If you’ve been down the Miners Bay pier this past summer, you might have noticed an unusual piece of equipment tied to the near end of the long dock: a white bucket, bobbing in the ferry wake, with a large water jug visible below the surface of the waves. Maybe you were down there at night and saw it all lit up, drawing creatures into its midst!

That was our light trap, and it is one in a network of 30 across Coastal B.C. This past April through to September, the Mayne Island Conservancy took part in the Hakai Institute’s Sentinels of Change light trap project. With the help of 19 island volunteers, the trap off the Miners Bay dock was emptied three days a week, with the main goal being to capture, count and measure Dungeness crab larvae.

Light trap at night, 2022. Photo by Katie Kushneryk.

The light trap project is inspired by and expands the Pacific Northwest Crab Research Group’s light trap network in the Washington Salish Sea. By monitoring populations and dispersal patterns of Dungeness crab megalopae (last larval stage), the project will provide additional information and tools to Dungeness crab managers and harvesters to support a sustainable fishery along the B.C. Coast.

How It Works

A megalopae is the last stage of a crab’s pelagic life, when they swim within the water column. After this, they become juveniles, shedding their carapaces and settling to the ocean floor to live as the scuttling bottom feeders we know them as: growing, moulting, and, if unharvested, living to approximately 8 years old. Dungeness megalopae are positively phototactic creatures (attracted to light) and inside the light trap is a bright LED light timed to turn on from dusk to dawn, drawing them in like moths to a flame. The trap is then checked the next morning and the catch counted and released.

Light Trap Check, 2023. Photo by Jackie Peterson. Here you can see the obvious size difference between Dungeness crab megalopa (the larger) compared to other species.

The goal is that data gathered from light traps will be used toward forecasting Dungeness crab abundance within a four-year cycle, potentially giving managers and harvesters advanced notice of a boom or bust year. It’s a long-term project in its second year in B.C. with lots to celebrate and many more discoveries to be made.

From 2022 to 2023, the number of organizations and communities involved has increased from 30 to 39, the number of light traps has increased from 19 to 30, and everyone included is looking forward to the 2024 season! With over 18,000 hours of light trapping this past year and the largest catch at a single site being over 20,000 megalopae in one day, the light trap community is approaching this upcoming season with a new set of developments and ideas for an even more successful outcome.

The Post Season Gathering

In October, I attended a Sentinels of Change gathering at the Hakai Institute’s Ecological Observatory on Quadra Island. Organized by Hakai scientists Heather Earle and Lauren Krzus, the gathering brought together light trap coordinators from along the coast, and was an inspiring event geared toward celebrating and reviewing the 2023 season and looking forward to 2024 with issues and solutions in mind.

The day began with an early breakfast, where guests sleepily ate toast and drank coffee together in the kitchen of our shared lodgings. There was a quiet early morning comradery as we got ready for the day and politely shuffled about, washing dishes and wiping up crumbs. Around 7:45am, it was time to head over to the Hakai Meeting House. After a short walk through a network of trails and driveways that lace through the Hakai property, joining together labs, lodgings and gathering houses, we arrived at a building that overlooked the water and offered a welcoming space to commence the day.

Lauren (left) and Heather (right) leading the discussion.

At 8am, everyone was gathered in the carpeted meeting room, settled in for an engaging presentation and discussion led by Heather and Lauren. Spurred on by hot coffee and a midmorning snack of buttery scones, the first part of the day brought a seasonal recap of current data, a Zoom presentation by the Pacific Northwest Crab Research Group’s Emily Buckner, and a site tour of the Hakai facilities. It was fascinating to learn about the variabilities of the light trap sites, ranging from Prince Rupert on the northern coast, all the way to south Vancouver Island and the mainland.

On the tour, we visited the Biodiversity Lab, which focuses on microbiology and plankton biodiversity, and The Marna Lab, which is a working lab with 40 mesocosms (controlled climate aquariums). Water for the lab is pumped up from the beach and put through a rigorous filtering process to remove cells, bacteria, and viruses. The mesocosms stood empty, in the midst of being prepared for a coralline algae research project set to begin the next day, but it was still intriguing to take a look around the world class facility, where the air was cold and tinged with the scent of salt water.

By lunchtime there was a familiarity within the group that made conversation lively and energetic. It was great to have the opportunity to connect with people who shared a common interest and experience and yet had many different perspectives to bring to the table. From Department of Fisheries employees to aquarium managers to community volunteers, everyone had valuable observations and notes to share throughout the day.

The meetings resumed after lunch with a discussion on ‘lessons learned’. Although many things went well, this light trap season was not without its challenges. Mortality of megalopae being at the forefront of many people’s minds, we got to work thinking of developments for next year’s traps that would take into account rising ocean temperatures (this year was a record-breaking year, with some sites logging 25 degrees Celsius), lack of oxygen in the traps, and processes for handling the large blooms of megalopae that were encountered throughout the summer.

Other common issues discussed were predator entry into the traps, biomass build up on the traps, technical issues with the timers and lights, waste build up from critters in the trap, and potential improvements to the app used for data collection. I am excited to see which solutions will be put into place next season; it will be especially rewarding knowing where the ideas originated from.

The Community Perspective

Although the variety of different sites and organizations brings a number of logistical challenges to the light trap project, it also offers an opportunity for something that is important to the Hakai Institute: that of community. Partnerships are essential when it comes to addressing environmental concerns that occur over large areas, such as fisheries management, marine pollution and the climate crisis, but working within a community makes it that much more rewarding and successful. The gathering was a terrific way to highlight the Light Trap community being built along the coast, from the U.S. up through Canada, and all throughout the Salish Sea.

Megalopae swimming in Miners Bay, June 2023.

Interested in joining the community and becoming a light trap citizen scientist? Email Justine at stewardship@mayneconservancy.ca and become a part of monitoring and preserving marine life in the Salish Sea. Families are encouraged to join as well!

Check It Out!

To view 2023 megalopae catch patterns, head to this interactive map. Look for the full report in the coming months.

1 Comment

Louis Vallee · November 9, 2023 at 12:12 pm

Thanks for the interesting article. Glad to see such research being done.

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