Brown Crab (Cancer Pagurus)

Brown crab can occupy a range of habitats from a sandy gravel seabed to rocky reefs. These habitats cover a wide range of depths, from rock pools along the seashore, to a depth of 100 fathoms.

You will recognise the brown crab by its distinctive “pie-crust” carapace which is reddish-brown on the upper side and pale creamy yellow underneath. It’s very large black-tipped claws equip the brown crab with very effective tools for feeding and fighting – if you look closely you will see one claw has developed as a cutting tool while the other is designed as a crusher. When a Brown Crab loses a claw, it can grow a new one, although this may take several years.

Reproduction occurs in winter; the male captures the female and holds her under himself until she moults. Internal fertilisation takes place before the hardening of the new shell, with the aid of two abdominal appendages. After mating, the female retreats to a pit on the sea floor to lay her eggs. Between 250,000 and 3,000,000 fertilised eggs are held under the female’s abdomen for up to eight months until they hatch.

Brown crab is abundant throughout the West Coast of Ireland because the waters are so clean, they are rich in essential marine nutrients which in turn provides excellent food for the crab that live and breed there.

Adult brown crab are nocturnal, hiding buried in the substrate during the day, but foraging up to 50 metres (160ft) from their hideouts at night. The main predator of brown crab is the octopus, which will even attack them inside the crab pots that are used to trap them.

Brown crab use their claws to feed on smaller crustaceans and molluscs and have few predators themselves except for the octopus.

As they have a hard exoskeleton, crabs are only able to grow by moulting, young brown crab moult several times a year while mature brown crab moult once a year or less. They cast their entire outer shell and puff themselves up with water before the new exoskeleton hardens. Full hardening will take 2 to 3 months by which time the brown crab will have increased in size by 20-30%. During hardening, they are the most vulnerable to predators and would be considered lesser quality by fishermen.