{"id":41848,"date":"2023-04-25T00:05:23","date_gmt":"2023-04-25T07:05:23","guid":{"rendered":"https:\/\/hakaimagazine.com\/?post_type=custom_features&p=41848"},"modified":"2023-05-02T08:37:35","modified_gmt":"2023-05-02T15:37:35","slug":"shining-the-light-on-baby-crabs","status":"publish","type":"custom_features","link":"https:\/\/hakaimagazine.com\/features\/shining-the-light-on-baby-crabs\/","title":{"rendered":"Shining the Light on Baby Crabs"},"content":{"rendered":"

It\u2019s 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\u2019s 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.<\/p>\n

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\u2019s fishing boat fleet. The silver-hulled Island Spirit II<\/em>, a seiner that hasn\u2019t fished in the past couple of years, sits docked at the pier as witness to the bygone years.<\/p>\n

As daylight begins to fade, Georgeson cuts short her reminiscence. It\u2019s already 8:20 p.m., and she needs to set a crab trap. Tonight, however, there will be no crab dinner\u2014a once-cherished meal for her family with its Coast Salish and Saht\u00fa-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.<\/p>\n

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\u2019s actually a fairly sophisticated sampling tool\u2014a 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\u2014all 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\u2019s 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.<\/p>\n

\"Jeannine<\/a>

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<\/p><\/div>\n

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\u2019s 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\u2014a much-loved treat on the coast that can grow to the size of an adult\u2019s outstretched hand\u2014is 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.<\/p>\n

As we walk back to our cars, I ask Georgeson how many baby crabs we could see tomorrow. \u201cIt\u2019s a guessing game,\u201d she says.<\/p>\n

Almost everything is a guessing game with Dungeness crab in the Salish Sea\u2014its 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\u2019s life history, until recently, came from its life in the open Pacific Ocean, a habitat that is very different from the Salish Sea\u2014which 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\u2014as much water as in an Olympic-sized swimming pool\u2014every second. Yet, our understanding of this crab species hinges on extrapolating bits and pieces from its life\u2014much like creating a city map with knowledge of only a few streets\u2014raising concerns about sustainability and the future of the species in the face of climate change.<\/p>\n

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. \u201cUnderstanding 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,\u201d he says.<\/p>\n

\"map<\/a>

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<\/p><\/div>\n

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.<\/p>\n

\n

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\u2014the long hug being a way to ensure another male doesn\u2019t claim her\u2014before 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.<\/p>\n

Marine biologist Alan Shanks has spent decades studying how the larvae of invertebrates make the journey from their pelagic stage\u2014floating in coastal waters\u2014back 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. \u201cIt worked amazingly well,\u201d he says\u2014the 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\u2019t work. Dungeness crab larvae aren\u2019t grabbers but they are attracted to light, so Shanks designed another inexpensive tool\u2014the light trap\u2014to accomplish his goal.<\/p>\n

Your browser does not support the video element.<\/p><\/video>\n

Light traps use a strip of LED lights to attract the larvae of Dungeness crab and other plankton. Video by Shanna Baker<\/span><\/p>\n

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.<\/p>\n

At first glance, the tiny megalopae may appear insignificant, but their numbers tell a story. Shanks\u2019s 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\u2019 time\u2014approximately 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. \u201cSo what we\u2019ve got is that the commercial landing is in fact set by the abundance of larvae returning to the shore, but in a complex way,\u201d explains Shanks.<\/p>\n

\"life<\/a>

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<\/p><\/div>\n

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\u2019 strength, each area along the coast gets a share of this pool of larvae, which then grow up to become adults.<\/p>\n

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. \u201cWhat I found [on the outer coast] almost undoubtedly does not apply there at all,\u201d he says. The lives of these larval crabs in more meandering waterways are largely a mystery. \u201cI think there [are] big questions about what crabs are doing in this much more heterogeneous landscape,\u201d says Whalen.<\/p>\n