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7 thoughts on “Green crab invaders settle in on Dungeness Spit, Olympic Peninsula

  1. I hate to say it but trapping Green Crabs cannot possibly affect the spread of the crabs. Consider that one pair of crabs can result in the release of four million eggs a year which are then spread by ocean currents. Even a survival rate of 1% will lead to exponential increase in the crab population until some equilibrium value is reached resulting from water conditions and the interaction with other biological variables; e.g., predators. As far as I know, no aquatic invasive species has ever been eradicated once it shows up. Documenting their spread and effect on marine food webs is worth while, however.

    Remember the big hoo-ha about invasive salps, I think it was? There’s still a small funded team doing some dock cleaning or something of the sort, but the scare at least has disappeared but the overall effects on the ecology of our inshore waters of these and other marine invasives don’t appear to have been investigated.

    San Francisco Bay is a good analog for the increasing number of invasive species in Puget Sound and their possible effects.

    1. Thanks for your thoughts, Herb. You’re absolutely correct that we face an uphill battle, but I disagree that trapping can have no effect. As you point out, the connectedness of marine systems makes control much more difficult than in more isolated freshwater or terrestrial environments, but I would argue that there are examples of successes, and that we currently have the best chance for successful control that we are ever going to get. Previous efforts in California (Sea Drift Lagoon) have demonstrated that when green crab populations are isolated, as this one appears to be, trapping can reduce the population to very low numbers. True, it’s labor intensive, but that’s not the same as saying it’s impossible, only that it’s a matter of how much resources people are willing to devote. The challenge in California is that because control wasn’t done early in the invasion, green crab are everywhere, and even though they could be locally eradicated from a lagoon, the water was awash with larvae from nearby areas, so new crabs just got washed back into the lagoon. Here, we have a different situation. We currently have infrequent larval dispersal and isolated populations. If we can locally eradicate crabs, it’s less likely that they would become immediately reinfested. San Francisco Bay is instructive, particularly in what happens when you don’t intervene until crabs are too abundant to control.

      With respect to successes, I’d argue that the challenges faced with respect to marine invasions are in part because, as mentioned earlier, marine systems are trickier to control, but also because historically, less attention has been paid to marine invasives as a management issue. There are very few examples of any monitoring or eradication efforts period! But there are successes. California’s work with the seaweed Caulerpa demonstrates that the early detection and rapid response model can work even in coastal systems. It’s often not a one shot deal, i.e. the potential of invasion will always be present here, so we will likely always have to be on the lookout for this crab. But early detection and even rapid response costs a whole lot less than trapping crabs when they are extremely abundant. And if, down the line, we were to see the impacts on species like Dungeness crab or eelgrass, our only recourse would be to trap green crab,anyway. Trapping now, when there are fewer, is preferable to trapping later when it will inevitably cost more and have less impact on the population.

      That said, you’re exactly right that we might not be able to keep green crab out entirely and forever. But we definitely will fail to do so if we let our best chance to intervene slip by. Nevertheless, even if we only managed to slow the course of the invasion, we benefit local shoreline economies and native ecological communities by buying them time to adapt.

  2. I don’t understand the last paragraph. Why leave one alone after finding it? Recording where you killed it instead would seem to make more sense.

    1. Bill,

      The basic idea is that green crabs are difficult for the average person to identify, and they are still quite rare, even in infested areas. If people were advised to kill crabs that they think are invasive, it could lead to the waste of a lot of native crabs.

      Experts on this topic may wish to weigh in.

      1. Hi Bill,

        Yes, it’s definitely counterintuitive to have to leave the crab in place, when our goal is to make sure we snuff out populations as soon as the pop up. The concern is based on more than a decade of experience by WDFW and other groups in public outreach on this species. In previous efforts, the public was asked to freeze any suspected green crab and mail them to WDFW. However, it turns out correctly identifying this species is just tricky enough, that misidentification caused the death of many native species. That is, many people mistook native crabs for European green crab, and froze them. Our recent experience in triaging suspected sitings confirms this. No correct identifications of European green crab have been confirmed in this way. We have a number of small native crabs that are green, that are confused with green crab. In an effort to avoid defeating the purpose of eliminating green crab by accidentally killing a lot of native crabs, we’re asking people send photos to crabteam@uw.edu and leave the crab in place.

        It’s a good reminder that it’s not legal to “take” (including kill on site) any crab (or other aquatic species) without a permit, either a recreational crabbing permit for Dungies and rock crabs, or a scientific collection permit for any other species. European green crab is a prohibited species in the state of Washington, so “take” without a dedicated Aquatic Invasive Species permit is not legal.

        However if you find a molted shell of a suspected European green crab, you can definitely remove that from the beach, and contact us. Molts are sometimes a way that green crab are found before they are found live, so looking in the wrackline at crab shells can be a great way to help out with early detection, even if you aren’t a Crab Team volunteer.

        We realize that it could feel uncomfortable to walk away from a suspected live green crab, but much of what I do is reassure people who believe they have found green crab that their beach actually has a healthy population of native spider crabs or helmet crabs!

      2. Green crabs can be identified by the five large pointed spines on either side of the eyes.

  3. I did a little research. On the east coast they have been trying to deal with the green crab problem for some time. An article that is two years old indicated that when boiled they make a great seafood broth. Instead of requiring a permit to take them, make it open season on them like they did when the Atlantic salmon were released into local waters from the pens. Then tell everyone how delicious they are and how to cook them.

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