Big Flathead being released

[Pistol_P]

This is an interesting one.

I was talking to a bloke yesterday who runs a river fishing guide here at Noosa.
This bloke knows his stuff and is on the water nearly every day.
We started talking about flathead as the Noosa river fishes well for flatties.
He then pointed out to me that while there are certainly more big flathead around due to the fact we have to release all the big girls it has had a negative impact as well.
He believes that all the big flathead are eating alot of the small ones....the capture rate of small flathead over the last two years has been VERY low he said and when he has kept and cleaned flatties around the 65cm mark they have had juvenile flatties in their guts.

This is not coming from me but a guide like I said.
It certainly got me thinking......

Cheers
Pete

[geoff72]

great point there pistol, certainly does get you thinking, my first thoughts were the same thing with mud crabs, i am a big believer in letting the gens go but think of the imbalance we are causing, to many femals not enogh males. may be im a bit off track but thats my fisrt thought. like to see what other people have to say/think.
good thread

[ffejsmada]

Yes it is an interesting thought. I have caught heaps of flathead over the years and have NEVER seen a small flathead in the gut cavity of a gutted fish. I inspect the gut cavity on every fish that I gut, and in the flatheads case I have never found a juvenile flattie. Interesting.

[DaMaGe]

This is somthing I have noticed also, and had thought alot about it before you even posted. I also feel this is a direct link to the decline of smaller flathead numbers. However this needs to be independelty researched.

[Matthias]

The more big females equals more babies simple as that. The survival ratio of baby flatties would not change with the amount of mature flatties even if they were cannibalistic.

If you have 10 females that have 10 babies (100) and they eat 5 each that leaves 50 babies. If you have 20 females with 10 babies (200) and they eat 5 each each that leaves 100 babies.

I think that the size of male mature duskies would have more to do with the imbalance because from what I've read males grow slower and not as big, so there is more chance of a mature male getting taken than a mature female. This would make an uneven ratio of males to females thus effecting their breeding cycle.

Pete.

[hooknose]

Late last year I released one big girl at the Pimpama that spewed up two( 10 to 15 cm) as I put her in the net before dehooking and releasing her. Same thing happened at the pin a couple of weeks later and then in december at Coombabah Ck I heard a big splash beside my tinny and looked around to see a huge lizard chasing a tiny one about 10cm along the surface before bailing out( that little lizard looked real scared).

I have not noticed this to happen in the past but I reckon there is something in what the Noosa guy reckons but dont know if its really a dangerous situation.

Cheers !!!

[Red Bull]

The more big females equals more babies simple as that. The survival ratio of baby flatties would not change with the amount of mature flatties even if they were cannibalistic.

If you have 10 females that have 10 babies (100) and they eat 5 each that leaves 50 babies. If you have 20 females with 10 babies (200) and they eat 5 each each that leaves 100 babies.

yep, my thoughts exactly Pete. I can't see how bigger numbers of breeding females in any given estuary system could be anything other than good for the future of dusky flathead. When big lizards eat the smaller ones, it's all part of the natural selection process, and I reckon it might indirectly relate back to the species strengthening it's own gene pool. But if there's more flathead breeding, then it follows that there will be more little flathead with a chance of making it to breeding age themselves?

Cheers
Red Bull

[Kleyny]

I'm with Pete and redbull.
with the eating of the smaller ones. its survival of the fittest.
shes getting rid of the annoying male and keeping the worker.(wouldn't all women like to do this.)

neil

[flyfisho]

maybe because most people who catch a legal Flathead keep it , its probaly got to do with the amount of people fishing Noosa and improved techniques ie. plastics as well as an old school mentality of why would you go fishing just to let it go , but i'm sure cannibalism reults in a small pecentage

[Squiggle]

Another thought???

Is there any evidence that an old girl still has the same fertility rate as she did when younger? Fertility doesn't mean the amount of eggs either, it means the amount of viable eggs.

[Jeremy87]

The more big females equals more babies simple as that. The survival ratio of baby flatties would not change with the amount of mature flatties even if they were cannibalistic.

If you have 10 females that have 10 babies (100) and they eat 5 each that leaves 50 babies. If you have 20 females with 10 babies (200) and they eat 5 each each that leaves 100 babies.

I think that the size of male mature duskies would have more to do with the imbalance because from what I've read males grow slower and not as big, so there is more chance of a mature male getting taken than a mature female. This would make an uneven ratio of males to females thus effecting their breeding cycle.

Pete.

Different scenario you have 10 females that have 10 babies each and they all eat 8 and 30 either die or are eaten by other predators including man = -10. this means you get an overall decrease in small flathead which is whats being debated.

Obviously this isn't the case in all estuarys otherwise flathead would have become extinct. Flathead are canabalistic i've had bigger flathead swim up behind smaller ones when angling them, i even know a guy who uses live flathead as bait to catch big ones.

I'm not sure weather all flathead are born male and change sex at a set size say 60cm or if the males just don't grow as large.

What if as size increases flathead consume more baby flathead and not only that but increasingly larger flathead. A 40cm flathead would have had to overcome much greater odds to reach that size compared to a 30cm, so eating 1 40cm flathead is like eating 10 30cm fish.

So if you have a top heavy population where there is a greater number of larger fish than what is the norm, it could be argued that they would be consuming more small fish than what is also normal. so our sum becomes more complicted. In a normal popuation of 10 females of varying size and egg laying capacity. The smallest female may have 10 babies and eat 4 the whole way up to the largest female that has 20 babies and eats 13. The normal 30 die from other predators etc. = an increase of 43.

So what if the same estuary with all large females and a heavier predation rate from man. The estuaries biomass will only support 7 of these big fish so our new sum is
7 flathead have 20 babies and eat 13, 40 are lost by other causes = an increase of only 9.

Of course this is all theory and would need to be proven some how but if true could change the way we think about monitoring healthy populations of flathead. It could just be a case of where this guy fishes is where only large flathead live, alot of juvinile flathead tend to find their way up feeder creeks away from alot of the larger predators.

[Matthias]

Jeremy- What is being debated is- the decrease in small flathead is attributed to the increase in female flathead. The variables you mentioned have nothing to do with what I said. It is simple in that the more breeding females means more babies. It doesn't matter what eats them, the chances of babies surviving are higher when there are larger numbers of them.

I only used a simple ratio as an example and if you were to put the survival rate of a flathead in to an equation you would be writing pages of sums.

Pete.

Ps. You can't have -10 flathead.

[Jeremy87]

Yes you can have -10. that would indicate a total decrease in population. 0 would be stable and a positive amount would be a population increase. I'm just putting forward another hypothetical situation where a population of larger flathead may attribute to a greater fatality rate. The numbers are just examples. I can rephrase it algebraically for you if you want but this way is easier to understand.

[Matthias]

I could name a hundred other variables that would be very relevant to this debate. There is absolutly no evidence to suggest there is a link between a rising large flathead population attributing to declining small flathead population.

Please Tell me if your variables would affect the same flathead population if there were less big females.

Pete.

[shayned]

Try this out as bigger flatties are canabalistic in nature the prime feeding spots are dominated by the larger fish. The prime feeding spots are where we target our baits and lures hence a skew in captures to larger fish.

Also I felt this years season was much better in terms of number of captures and the size caught.

Also comparing my fishing experiences in NSW with Qld I feel the flathead population up here is healthier.