Recent visitors to the second floor of the Audubon Aquarium of the Americas may have noticed something a little different about its seahorses.

Each member of the aquarium’s resident herd of seahorses has been tagged with a “necklace” of soft thread and tiny laminated pennant, part of a program to help researchers understand more about the popular yet mysterious fish. Every tag displays a three-digit number that definitively identifies each individual seahorse. The tags have an electrical wire casing that loosens as the tagged seahorses continue to grow.

“Seahorses subtly change color based on mood and surroundings, making individuals quite difficult to tell apart,” said Audubon Aquarium aquarist Joshua Tellier. “These tags will help us keep records of related animals, animal origins, gender and age.”

Developed to track wild seahorse populations, the tagging technique has been used in studies around the world. Yet despite these studies, said Tellier, due to their elusive, secretive nature, there is still a great deal to learn about seahorses, especially in the wild.

“Seahorses don’t necessarily form large schools in central places in the wild,” said Tellier. “To a certain extent, they are solitary animals, and that makes them very hard to spot.

“Studying them in the wild is labor-intensive, and there is a deficiency of data regarding wild populations, especially when it comes to big questions like migration and population size.”

But, he said, a number of studies suggest that populations of some seahorses, such as northern or lined seahorse, have dropped significantly over the past few decades. Techniques such as these are critical in learning more about their numbers, he said.

Belonging to the genus Hippocampus (hippos meaning “horse” and kampos meaning “sea monster”), seahorses are unique for many reasons, not least of which is their distinctive and deceptively fragile-looking equine appearance.

Swimming upright, their bodies encased in segmented bony armor, they use their curled prehensile tails to anchor themselves to underwater vegetation as well as each other. Due to the simple nature of their digestive systems — they lack teeth and a true stomach — they must feed almost constantly to survive and are voracious ambush predators, consuming thousands of small aquatic creatures, such as brine shrimp and plankton, each day.

There are more than 40 known species of seahorse. On average, the Audubon aquarium has approximately 50 lined seahorse adults in its care, along with approximately 55 potbelly seahorses.

Found along the eastern United States’ coast, the Gulf of Mexico, and down through the Caribbean toward Venezuela, lined seahorses live in shallow water among seagrass beds, mangrove forests and other types of aquatic vegetation.

“People tend to think that seahorses are delicate,” said Tellier. “But in many other ways they are extremely hardy. Other than man, they don’t have a whole lot of natural predators. They don’t have a lot of muscle or fat deposits like you see in other fish, and their outer bony armor is extremely tough. They can also tolerate changes in water salinity — at least in the short term — that would quickly kill other types of fish.”

While the data on wild seahorses is sparse, said Tellier, in the short term, data gleaned from tagging captive seahorses may be helpful in promoting sustainable populations.

“And long term, we may not only get a better idea of how long seahorses live in captivity, but, over time, how seahorses in general go about their lives,” said Tellier. “By allowing us to track individual seahorses and attach meaningful information to specific animals, I cannot even speculate what kind of information we will discover, but I do think that it will be interesting to look back in three years and see interesting trends that we didn’t know about before.”

“For aquariums, seahorses are almost like the final frontier,” said Tellier. “These animals teach me something new every time I come to work; there is a sense of wonder about them and they affect all people that same way, whether you are a guest at the aquarium, or, like me, a person who is lucky enough to get to work with them.”