Checking in on the world’s most endangered seahorse

By Ally Stocks

The Cape or knysna seahorse ( H. capensis ) is listed as 'Critically Endangered' on the IUCN Red List.  Photo: Ally Stocks/Project Seahorse

The Cape or knysna seahorse (H. capensis) is listed as 'Critically Endangered' on the IUCN Red List. Photo: Ally Stocks/Project Seahorse

When I travelled to South Africa’s Western Cape province to look for the Knysna seahorse — the world’s most endangered seahorse species* — I thought I would be tromping through mucky, shallow water in waders for hours to find one or two animals. I didn’t expect that within two minutes of meeting Louw Classens, a PhD student and expert on the species, we would find four seahorses in a ten-metre stretch of dock, without even getting in the water!

My trip to South Africa was part holiday, part seahorse detective mission, and Louw was at the top of my list of people to see. We met on Thesens Island, located in the middle of the Knysna estuary. In the bright South African sunshine, she led me down to a small marina where a few boats were docked. Louw is energetic and friendly, and we got along right away. Pointing to mesh netting a few centimetres below the water’s surface, she said, “There’s a juvenile male.”

I couldn’t believe my eyes. This seemed too easy. During my own field work in Vietnam last year, I’d spent hours diving to find other, more common species such as the hedgehog and common seahorse (Hippocampus spinossisimus and H. kuda). The Knysna seahorse is mottled black-and-brown, lacks a coronet, and is around 10cm in height. Louw and I chatted away about seahorse conservation while she pointed out a few other individuals – we watched them swim around, foraging for food in the mostly man-made habitat of the marina.

The Knysna seahorse (H. capensis) is South Africa’s most famous seahorse. It’s thought to be restricted to three estuaries – the Knysna, Swartvlei and Keurboom, all found in the Western Cape Province — and its tiny geographical range makes it extremely vulnerable to human pressures such as habitat destruction. Hence its ‘Engandered’ status on the IUCN Red List of Threatened Species.

Though it’s the most-studied seahorse in South Africa, there is still a lot to learn about it. Louw is the lead biologist on the Knysna Seahorse Status Project (KySS) , which is part of the larger Knysna Basin Project. The KySS aims to understand and protect the Knysna seahorse population, and is currently surveying various habitat types to understand the seahorses’ behaviour in different areas of the estuary. They hope to expand their studies to the nearby Swartveli and Keurboom estuaries. A University of Johannesburg study is also underway to determine whether genetically distinct populations exist in the three estuaries.

The local community is very supportive of the KySS, and a few locals have been stewards of the seahorse population for decades. Peet Joubert, a former manager of SANParks, has watched the Knysna seahorse population fluctuate due to freshwater floods, local development, and changes in sewage treatment.

“We do our best to protect the seahorses, but the variation in population size seems to be immense,” Peet told me, recalling times he’d spent diving in the estuary. “After the floods, seahorses were much harder to spot, but as populations are able to recover, their numbers bounce back.”

The KySS is hoping to better understand the nature of the Knysna seahorse’s reliance on its local habitat, and its ability to withstand external pressures. That way, conservation and management can be better informed for the protection of endangered species.

So what about South Africa’s other seahorse species? In addition to H. capensis, the thorny seahorse (H. histrix) is also found here. I traveled up the eastern coast of South Africa with Thembisa Jordaan from Kwazulu-Natal Wildlife to visit one of iSeahorse’s newest trends monitors. Thembisa and I sweated for hours in a car without air conditioning until we arrived in Sodwana, part of the iSimangaliso Wetland Reserve and one of South Africa’ top diving destinations. There we met up with Triton Divers, a local dive group doing excellent underwater research, particularly on H. histrix.

Eve Perrins (left), the author (center), and Thembisa Jordaan (right).  Photo: Ally Stocks/Project Seahorse

Eve Perrins (left), the author (center), and Thembisa Jordaan (right). Photo: Ally Stocks/Project Seahorse

Unlike the Knysna seahorse, H. histrix can be found throughout east African waters and as far abroad as Southeast Asia. It’s not limited geographically, but like many other seahorse species, it is threatened by overfishing. Eve Perrins, the director of Triton, took us on a couple of fantastic dives around Sodwana. Although we didn’t spot any seahorses, her enthusiasm was undimmed. The local population appears to be in good shape: Her dive group regularly spots thorny seahorses at a deep nearby reef.

As for the other South African species, I travelled to aquariums, research libraries, and even a botanical garden on the western coast to find everything I could about them. Like most quests for seahorse information, the answers remain as elusive as the sneaky little creatures themselves. Keep your eyes peeled for an upcoming article that I’m working on with Louw for the full story on South Africa’s seahorses!

*Of the 48 species on the IUCN Red List of Threatened Species, 26 are currently listed as ‘Data Deficient,’ meaning that we don’t yet know enough about them to determine their conservation status.

Ally Stocks (@ally_stocks) is an MSc student with Project Seahorse.