Crab, Blue Manna

(Portunus pelagicus)

Commonly referred to as Bluey‘s or blue swimmers!

Blue manna or swimmer crabs are a tasty crustacean highly regarded for their fine eating qualities and stunning looks, they are prevalent throughout most Australian estuary systems and are not only relatively easy to target but also great fun for the entire family. They are one of the few crab species that is capable of swimming well and can often be seen paddling along side ways on their way to and from a feeding or spawning aggregation.

Distribution

Blue manna or swimmer crabs can be found from cape naturalist right up to the Kimberley region throughout Western Australia. They are also commonly encountered in N.S.W and Queensland.

Growth

Blue manna or swimmer crabs are a fast growing species of crustacean that grow to a maximum size of around 25cm across the carapace.  Male or buck crabs have a pointed anal flap and females or jenny’s have a more rounded anal flap which is sometimes covered with eggs. Female blue manna’s also tend to be smaller and have shorter, stumpier claws.

Habitat

Blue manna crabs prefer warm, shallow estuarine environments and can be found in large numbers throughout most of our Australian estuary’s. Areas of mostly sand bottom with some shelter or cover near by such as weed, reef or deeper channels are ideal habitat for targeting blue manna’s.  Water depths of  6 – 25 meters are ideal.

Identification

Blue manna or swimmer crabs can vary in colouration from dull brown shades to bright blue’s and purple’s, the male specimens have long, brightly coloured claws and a pointed anal flap with females proving to be typically smaller in size, dull brown in colouration with shorter, stumpier claws and a more rounded anal flap which can sometimes be covered in eggs called berries. Their carapace is broad with a spine on each side with light cream or white mottled markings amongst the prominent browns, blues and purples. Blue manna’s or swimmers as they are some times referred to have a rear set of legs that have converted into paddles which allow this species of crab to swim with a certain degree of speed and agility hence the name blue swimmer crab. Blue manna or swimmer crabs can also be scooped on dark nights using a powerful spot light from a boat as they swim around on the surface along with tasty prawns!

Taste rating

  • One hundred Taste Rating
    100%

Blue manna crabs are highly sought after for their fine eating qualities and just happen to be one of my all time favourite personal delicacies.

Sport rating

  • Eighty Sport Rating
    80%

Blue manna crabs are highly sought after for their fine eating qualities and are also great fun for the entire family to gather.

Tackle requirements

No rods, reels, lines and leaders necessary for targeting blue manna‘s although they can sometimes be landed by anglers targeting other estuary species on rod and reel they are generally targeted using drop nets, the only legal method of trapping crabs allowed by recreational anglers in W.A. At the time of writing 10 drop nets are legally permitted to target blue manna crabs with a daily limit of  20 crabs per boat or 10 per person from shore. Please check with local fisheries departments in your area for up to date size, licence and bag limit information before attempting any crabbing/fishing. Wading shallows with a wire crab scoop is also a very productive method of collecting a feed of blue manna’s in W.A although the size of crab is generally smaller scooping from shore compared to using drop nets from a boat or wharf depending on location. Using the larger sized drop nets in deeper sections of the estuary will generally produce larger crabs. Blue manna or swimmer crabs can also be scooped on dark nights using a powerful spot light from a boat as they swim around on the surface along with tasty prawns!  Withes hat shaped net traps are used on the east coast of Australia to target blue swimmer crabs but are generally frowned upon by the rest of the country for their high mortality rate of other estuary species both during fishing and when lost. Withes hat styled traps are also incredibly difficult to remove crabs from once they have become entangled. A crab size gauge is also very important to measure the legal size of all crabs! Again please see local fisheries for size, bag limits etc.

Recommended baits, lures and rigs

Many baits can be placed into drop nets to entice crabs aboard with some of the all time classics proving to be spleen, mullet, chicken necks and  whole fish heads. Spray on Chum Line and other assorted fish oils are also handy to bring crabs to your baits from a distance or in current. Drop net baits may need to be enclosed in a wire bait wallet in some estuary systems to prevent blow fish and other nuisance species from devouring trap baits.

Handy hints and tips

Try not to handle blue manna crabs as they have large, powerful claws capable of inflicting some serious damage to human fingers and toes etc. Welding gloves are handy for beginners handling larger crabs. Always place the crabs you intend to keep into an iced slurry immediately upon capture as this sends the crabs into an unconscious state and apart from keeping them cool and fresh also prevents them from throwing their claws and legs during the cooking process. Always try to take some clean sea water home with you to cook your crabs in as this improves the taste remarkably.

Preferred fishing times and tides

Rising or full tides are best suited for targeting blue manna crabs although some deep water locations will also produce good numbers of larger crabs during low tides.

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