Commercial Harvesting of Marron from Farm Dams

Marron can be farmed in two ways. Firstly, by building many specially designed and equipped marron ponds at a favourable location and managing the farm intensively to give large harvests of marron. Or, secondly, without any great expense and worrying commitment, an agricultural farmer can diversify by cropping small numbers of marron from existing farm dams. This farm dam method, explained in this Aquainfo, is worthwhile because marron bring high prices.

You need a licence to sell marron

Farmers can obtain a Commercial Aquaculture (Freshwater Crustaceans) Marron "Trapping" Licence to sell legal -sized marron (not less than 76 mm carapace length) taken from their farm dams. You should contact your local Aquaculture Development Officer at the Department of Fisheries details of the licensing procedure and application forms. These application forms can also be obtained online.

Selling your marron

Marron are marketed alive, and with all legs intact, to get the best prices, particularly for export. To get started, you should contact an established licensed marron processor in your area (a list is obtainable from Fisheries, above). The processor will tell you how to handle and transport live marron to the processing shed, so they will be in top condition for you to get the best price. A good processor will have a considerable capital investment in purging tanks, chillers, packaging and contracts with markets, all of which are essential for successful long distance, live transport and sale. The marron farming industry has a "Code of Best Practice", obtainable from your processor.

The best dams for marron

There are several types of dams in the south west of Western Australia. The best type of dam for marron is the clear-water gully dam (a wall across a small valley or gully) and the most productive of these dams have a fertilized (pasture or crop) catchment. These dams occur mainly in the hillier, higher rainfall coastal region, with fewer inland, passed the tree line out to about the Albany Highway.

Farther inland, gully dams are replaced by small hillside excavated tank dams for stock watering. Marron can do well in these muddy dams. But when dams are polluted by excessive decomposing organic matter, from summer runoff, the sensitive marron does poorly. These dams are the basis of the commercial trapping industry for the more hardy, introduced yabby (banned from more coastal areas).

Round, spread- bank (catchment) or ring dams in very flat country (near Esperance) also become too silted and polluted for marron. Small house dams fed by rainwater and turkey nest dams fed by ground water tend to be too sterile and unproductive. Some large freshwater lakes on private property, particularly those formed by water-logging following clearing along the south coast, are suitable for marron.

Good and bad farm dam water

Marron can tolerate a moderate amount of salinity, but they are basically a freshwater crustacean and dam stocks will only prosper at salinities below about 20% that of seawater. Higher salinities are found in inland catchments with salinization problems.

Marron prefer well-oxygenated water and they live by crawling on the bottom. Most gully dams are well-flushed by winter runoff and overflow. However, large amounts of black rotting organic matter on the bottom and/or green water ("blue green algae") cause poor growth and breeding, dirty shells (poor for marketing) and usually many deaths. Dams with these problems should be avoided or drained and cleaned out. Attempts to feed marron in farm dams can cause these poor water conditions which can't be countered in dams. (see Aquainfos for purpose-built ponds, aeration and feeding).

How much marron can be cropped from a dam

The average farm dam supports 300-400 kg/ha of marron of all sizes and about 100 kg/ha of legal-sized marron can be cropped of each year. Marron are long-lived (up to 15 years of age) and large old marron prey on and suppress juveniles. Very few females are needed to keep a dam stocked. So, cropping of legal-size marron, both male and female, promotes stock turnover and increases growth and survival.

Catching your marron

Marron are caught overnight in baited traps and with baited drop nets or even a scoop or snare over chicken pellet baits laid in shallow clear water after sunset. Looking after sunset with a torch gives a good idea of stocks, too. You will not catch all the marron with baits; about 30% at the best, depending on number of baits and, mainly, water temperature, moon phase and time of day. Marron caught with baits tend to be the larger males and are in hard-shelled condition. Marron in traps lifted from water with disturbed black sediment should be "gill-washed", immediately. Complete harvest by draining is only practiced in constructed marron ponds and in winter when easily damaged soft-shelled (moulting) marron are absent. Diving can be considered for dams as a more efficient method of harvesting than traps.

Predators that take your marron

Marron in clear water are preyed on by bird and other predators, notably cormorants. In rivers, marron have many natural places to hide during daylight hours. However, man-made dams are usually very bare of hiding places and stagnant deep water is devoid of oxygen. Construction of rock or log piles in the shallower water of gully dams provides especially good hiding places for marron. The muddy water of wheatbelt excavated tank dams is very effective cover for crayfish against sight feeding cormorants.

Marron will not prosper in dams where yabbies or redfin perch have been introduced; both these species breed in overwhelming numbers. Trout don't bred in dams and their fewer stocked numbers appear to have little impact on marron.

Keep toxic farm chemicals away from your dams

All modern farm and domestic pesticides (insecticides) and cattle and sheep dips are extremely toxic in very small amounts to crayfish and other aquatic life. Herbicidal and fungicidal orchard and vineyard sprays and fumigants destroy natural aquatic food chains, which are based on plants, bacteria and fungi.