Portunus pelagicus, Blue manna crab, Blue swimmer
This species is not easily mistaken for other crab species, it has flat, disc-shaped hind legs and long claws that may be blue or purple and white in colour. The belly is white and the ‘flap’ on the underside of the crab helps distinguish between males and females; it is noticeably wider in females and has appendages for carrying eggs. The carapace is pointed at its widest part and has nine small horns on its carapace between its eyes. Blue swimmer crabs can reach up to 25cm across their carapace (they are measured from point to point on the carapace).
Found from the Northern Territory border in the north to the South Australian border in the south, although they are most common between Albany and Karratha. They are found mainly in the lower reaches of estuaries but also sheltered bays and some inshore waters. They are most often associated with sandy bottoms as they hide in the sand during the day.
Rigs and Techniques
The most common methods for fishing for blue swimmer crabs is using drop nets or scoop nets, although free diving is not uncommon. Drop netting usually occurs from boats or jetties, where a baited two hoop drop net is used. Ideal baits are old fish heads. Scoop nets can be used in areas of shallow mud or sand flats by looking out for crabs as they are swimming or searching for eyes poking out of the sand and disturbing the sand in order to scoop the crab into the net. This technique works best on a falling tide when the crabs will be actively swimming towards deeper water and hence easier to target.