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Dragons in name alone


 
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David Booth, Professor of Marine Ecology at the University of Technology Sydney, introduces us to sea dragons. These unlikely looking fish which can be as large as 50 centimetres in length, are endemic to Australia (living only in the southern Australian waters). This actually protects them from the fate suffered by their relatives, sea horses, which are more widely distributed across the oceans and are often caught and ground up for aphrodisiacs. In Australia sea dragons, and the smaller related sea horses and pipe fish are protected to various levels around Australia, and although regarded as threatened there is often insufficient evidence to verify that status. Destruction of the kelp among which they live and feed poses the most likely potential threat - be it from industrialisation or effects of climate change.

 

 
There are two species of sea dragons. The Weedy sea dragon is found from Port Stephens all the way south to Tasmania and across to Western Australia and the Leafy sea dragon is found further south around South Australia. Interestingly, there is a difference in the number of appendages in the Weedy sea dragons according to whether they live further north in New South Wales or in the southerly regions around Tasmania. To research the life history of sea dragons, a team tagged cohorts in Botany Bay and Bondi, in Sydney, and were followed from 2002 until 2009. That is a much longer life span than pipe fishes which last two or three months (which means some pipefishes must be well adapted for solely a winter life while others must cope wirth the very different conditions of an estuary in summer) and longer than sea horses which live for around three years.

 

 
The fish are injected with inert elastomer (silicone-based) paint which fluoresces so they are easily tracked by underwater ultraviolet torches (shown above). The team has found that sea dragons generally have a home range of no more than about 50 metres throughout their entire life, making them useful monitors of the health of the local environment. They eat tiny crustaceans that live among their seaweed habitats.

In October the female will produce some 100 eggs which the male inseminates and then places them on his tail where they grow (shown below). This male parental care is quite common in the relatively small number of fish species that have nests. With the eggs in tow male dragons will move to shallower waters and sometimes disappear among the seaweed for a while, usually around November.

 

 
Professor Booth regards these gentle creatures as delightful to study. Even to catch them for tagging is simply a matter of reaching out and holding them carefully while the dye is injected, the fish then drifting away placidly. They are dragons in name only.

David Booth was interviewed for A Question of Balance by Ruby Vincent.  All images are of Weedy sea dragons and are by Jaime Sanchez-Camara and provided by David Booth. Summary text was prepared by Victor Barry,  December 2010

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