CSIRO PUBLISHING www.publish.csiro.au/journals/mfr Marine and Freshwater Research, 2006, 57, 737–745 Density,habitat use and behaviour of the weedy seadragon Phyllopteryx taeniolatus (Teleostei :Syngnathidae) around Sydney, New South Wales,Australia Jaime Sanchez-Camara A , David J. Booth B,E , John Murdoch C , David Watts C and Xavier Turon D A Paisajes Marinos Aquadec S.L. C/Al Salam 5, 18680 Salobreña, Granada, Spain. B Department of Environmental Sciences, University ofTechnology, Sydney, PO Box 123, Broadway, NSW 2007, Australia. C The Sydney Aquarium, Aquarium Pier, Darling Harbour, NSW 2000, Australia. D Department ofAnimal Biology (Invertebrates), Faculty of Biology, University of Barcelona, 645 Diagonal Ave, Barcelona 08028, Spain. E Corresponding author. Email: david.booth@uts.edu.au Abstract. The vulnerability of marine fish species, particularly those inhabiting coastal waters, is an increasingly important issue in marine conservation. Although the weedy seadragon Phyllopteryx taeniolatus (Lacepede, 1804), a syngnathid fish endemic to southern Australia, is legally protected in New South Wales, there are no studies on population density, habitat use and behaviour to support this protection.We investigated the abundance, sex ratios and distribution of the weedy seadragon at three sites near Sydney,Australia. The distribution, density and sex ratios of seadragons were temporally stable, suggesting no large-scale seasonal migrations. Estimated population densities varied among sites from 10 individuals per ha to 65 individuals per ha, with sex ratios close to 1 : 1. Survival rates from one encounter to the next (approximately weekly) were high, being slightly lower for males (0.985 ± 0.006, mean ± se) and females (0.987 ± 0.005) compared with juveniles (1.000 ± 0.000). All size classes and both sexes were most common near the border of kelp and sand except when exhibiting hiding behaviour, when they were more often found in kelp beds. Kelp beds were the least-used habitat when feeding. Pregnant males tended to hide more often than other groups and therefore were more frequently found in kelp and kelp patches. Seadragons tended to be solitary, although pairing and grouping behaviour was also observed. Results of the present study show that weedy seadragons are resident in the same area throughout the year and have a strong affinity with heavily weeded rock and/or sand habitat. It is therefore recommended that the current species-based protection laws be used in concert with habitat-protection zones as a necessary measure to ensure the conservation of weedy seadragon populations. Extra keywords: common seadragon, endemic fish, grouping, habitat choice, sex ratios. Introduction The assessment of extinction risk to marine fishes cuts across many disciplines, including population biology, ecology and behaviour (Dulvy et al. 2004). Notably, species most at risk from over-fishing and habitat disturbance are those with sparse distribution, small home ranges and low fecundity (Foster and Vincent 2004), all features characteristic of syn- gnathids (seahorses, pipefishes, pipehorses and seadragons). Syngnathids are a highly unusual group of fishes read- ily identified and positively perceived by the general public. They have the potential to act as emblematic, flagship taxa that could be used to arouse conservation concerns within the public arena. The weedy seadragon, Phyllopteryx tae- niolatus (Lacepede), is a charismatic syngnathid that would be particularly suitable for use as an icon for conservation. Weedy seadragons are unique to southern Australian waters and the only member of the genus Phyllopteryx – such mono- typic taxa often receive high priority in conservation policies and in evolutionary studies (Vézquez and Gittleman 1998). They are one of the largest syngnathids at up to 45 cm length (Kuiter 1993), with a distinctive shape and striking colour pat- tern. They are found in coastal habitats and are often observed at close quarters by recreational divers. They may also be found stranded on beaches after storms. In addition, there are long-term monitoring and educational programs based on this species (see Baker 2000; Howe 2002). The weedy seadragon is considered ‘Data Deficient’ on the IUCN Red List of Threatened Species (2006) and is listed as ‘Lower Risk’ (conservation dependent) by the Department of Envi- ronment and Heritage of Australia (Pogonoski et al. 2002). © CSIRO 2006 10.1071/MF05220 1323-1650/06/070737