Where do Jacks Breed..?

[Pistol_P]

Whats everyones thoughts on this topic...?

I know the belief is that once Jacks reach maturity they head out to the reefs to breed and live their lives out on the reefs.

If this is so how on earth do so many tiny juvenile jacks get way way up into brackish sections of our creeks etc...???
I just cannot imagine that fertilised roe would travel such a massive distance and find its way into these creeks which are so high up river...?

Or is it a case of the newly hatched jacks making their own way into these creeks..???

Didley, you are the man for this one..

Pete

[LostNearBribie]

Mate I always thought they left the creeks after breeding?
Once they have had their cycles they bugger off to eat some pretty fish on the reef til they die.
I'm not saying this is true, but it is what I have always thought.
I have caught plenty of tiny jacks in the creeks.

[Chamelion]

I recall reading that the baby jacks beeline for the nearest estuary (how they find one is any ones guess) once hatched, remain their until maturity and then head out onto the reefs.

[Pistol_P]

Mate I always thought they left the creeks after breeding?
Once they have had their cycles they bugger off to eat some pretty fish on the reef til they die.
I'm not saying this is true, but it is what I have always thought.
I have caught plenty of tiny jacks in the creeks.

Well thats what I think too red..?

I reckon they breed in the creeks and then move out to the reefs later on..?....BUT if you do any research on it ever bit on info suggests they breed on the reefs..?

Pete

[supertuned]

Pete, like most fish they sense current flows, most fish have these things programmed into them. there isnt a lot of boundaries on the oceans but the same rules hold true most of the time. theres a lot of tiny coastal creeks which are literally freshwater from the beach, plenty of small jacks reside in them. The research has always pointed to jacks not being mature fish under 60cm long. If big lake jacks could breed for example i suspect we would see massive amounts of tiny jacks in those systems but we dont.

[jeffo]

I am sure I read once that Mud crabs head out to sea to spawn? I have seen quite a few Big muddys cruising along the surface in 50m of water 12 miles off the Coast here since.

[randell]

There is a very interesting report on jacks done by the Qld DPI , and is available to download.
It says they breed offshore, and the little fish make their way to the estuary.
I was at the quantity of 50 to 60 cm fish they found in estuaries .
They acquired fish from rec, and pro fishers as well as electrofishing.
It is a scientific work, some of the graphs are pretty bewildering.......... to me anyway... but a good read.
randell

[Didley]

As far as I know its excepted they breed on off shore reefs, how the little buggers get up stream is a miracle. Once they get to a river / creek mouth its easy, just move up stream with every incoming tide, and hold their position with every outgoing tide. But from reef to river mouth is another matter. Direction would be from following the fresh water trail, but that's a hell of a swim for a little fry. Must be a huge mortality rate.

[ffejsmada]

There's nothing unusual about the migration back to an estuary for a baby Jack.

Short-finned eels (a freshwater specie), travel to the Coral Sea to breed.
Even eels from Victoria, NSW etc.
When the females breed at depth they explode and die, the young elvers then migrate back to the exact lake their parents lived in.

It's a much easier trip back to an estuary for a Jack than it is for a Short-finned eel.

Nature is incredible.

[mangajack]

I think that jacks and jungle perch have similar habits. Both breed outside of the river systems, JP's inshore reef habitats for breeding, jacks inshore and offshore breeding locations. I also think that the jacks up to about 60cm will venture to inshore reefs during the breeding cycles and return to the creeks soon after. Why? Because of the numbers of jacks i have seen that are about 35-60cm on inshore reefs during the breeding season at some places i have dived in CQ and NQ. A week later there were none in the area. I dunno, maybe they have a few dry runs before productive breeding takes place??