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Tracking crabs near the mouth of the Columbia River

Researchers look at the impact of dredging on crabs
By Katie Frankowicz

The Daily Astorian

Published on September 4, 2017 9:07AM

Curtis Roegner, left, a fisheries research biologist with the National Oceanic and Atmospheric Administration, tosses a Dungeness crab back into the waters of the Columbia River during a recent study of the species.

Colin Murphey/The Daily Astorian

Curtis Roegner, left, a fisheries research biologist with the National Oceanic and Atmospheric Administration, tosses a Dungeness crab back into the waters of the Columbia River during a recent study of the species.

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Fisheries biologist Jake Biron removes a Dungeness crab from a trap to study and tag the species.

Colin Murphey/The Daily Astorian

Fisheries biologist Jake Biron removes a Dungeness crab from a trap to study and tag the species.

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Dungeness crab wait for the glue holding radio tags on their backs to dry before they will be returned to the Columbia River.

Colin Murphey/The Daily Astorian

Dungeness crab wait for the glue holding radio tags on their backs to dry before they will be returned to the Columbia River.

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A Dungeness crab before being fitted with a radio tag that will allow scientists to better study the species.

Colin Murphey/The Daily Astorian

A Dungeness crab before being fitted with a radio tag that will allow scientists to better study the species.

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Biologist Jake Biron, right, measures a Dungeness crab pulled from a trap placed in the Columbia River last week. The measurements are part of a study aimed at learning how the species adapt to changes in the environment.

Colin Murphey/The Daily Astorian

Biologist Jake Biron, right, measures a Dungeness crab pulled from a trap placed in the Columbia River last week. The measurements are part of a study aimed at learning how the species adapt to changes in the environment.

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Jake Biron, left, and Curtis Roegner, right, measure Dungeness crab on the Columbia River last week as part of a study to learn how the animals adapt to changes in their environment.

Colin Murphey/The Daily Astorian

Jake Biron, left, and Curtis Roegner, right, measure Dungeness crab on the Columbia River last week as part of a study to learn how the animals adapt to changes in their environment.

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Part of the study involves securing a radio tag to the shell of the Dungeness crab as a way to track the animal’s movements in the Columbia River.

Colin Murphey/The Daily Astorian

Part of the study involves securing a radio tag to the shell of the Dungeness crab as a way to track the animal’s movements in the Columbia River.

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A small radio tag will be glued to the shell of a Dungeness crab in order to track the animal’s movements in the Columbia River.

Colin Murphey/The Daily Astorian

A small radio tag will be glued to the shell of a Dungeness crab in order to track the animal’s movements in the Columbia River.

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Biologists Curtis Roegner, left, and Jake Biron, right, haul in a crab trap on the Columbia River last week as part of a study to learn more about the species.

Colin Murphey/The Daily Astorian

Biologists Curtis Roegner, left, and Jake Biron, right, haul in a crab trap on the Columbia River last week as part of a study to learn more about the species.

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It takes six hands to tag a Dungeness crab.

One pair of hands preps and tests small cylindrical, acoustic tags. A second pair lifts a crab from a bucket and gently dries a spot on top of its shell. A third has been busy mixing up epoxy in paper cups and now dabs a bit along a convenient groove at the top of the shell. The second pair of hands pushes the tag gently down onto this puddle of epoxy.

The crab looks a bit like a coal miner afterwards, head lamp in place, ready to plunge back into the darkness.

For the past three years, Curtis Roegner, a fisheries research biologist with the National Oceanic and Atmospheric Administration, has been tagging crabs in and around the Columbia River estuary, tracking their movements and trying to get a better understanding of how these animals respond to a variety of events and conditions, especially how they weather dredge operations near the river’s mouth.

As the dredges maintain the depth and width of important shipping channels, they dump sediment at various spots out in the ocean and near to shore. Sediment dumps close to shore are intended to increase the amount of sand on beaches and alleviate erosion, but researchers weren’t sure what the process meant for Dungeness crabs, a multimillion-dollar fishery for Oregon and Washington state.

“So far we’re finding there don’t seem to be any negative effects,” Roegner said. But, he added, their research is still preliminary.

For as much as they have discovered, many questions remain. Roegner says the unanswered questions become even more important as researchers chart changes in the crabs’ marine habitats — from low levels of dissolved oxygen in the water to ocean acidification and the widening sweep of climate change.


Questions


Dungeness crabs can use both the estuary and the ocean. Those that make it into the estuary appear to benefit from the experience, growing faster and, as a bigger crab, encountering fewer predators. But they can’t reproduce here and must return to the ocean eventually.

“When they do that, where they go out there, we don’t know,” Roegner said.

When they decide to go, though, the crabs leave quickly, floating and scuttling north. One of the crabs, tagged near Hammond recently, was caught not long after by a commercial fisherman in La Push, Washington.

In addition to studying the effects of dredge operations on the animals, NOAA biologists are also studying these apparent migration routes to better understand the Dungeness crab’s life cycle. The tags they glue to the crabs’ backs give off a coded signal and are intended to stay on a crab until its next molting.


Catch and release


On Friday, the Columbia River was smooth. The only wakes came from passing Buoy 10 fishermen intent on salmon. The Columbia River Bar, which can be a fearsome presence even on a good day, looked calm, just a scattershot of waves breaking between the arms of the North and South jetties.

After some issues with getting the epoxy mix just right, Roegner and contractors Jacob Biron, a biologist, and Brian Kelly, a boat operator — both with Ocean Associates — found their rhythm tagging five female Dungeness crab. Epoxy, tag, crab, repeat.

Crabs waiting for the epoxy to dry rested in shallow plastic bins, blowing bubbles. The researchers use female crabs because fishermen who catch them are required to throw them back, and Roegner wants these tagged crabs in the water for as long as possible.

Once the epoxy sets, the crabs were dropped over the side of the boat. They disappeared quickly in the murky water. Then Roegner and Biron lowered a hydrophone over the side to see if they could pick up signals off the tags. The machine made an open, echoing sort of whirring noise for a while before Biron heard the hollow “pings” that tell him it has registered a tag. He checked the number: It matched one of the crabs they just released. A minute later, more pings. This time it’s an unfamiliar number.

“That’s a sturgeon, maybe?” Roegner says. They’ll see the same sturgeon numbers pop up in the estuary from year to year. Once, they got a ping on a tag that belonged to a great white shark cruising around the estuary.

Several minutes later all five crabs were accounted for, and Kelly turned the boat back toward the Warrenton Marina.


Dredge passing


The crabs tagged Friday were caught and released on the Washington side of the river, outside of Ilwaco’s Baker Bay, near a dredge dispersal site. It is likely they could encounter, or already have encountered, a dredge dump.

Roegner and his team once dropped cameras down in the water attached to a lander — it looks a bit like a barbecue grill’s circular cooking grate — loaded with bait to see what happens to the crab and other animals when a dredge passes through.

Within minutes of the lander hitting bottom, the camera showed Dungeness crabs checking it out. They skittered sideways, circled each other, poked at the bait. If crabs can be happy, these crabs were happy. Surges washed over them, making them sway and river sediment blew past in underwater clouds. But strong currents and blowing debris do not bother Dungeness; they are adapted to this environment. They remained focused on the bait.

Then Roegner showed the dredge spoil dump from the dredge vessel Essayons — in slow motion, the camera at eye-level.

One minute, crabs clustered around the bait canister. The next, a cloud of dust and debris began to bloom behind them. Fish — just pale flashes trying to race ahead of the clouds — zoomed past. The crabs joined them, legs sprawling, as the dredge spoils hit them like a storm and turned the screen black.

Traumatic? Maybe. But within half an hour or an hour, the crabs were back, jabbing at the bait. Just another day.

Roegner asks any fisherman who lands a tagged crab to write down the number listed on the tag and make a note of the date and location — coordinates if possible, but a general place name works, too. E-mail this information to curtis.roegner@noaa.gov











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