By Dr. Tse-Lynn Loh
Dr. Tse-Lynn Loh is a postdoctoral research associate based at John G. Shedd Aquarium, Chicago. Her work is part of a joint Shedd-Project Seahorse partnership. This blog originally appeared on National Geographic Newswatch.
The wind blew steadily, whipping up whitecaps in the distance as our little long-tail boat made its way out of Panwa Bay, at the southeastern corner of Phuket, Thailand. My co-worker, Lindsay, already wore her dive gear, and our research assistants, Tum and Arm, hunkered down at the back with stoic expressions. We were about to get soaked.
Our boatman skillfully negotiated his way through the roiling waves as we left the bay, but we couldn’t escape the constant spray and waves that broke over the bow of the boat. Wiping saltwater from my eyes for the umpteenth time, I thought: I hope we see a seahorse today.
As part of my postdoctoral research position at the Shedd Aquarium, in collaboration with Project Seahorse, I’m searching this vast part of Southeast Asia for tiny seahorses (genus Hippocampus). My goals: to find out where seahorses live and what marine environments they prefer, how many species exist, whether seahorse populations here are under threat, and promote their conservation.
Species at Risk
Why are seahorses species of concern? According to the Convention of Trade in Endangered Species of Wild Fauna and Flora (CITES), seahorses are heavily traded on the global market, with millions of animals exported globally every year. Dried seahorses for traditional medicine comprise the bulk of the trade, but animals are also sold for curios and live in the aquarium trade. Bottom trawling is the biggest contributor of seahorses in trade: the incidental harvest of seahorses, or bycatch, accounts for up to 95% of dried seahorses. Given what we know about seahorse biology—they have low rates of reproduction and tend to mate for life—wild seahorse populations can easily be overexploited. Seahorses also live in important marine habitats that are among the most heavily impacted by human activities, such as coral reefs, seagrass beds, mangroves and estuaries.
The Science of Seahorses
Seahorses are too unique to be consigned to extinction. Unlike most other fishes, seahorses lack the aerodynamic body shape for gliding through water. Instead, their prehensile tails grasp structures on the sea bottom for support. In a wild departure from the majority of the animal kingdom, the male seahorses are the ones who get pregnant, protecting and nourishing embryos in a special brood pouch on their abdomens. Pairs of many species are monogamous, with couples greeting each other daily in a courtship dance, sometimes while changing colors, to reinforce the pair-bond.
Despite their magical characteristics, we really don’t know that much about seahorses. They tend to be rare, well-camouflaged, and patchily distributed, making them difficult to find and study. We know the biological traits of seahorses that make them vulnerable to overfishing, but we need to build upon existing knowledge to improve their conservation. Hence, my current efforts.
I’m in Thailand because according to CITES trade reports, Thailand exports the highest number of seahorses in the world annually (~5 million individuals per year from 2004-2008). Here, I’m working with the CITES authorities in the Department of Fisheries and researchers from Kasetsart University (Bangkok) to find out where seahorses live along the coast of Thailand, how many seahorses are out there, and if different species have habitat preferences. These data will help the Thai government to assess the seahorse trade in Thailand, and ensure its sustainability.
As we swam along the second 50 meter transect at our survey site, a patch reef off Koh Khai Nai (Khai Nai Island), I spotted a flash of yellow under an overhang—a seahorse! It was a female Hippocampus comes, the tiger-tailed seahorse, the first I had seen in days of surveys. We quickly took some body measurements with a caliper to minimize stress to the animal (a good-sized seahorse too, with a height of 14cm), and placed her gently back in the crevice. We found five seahorses on this patch reef, giving an approximate density of 1 individual per 1,000 square meters – definitely uncommon. As you might imagine, it takes a lot of effort, usually a few days of intense searching, to find seahorses in a large survey site. We’re getting used to seeing several “empty” transects, or search areas with no seahorses, as we progress, but that makes each seahorse we find more valuable to our database. Despite the wind and the waves, our trip to Koh Khai Nai in search of seahorses was time well spent, indeed.