The East Australian Current (EAC) is a phenomenon that pushes warm water from tropical regions down our easterly coast every summer for a few months. This year it has been pushing especially strong and as a result we have seen many new tropical fish arriving in Sydney, many extending their previous southerly range limits by considerable kilometres. Here is a gallery of some of the more special ones to have arrived in Cabbage Tree Bay Aquatic Reserve, some of which are first time arrivals here!
2022/2023 has seen an especially strong Eastern Australian current (EAC) pushing many tropical larvae further south than usual. As a result the aquatic reserve in Cabbage Tree Bay, Sydney is witnessing large volumes of tropical visitors, especially Speckled Damselfish, Moorish Idols, and many other species. The observation of juvenile Princess Damselfish and Bluespot Damselfish is quite unique as the southern limit of their normal distribution is Bundaberg in Queensland.
In addition a Snowflake Moray Eel has taken up residence on the south side of the harbour. This too is a tropical species rarely spotted south of Coffs Harbour.
Whitebarred Gobies have also been found inside Sydney Harbour.
Despite the relentless rain La Nina has brought to the East coast all summer, and flooding that made it undiveable for weeks, this summer has seen a huge number of tropical fish larvae arriving in the aquatic reserve, and warm waters has allowed many to grow significantly in the last few months. The latest is this black and white Doubleheader, at the southernmost point of its described range. They usually are a social fish inhabiting shallow reef.
The Dogtooth Tuna is a tropical fish prized by game fishermen due to its strength. It’s normal distribution range extends south to Brisbane, with infrequent sightings around Coffs Harbour. Cabbage Tree Bay hosted a small group of three juveniles this week, a significant extension to the range. Being fast and shy though proved difficult to capture a good photograph in somewhat murky water.
The Pennantfish or Threadfin Trevally (Alectris ciliaris) has been spotted recently in the aquatic reserve. The juveniles in the picture above have long trailing fins that deter predation due to the resemblance to “Jimbles”, a less harmful cousin of the box jellyfish, that inhabits our waters.
This fish is extremely shy, and every attempt to photograph it to date has been unsuccessful. It hides under a ledge and as soon as a light shines on it, it disappears into the deep recesses of its home. Today I tried taking video without lights and managed to get a short clip, from which this image is taken. I’ll keep trying until I get a better quality photo! It is a new species for me in the aquatic reserve.
A Shortfin Devilray (Mobula kuhlii) cruising along – Photos by Sarah Waddington
To a lucky few this week there has been a very rare visitor to Cabbage Tree Bay. The Shortfin Devilray resembles the better known Manta Ray, with the mouthparts that extend to the side of the head, and large pointed wings, and is south of its normal distribution range in Sydney. Whilst initially only one individual was spotted over a number of days, two individuals were spotted swimming together almost a week later in the same spot. Unfortunately they were very fast and took off very quickly before I could take a photo, but these photos were taken over a period of 15 minutes whilst it appeared to be feeding.
Photo by Sarah WaddingtonPhoto by Sarah Waddington
Sydney diving tends to be best at the end of summer from March through to June. Algal blooms start dying off improving visibility in the water, and the ocean temperature is still warm. Once the temperature drops below 20 degrees there is a “changing of the guard” underwater as tropical migrants start to perish, or get eaten, and the variety of species does decline as a result.
Today there were a few temperate climate butterfly species hanging in, but it was nice to see an Eastern Talma, the only Butterflyfish family member that lives here all year round. A male Eastern Australian Angelshark did a swim past, and a couple of Weedy Seadragons were feeding of mysis shrimp amongst the weed. This is the biggest species of Seahorse in the world and unfortunately numbers have crashed at this site in recent years. There has been a slight recovery but these are hard to find and photographers are advised to only take a handful of shots to minimise stressing individuals. I only take a maximum of 5 photos then move on, as I believe the impact of strobe lamps, from over enthusiastic photographers, on their eyesight has played a part in their demise.
The bay does have a population of Sydney Pygmy Pipehorses too, but they are very difficult to find and most photographers frequent the sites in Botany Bay to secure their photos
Could this become a significant reef in coming years?
It’s been a while since I have posted but I thought an update on the Pocillopora coral growth within the aquatic reserve would provide some good news. Sandstorms, ash from the devastating fires throughout the State has been scattering over the eastern seaboard all summer, together with blistering heat, algal blooms have flourished leaving visibility for divers as bad as I can remember it ever being. Well as days shorten and the suns intensity wanes, the algae dies off and visibility is returning.
A couple of recent trips to the corals has shown remarkable growth in the last year, with colonies merging together as they cover the rock barrens.
Temperature loggers on transect markers
A team of scientists from the University of Technology, Sydney (UTS) have commenced some studies on the area now, with survey transects, and temperature loggers in place. Specific colonies have also been identified for 3D analysis and to measure growth rates.
Despite the dramatic growth, the number of tropical migrants, that come down the coast with the eastern Australian Current, as larvae, appears to be low this year. Damselfish, rarely seen elsewhere in the reserve, have flourished in the coral structures for the last two years, and despite warming ocean temperatures none have managed to survive the winter yet. The interesting thing though is that the water temperatures around Sydney only need to rise about 1 degree before fish will start over wintering, then potentially breeding.
Colonies can also be found in shallow water close to shore
The coral is populating barren rock platforms, and without any direct competitors is flourishing. Over 5 years it has spread over an area extending up to 50m in length, and new colonies are appearing in areas accessible to observant snorkelers only metres from the shoreline. It will be exciting to watch how it grows in the next 5 years – who knows we might start seeing a big change in the ecosystem, and emergence of a new coral reef in Sydney.
Mimic, or Blacksaddle Filefish (Paraluteres prionurus)
A long way from home
At the end of every summer the water temperature lingers above 21 degrees and plenty of juvenile tropical fish can still be found in Cabbage Tree Bay aquatic reserve. Today a new one popped up that I have been looking for for some time now. I often find the Mimic Filefish and today I assumed the one on the left was the same, until corrected by a fish expert on iNaturalist (a fantastic website). The two are differentiated by length and position of dorsal fin, and if you look closely the spine on the top of the filefish dorsal fin is typical of the filefish / leatherjacket family (if you are lucky enough to see it raised).
This Black-saddled Toby is a long way beyond its normal distribution, with most southerly sightings being the Solitary Islands in northern NSW and Lord Howe island. As oceans warm up this is becoming an increasing trend to see more and more species beyond their normal distribution.
Fish of Cabbage Tree Bay Aquatic Reserve, Sydney 