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    Sea Dragons - Home Range and Reproductive Cycle
    The common sea dragon is also known as weedy sea dragon. I prefer to call them common sea dragons or just sea dragons as many people confuse leafy sea dragons with weedy sea dragons due to the very similar name. Hence , I will only refer to them as sea dragons or common sea dragons. The common sea dragon, Phyllopteryx taeniolatus is only found in the southern half of Australia. Together with the leafy sea dragon (Phycodurus eques), they are the only representatives of what are commonly called sea dragons. They are closely related to sea horses, pipefishes and pipehorses and are all members of the Syngnathidae Family.

    One common thing about Syngnathidaes is that they male of the species hatches the eggs. In the case of the sea dragons, the eggs are deposited by the female on underside of the male's tail and the eggs remain there till they hatch.

    Common sea dragons are only found from about Port Stephens just north of Newcastle in New South Wales round to Geraldton in Western Australia. They are also found in Tasmania (where they seem to be bigger than the NSW ones).

    The best place in Sydney (and in fact in NSW) to see sea dragons is at the entrance to Botany Bay. The southern side of the bay's entrance is home to the most number of sea dragons known from one location. This includes the dive sites called The Leap, Inscription Point and The Monuments. Across the northern side of the bay, Bare Island has sea dragons all around it (I once counted 35 on one dive) and also near Henry Head and Minmi Trench. Other places in Sydney where many are seen includes North Bondi, Shark Point, The Split, South Maroubra and a few other places. The Gutter at Bass Point at Shellharbour also is well known for sea dragons as is all of the Jervis Bay dive sites.

    Sea dragonBaby sea dragon
    A close up of a common sea dragon at Inscription PointA baby sea dragon on the Deep Wall

    Jaime Sanchez-Camara from the Department of Animal Biology, faculty of Biology, University of Barcelona, Spain, has been studying common sea dragons since 2001. The following represents a summary from papers he has published (with others - see references - for the purposes of this article I will refer only to Jaime but some of the actions could well have been carried out by the other researchers) as well as information he supplied me when I took him diving.

    Common sea dragons preferred habitat appears to be the boundary between sand and a rocky reef, with an abundance of kelp (Ecklonia radiata) living on the rocks and free on the sand. Normal depth ranges appears to be from about six metres to up to 30 to 35 metres (the maximum depth being my personal observation).

    Since June 2001 Jaime has been studying the sea dragons at Inscription Point and The Monuments (he has also studied them at North Bondi but as that was a smaller sample, I will not be referring to it here). In June 2001 he began tagging sea dragons. He split his area of study into two sites that almost exactly correspond with the above dive sites as covered by me on my web site. For the purposes of this article, I will use my site names when referring to the study areas.

    At Inscription Point, Jaime identified a total of 47 sea dragons, 18 males, 19 females and 10 juveniles. At The Monuments, he identified 36 sea dragons, 17 males, 15 females and 4 juveniles (there were a further 9 identified at Bondi). These were identified from June 2001 to January 2002. Seventy of the sea dragons were tagged using an injection of fluorescent elastomer paint under the skin. Using a combination of four different colours and injecting this at certain spots on the right, left or top of the body, a simple and easy to later check record was made. The paint was later viewed using a ultra violet flashlight and special goggles. As I can attest, the tags were very easy to see and record for later checking. Twenty of the sea dragons were identified solely by natural markings (damaged appendages mostly).

    At Inscription Point and The Monuments, a transect line was laid from one end to the other. This basically covered a total of 700 metres, approximately equally in each dive site. The transect was laid along the reef adjacent to the sand edge, the most common place sea dragons are normally sighted here (and at most sites). The method of the research was to travel along the transect and record and mark the sea dragons seen. Later searches were carried out the same way. At the same time, the depth was recorded as was the size, sex etc.

    Sea dragonSea dragon
    A close up of a common sea dragon at The LeapEggs on a male sea dragon at The Monuments

    For Inscription Point the transect stretched from the left of where you enter the water out to the right. From the diagram provided in one of the references, it appears that the entry point is about mid-point on the transect. The majority of the sea dragons sighted were located near this point. The depth was approximately 9 to 12 or 13 metres.

    For The Monuments, the transect stretched from about 100 metres to the right of the entry point back another 250 metres into the bay. The majority were sighted right in front of the entry point at a depth of 10 to 14 metres, although five were seen right at the western end.

    Over the later dives, the location, depth and size of the sea dragons was also recorded. These surveys were carried out from June 2001 to June 2002. For Inscription Point, during the survey period, almost 70% of the sea dragons were resighted in the 3 to 6 month period, 40% in the 6 to 9 month period and 45% in the 9 to 12 month period.

    For The Monuments, during the survey period, over 60% of the sea dragons were resighted in the 3 to 6 month period, almost 60% in the 6 to 9 month period and 30% in the 9 to 12 month period.

    These resightings showed that generally, sea dragons only moved a very limited distance. The average was 110 metres for Inscription Point and 124 metres for The Monuments. The majority of the resightings for most sea dragons showed that they stayed in a much smaller range of the site. My estimation is that it was closer to 50 to 75 metres for a majority. Of the sea dragons first tagged (and I include visual identification here as well) in the Inscription Point site, only five were sighted in The Monuments site. Of these, both were originally sighted very close to the border. Of those first sighted in The Monuments, only four were seen in the Inscription Point site. While some of the sea dragons generally appeared to have very small ranges (six with less than 40 metres mostly), overall they ranged much further. Males and females overlapped ranges, with no apparent domination by any males. The latitudinal range of the sea dragons were all less than 50 metres.

    Sea dragonSea dragon
    A close up of a common sea dragon at Bare IslandA common sea dragon at Henry Head

    In regard to depth, the vast majority of sea dragons only ranged only 2 to 3 metres, although at The Monuments they ranged about 3 to 4 metres. Pregnant males were seen to travel into shallower water to give birth.

    Searches were carried out to the east of the Inscription Point site and to the south-west of The Monuments site. No tagged sea dragons were sighted at these locations. Searches were also made at Bare Island on the northern side of Botany Bay and again, no sea dragons were seen. However, in November 2004 Jaime contacted me about information on my Bare Island Isolated Reefs page that we regularly saw sea dragons there. He had done a number of dives but never seen any. I agreed to take him diving at this location. On 12 December 2004 a few members of the St George Scuba Club and I took him to this site. We sighted 10 sea dragons. One of the sea dragons was a tagged one from (I think) the Inscription Point site. This shows a movement of about 1.4 kilometres across sand and represents the longest known movement of sea dragons.

    Another part of Jaime's study was to look at the reproductive cycle and growth of sea dragons. As mentioned, when the sea dragons were tagged or identified, measurements were also taken. Using the measurements and after testing many growth models, a von Bertalanffy growth curve was used. This equation (which I will not detail here as I cannot reproduce it in html) uses known maximum size, known birth size and enables you to work out the exact (well as exact as you can) birth date and age of sea dragons.

    The surveys showed that sea dragons become pregnant about June and the last ones are pregnant in mid-December (although I have seen a number pregnant on 10 January 2004 and one pregnant on 28 January 2005). Pregnancies last between 30 and 38 days. Some of the males became pregnant twice in the one year, with a gap of 57 to 60 days between the end of one pregnancy and the start of another. The males appear to move into the shallows to give birth, presumably because there is more protection and food here. It appears that sea dragons may only become pregnant when water temperatures are on the rise.

    Sea dragons are born about 30 mm long. Within a month they have doubled in length to 60 mm. By two months they are about 95 mm and 125 mm at three months. The sea dragons reach 150 mm at four months and 200 mm at six months. After a year they are 300 mm and they reach a maximum of about 400 mm for females and 415 mm for males. Note that this reflects the growth rates in Sydney, the growth rates in southern NSW are slower but they appear to grow bigger (460 mm).

    Once sea dragons reach about 300 mm the sex can normally be determined. Males generally have thinner bodies and thicker tails while females have deeper bodies and thinner tails. It is believed that sea dragons are sexually mature about this size, that is, when they are about 12 months old.

    The following table sets out the size versus age.

    Length in mmAge in months

    I have seen one as small as 30 mm once, on 23 March 2002 at Pizza Reef. I saw one 75 mm long on 29 December 2000 at Bare Island Left. I have seen quite a few in the range of 125 to 150 mm. One thing that distinguishes juvenile sea dragons is that they have small appendages on their snout that later (normally) disappear.

    When males are ready to receive eggs, their tails get wider and thicker and become spongy. The eggs are laid onto the underside of the tail. Once the eggs hatch, they leave for a while indentations that can be clearly seen. When the eggs are almost due to hatch, sometimes the young can be seen inside, even eyes are visible. Each male sea dragon carries about 250 eggs at a time. At Botany Bay, the period that males are pregnant seems to coincide with increasing water temperatures (when the study was carried out, water temperatures started rising from about 14C in mid-July to just over 21C in mid-January or early February).

    When the males are about to "give birth", they appear to move into the shallows. Of the males, 93% at Inscription Point were pregnant at some time between September and December 2001 compared to only 50% at The Monuments. More males are pregnant in December than at any other time of the year (this corresponds with my observations).


  • Movement, home range and site fidelity of the weedy seadragon Phyllopteryx taeniolatus by Jaime Sanchez-Camara and David J. Booth, published in the Environmental Biology of Fishes 70, pages 31 - 41, 2004
  • Reproductive cycle and growth of Phyllopteryx taeniolatus by J. Sanchez-Camara, D. J. Booth and X. Turon, published in the Journal of Fish Biology (2005) 67, pages 133 - 148
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