It is hard to find a better way to spend your summer afternoons than wading the estuary flats with a crab scoop in hand. In fact, crabbing for Blue Swimmer Crabs (Portunus armatus) is one of the most popular fishing activities in Western Australia.
Stocking of many of WA’s favourite finfish has occurred across the state with Pink Snapper, Black Bream, Barramundi and Mulloway all being stocked, yet there has been no stocking of crabs. Given their popularity and the importance of crabbing to WA culture, investigating possible stocking options for Blue Swimmer Crabs was identified as a way to enhance crabbing and crab stocks in WA.
Recently the Australian Centre for Applied Aquaculture Research (ACAAR) at South Metropolitan TAFE received a grant from the Recreational Fishing Initiatives Fund (RFIF) to identify future restocking options for Blue Swimmer Crabs. Since the culturing of Blue Swimmer Crabs from berried broodstock had never been done in WA, this project would first investigate if this process was feasible, and if successful, result in the first stocking of crabs in WA.
Collecting the broodstock
• With assistance from Department of Primary Industries and Regional Development (DPIRD) Division of Fisheries, a handful of wild berried broodstock were collected from the Peel Harvey Estuary and transported to ACAAR’s facility in Fremantle
• The berried females arrived full of eggs at an early stage of development when the eggs are still yellow (Figure 1). Conditions and temperature in the tank were then altered to assist the crabs developing their eggs to a later stage where the eggs turn a darker colour and are ready for spawning (Figure 2).
From hatching to release
• Once the eggs hatch, the earliest stages of a crab’s life cycle begins to be visible when viewed through a microscope. This first stage (below) of a crab’s journey is called a Zoea and resembles something more closely out of an Alien movie than of a crab. At this stage, the Zoea have limited ability to move to avoid predators and find food and are at the mercy of their environment. Hatchery conditions and food availability must be carefully managed during this vulnerable stage.
• Day by day the Zoea continue to grow and develop and after 12 days they make their next big transformation as part of their life cycle, metamorphosing into a Megalopa. At this stage they are starting to look much more similar to their parents having grown biting claws and gained the ability swim freely.
• After 19 days from hatching, the project reached an important milestone with the Megalopa undergoing their final metamorphose into a Crablet. This is a dangerous stage in the development of the crabs as the crablets quickly become highly cannibalistic and aggressive, apparently maximising the use of their newly grown claws.
• From the broodstock crabs that contributed to the spawning, the final stage of the projects saw the release of 3700 crablets into the Peel Harvey Estuary.
The success of this WA first project has opened the door to future potential restocking programs for crabs that could play a role in continuing to create great fishing experiences for the WA community forever. A second project, also funded through licence fees aims to release up to 100,000 crabs into Metropolitan waters and start to design a larger scale stocking program for WA.
This project was funded through the RFIF and supported by DPIRD, Division of Fisheries and Recfishwest.