Whales and dolphins spend a good chunk of their time close to the surface, especially when they are resting or socializing. With no shade around, do whales get sunburnt? Do they have a natural defense against UV radiation? In this article, we come to the surface of the ocean to see how UV radiation affects whales’ skin and how their bodies can protect them against overexposure.
Let’s Talk about the Sun
Our sun is 91.449 million miles away, which may seem far. Yet, we still greatly feel the effects of it. The sun sends over its energy in three ways: visible light, waves you cannot see but feel (infrared radiation), and energy you can neither see nor feel (ultraviolet radiation). Most living organisms need all forms of the sun’s energy to thrive, as long as they come in small doses. Ultraviolet radiation can be very detrimental if we receive too much of it. Overexposure may have negative effects such as sunburns, skin cancer, and skin aging. Overexposure can also lower your body’s ability to fight illness in the long run.
Fortunately for us, the earth is equipped with a defense mechanism: the ozone layer. However, human-driven interactions have depleted this protective layer in certain areas, along the poles for example. Even though it has gotten better as the years have progressed, we can still feel its damage. We have many methods for avoiding over-exposure: staying inside, applying sunscreen, wearing hats, umbrellas, UV protectant clothing, etc. Most animals have fur, wool, hair, scales, or feathers to protect them from the sun, but it is not the case for our slippery hairless friends; whales, and dolphins.
Ouch! That hurts
Scientists reported that UV radiation plays a significant role in whale skin lesions. When looking at skin biopsy samples, scientists look for small blisters and melanin pigments that indicate prolonged sun exposure. Scientists can also assess mitochondrial DNA (mtDNA) UV-induced damage. Essentially, mtDNA has a higher mutation rate than nuclear DNA. These mutations cause DNA damages that accumulate throughout the life of an individual. In this case, mtDNA becomes a reliable indicator for cumulative UV exposure.
Tanning to prevent damage?
Scientists noticed that whales that have darker skin, like fin whales, have fewer skin abnormalities. Laura M. Martinez-Levasseur and her team’s research in 2013 suggested that higher melanin levels were linked to a reduced level of microscopic skin lesions. Their study provided further evidence that melanin can protect animals such as whales against UV exposure. For example, they noticed that migrating blue whales tan in the tropics to help darken their skin and protect it from the sun.
The team noted that sperm whales had a different strategy to protect their skin from over-exposure. Sperm whales spend quite some time at the surface between each deep dive. Soaking their skin in the sunlight allows their bodies to create protective proteins that repair the damaged DNA. This is similar to how humans produce antioxidants.
What about captive dolphins?
Now, what about the whales and dolphins in captivity? They spend much more time at the surface than their wild counterparts, which puts them at higher risks of sunburns. Human caretakers thus have to step in: they must provide the necessary amounts of shade in dolphin’s habitat enclosures. If shade is missing and the dolphins are at risk of getting sunburns, their trainers need to apply zinc oxide sunscreen on the dolphins’ skin.
Sources and further reading
- Martinez-Levasseur, Laura M., et al. “Whales use distinct strategies to counteract solar ultraviolet radiation.” Scientific Reports 3.1 (2013): 1-6.
- Martinez-Levasseur, Laura M., et al. “Acute sun damage and photoprotective responses in whales.” Proceedings of the Royal Society B: Biological Sciences 278.1711 (2011): 1581-1586.
- Morales-Guerrero, Blanca, et al. “Blue Whale (Balaenoptera musculus) Skin Contains Eumelanin and Pheomelanin.” Aquatic Mammals 45
- Spectral reflectance of whale skin above the sea surface: a proposed measurement protocol
- Ultraviolet (UV) Radiation and Sun Exposure
Did you enjoy this post about how whales fight sunburns? Find out how they stay warm in cold waters:
Naomi Mathew is a PhD student at University of Louisiana at Lafayette. She works on bioacoustics in marine mammals from the Gulf of Mexico. She is the co-founder of Whale Scientists. You can read more about her here