain solid data. What we do know is that where dolphins lack in their olfactory senses, they make up for in their oral senses. The sensory system of these majestic creatures continues to fascinate us, and as technology and research advances there will hopefully be more answers revealed about our aquatic friends.
References:
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- Can sharks really smell a drop of blood a mile away? Ocean First Institute. (2023). Retrieved on May 8, 2023 from https://www.oceanfirstinstitute.org/what-we-do/research/citizen-science-project/
- Clark, S. (2016, August 21). The Beach Bums of the Galapagos. In Darwins footsteps. Retrieved on May 8, 2023 from http://darwinsfootsteps.com/the-beach-bums-of-the-galapagos/#prettyPhoto
- Kishida, T., Thewissen, J. G. M., Hayakawa, T., Imai, H., & Agata, K. (2015). Aquatic adaptation and the evolution of smell and taste in whales. Zoological Letters, 1(1). https://doi.org/10.1186/s40851-014-0002-z
- Klimley, A. P. (2012). Genetics of sharks, Skates, and Rays. Biology of Sharks and Their Relatives, 503–520. https://doi.org/10.1201/b11867-25
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- Kremers, D., Célérier, A., Schaal, B., Campagna, S., Trabalon, M., Böye, M., Hausberger, M., & Lemasson, A. (2016). Sensory perception in cetaceans: Part I—current knowledge about dolphin senses as a representative species. Frontiers in Ecology and Evolution, 4. https://doi.org/10.3389/fevo.2016.00049
- Lubis , M. Z. (2016). Behaviour and Echolocation of Male Indo-Pacific Bottlenose Dolphins (pp. 21-27). LAP LAMBERT Academic Publishing. https://doi.org/10.13140/RG.2.1.4603.7520
- Perrin, W. F., Würsig Bernd G., & Thewissen, J. G. M. (2002). Encyclopedia of Marine Mammals (second). Academic Press.
- What do bottlenose dolphins eat? American Oceans. (2021, February 18). Retrieved on May 8, 2023 from https://www.americanoceans.org/facts/what-do-bottlenose-dolphins-eat/
