What has eight legs, two light-tipped claws, and huge cultural, commercial and ecological value on the west coast? Dungeness are a widely loved large crab, known for their sweet, mild taste. In the Hul’qumi’num dictionary, this culturally significant species is noted as the most commonly eaten type of crab for First Nations along the west coast. These crab also have immense commercial value, earning them the title of “most important crab species harvested in British Columbia” according to Fisheries and Oceans Canada (DFO). Humans aren’t the only ones who enjoy eating Dungeness. These crab are an essential link in local marine food webs, providing food for everything from harbour seals to halibut. Before reaching their adult form, they float free on ocean currents as larvae, and are eaten by a wide variety of fishes and invertebrates.
Identifying Dungeness Crab
Whether they’re hunting for smaller invertebrates in meadows of eelgrass or resting between rocky intertidal shelves, adult Dungeness crab spend most of their time in water shallower than 50m. They’re distinctly a western North American coastal species, found in waters from Alaska to southern California. Their back shell, or “carapace,” is oval shaped and can vary in colour from yellow-brown to purple. Their carapace can measure over 20 cm across, but adults rarely live long enough to grow to this size due to fishing pressures. Females produce 200,000 to two million eggs per breeding season, depending on their size, and eggs hatch between late winter and early spring. After several moults, the larvae look like miniature crab and can be found near shore between May and September.
Red rock crab are often found in overlapping habitats with Dungeness, but have smaller bodies and larger, black-tipped claws. Dungeness have comparatively slender claws with light tips. The European green crab, an invasive species in the Salish Sea, can be distinguished from native crab species by their spines: green crab have five sharp spines on each side and three rounded lobes between their eyes.
Perils and Unanswered Questions
Dungeness and other marine invertebrate populations along the west coast are faced with multiple risks. Commercial harvesting, habitat destruction, ocean acidification, low oxygen conditions, pollution, and competition and predation by European green crab, to name a few, all have the potential to negatively impact populations. In some areas, crab harvesters are reporting increased difficulty harvesting Dungeness, suggesting the numbers have declined.
Unanswered questions that are critical to effective management include the ways in which environmental variables influence these crab throughout their lives, as well as population distribution and abundance. Understanding the timing, distribution, and connectivity between populations of Dungeness crab in their early life stages is vital for rebuilding populations. By learning more about crab larvae, we can also learn more about Dungeness abundance: the abundance of crab larvae is a strong indicator for adult abundance years into the future.
Light Trap Monitoring
To address these knowledge gaps and contribute to a growing body of crab research in the Salish Sea, we are excited to be partnering with Hakai Institute and participating in their Sentinels of Change initiative. This community-based research project focuses on improving our understanding of marine invertebrate populations throughout the region. Data will be provided to managers, policy makers and harvesters to help these bodies make informed conservation decisions.
To monitor Dungeness crab larvae in Active Pass, a light trap will be deployed off the Miner’s Bay dock this spring and will be monitored until the fall. Light traps float at the ocean surface and turn on at night, attracting marine animals such as larval crab, shrimp, fish and octopus. Larval Dungeness crab found in this trap will be counted and released to help assess population dynamics.
Light traps are now deployed and monitored throughout the Salish Sea, on both sides of the Canada-USA boarder. This research is inspired by and comparable with an existing light trap network in Puget Sound, coordinated by the Pacific Northwest Crab Research Group. Together, our efforts will help provide a holistic picture of larval Dungeness distribution and abundance.
Marine Research Volunteers
Calling all citizen scientists! We will be looking for volunteers in the coming months to help us monitor the light trap and collect vital marine data. From April 15th to September 1st, our volunteer pairs will each check the trap once a week and record the number of Dungeness larvae found within. If you’re interested in getting involved with this exciting marine initiative, contact our Stewardship Coordinator Katie (katie@mayneconservancy.ca) for more information.
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