Obtained by fishing up Prawn balls and uncurling them.
Uses:
At level 72 Construction this along with 5 bronze bars and a Fishbowl can be used on the Diving suit hotspot in your POH to create a Mermaid hunter suit giving 17 Construction xp.
At level 81 Construction this along with 8 mahogany planks can be used on the Prawnbroker hotspot in your POH to create Boutique prawnbrokers giving 1130 construction xp.