One-of-a-kind golden shark discovered in Costa Rica
Scientists say the golden shark has a rare combination of skin conditions that has never been seen before.
Last summer, a group of sport fishermen was casting lines off the coast of Tortuguero National Park in Costa Rica when one of their hooks caught a creature the likes of which no one had ever seen before: a six-foot nurse shark with white eyes and golden skin.
The astonished fishermen released the shark, but not before snapping a few photos to share with local scientists.
“At first, nobody could believe it. A lot of people said the picture must be manipulated,” said Daniel Arauz Naranjo, executive director of Costa Rica’s Rescue Center for Endangered Marine Species (CREMA) and a National Geographic Explorer.
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But upon further investigation, Naranjo and his colleagues determined that the photos were not only genuine, but also that the shark’s coloration was the product of a rare skin condition known as albino-xanthochromism.
Their findings, which were published last month in the journal Marine Biodiversity, were especially surprising because the condition impedes a crucial survival tactic used by nurse sharks—camouflage.
A unique combo of two rare genetic conditions
Albino-xanthochromism is a combination of two rare genetic conditions: albinism, which reduces the amount of melanin in the body and leads to pale skin, hair, and eyes; and xanthochromism (also known as xanthism), which causes unusually yellow or orange pigmentation in animals.
“Albinism and xanthism typically occur separately,” said Marioxis Macias, a PhD student at Federal University of Rio Grande in Brazil and co-author of the paper. “Finding both conditions in the same individual was indeed a surprising and unprecedented discovery.”
While sharks have been found with albinism and xanthism, this pale-eyed, gold-skinned shark is the first nurse shark documented with both traits, according to the new paper. Experts who spoke with National Geographic also suspect it’s the first shark of any species documented with both traits.
“Beyond xanthism, there have been reports of leucism (partial loss of pigmentation) and even piebald patterns in a few species, including nurse sharks,” said Melissa Cristina Márquez, an independent shark scientist who was not involved with the new paper.
Márquez called the discovery of the golden shark “fascinating,” adding, “It’s always exciting to see examples of rare coloration in sharks because it reminds us just how much natural variation exists, even in species we think we know well.”
How camouflage aids survival
Found in warm, shallow waters in the western Atlantic and eastern Pacific oceans, nurse sharks spend most of their time near the seafloor in search of prey hidden beneath the sand.
Their skin typically ranges from light to dark brown, a coloration that allows them to blend into their sandy surroundings. This natural camouflage enables nurse sharks to sneak up on their prey and evade predators. Though formidable foes when they’re large, nurse sharks are preyed upon by everything from tiger sharks to crocodiles when they are small.
The golden shark found in Costa Rica was full-grown and appeared healthy at the time of its capture, suggesting that the shark’s unusual coloration hasn’t hindered its ability to survive. But how is this possible? Naranjo has a theory.
“This shark was found near river mouths, where the water is very murky. Maybe it discovered that being in water where the visibility is poor is a good strategy,” he says.
Márquez says this is one of many possible explanations for the shark's survival, including a lack of natural predators in the area or even unique behaviors by the shark.
Regardless of how the shark managed to reach adulthood despite sticking out like a sore thumb, Naranjo is glad the shark defied our expectations. The shark’s presence, he says, “is good for the species and good for Costa Rica. Who knows, maybe people will come here to try and snorkel with it.”
The discovery of this shark, Naranjo says, also serves as a reminder that all those who venture into the ocean, be it scientists, fishers, or snorkelers, should share their unique findings.
“The ocean still can still surprise us,” he says.
