Morphometric regressions for the endangered Knysna seahorse, Hippocampus capensis, in the Swartvlei Estuary from mass stranding events

Abstract

The Knysna seahorse, Hippocampus capensis, is listed as endangered on the IUCN Red List of Threatened Species, with the only known, apparently isolated, populations occurring in the Knysna, Swartvlei and Keurbooms estuaries along the south coast of South Africa. The Swartvlei Estuary population is the most genetically distinct (Mkare et al. 2017). Despite all three known populations occurring within protected areas and there being no commercial or subsistence use of the species, population sizes are still thought to be declining because of habitat degradation across much of its range (Pollom 2017). Environmental management authorities have outlined strategies for the conservation of H. capensis, including listing it as a species of special concern in the Estuarine Lower Level Plan of the Garden Route National Park (South African National Parks 2020) and setting management objectives for the Keurbooms population in the Keurbooms–Bitou Estuarine Management Plan (Western Cape Government 2018).