Annual Spider Crab Migration in Port Phillip Bay

We fish we care

Annual Spider Crab Migration in Port Phillip Bay

By James Gardiner

Every winter, Southern Port Phillip bay is the site of one of nature’s amazing phenomenon’s where spider crabs migrate for their winter moult. The crustaceans congregate in their thousands, covering the sandy seabeds of Southern Port Phillip bay creating spectacular moving mounds. Despite the growing interest in this migration by divers and fishers, there is still some ambiguity surrounding just why they migrate and where they go after they congregate to moult.

It is believed that safety in numbers could protect them in their most vulnerable time – post moult, when they have shed their protective exoskeleton. This then exposes a soft underbody before the new shell can harden. Large rays, seals and birds are known to take advantage of this migration, feasting on the spider crabs when at their most vulnerable to predation.

With the growing fame of this amazing migration, there is an ever increasing amount of fishing and tourist activity surrounding the migration of the species. This is such an amazing natural resource and one which needs to be preserved so that the species can be protected during their most vulnerable period. There is currently research being done to track the migration of the species via satellite trackers. The research will enable for decisions to be made to better understand the population dynamics and migratory patterns of the species, allowing for a deeper understanding of the management requirements of the fishery.


Image: Giant Spider Crabs, Leptomithrax gaimardii. Rye, Port Phillip, Victoria. Photographer: Julian Finn Source: Museums Victoria

Museums Victoria. 2020. Melbourne’s Annual Congregation Of Giant Spider Crabs. [online] Available at:

Victorian Fisheries Authority. 2020. Giant Spider Crabs [online] Available at:

Australian Geographic. 2020. March of the Spider Crabs. [online] Available at: