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Ongoing efforts to prevent a rise in the invasive European green crab population continue to yield positive results in Dungeness.
After first detecting the creatures in 2017 after years of monitoring, resource managers at the Washington National Wildlife Refuge in Dungeness north of Sequim caught just three green crabs for the 2020 season with more than 1,800 traps set between April-October 2020.
“Who knows, maybe we caught the last three crabs in the channel,” said Lorenz Sollmann, deputy project leader at the Refuge.
Since that first detection in 2017 with 96 green crabs caught, the numbers have dropped each year to 69 in 2018 and 57 in 2019.
But the effort to stop them hasn’t dwindled. In that span, Sollmann, his staff and volunteers have placed more than 10,800 traps to catch the crab.
Why such a large effort for such a small creature? Sollmann said the green crab, known for its five spines on the side of each eye, threatens eelgrass locally, which is the “nursery bed for so many things like endangered salmon and Dungeness crab, it’s a food source for other fish and birds, (and) herring lay their eggs in (it).”
“(Green crab) don’t actively eat it, but they uproot it foraging,” he said.
“Our eelgrass beds are already under a lot of pressure from all sorts of environmental factors.”
The three male green crabs from 2020 were all found in the Dungeness Spit’s base lagoon, which is promising, resource managers say, because females can release hundreds-of-thousands of larvae at least once a year. They can travel as far as 100 kilometers and possibly further, depending on currents and temperatures.
“This is the result of dedicated effort on the part of (the Refuge), as well as a little help from nature,” said Emily Grason, a marine ecologist and the University of Washington’s Crab Team program manager.
She said Dungeness, Sequim, Blyn, Port Angeles and Port Townsend/Jefferson County “may not have been subjected to an influx of more larvae from coastal or other sources.”
“Trapping in Dungeness Bay has shown that a dedicated effort, combined with favorable environmental conditions, can result in effective local population control,” Grason said.
Grason reports that no other green crabs were found in 2020 inland along the North Olympic Peninsula.
Neil Harrington, environmental biologist for the Jamestown S’Klallam Tribe, said they trapped in Sequim Bay last year with no green captures and intend to continue trapping this year, too.
Grason said a La Niña winter could be less favorable to survival of green crabs and resource managers look to capitalize on that with continued trapping.
Neah Bay
Neah Bay continues to see its green crab population remain consistent despite ongoing trapping efforts.
Adrianne Akmajian, a marine ecologist for Makah Fisheries Management, said volunteers caught 1,030 green crabs, which is down from 1,262 in 2019 between the Tsoo-Yess River, Wa’atch River and near Tsoo-Yess Beach.
However, she said their catch rate was higher.
In 2019, they caught about 0.56 crabs per trap compared to 1.9 crabs per trap last year.
Akmajian sad she attributes this to methodology as only a few part-time staff could go in the field at a time, so they switched almost entirely to recreational shrimp pots.
“We were able to set up to 12 shrimp traps (at six per river) and found that we would catch the same number if not more green crabs than we normally would have with the other trap types,” Akmajian said.
“We unfortunately had to cut our season short due to the wildfire smoke and my technicians heading back to college, so I think that also contributed to slightly lower catch than prior years.”
Green crab trapping efforts started there in 2017 when a visitor saw a green crab by the Wa’atch River and reported it to the Washington Sea Grant/Crab Team, which led further discoveries.
This year, Akmajian said she only has funding for dedicated trapping through June 30, but did receive research funding in July and August.
She and staff will perform studies and take underwater video to record interactions between green crab and Dungeness crab in the Wa’atch and Tsoo-Yess Rivers.
“We hope to document any direct negative interactions between subadult and adult crabs,” she said. “At the end of the project, we will do sort of a ‘trapping blitz’ for a couple days to try to remove as many green crabs as we can.”
She hopes to secure more funding in 2022 for dedicated trapping and research.
Two-three staff at the Washington National Wildlife Refuge will set traps for European green crab in April and May along the Dungeness Spit and potentially bring in volunteers as they are able with safety guidelines in place and government restrictions lifted due to COVID-19 protocols. Sequim Gazette photo file photo by Matthew Nash
Next in Dungeness
Because of the pandemic, volunteers in Dungeness and Neah Bay were unable to participate in trapping efforts.
Sollmann said COVID-19 changed 90 percent of the green crab effort by only using three staffers and not 30 volunteers due to health concerns.
At the beginning of the pandemic, he said they received approval for three staff to continue trapping with safe practices in the field.
“Social distancing in the field is very easy,” Sollmann said. But they all had to drive their own vehicles, which wasn’t fuel efficient, he said.
“Our volunteers are mostly retirees who are of a vulnerable age group but as they get their vaccines we’ll be set to bring them back out in a safe manner. We’re just not quite there yet.”
When resource managers begin trapping again on April 1, it’ll be two-three staff continuing the trapping effort but only in April and May.
Sollmann said most of their crabs, 67 percent, are caught in April and May.
“If we’re not catching anything, we’re not going to keep saturating,” he said. “Other projects have been held back.”
If the numbers are low or nil, then for the rest of the summer they’ll revert to a monthly monitoring program.
“If the crabs keep coming in from somewhere else then we’ll be ready. We’ll keep our finger on the pulse. We’ve shown you can be successful. It takes a lot of effort and commitment, but it can be done.”
Identification
Resource managers say if you find a live green crab or its shell in Washington, report it online to crabteam@uw.edu, but leave the crab in place.
For more information about crab identification, visit wsg.washington.edu. For more about aquatic invasive species, visit wdfw.wa.gov/species-habitats/invasive.
Since 2017, resources managers and volunteers at the Washington National Wildlife Refuge have placed more than 10,800 traps to catch the European green crab. They hope their efforts have dwindled the population enough to switch to a monthly monitoring program. Photo courtesy of USFWS
The Link Lonk
March 31, 2021 at 03:30PM
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Invasive green crab numbers dwindle in Dungeness - Sequim Gazette
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