The biology, ecology and conservation of White's seahorse Hippocampus whitei

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Seahorses are iconic charismatic species that are threatened in many countries around the world with several species listed on the IUCN Red List as vulnerable or endangered. Populations of seahorses have declined through over-exploitation for traditional medicines, the aquarium trade and for curios and through loss of essential habitats. To conserve seahorse populations in the wild, they are listed on Appendix II of CITES, which controls trade by ensuring exporting countries must be able to certify that export of seahorses is not causing a decline or damage to wild populations. Within Australia, seahorses are protected in several states and also in Commonwealth waters. The focus of this study was White’s seahorse Hippocampus whitei, a medium-sized seahorse that is found occurring along the New South Wales (NSW) coast in Australia. The species is listed as ‘data deficient’ on the IUCN Red List and there is little research information available to assist in the conservation of the species. Research on H. whitei was undertaken from 2006-2009 and primarily focused on determining the species’ life history parameters, its distribution and relative abundance, habitat preferences and site fidelity, and response to marine protected area (MPA) protection and habitat modification. Research primarily occurred within Sydney Harbour and Port Stephens. Field surveys found that H. whitei is endemic to coastal estuaries along 300 km of NSW coastline. It is a medium-sized seahorse (max LT 162 mm) that displays rapid growth (Port Stephens: females L∞ = 149.2 mm and K = 2.03 per year and males L∞ = 147.9 mm and K = 2.52; Sydney Harbour: females L∞ = 139.8 mm and K= 1.28 and males L∞ = 141.6 mm and K=1.22), becomes sexually mature at approximately 6 months, and can live for up to 5 years in the wild. The species displays life-long monogamy with several pairs observed breeding over three consecutive breeding seasons, and strong site fidelity with seahorses remaining at the same site for up to 56 months for males and 49 months for females. Adult male and female H. whitei exhibited a significant preference for sponge and soft coral Dendronephthya australis habitats whilst juveniles had a strong preference for gorgonian Euplexaura sp. habitat. Hippocampus whitei in Port Stephens were significantly less abundant within the no-take MPA and there was a negative correlation with predator abundance. Long-term monitoring of H. whitei in Port Stephens found that populations declined over a period of six months for no apparent reason; however, they recovered within three years. A manipulative experiment undertaken on protective swimming nets in Sydney Harbour found H. whitei had a positive association with epibiotic growth and proximity to the sea floor. An experiment on the effects of flash photography found it had no significant effect on movements, behaviour, or site persistence of H. whitei and concluded that flash photography by divers is a safe and viable survey technique for this species. The information obtained from this study should contribute towards a reassessment of the species under the IUCN Red List and also provides the necessary data to ensure adequate management of the species within NSW waters.
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