How Northern BC’s Crab Fishermen Use Science to Predict Moulting Periods in the Hecate Strait.

How Northern BC’s Crab Fishermen Use Science to Predict Moulting Periods in the Hecate Strait.

On BC’s North Pacific Coast, the Hecate Strait is home to the province’s largest commercial crab fishery. With 42 fishing vessels ranging in size from 35-60 feet, the Area A Crab Association represents over 200 harvesters. 

As wild Dungeness crabs grow, their rigid exoskeleton must be shed. Known as moulting, crabs break apart their shell and find themselves very vulnerable until a new exoskeleton hardens over time, providing protection and support until their next moult. While moulting plays a crucial role in the lifecycle of a crab’s growth, it also greatly increases the chances of crab injury and death during fishing.

To protect soft-shell Dungeness crabs in the Hecate Strait, the Area A Crab Association has a unique scientific charter program funded by fishermen themselves. For the past 20 years, every Spring leading up to the moulting period, a charter boat is hired from within the fleet to test the shell hardness of crab in the Hecate Strait. Charter vessel crew must go through training to learn how to collect the biological sampling data. Shell hardness is determined by squeezing the crab’s “armpit”, where the claw joint meets the carapace.

Based on the amount of days or months since the crab’s last moult, there are four (4) different types of soft shell crab: springy soft, crackly soft, plastic soft, and moulting. The charter boat sets 75 traps in predetermined locations across the Hecate Strait and checks them every two weeks and records data on everything they catch. The data is then reviewed by a committee of harvesters and DFO crab managers. 

If 5% or more of the legal-sized male crabs are designated as having a soft shell, this indicates the start of a moulting period, and the fishery closes. The same process is then repeated for determining when the majority of crabs shells have hardened, triggering a re-opening of the fishery.

In addition to protecting the long-term viability of Dungeness crabs, the Area A softshell charter helps to maximize fishing time, while minimizing the number of crab injuries or mortality during fishing, improving both the economic and biological returns. It’s also the longest-running scientific database on crab moulting periods for an area and helps to understand better how changing ocean conditions are affecting crab populations. 

Other crab management areas across BC also work hard to protect soft shell crabs. Opting to either have set closure dates that happen every year during the major moulting periods or haul restrictions that work to minimize crab injury and mortality by only allowing harvesters to haul their gear once per week. Protecting crab during the most vulnerable times is just one of the ways that BC harvesters ensure the long-term viability and sustainability of our Dungeness crab stocks. You can find more information on sustainability measures and fisheries management tools here.

This project is supported by the BC Government’s Buy BC Partnership Program; delivered by MNP LLP with funding from the Government of British Columbia.