Hakai Magazine

juvenile Dungeness crab in person's hand
By counting megalopae—larval crabs—caught in a series of traps in the Salish Sea, British Columbia, researchers are gaining insight into the subtleties of the population distribution of the Dungeness crab. Photo by Anna Smith

Shining the Light on Baby Crabs

In British Columbia, a monitoring project with light traps may illuminate the future of the prized crustaceans.

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by Spoorthy Raman

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It’s a gray summer evening on Galiano Island, a long strip of land about 1.5 kilometers across at its narrowest. Home to nearly 1,400 people, it is one of the 200-odd islands and islets in the Gulf Islands archipelago dotting the Salish Sea between Vancouver Island, British Columbia, and the mainland coast. The air here at the wooden pier in Whaler Bay on the island’s southeast end is heavy and moist, tinged with a whiff of boat fuel and old wood, and infused with sea salt. Amid a lineup of motorboats, pleasure boats, and tugboats, I spot Jeannine Georgeson on the boardwalk, dressed for the weather in jeans and a black rain jacket.

Georgeson is the coordinator of the Institute for Multidisciplinary Ecological Research in the Salish Sea (IMERSS), a local grassroots organization comprising scientists, scholars, artists, and community members like herself, who take part in a variety of research, from mapping local biodiversity to monitoring microclimatic changes. As we saunter down the boardwalk, Georgeson reminisces about her childhood here: playing on the pier and fishing off the dock while her uncle and grandpa worked on their boats. Over the past two decades, however, things have changed. The number of fish in the bay has dwindled, and so has the size of her extended family’s fishing boat fleet. The silver-hulled Island Spirit II, a seiner that hasn’t fished in the past couple of years, sits docked at the pier as witness to the bygone years.

As daylight begins to fade, Georgeson cuts short her reminiscence. It’s already 8:20 p.m., and she needs to set a crab trap. Tonight, however, there will be no crab dinner—a once-cherished meal for her family with its Coast Salish and Sahtú-Dene roots. Instead, this trap will catch larval crabs as part of a study that, in time, could help ensure crab dinners in years to come.

At the corner of the pier, wiping raindrops off her face, Georgeson pulls up what appears to be a half-submerged white bucket, but it’s actually a fairly sophisticated sampling tool—a light trap. Below the bucket, a series of funnels and sieves is plugged into a plastic jar. Inside, a pipe holds a strip of LED lights—all contrived to lure and trap months-old, pea-sized Dungeness crab larvae, which, like many zooplankton, are attracted to light. As she unscrews the bucket’s lid and removes a timer from a yellow case, a school of shimmering anchovies swims by and a distracted Georgeson exclaims in joy. Sights like these are rare on the island these days, she explains, but when she was young, her uncle would catch anchovies in a tote and bring them home for her to see. She watches the school until the last bit of silver is gone, then turns back to the trap and sets the timer to turn the light on at 8:30 p.m., half an hour before sunset. She gives the trap a thorough check and drops it back in the water.

Jeannine Georgeson, coordinator of the Institute for Multidisciplinary Ecological Research in the Salish Sea, lowers a light trap off the dock at Whaler Bay, Galiano Island, British Columbia.

Jeannine Georgeson, coordinator of the Institute for Multidisciplinary Ecological Research in the Salish Sea, lowers a light trap off the dock at Whaler Bay, Galiano Island, British Columbia. Photo by Shanna Baker

The light trap at Whaler Bay is one in a network of 20 traps placed throughout the Canadian side of the Salish Sea, from Read Island in the north to James Island near Sidney in the south, as part of the Hakai Institute’s multiyear Sentinels of Change program. Launched in 2022 to mark the United Nations Decade of Ocean Science for Sustainable Development, this community-centered initiative involves understanding how marine invertebrates are adapting to the changing environment. The light trap project, which focuses on the native Dungeness crab—a much-loved treat on the coast that can grow to the size of an adult’s outstretched hand—is a part of this program. The project partners with over 30 organizations, such as IMERSS, First Nations communities, and institutions such as the Shaw Centre for the Salish Sea in Sidney, to manage the network of light traps. Just like Georgeson, volunteers from other partner organizations deploy similar traps in the evenings and monitor them at least every two days starting in April and continuing until the end of August.

As we walk back to our cars, I ask Georgeson how many baby crabs we could see tomorrow. “It’s a guessing game,” she says.

Almost everything is a guessing game with Dungeness crab in the Salish Sea—its life history, numbers, and distribution, particularly in the larval and juvenile stages. For a species that is culturally revered by Indigenous peoples on the coast, a once-in-a-while feast to seafood aficionados on both sides of the border, and worth anywhere from CAN $60-million to $210-million per year for the Canadian economy (based on the wholesale value from 2011 to 2021), our understanding of the species is checkered at best. What we know about their distribution in Canada is largely based on their adult lives. On the US side of the border, most knowledge about the crab’s life history, until recently, came from its life in the open Pacific Ocean, a habitat that is very different from the Salish Sea—which straddles the Canada-US border and extends into Puget Sound in Washington State. Unlike the outer coast, an intricate network of islands and waterways in the Salish Sea creates a convoluted coastline of coves and beaches, islets and reefs, all of which meddle with the ocean currents. As well, the mighty Fraser River adds, on average, over 2,700 cubic meters of fresh water—as much water as in an Olympic-sized swimming pool—every second. Yet, our understanding of this crab species hinges on extrapolating bits and pieces from its life—much like creating a city map with knowledge of only a few streets—raising concerns about sustainability and the future of the species in the face of climate change.

The network of light traps can fill these gaps in our understanding of Dungeness crab in the Salish Sea. Matt Whalen, a marine ecologist now at Virginia State University who led the Sentinels of Change program for the Hakai Institute until the end of 2022, says that the goal of the monitoring project is to track the arrival and abundance of larval Dungeness crab. “Understanding when these larval crabs arrive and how abundant they are can give us a sense of how strong the population is and how strong the fishery will be in three to five years,” he says.

map of light trap locations in the Salish Sea

A network of light traps (the yellow dots), which is coordinated by the Sentinels of Change project of the Hakai Institute on the Canadian side of the border and by the Pacific Northwest Crab Research Group in Washington State, monitors the distribution of Dungeness crab larvae in the Salish Sea. Map data by ArcGIS, monitoring station location data by Sentinels of Change

Since 2019, the Pacific Northwest Crab Research Group (PCRG) has set up a similar network of light traps in Puget Sound. On the Canadian side, however, none of this data existed prior to 2022. As the PCRG continues its work and the Sentinels of Change program ramps up, the hope is that by the end of this decade the data from both sides of the border could help fisheries managers make decisions about how the crab can be harvested sustainably into the future.

The Dungeness crab larvae that Georgeson hopes to catch in her trap tonight began their journey months ago. Between spring and summer, female crabs molt, shedding their old shells and growing new ones. Just before the female begins to molt, the male grabs her in a premating embrace that can last for days—the long hug being a way to ensure another male doesn’t claim her—before finally releasing his sperm when she sheds her old shell. Females store the sperm until fall and then fertilize their cache of eggs, which can number between 200,000 and two million. Finally, in late winter or early spring, the transformed eggs hatch as free-floating larvae called zoeae. The microscopic hatchlings are now at the mercy of predators and ocean currents.

Marine biologist Alan Shanks has spent decades studying how the larvae of invertebrates make the journey from their pelagic stage—floating in coastal waters—back to the shore. In the 1980s, he studied the arrival of lined shore crab larvae around San Diego, California, using string mops hung from a pier. “It worked amazingly well,” he says—the larvae grabbed onto anything floating and the mops garnered tens of thousands of them. But when he began studying Dungeness crab larvae in the 1990s during his time at the University of Oregon, where he is now professor emeritus, the mop technique didn’t work. Dungeness crab larvae aren’t grabbers but they are attracted to light, so Shanks designed another inexpensive tool—the light trap—to accomplish his goal.

Light traps use a strip of LED lights to attract the larvae of Dungeness crab and other plankton. Video by Shanna Baker

By meticulously counting the number of larval crabs that arrived at Coos Bay, Oregon, during spring and summer over five years, and mapping the data against the tides and ocean currents, Shanks found that currents in the Pacific Ocean played a role in how the larvae moved. In the winter, the northward-flowing Davidson Current gives a free ride to the freshly hatched zoeae. On this four-month-long journey, they metamorphose into the next larval stage, the megalopa. These pea-sized, crablike blobs are then carried south by the California Current in late spring and early summer and pushed toward the shore. By then, the larvae are ready to morph into fingernail-sized crabs that sink to the bottom to begin their benthic lives and, over the next four years or so, grow from juveniles into harvestable adults.

At first glance, the tiny megalopae may appear insignificant, but their numbers tell a story. Shanks’s work with light traps on the Oregon coast shows that the number of megalopae in an area today gives an estimate of how many adult crabs will be there in four years’ time—approximately when they reach harvestable size. When he compared his calculations with the actual catch numbers reported by the Oregon Dungeness Crab Commission, his estimates were off by only a small fraction. “So what we’ve got is that the commercial landing is in fact set by the abundance of larvae returning to the shore, but in a complex way,” explains Shanks.

life stages of juvenile Dungeness crab

Dungeness crab at several life stages (left to right): zoea and megalopa larvae, which are pelagic (suspended in the water); and a juvenile, which lives on the seafloor. Photo by Washington Department of Ecology

Since these crab larvae all hatch on the outer coast at around the same time and are moved along by the same currents, they are thought to be one connected population. Depending on the currents’ strength, each area along the coast gets a share of this pool of larvae, which then grow up to become adults.

But in the Salish Sea where numerous islands break up the contiguous ocean and disrupt the currents, Dungeness crab larvae do not move as they do on the outer coast and can get isolated by tides and geography, explains Shanks. “What I found [on the outer coast] almost undoubtedly does not apply there at all,” he says. The lives of these larval crabs in more meandering waterways are largely a mystery. “I think there [are] big questions about what crabs are doing in this much more heterogeneous landscape,” says Whalen.

This animated map shows when and where larval crabs were caught in the light traps during the 2022 field season of the Sentinels of Change project. Map by the Hakai Institute/Sentinels of Change

The larvae that are drawn to the light in Georgeson’s trap—and others throughout the Salish Sea—will help reveal some of these details of Dungeness crab biology, giving fisheries managers a better sense of what’s really happening in a large swath of their habitat.

Back at the Whaler Bay dock the next morning, Georgeson and I meet Whalen and Heather Earle, then the coordinator of the Sentinels of Change program and now its lead. Eager to see the crab larvae in the trap, we start down the boardwalk. Georgeson walks in with a blue Walmart bag that has all the tools of this science: two plastic spoons, a black cloth the size of a handkerchief, a notebook-sized transparent plastic tray with a piece of measuring tape stuck to a corner, a plastic measuring cup, and a plastic dishwashing tub.

Georgeson steadies her feet, grips the line, and hauls up the water-filled light trap, letting it drain for a minute. She unscrews the pipe at the bottom end of the trap and pours the “larva soup,” as she calls it, into the plastic tub, and bursts out—“Wow, this is crazy!” In the tub, hundreds of megalopae hover as though they just woke up from a slumber. About 10 juvenile sticklebacks, three bristle worms, a pipefish, and a few bits of algae that have found their way into the trap are quickly released by Earle and Georgeson. Then, they begin to count the megalopae, painstakingly scooping each one with a spoon. As per the protocol, they put the first 30 into the plastic tray, and Georgeson takes a picture with her phone so the megalopae can later be measured using a software program. The rest go into the plastic cup one by one and we count a final tally of 247—the highest single-day count recorded at Whaler Bay. As observed in the PCRG traps on the US side, at the start of the season in April and May and toward the end in August, the catch numbers typically taper off—often reaching just 10 or fewer and sometimes even none. Until today, the highest Georgeson’s traps had caught was 100 megalopae in June. Two days after my visit in August, she counted 96, and by the end of the month, the season’s total was 550.

Jeannine Georgeson and Heather Earle

Georgeson and Heather Earle, lead researcher for the Sentinels of Change project, count megalopae caught in the light trap at Whaler Bay. Photo by Shanna Baker

The first year’s data from the light trap monitoring network, which involved about 200 volunteers catching just under 20,000 megalopae between April and August 2022, shows marked differences in crab distribution across the Salish Sea. While it may take a few more years of data to confirm any patterns, Whalen says the 2022 data hints that a part of the outer coast larval pool might enter the Salish Sea through the Juan de Fuca Strait (south of Vancouver Island and along the Canada-US border), travel north along the east coast of Vancouver Island to Quadra Island, and then turn east toward the BC mainland. To date, the sites closest to the open ocean seem to have caught more megalopae early in the season, with numbers generally declining as the distance increases.

The trap at Hope Bay on Pender Island, for instance, which is close to where the Salish Sea connects to the open Pacific, caught 5,015—the most for a site across the network in 2022. On the other hand, the trap at Heriot Bay on Quadra Island, farther away from the open Pacific connection, recorded only 11. And while the first megalopae of the season were caught in May on Saturna, Galiano, and Mayne Islands in the southern Gulf Islands, it took until mid-June for a trap on the mainland coast to snare its first larvae.

juvenile crab on a plastic spoon

The beauty of the light trap project is the accessibility of its sampling gear, including a simple plastic spoon used to count megalopae. Photo by Shanna Baker

In Puget Sound, the number of megalopae caught in PCRG’s light trap network also showed a general catch pattern. For the most part, light traps at the northern sites, which are closer to where the Salish Sea meets the open Pacific Ocean, caught between 25,000 and 100,000 megalopae during the 2022 season. In contrast, sites farther south in the sound caught as few as 10 to 20, although PCRG researchers stress that there is variation along this gradient, with some northern sites performing as well as or worse than sites to the south.

While Earle and Whalen can’t yet say if 2022 was a good or a bad year for the larval crabs on the Canadian side, since there is no baseline data to compare against, these numbers start to stitch together a story about where the larval crabs come from and how they move in the Salish Sea—a key insight that didn’t exist until now—and possibly how that will translate to crab harvests four years from now.

Fisheries and Oceans Canada (DFO), the federal organization that manages the Dungeness crab fishery in Canadian waters, treats crabs on the entire BC coast as a single stock biologically. According to its current assessments, the crab stock is determined as healthy based on steady commercial catch numbers. “Since [the crab fishers are] catching a lot of them, we can use that as a proxy for abundance,” says Brendan Aulthouse, the Dungeness crab stock assessment biologist at DFO. The agency also collects biological data in specific areas by deploying baited crab traps for 24 hours in each of May and October—before the harvest season opens and at its end. These stock assessments note shell condition (for molt timing), injuries, sex, and size, among other traits, all of which will help determine if the ratio of males to females can sustain reproduction and the availability of crabs for recreational and First Nations harvesters.

Matt Whalen, lead of the Sentinels of Change project until the end of 2022, empties a light trap at Heriot Bay, Quadra Island, British Columbia. Video by the Hakai Institute

Unlike other species, for which there are set quotas, crabs are largely managed through specific harvesting restrictions. DFO uses the 3S (sex, season, and size) management strategy, a practice that’s more than a century old, to restrict crab catches. Fishers can only retain male crabs that are larger than a specific size (in Canada the minimum is 165 millimeters) and not in their soft-shell stage, which is right after molting. This keeps egg-laying females in the water and gives males at least one opportunity to mate before they are caught. When the Dungeness crab fishery began in San Francisco Bay in the 1840s, where the 3S strategy first came into practice to prevent decades of overharvesting, the regulation was sufficient to save the fishery from collapsing because the harvested crabs were, in theory, replaced by the newly arriving larvae each year.

But when fishing pressure increases in the inner waterways, where crab populations may not be replenished like on the outer coast, long-term sustainability is questionable. In the past few years, the cracks in current management practices have begun to show up.

The Indigenous peoples living on the central coast of British Columbia have had a deep relationship with the land and sea for millennia, and the ocean’s bounty has shaped their cultures. Dungeness crab, for instance, is more than just food—it’s a vital part of ceremonies and potlatches. In the early 2000s, members of the Heiltsuk Nation noticed a sharp decline in the crab numbers in their territorial waters and reached out to their fisheries manager, Mike Reid. The neighboring Kitasoo/Xai’xais, Wuikinuxv, and Nuxalk First Nations also witnessed similar declines and blamed them on the harvesting pressure from commercial and recreational fishers. Distraught, the First Nations sought DFO’s help to close the fisheries in their waters to revive the crab numbers. But DFO’s coast-wide stock assessment methods failed to catch these local declines, and DFO dismissed the nations’ concerns.

Frustrated with a pattern of losses in culturally important marine species like abalone, rockfish, eulachon, and now Dungeness crab, the nations took matters into their own hands and set up the Central Coast Indigenous Resource Alliance (CCIRA) to restore healthy ecosystems in their traditional territories. One of the mandates for the organization, says Alejandro Frid, a marine ecologist hired by CCIRA, is to collect necessary data about various species, including Dungeness crab, to demonstrate to DFO that there is indeed a problem.

Nuxalk Guardian Watchmen conducting Dungeness crab stock assessments in Heiltsuk First Nation waters

Coastal Guardian Watchmen from the Nuxalk Nation measure an adult Dungeness crab as part of a Dungeness crab stock assessment on the central coast of British Columbia. Photo courtesy of the Central Coast Indigenous Resource Alliance

In 2014 and 2015, using traditional laws, the nations closed 10 sites in their territorial waters to recreational and commercial crab fishers and earmarked another 10 sites where the fishery was open to all. Over a period of 10 months, they monitored the crabs at these sites. A study led by Frid found that in the closed areas, male Dungeness crabs of legal size were, on average, 1.3 centimeters larger than those at sites where fisheries were open. They were also more abundant—one additional male was caught per trap at closed sites as compared with traps at open sites. “That means, if you stop exploiting them, they will bounce back relatively quickly,” says Frid. The results were not enough to persuade DFO that First Nations in the region were unable to catch enough crabs for cultural purposes, and the fisheries remained open.

Determined to highlight the impact that declining crab numbers had on the way of life for nations on the central coast, in 2016, Frid and his collaborators from the University of Victoria in British Columbia and CCIRA compiled observations of crab abundance, drawing on the extensive knowledge and lived experiences of First Nations peoples. Between 1926 and 1996, fishers reported catching, on average, about 24 crabs per trap—more than enough for their families’ needs. But between 1996 and 2016, that number fell to a staggering six, a decline in average catch rate of about 77 percent. Fishers also expressed that a successful trip—one that would garner enough crabs for ceremonial and food purposes—was 15 crabs caught over 24 hours. Of the nine study sites, only one site showed that probability of success.

When presented with this data, amid mounting pressure from the nations to act, DFO agreed to come to the table. After several rounds of discussions, some of which are ongoing, 17 areas in the central coast were closed to commercial fishers in 2021. Fifteen of these were also closed year-round to recreational harvesters, and two were closed seasonally. While it was a start, Reid notes that a lot of areas within Heiltsuk territory were still open for business. Of the 60 or so designated areas within their territory, only five were closed.

The nations blame the crab declines in their territories on commercial and recreational crab fishers, who have thronged the central coast in recent decades. “If you’re here in Bella Bella, you would see sports and recreation boats coming and going all the time,” says Reid. Currently, DFO mandates commercial crab fishers to report their catch numbers, but data from recreational fishers is scarce. “We don’t really have quality data on where recreational fishers are harvesting crabs,” says Aulthouse. Instead, DFO relies on recreational fishers to disclose their catches for a specific month of the year through a self-reporting program for all adult license holders and, at times, may ask fishers for additional information.

A similar tale of crab declines has played out in south Puget Sound, where tribal and recreational Dungeness crab catches dropped from 97,252 kilograms in 2012 to 3,937 kilograms in 2017. Although the Washington Department of Fish and Wildlife (WDFW) and the surrounding tribes have closed the fishery in some areas since 2018, the numbers are yet to recover. The WDFW refutes overfishing as the cause of crab declines because, according to them, these numbers should have been replenished by now, as happens on the outer coast. But, as Shanks points out, in labyrinthine waters where there may not be regular pulses of larvae, local declines are possible. Without granular details of the crab’s life stages, it is hard to predict or decipher the reasons for such local declines.

A megalopa larva of a Dungeness crab. Video by the Hakai Institute

On the Canadian side, DFO is trying to bolster fisheries management decisions for Dungeness crab by adding data points. But monitoring crab numbers across the 27,000-kilometer-long coastline—over half of the Earth’s circumference—with only Aulthouse at the helm is a massive task. Stock assessment surveys provide some data points about adult crabs, but the organization has no data about the first two years of life—a period that is critical for understanding crab biology and life cycle. “[The light trap] project does potentially fill that knowledge gap and could lead to better science in the future,” Aulthouse says. As such, DFO has been involved in the project since its beginning and monitors a few light traps in the network.

Despite the enthusiasm and quest to understand Dungeness crab biology in the unique seascape of the Salish Sea, the greatest missing data point is how climate change may impact these crustaceans. When I ask Shanks how the crabs would fare in acidifying oceans and warming waters, he is at a loss: “Climate change, oh God! I don’t know what’s going to happen!” So far, a handful of studies have looked at climate change effects on Dungeness crab, and the findings are concerning.

A 2020 study found that increased ocean acidity dissolved larval crab shells and impaired the development of hairlike sensory organs that help the larvae navigate. Another predicts that by the end of the century, if emissions continue unabated, depleting oxygen levels in the warming coastal waters would be the worst stressor for Dungeness crab at all life cycle stages, while ocean acidification and increasing water temperatures would mostly affect larval crabs. Low oxygen levels in the water due to upwelling, when nutrient-rich and oxygen-poor waters are brought to the coast in spring and summer, decrease the survival of these crustaceans. In the Salish Sea, where crab numbers may already be constrained, climate change may result in their further decline. But Whalen hopes that multiyear larval abundance data, which the light trap project will collect, may also increase our understanding of how well the crabs may fare in their changing habitats—a crucial data point for fisheries to manage crab populations sustainably.

For Georgeson, who is at the Whaler Bay dock almost every other day in the spring and summer to work with the trap, the motivation to be involved in the light trap monitoring project goes beyond science. It’s a way to connect with her culture, in which crabs hold a dear place, and to preserve family traditions, she says. She likens the work to her efforts to learn Hul’q’umín’um’, her family’s Coast Salish language. I ask her if she’ll continue to be involved in the project next year. “I’d love to do this for another 10 years,” she says if that means preserving the Dungeness crab and its cultural significance for future generations. “I want my granddaughter to know what it’s like to be able to be a part of this.”

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Cite this Article: Spoorthy Raman “Shining the Light on Baby Crabs,” Hakai Magazine, Apr 25, 2023, accessed May 17th, 2024, https://hakaimagazine.com/features/shining-the-light-on-baby-crabs/.

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