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Author Topic: Barra over the wall- Will it bow the food chain??  (Read 2735 times)

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Barra over the wall- Will it bow the food chain??
« on: January 07, 2011, 01:48:17 PM »
In a natural system, shown below, there is always enough food for the organisms in the next step up in the pyramid. There is a balance in the system.
The approximate pyramid in a normal system is as follows
                                                                                     Top
                                                                                    Order
                                                                                  Predators
                                                                               (Cod, Barra, Yellow-
                                                                              belly, Bass. etc)
Middle/ Low Order Predators
(gudgeons, pygmy perch, rainbow fish, blackfish, etc.)
Zooplankton
Free floating organisms that eat other plankton. Important food source for high order animals
Phytoplankton (algae)
Primary producers (use the sun to make energy).
Base of the food web and source of food for all animals above.


If over stocking, or a mass introduction, occurs in a system, top order predators will put massive pressure on the population size of middle and lower order predators. This system becomes top-heavy. Algae and zooplankton dominate which is one reason why algae blooms can occur more frequently. On top of this, a healthy system won’t need stocking because fish populations are self sustaining.
An impoundment situation is different, in that it is stocked as a put and take fishery, however problems develop if large numbers of fish escape over the wall.

Just thinking out loud guys.What to do....What to do???
Matt Hansen


Matt Hansen. Dubbo Catches and the Central West Angler Author. Lake Burrendong Classic President- Not for profit Catch and Release annual comp- Easter every year. All proceeds to re stocking. www.iwra.com.au
Sustainable Fishing - Not Freezer Filling!

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Re: Barra over the wall- Will it bow the food chain??
« Reply #1 on: January 07, 2011, 02:16:08 PM »
Algae and zooplankton dominate which is one reason why algae blooms can occur more frequently.
Matt Hansen

G'Day Matt,

Zooplankton / micrograzers feed on algae.

A very generalised theory below, however it seems to work.

Stocking of middle & high order predator fish = fall in forage fish numbers = increase in micrograzers = less algae.

Cheers,

fitz..

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Re: Barra over the wall- Will it bow the food chain??
« Reply #2 on: January 07, 2011, 08:27:39 PM »
I've never been in favour of stocking into a healthy river system. One because if it's healthy it should not need re-stocking, it should be naturally occurring. Two because if the system is not healthy there's little point in putting more fish into it. The trick is to make it sustainable and make sure that bankside vegetation is properly restored so that fish are able to breed naturally. Given half a chance, and given that the place has not been netted to death it should bounce back. I could say more but it would take pages. Consider what's happened to the Mole and Dumaresq Rivers. Overstocking has bought about a shortage of food for the top predator; Cod. therefore most of the Cod you catch in these rivers while abundant are stunted due to a lack of food. One good thing tho, they pretty much ate out the Carp.
JD

 

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