For many recreational fishers in Moreton Bay, this time of the year spells banana prawns! Bramble Bay has long been a hotspot for fishers to catch them using cast nets.
The life cycle of the banana prawn is short, but they pack a lot of living and travelling into their short lives. They complete their life cycle in about 12 months.
It all starts in the mangroves and the muddy channels that drain into them. Without healthy mangroves we would not have banana prawns. Banana prawns typically move into mangrove habitat at high tide from adjacent rivers or creeks. The mangroves provide them protection and food. Juvenile banana prawns east a wide range of animals including very small worms and shellfish as well as decaying mangrove leaves.
The juvenile prawns grow over winter, spring, and early summer and in response to rainfall and river flows, the prawns commence to move out of upstream mangrove areas in rivers and creeks and start to make their way into Moreton Bay. Rainfall is critical for the banana prawn life cycle and the timing and volume of rain not only influences this year’s crop but next year.
Banana prawn populations naturally have substantial variation in populations between years.
Once in Moreton Bay, banana prawns mature, and a single female can produce between 100,000 and 450,000 eggs! They can form large aggregations, which is why unlike other local prawn species they can be consistently in large numbers in a short period of time.
After spawning, the fertilised eggs develop initially into a type of a larvae called a nauplius. Then there are two other larval stages called a protozoea and a mysis, before it develops into a postlarvae which is recognisable as a tiny prawn. They spend about two to three weeks in these various larval forms.
Currents and tidal movements assist the larvae to make it make it to mangrove areas. When the larvae are trying to move back to mangrove areas, continuing river flows after significant rainfall though can hamper them doing so. If they do not make it back to mangroves, the chances of survival are extremely low.
If they do make it back, they will feed in the mangroves, keeping an eye out for the various predators and hopefully after growing make it back out to sea for spawning.
Next time you catch banana prawns, think about the journey they have made and how the environmental and habitat conditions must be just right to sustain them.