Life History of the Weedy Sea Dragon
Sea Dragon© Jaime Sanchez-Camara
Weedy or common sea dragons are only found in the waters off southern Australia. While commonly sighted by divers and collected for the aquarium trade there is insufficient information available about to make an assessment of the species risk of extinction. Because of this they are listed by the World Conservation Union (IUCN) as 'data insufficient'.
Like their relatives the sea horses, the male sea dragons brood the eggs. A male indicates that he is ready to brood eggs by wrinkling the lower half of his tail, where the female deposits about 250 eggs.
Professor David Booth and PhD student Jaime Sanchez-Camara from the University of Technology, Sydney, recently investigated the reproductive cycle and growth of the common seadragon in their natural environment in-situ around Sydney.
Measuring an adult © Jaime Sanchez-Camara
A number of interesting findings were made during the study including: sea dragons have well defined home ranges but the males move to more suitable site to look after their eggs and give birth to their young; some males have more than one brood per season with around 60 days between broods; breeding peaks just prior to the time of warmest water temperatures; the young grow very quickly in the first few months when the water is warm and there is an abundance of food (small mysids) but they do not grow as large as animals found further south; both males and females become sexually dimorphic between 11 and 16 months and at a length of 30 cm and sexually mature at 28 months and 33cm. Tagging studies have revealed a longevity of seadragons of up to 6 years, compared with only several months for pipefishes the team has investigated.
These findings indicate that sea dragons have a lower recruitment rate than seahorses and pipefish and that their populations may be more vulnerable to habitat destruction and collecting for the aquarium trade. Because survival of the young is dependent on the presence of food species (mysids) that are very sensitive to pollutants degradation of their habitat may be their main threat.
