Life on Balmoral Net

Author: Colin Piper, Photo by: John Turnbull

The URG has undertaken a research project to monitor the re-growth of marine life on the newly replaced rope netting which encloses the Balmoral baths in Sydney harbour. The netting is often been visited by URG divers returning from boat dives. The site is an excellent location to "use up" the dregs of air in a scuba cylinder.

The nets main attraction is the resident community of sea horses. (White’s Seahorse – Hippocampus whitei). These cute creatures are very delicate, yet agile as they swim through the net swinging from their tails. Refer to the Australian museum for further information on these creatures.

Two URG research tags have been placed at the eastern (seaward) side of the netting some two metres apart. The tags sit in about 2-3m of water. Over the coming months this site will be re-visited and a series of photo taken to form the basis of a longitudinal study.


Colin Piper (who initiated this project) has kindly provided some background observations prior to the URG tags being placed onto the net in October 2001.

6 Apr 2001

Colin Piper counted 39 sea horses on the overall net. There were several large holes in the net from storms. This damaged net (the old one) being hung on the outside of the board walk which surrounds the pool. Colin reported seeing an angler fish on an earlier dive there as well not far seaward from the wharf

16 Aug 2001

There is a new net hung inside the old one. The new new net is the one presently in situ (on the inside of the boardwalk). It was very new and clean (i.e. no growth at all on it). Colin counted 73 sea horses on that dive, 55 were on the new net and VERY visible needless to say. The balance were on the old net.

21 Sep 2001

Colin counted 75 seahorses, all on the new net as the old one had been removed. Parts of it were lying on the sand with a considerable amount of fish life using the remains as shelter. The new net was no longer pristine. It was covered with the first stages of growth. There were also several new stainless steel retaining wires at various places around the pool. These were very shiny and new.

12 Oct 2001

It is estimated that the net has now been in place for about 3 months. Significant amounts of algae are now present. Prolific juvenile fish life move in and around the net. Two URG tags were installed on the eastern side of the net. No sea horses sighted between the tags, although about 20 where seen on the net overall. Significant pollution of the sea bed was evident (plastic bags, fishing nylon etc)

16 Oct 2001

Colin Piper counted 30 sea horses on the whole net this day The net was more covered and the stainless steel wires were also well covered. The latter was surprising because they were so clean only 3 1/2 weeks before. Most of the old net had been removed from the bottom.

18 Nov 2001

Dive completed following some light rain. Increased growth since November. Two sea horses were counted on the net panel containing the URG research tags. The general consensus of those who dived, was that the sea horse numbers are still less than compared to before the net was replaced. The harbour bottom around the net continues to be littered with rubbish, including a mobile phone. The "heavy metal" contamination from the leaking battery is of great concern.

30 Nov 2001

Robert Pearce and Colin counted 50 sea horses on the overall net. There was no specific count at the URG tag site. They noticed, and reported to a Council ranger that there was some damage to the net as a result of the large seas. This was when we heard about the possible removal of sea horses by people in the dead of night. Should this alarming news prove to be true, it is more important than every to continue to monitor this site.

22 Dec 2001

Only one sea horses at the URG tag site.

28 Dec 2001

Colin observed 2 at the URG tag site. Colin also noted that it appears that the sea horses are more abundant on the sheltered sides of the net (i.e not on the sea-ward facing areas).

1 Jan 2002

A late evening dive recorded zero sea horses at the tags. There had been some very large tidal movements, and at one stage approximately half the net had been exposed at low tide. Algae growth on the net is rapid in the warm summer water. The URG tags placed in October had to be cleaned to remove excessive growth.

28 Jan 2002

On an early morning dive, David Oatley counted 22 seahorses on the entire net, none at the URG tag site. Colin Piper's earlier hypothesis about there being unequal distribution was proved true. (Refer diagram on right). Twenty seahorses on the section indicated with red arrows and, two on the remainder of the net.

Note the level of marine growth in photo A from the northern side. The URG tag site has markedly less growth in which the seahorse may shelter. Photo B - Some of the other marine animals spotted on this dive.

3 Mar 2002

"Clean up Australia Day" was conducted today at Balmoral. The URG removed a significant quantity or rubbish including plastic bags, fishing rods, milk crates an even a shopping trolley. A less than thorough count was conducted with only about 12 seahorses seen, with 1 at the tag site. A more complete count will be done later this month.

10 Mar 2002

A small group of URG divers drop in for a count, following a morning dive elsewhere. Only 5 seahorses were counted from the beach east to the URG tag site. Zero were at the tags. The net panel at the tag site has very little growth, and hence the zero count is not surprising. A key question is why there is such as unequal distribution of growth around the perimeter? Three theories exist (if you have one let us know!):-

(a) Large recent influx of fresh water from rain has purged the net.

(b) There is a prevailing current around the bay which "ventilates" one side of the net more than another.

(c) The URG tag site is close to, and faces a cluster of moored boats. Could the anti-fouling paint be leeching and stripping the growth from the net in this area?

Time to start some experimentation!!

1 Apr 2002

Four divers were unable to positively locate the tag site on the net. The green stinger net seems to have collapsed down the main netting. Either the tags have been removed, or are now obscured by the stinger net. No seahorses were counted near the tag site, this probably being due to the stinger net smothering the main net.

Eight seahorses were counted from the tag site back to the beach, via the wharf. Colin Piper has the treat on witnessing a marine bird swimming underwater with him.

10 Apr 2002

Colin Piper did a count sea horse count this day. Colin was joined by Tina Brain, so it was a very accurate count. They did it from INSIDE the net…much easier to see the critters, and made it possible to see the net which is usually hidden/obscured by the stinger net.

Between the beach and the wharf they counted 5. In the area of the wharf and the northern swimming platform there were 14. Between there and the corresponding swimming platform on the southern side there were 9. None were seen on the URG tag site. Between the southern swim platform and the beach there were 9

In total, 37 were counted. There were a couple which appeared to have, they were pretty 'swolen'. Both in the wharf area. There were a few very small ones, and one was quite big…interestingly enough…this one was near the URG site.

Last year on April 6th Colin counted 39 in all. Taking the same area counted, this year there were 34. This is the first time that there has ever been a proper count on the southern side of the pool, where there were only 3 .

The net is mostly well covered with growth…though I leave those observations to others more qualified than I am to comment. The stinger net has the effect of 'rubbing' clean the upper part of the actual net very visible from inside the pool. Colin recommended that we always count from inside the net in future, as it is so much easier to see the seahorses.

5 May 2002

A partial circuit of the net was made following a dive elsewhere. This quick dive started at the tag site and proceeded south. The tags are covered in fine barnacles, but the net is very clean in terms of algae, with no seahorses being present. Only one other was seen on the swim to the boatshed.

6 Jul 2002

36 seahorses around the net perimeter. The tag site could not be found. Last month the tags were totally un-readable, so they may just been missed. The net is very badly damaged. Ther