Eastern King Prawns have nurseries at Toondah Harbour

2022 has been a busy year in academia for me with my international programs with Stanford University and the University of California recommencing after a three year hiatus. Professional support staff had to be engaged, my lectures dusted off and lecturers engaged. Execution of those programs this Spring and early Summer 2022 came at the very worst time for one of the most significant recent challenges to Quandamooka (Moreton Bay) – the Toondah Harbour Environmental Impact Statement. To those in the know, this was a huge document with many parts. As one of the folks who has published quite a bit of science regarding the Bay the hoped-for task of reviewing and commenting on the EIS dropped at the very worst time given my teaching workload. With the 6th December deadline for submissions rapidly approaching, I decided to ignore the document and to instead use my field skills to hunt for facts. I went for a walk on the seldom appreciated muddy shores of Toondah Harbour.

Previous work through my lab has found that intertidal pools and streams in Quandamooka support the early life history stages of important commercial species such as prawns and whiting. If such features occur at Toondah and if those features hold juveniles, then the Toondah flats might contribute fisheries that support more than 1000 jobs and contribute $24 to $30 million annually to the economy of Queensland. As my previous studies had been mainly focused on the eastern shores the Bay, I had to visited Toondah at low tide to see if water features on that shore might hold fisheries value.

Certainly, despite the inclement weather, my first visit on Saturday 3rd December was encouraging. I noted streams and pools that had lots of small critters skittering around as I walked the shore. I used small aquarium nets to try capture the darting crustaceans, managing to capture several. Despite some being blown out the net by the wind, I managed an image or two on my iPhone 12. I realised two things: first nets alone would not suffice to capture these elusive creatures; and second, that upon magnifying the phone image that the animals appeared to be penaeid prawns – the yummiest kind of crustacean. Encouraged by this preliminary finding I plotted my Sunday visit.

Sunday found me enjoying similar conditions to the previous day – very strong winds and scattered showers. It also found me on my knees in the mud with jam jars trying to herd near invisible small critters into the jars or trap them against a small wall of sediment in order to effect their capture by hand. Initial success was followed by some effing and blinding as the wind managed to evert my nets or topple sample jars, thereby releasing some of my intended victims. But in the end, I brought home five tiny prawns for examination under my personal microscope – as one does.

Struggling to capture an image through the eyepiece of my dissecting microscope, I tried instead just with the iPhone zoomed in to the max. Bingo! The image was pretty good and the feature I could see diagnostic using Peter Young’s key to juvenile prawns, of which by good fortune I happened to have a copy.

The darting critters in the shallow rivulets and pools at Toondah proved to be Eastern King Prawns, Penaeus plebejus. All penaeid prawns have a pointy bit at the front end called a rostrum. These are the things that can either poke holes in plastic bags and introduce prawn juice into your shopping bag or draw blood from the careless prawn handler. EKPs as Eastern King Prawns are known to fishers and fisheries folk, have tooth like projections on the top of the rostrum has teeth, and the bottom of the rostrum has a “tooth”. Diagnosis = EKP.

The presence of two size classes indicated to me that they represented two different recruitment events, so their presence was unlikely to have been purely by chance. Toondah is a prawn nursery!

Also at the site were high abundances of the mudwhelks Pyrazus ebeninus and Batillaria australis, the predatory and scavenging whelk Nassarius dorsatus and the air-breathing sea slug Onchidium daemelii. Hermit crabs (Clibanarius spp) and fiddler crabs (Uca spp.) were also prolific. Gobies and juvenile fishes were seen in the pools as well as many mudskippers, Scartelaos histophorus in muddy pools adjacent to pneumatophores (peg-like aerial roots of grey river mangroves, Avicennia).

My main take aways from my mud walks on Toondah were that the muds, shore drainage and pool features in the proximity of Toondah Harbour contain numerous juvenile eastern king prawns at the time of my visit. The presence of a high diversity and abundance of other organisms on this mud flat indicate that this is a healthy and productive environment that may continue to provide such biodiversity and economic benefits well into the future.

My other thoughts in concluding this report are 1) if you are inclined to walk a shore, get down on your knees and look carefully you might find some surprising things, 2) if you have a good phone/camera then an image can be used to identify the critters – you do not need a microscope; 3) if you are inclined to do 1) and 2) then please send images to me and I can have a crack at identifying what you find. Who knows, you might uncover another nursery habitat and by dint become a citizen scientist.

So, during this holiday period, should you find yourself faced with a bowl of delicious prawns, do dwell on where they grew up and why we should protect such shores and pay our respects to the Traditional Owners of Quandamooka who continue to care for Country as they have done for thousands of years.

Merry Christmas, Ian (Director, The Moreton Bay Foundation)

Figure 1. Study site adjacent to Toondah Harbour (© Nearmaps)

Figure 2. View of shore surface drainage features at GJ Walter Park. A) shallow pool with Avicennia pneumatophores; B) possible stingray pool; C) shore drainage stream.

Acknowledgements

I acknowledge and celebrate the many thousands of years of custodianship of Quandamooka Country by First Nations communities and pay my respects to their elders, past, present, and emerging. My thanks to David Brewer and Tim Skewes for comments on earlier drafts of the manuscript, and to Dr Peter Rothlisberg for advising me of the new old Latin genus name for eastern king prawn. Funding from SUSMB provided the tools and capacity for this short work. The survey and collection were conducted under Moreton Bay Marine Park Permit # P-MPP-100245398 and General Fisheries Permit # 258395 both of which are held in my name.

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