The Knysna seahorse is the world’s only fully estuarine seahorse and is endemic to the Garden Route’s Knysna, Swartvlei and Keurbooms Estuaries. It is also the only seahorse listed as Endangered on the IUCN Red List of Threatened Species. This warrants concern for the well-being of this iconic Garden Route fish and Knysna’s flagship conservation species.
Words by Clement Arendse. Originally published in SANParks Times.
The Knysna and Swartvlei Estuaries fall within the Garden Route National Park. The Knysna Estuary hosts the largest, most stable seahorse population and the Swartvlei Estuary hosts a smaller population that is subject to large natural fluctuations. Swartvlei Estuary is also subject to natural mouth closure on a near annual basis, which may lead to mass periodic die-offs of seahorses after the river mouth breaches and the water level rapidly drops.
SANParks has initiated a programme to monitor the fluctuating population in the Swartvlei Estuary. The Knysna seahorse is a rather enigmatic species, perfectly camouflaged and often difficult to locate in the dense eelgrass beds it is known to inhabit. This is a trait seahorses use to avoid predators, and to capture prey. Knowing the distribution of the Knysna seahorse in the estuary is particularly important, as identifying areas of highest abundance focusses conservation efforts.
Seahorse distribution and abundance are determined using underwater visual survey techniques like SCUBA and snorkelling. Another method is to carry out rapid surveys after mouth breaching events when many seahorses become stranded due to the rapid drop in water levels. These seahorses eventually die as they cannot reach deeper water fast enough.
Through a citizen science project under this seahorse programme, locals from surrounding towns who registered as part of the project will assist SANParks with returning these stranded seahorses to deeper water. The number of stranded seahorses per area will be recorded by citizen scientists before they are given a second chance at life. Any dead seahorses collected will be handed over to SANParks staff for analysis.
The information gathered by citizen scientists will also help determine if areas that flood when the mouth is closed are used by seahorses as habitat.
Citizen scientists will therefore play a key role in helping reduce mortality of seahorses in Swartvlei Estuary and provide invaluable information on their distribution and habitat, aiding management of this iconic species.