Sponges have been employed for thousands of years for a wide variety of purposes, most commonly for basic hygiene (bath/toilet sponges), padding (historically under armour and saddles) and in certain manufacturing processes. World production from the wild harvest has, however, declined significantly this century due to over fishing, pollution and disease in the traditional fisheries (Mediterranean and Caribbean). Concurrently with this decline the demand for natural sponges for domestic (many people prefer to use a natural product), industrial and medical purposes has risen.
Three commercially viable species of sponge have been identified in this report from Northern Territory waters. All three are found adjacent to indigenous homelands in Arnhem Land and are known to some of the inhabitants of the area. With the backing of Homeland Associations, several Traditional Owners have expressed a strong desire to pursue sponge farming as soon as practicable. The adoption of sponge farming would directly benefit the homelands by providing ‘real’ employment, financial return for effort and a reduction in dependence on government funding. Sponge farming also has very good potential to provide a valuable new export product for Northern Australia.
Sponge farming is environmentally friendly. Apart from the initial collection of parent stock, there is no appreciable impact on the environment from sponge farming. Once the farm is established all stock replacement is produced on the farm and there is no need for further wild collection. Sponges are non-polluting—they are nett users, rather than producers, of nutrients and also feed on bacteria from the water column. Sponges process hundreds of litres of water per hour and remove up 95% of nutrients and bacteria—this has created interest in using sponges to reduce the effluent being discharged into the sea by both humans and aquaculture farms.
Farmed sponges are propagated asexually. A mature sponge is cut into pieces approximately 2–3 cm square on each side, the pieces threaded onto a piece of thin rope, wire or bamboo and hung in the water to grow. Once the sponge is placed in the water it needs no further direct care until it is harvested. Sponges are self-cleaning and have few predators (except turtles in some places). Growth rates of sponges placed in the right environment are good, in Townsville the sponges grow to market size in 18 months – 2 years.
Identified markets for ‘bath’ and ‘cosmetic’ sponges are extremely buoyant. Over-fishing and disease have caused a severe downturn in production of sponges from traditional sponge fishing regions (the Mediterranean and Caribbean seas). This has left gaps in the market which have not been filled and are open to new producers. Sponges produced from pristine waters, such as those off North Australia, are likely to have a general marketing advantage over those from ‘polluted’ areas. In addition, sponges that can be labeled as being produced from aquaculture that is carried out by indigenous homeland communities will have a strong advantage in extensive niche markets, especially the tourist market.
Economically sponge farming appears to be well suited to remote areas. Sponge farms are inexpensive to set up ($13,500 including purchasing a suitable dinghy and motor) and operate ($3,000 per year). Experience in Micronesia shows that establishing and maintaining a farm of 30,000 sponges requires approximately 20–30 man hours per week. A farmer can expect a minimum return from a farm this size of $45,000 per year after four years. Niche markets available in Australia could mean that this return is at least double for Australian indigenous producers.