Production technology for redclaw crayfish (Cherax quadricarinatus)
Final report
This research and development project aimed to define specific guidelines for the aquaculture production of redclaw crayfish, Cherax quadricarinatus. This aim was achieved, and a comprehensive list of such guidelines is now documented.
Redclaw crayfish aquaculture was a small industry when this project was initiated, generating less than 40 tonnes of product per year. Production technology was undefined and extremely variable across the industry. Now, in 1996, production has risen to around 100 tonnes and a more consistent and appropriate approach is applied to production. This is due to a large extent to the technologies developed by this project, the full benefits of which are still flowing to industry.
Armed with a ‘best practice’ approach, the redclaw aquaculture industry is poised for significant expansion, which will enable it to more fully exploit the excellent export opportunities which have been clearly identified for the product.
A study of the sand crab (Portunus pelagicus) and its exploitation in a sub-tropical multi-sector fishery
Final report
Based on logbook records the sand crab commercial pot fishery in Moreton Bay is worth in the vicinity of $2 million wholesale annually. Sand crabs are also taken as an incidental by-catch by otter trawlers and in addition Moreton Bay supports a substantial recreational fishery.
Sand crabs are caught throughout the year but fishing effort is greatest from October to June. Peak catches in the pot fishery occur during March and April when daily catch rates may exceed 3 legal males per pot. Gravid females are present throughout the year but the highest proportion of egg bearing females is found in the population during August and September. Peaks in mating activity occur in autumn and spring with recruitment of juvenile crabs commencing in November. The parasitic barnacle Sacculina granifera infects 3% of all sand crabs in Moreton Bay and a previously unreported microsporidian parasite is found in 0.7% of the population.
Tagging studies show that fishing effort and mortality of sand crabs is highly variable throughout the Bay. Recapture rates for different areas vary from 1% to 65% with an overall return rate of 14%. The pattern of tag returns does not indicate any ordered directional movement of crabs either into or out of the Bay.
Male and female sand crabs exhibit differences in preferred habitat. Large males are generally more abundant in deeper water, whereas females predominate in shallower water, particularly on the top of sand banks.
Management recommendations arising from the project work include a change in the method of sand crab measurement to the width at the base of the antero-lateral spines, lowering of the existing size limit, the introduction of a bag 1 limit for recreational fishermen and an abolition of the prohibition on taking females provided that suitable management conditions can be maintained.