(sea whooshing) (birds cawing) - [Narrator] On this summer day in 2022, Cat de Rivera and her team from Portland State University are conducting a survey of European Green Crab in Siletz Bay.

Since their arrival on the West Coast in the 1980s, these little green monsters have established themselves as some of our most successful and destructive invaders.

- Green crabs are voracious shellfish eaters.

They'll eat the baby Dungeness crabs as well as clams and oysters, and green crab densities can get very high, totally depleting the number of clams or oysters in that area.

So that's why we're worried about them.

It looks like we have some green crabs and some Dungeness and sculpin in this trap.

- [Narrator] The survey is one of many long-term studies aimed at controlling their numbers and will take the team from the salty ocean side to the fresher, warmer waters of the upper estuary.

- We have another male, Dungeness.

Green crabs have incredible tolerances for temperature.

They can be much warmer than our native crabs can and thrive, but they're also pretty successful at cold temperatures.

Similarly, they're very tolerant of different salinities, so they can be fully marine, they can live at 5 parts per 1,000, which is very fresh.

- [Cat] Salinity?

- Salinity 6.3.

- [Cat] And what about temperature?

- [Luna] 23.9.

- They're great survivors, and this is why they've managed to invade so many areas around the world, and now in Oregon too.

So we have five juvenile green crabs... - [Narrator] we first met Cat back in 2006 when she and her colleague Sylvia Yamada from Oregon State University were documenting the early stages of the invasion.

- Back in 2006, red rock crabs, which are our native crab we have, would prey on them, and they could keep their numbers in check.

So we were keeping our eye on them, but we weren't as worried for Oregon shellfish as we are now.

- [Narrator] Much of that worry comes from the enormous impact these crabs are having in Washington State, the US's largest shellfish producer.

One hotspot is the Lummi Sea Pond near Bellingham, an important aquaculture site for the Lummi tribe.

Exponential growth in populations there have led to an intensive strategy of year-round trapping.

While Oregon's shellfish industry is orders of magnitude smaller than that of Washington, economics are not the only issue.

- Green crabs dig up eelgrass.

Eelgrass is a really important habitat, and they can destroy just the whole ecology of the systems as well.

- [Narrator] Spend an afternoon at Neetarts Bay on Oregon's North Coast and the problem becomes clear.

- When green crabs first invaded Oregon, this was one of the sites that they turned up in, you know, moderate numbers, and now they're really coming up again.

So I'm just gonna look under rocks here for them.

All right, here's our first green crab of the day, just stuck in the mud here.

She's a female with a bunch of eggs, and each of these eggs is just tiny.

That's two eggs on my finger, like right above my fingertip there.

Females will live five years, sometimes six years, so they can produce potentially hundreds of thousands of eggs in a lifetime each.

So I always feel good about removing females.

One down, let's see how many to go.

(water burbling) Oh, we have another female.

All right, let's see if anyone else is buried in here.

Well, yes, under the same rock, we have crab number three, another female.

She's missing both of her claws.

This one here, yes.

So many eggs for her body size.

I see two, I see three.

Don't pinch me, please.

I'm finding good number here for sure.

- [Narrator] Along with the wide tolerances for temperature and salinity, European green crabs have a number of special traits that give them advantages for survival.

They have flatter rear legs, which make them pretty good swimmers.

- [Cat] They have a crusher claw.

- [Narrator] And specialized claws that help them crush and slice into clams and mussels.

- They're amazing survivors.

So we've got 21 from just under that one rock.

Oh, here's another one, I got you.

22 and more and more!

(chuckles) Today, in a very short time, we've pulled up so many crabs, and there's no way we would've seen anything like that in 2006.

Another female with eggs, just a lot of reproductive capacity.

- [Narrator] In all, Cat found 263 crab today.

She has a special permit to take that many.

But for the general public, there's a limit of 35 per day per person.

- [Cat] We got the males.

I think there should be no limit on their take, and ODFW has that limit because they're worried that people can't identify them from the natives.

- From our perspective, it's essential that the public be able to recognize European green crab from our native species of crab.

- [Narrator] Steve Rumrill is the Shellfish Program Manager for the Oregon Department of Fish and Wildlife.

- Green crab can be easily misidentified.

These are just native shore crab.

So the well intended person that may go out and try to catch 300 or 400 green crab, there would likely be an unintended by-catch, 30, 40, 50, 60 native crab.

And we don't want that to happen, so we're comfortable withholding that limit at 35.

- [Derek] I think we'll have a few in there today.

- [Summer] Yeah, I think so.

- [Narrator] So just how hard is it to tell a European green crab from say a native Dungeness?

- [Derek] Oh, it looks like we've got a few in there.

- [Narrator] Well, for one thing, they're not always green.

- [Summer] There's a lot of color variation in the European green crab.

See, this one is very orange and red.

Compare that with this one, also a green crab, it's kind of a yellow tan.

They can also be quite green.

So using color, it's impossible to correctly identify them, but there is a really good, easy method you can use to identify green crab.

European green crab have three bumps in between their eyes and five spines on either side of their eye.

One, two, three, four, five.

Dungeness crab have 10 spines, so that's a clear way to id.

And it doesn't change with age or color, so it doesn't lead to the same misidentification concerns.

- This is a Dungeness.

We're gonna let this guy go back into the, where we caught him.

(water burbles) - [Narrator] Another conundrum is what to do with these invasive crabs if you catch them.

- [Derek] It looks like the last one there.

- [Narrator] ODFW has a Pottery Barn policy.

- That's yours, you bought it, that's yours.

So we ask you to take it home with you and dispose of it.

- [Narrator] And the best way to do that?

- [Derek] You can eat these just like you would a Dungeness crab or a red rock crab.

You can see they have big meaty claws, so that holds a lot of meat in there.

- [Narrator] And if you aren't going to eat them, ODFW says freeze them.

- It slows the whole body process down, and so they essentially go to sleep pretty quickly, and then their body just shuts down and they freeze right up.

- [Narrator] After that, wrap them up and put them in the trash can, or chunk them up and add them to your garden as fertilizer.

- Cover it up nice, give a little pat, and that works really well.

- I see more green crabs.

Once people can identify green crabs, then we can remove them, and everybody doing their part, removing some green crabs, could keep the numbers down.

- [Narrator] So just how urgent is the problem?

- On one sense, it's fairly urgent because their numbers have increased.

On the other side, we have not really come to the point of an emergency for Oregon.

- One of the problems is, when they're not concerning, they're easier to remove.

And once they're really high numbers that you have thousands in a small spot, then it's harder to get all of them out.

- [Narrator] One thing that both Steve and Cat know is the clock is ticking.

- We are now seeing changing conditions in our global climate that will be favorable to the green crab, so it's really a complex, unfortunate, and alarming problem.

- [Narrator] The research, assessment, and planning that go into formulating policy all take time.

One cautionary tale comes from Cat's own experience near California's Bolinas Lagoon.

- After years of removing them, we had brought that population down from about 100,000 to about 3,000, and we came back one year and there were about 300,000.

They just rebounded really quickly, and it is something like that that makes me really worried.

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