Solutions to invasive, green crabs off the coast of Maine?

Believe it or not, there is a fishery for these in some places - particularly to be used as bait for Tautog fishing. They crowd pretty easily into lobster pots, in my experience, with no bait needed, as long as you place the cages in the right spots. You won't be able to eradicate them in this manner, but you might be able to slow their population growth.

With that being said, I would take a wait and see approach. Where green crabs have been long established, the ecosystem has responded just fine. For instance, in areas on Long Island where we have large green crab populations, we still have healthy seagrass and mussels where water quality is appropriate. In Massachusetts, the green crab is at least partially responsible for the recovery of salt marshes which were destroyed by a marsh crab. Invasions are always worst initially. Few studies track invasions over long time periods, but those which do typically find drastically different results after years or decades than they find when the invasion is still new and the ecosystem has not yet responded. That's not to say that green crabs won't continue to cause problems in Maine, but just something to keep in mind.

David Garbary has done some work on this problem in Nova Scotia. He'd probably be happy to try to address this and is on RG at:

At the Seaside adjunct of Kejimkujik National Park in Nova Scotia, they have done some control work in seagrass beds, which I think involved Mi'kmaq people testing the idea of capturing crabs in the park and using them as bait (probably lobster bait).

There has been a lot of work in Canada on this problem and there are no easy answers:

RE: Control.

There has been some efforts by researchers at Portland State University, UC Davis and the Smithsonian to test the efficacy of manual removal through baited and unbaited traps. After removing thousands of crabs, some members of the native community appears to be responding 'positively'.

Good morning!

As we are neighbours, here in Atlantic Canada, we have the same problems with green crab. This said, our Aquaculture and Coastal Ecosystems section (Fisheries and Oceans Canada) has been working on monitoring, treatments, eradication trials,impact on shellfish aquaculture and even fisheries for numerous aquatic invasive species (AIS) found in our region such as green crab. Feel free to send me a formal email remi.sonier@dfo-mpo.gc.ca and I could direct you to our researchers working on the topic as well as our section head biologist.

Cheers,

Remi Sonier

We also have green crabs in eastern Canada, most recently in Prince Edward Island and Newfoundland. Like most other areas we have observed some impacts on small shellfish, inverts, and also on eelgrass (David Garbary has a lot of information on it from NS) but their ultimate effect on the ecosystem is still to be seen. I heard that a fishery or harvesting for green crabs is starting in NS with the intention to control numbers and use the crabs for bait. That's also an idea that may be implemented here, in Prince Edward Island, but it's not yet clear in which particular timeline. I agree with my colleagues on that it is impossible to eradicate them, so the challenge is to mitigate and find a use for them. P.

Hello Bill,

Thanks for posting such a great question.

There's such a long and complex story about Gulf of Maine marine life, how it's changed, and how it's changed with invasive species. I know that a lot of the marine science researchers in the northeastern seaboard region (i.e. ME, NH, MA) that I am acquainted with, would be able to speak much better than myself on the subject you've mentioned.

Personally, I immediately think about the usual biological [genetics, adding a control spp.] , physical [removal], and chemical control methods of such an invasive species, and also how these methods can be practically applied with minimal damage to the environment.

With regards to controlling, managing, and removing invasive species -- I also wonder when the food web would completely adapt to such invasive spp. additions, and/or changes because of invasive spp. I am also curious whether or not such a "steady state" with a new ecological regime, including an invasive species (like Green Crab) could be reached where a removal attempt [or one of the methods wouldn't be worth the ecological Cost-Benefit Analysis] would actually harm the ecosystem as a whole?

Thinking like a conservationist, I am reminded of the story of trying to re-initiate the wolf population in Yellowstone/great west american national parks and how it changed the ecosystem, food web, and ecological dynamics, albeit for good whereas I am reminded also about other failed attempts at species introduction to fix an invasive species problem.

On a side note, have you heard about the Lionfish in Florida?

I hope my answer stimulates your thinking and I am looking forward to reading more.

Best,

Jack P.

Pedro, Remi, and Dr. Willison,

Thank you for your responses. Maine is beginning to look in this direction as well. Also, there has been speculation about how to convert them into a food source, seeing as their meat is so sweet, but presently there isn't enough of it to make the shelling process worth our while. As far as I know, any sort of large-scale research about turning them into bait isn't yet afoot.

Timothy - that report is hopeful. Thank you. John what you said about slowing their population growth accords well with Timothy's information.

I have wondered about grinding them up and using them in the feed used in aquaculture (I realize that due to demand this is numerically not a solution); drying and grinding them for usage in fertilization of soil (especially in hydroponics); and perhaps the possibilities of developing some sort of an Asian market niche for their usage, since Asians have repeatedly shown interest in species which we disregard or have little use for.

Pedro, correct me if I'm wrong, but I beleive on PEI green crab by-catch by eel fishermen (and others) are composted for further potatoe fields (or gardens) fertilization.

The safest approach, in my opinion, is physical removal. It can be problematic because it requires resources, e.g. a dedicated volunteer citizen corps as is being used to control the lionfish in the Caribbean, and/or industry investment. But it is safer than ecological controls, which generally center on the introduction of controlling species. There are too many examples of that going horribly wrong. And there are recent encouraging reports from the Caribbean that the lionfish can be controlled in areas where they are harvested heavily.

On the other hand, as someone pointed out, you also need assessments of what the ecosystem impact could be in your area. The lionfish seems to be devastating prey fish populations, but here in San Francisco Bay, the most heavily invaded estuary in the world, we haven't yet seen any catastrophic impacts on native species. Granted, we have very little idea of what the Bay ecosystem looked like originally, since it was already altered heavily by the mid 19th century.

Hi Bill,

This is going to be a long-term problem. Within its native range we have not been able to control the species and even with trapping to control it there is a large effort that is not economically rewarded. We tried trapping in Ireland but the follow-up for the use of crabs in Spain in soup did not subsequently materialise. this was in the 1980s. The invasive grapsid crabs may make a difference in terms of controlling the intertidal component of small and recently settled green crabs. Incidentally, do not think of introducing Sacculina as it does not control green crabs in its native environment. In Ireland we have no indication of damage to Zostera meadows but for shellfish cultivation, such as the manila clam, one needs to be vigilant and use parc fencing and mesh covers.

Not sure if this totally addresses your concerns, but the species is a problem even in its home range - should this provide some comfort!

Hi Bill, I concur with Dan Minchin. There are very few examples of successful eradication of an invasive species, as exemplified for decapods by the European situation with North American freshwater crayfish. Predators will probably increase, and this may favour rarer predatory species but could have damaging impacts on native prey species. Removal (by trapping) is only a partial solution, but you have had various interesting suggestions about utilisation.

”Any suggestions for either possible eradication or for a way to lessen their impact upon our estuaries and other tidal regions? ”

Well, this issue could be a proper subject for future research-projects to be developed by Your university in partnership with our institute...

Hi Bill, I'm sure you're aware of Denise Skonberg's (UME) studies on utilizing green crab for human consumption as I believe that is what you allude to in a prior thread...basically, too much labor/cost for such a small yield of crab meat. I am pleased that ME DMR recognizesgreen crab populations have exploded in the GOM and there is a problem, as evidenced from the Green Crab Summit Meeting. I don't think we'll ever be able to eradicate green crabs but should think more along the lines of control and mitigating damage. We've done several studies at UNH assessing green crab populations. There was mention of using green crabs as tautog bait. I know there are a few guys in NH who fish for green crabs for tautog and black sea bass bait for use in NY. Also in MA, green crabs are starting to replace a portion of horseshoe crabs as bait in the channeled whelk fishery. Supposedly in Nova Scotia, they're used as bait for lobsters. Still, there is far more surplus than these fisheries could utilize. A former student of mine (Beth Fulton) and I published a paper in 2013 about the nutritional profile of whole ground green crab to explore its use in animal feeds. I would love to see green crabs tested and incorporated into formulated fish feed. I tried multiple times to get funding for such a project about 10 years ago but had no luck. Perhaps now is the time to try again. I'd be happy to talk more in detail: elizabeth.fairchild@unh.edu.

..I'd like to ask if there is any documented literature on aspects of reproductive/spawning biology of these invasive species? do these invasive species spawn all through the year? do the males and females have different trends in habitat use? what environmental parameter do you think could be a limiting factor tot he proliferation of these invasive species if altered?

My line of thought is, if a critical point in the reproductive chain of these invasive species could be interrupted their proliferation could be tangibly interrupted. for instance locating their spawning season and spawning sites and evacuating gravid females at a time when they are most abundant.

...i suggest the strategic removal of a life stages of these invasive species as a means of limiting suppressing their spread. This will be a more cost effective approach rather than managing the damages they cause.

Hello!

You can find some informations about Carcinus maenas in this document : http://www.dfo-mpo.gc.ca/library/330845.pdf

"A BIOLOGICAL SYNOPSIS OF THE EUROPEAN GREEN CRAB, CARCINUS MAENAS", 2007. G. Klassen and A. Locke

Hi. Carcinus maenas, as the cousin C. aestuarii, is not an invasive species. In native areas, especially in estuaries and lagoons, shows fluctuations of the population, but is well integrated into the ecosystem. It is likely that in Maine, it has found the ecosystems in crisis, where predators are not sufficiently present. This species has many predators, and it is known to be opposed by Sparus aurata, Chrysophrys major, Diplodus vulgaris, octopus, cuttlefish, etc.. The bloom, e.g., could be countered by a seeding of juvenile sea bream (at least half a million) purchased from commercial hatcheries, with a relatively modest public spending.

However, as someone else said, it can be used as bait in lobster pots, but above all it can be eaten by humans (!). It can be the basis for excellent “risotto” and soups, especially in the period of egg maturation. Bon appetite

Hi all I have been following this discussion with great interest. Unfortunately i cannot offer any useful advice on how to eradicate this beast. Rather i am following as a scientist in charge of trying to keep it out and stockpiling the information 'just in case'. While present in other parts of Australia it is not in Western Australia and we regularly monitor to try and detect this and other species. In that respect i have a somewhat unusual request would anyone be willing to capture and send me some samples? As we do not have this species we are trying to build up a useful resource for education and identification purposes. I am more than willing to pay costs associated with postage etc... I would be more than happy to discuss and provide postage details. my email is justin.mcdonald@fish.wa.gov.au

In Italy this crab is exploited for human feeding. They are particularly appreciated soon after carapace moulting. You can find them in fish market, representing therefore an economic resource. Furthermore, they are sold to sportfishermen as bait for the sea bream (Sparus aurata). If you start eating or using them as bait, you will obtain a sort of control of population growth.

I think we should consider the point Elizabeth raised that ''there is far more surplus of these crab harvest than fisheries could utilize''

On the northeastern coast of Long Island Sound we have a large abundance of green crabs, although they have been invasive in this range for a lot longer than in Maine. Confirming what others have said, there is a market for these crabs for Tautog (Blackfish) fishing. However, the relationship between Green Crab and Tautog is a double-edged sword from a management standpoint, unfortunately. If you promote Tautog fishing to sell the Green Crabs, there will be less Tautog in these waters feeding on Green Crabs as part of their normal diet. Likewise, if you strictly regulate Tautog fishing to keep the Green Crab population in check, you will kill the bait market for them. Until this relationship is explored in detail, I think it would be rash to take either of these approaches

The second approach I hear frequently is to create a seafood market for them in New England. I see this as an incredibly slow approach at best, from my experience in the success of doing this with other invasive species.

I would suggest instead of creating a seafood market here in the states we explore foreign markets for the Green Crab, exploiting both the ease of catching them and the need of extra income in many coastal communities. Personally, with a $40 crab trap I can catch15-20 crabs a night off my dock in Long Island Sound, with no bait. All it would take is a licensed buyer in town that had the resources for export. I know many individuals that would take advantage of this, and there are many public areas offering coastal fishing access.

Alternatively, as others have also suggested the key is to exterminate early life stages. This has been done very successfully by the NYSDEC in Lake Ontario with Sea Lampreys. The lampreys spend their juvenile life stage buried in exposed sand and mud along the coast, allowing for an easy application of a specific biocide. If a juvenile habitat niche of green crab can be exploited, that's also an option.

I'm a bit confused by the export market argument. Export them to whom and for what purpose? There are three arguments against this: (1) if they are not suitable for local people to eat or use, why would a foreigner want to eat or use them, (2) price is affected by transport costs, so the further they travel the more they cost and the greater is the risk of wastage, and (3) the environmental costs rise as the distance to market increases. I think we need local solutions for local problems.

Martin I had thought about Richard's suggestion as well. I'm sure you have the same experience of seeing the Japanese pay a lot of money for certain species which we don't necessarily value very highly. Sea urchins are just one of the marine animals that we have no real use for, upon which they place a high value. The issues you raise are significant, and I cannot envision a particular market where they would be highly prized, but it would seem to warrant a little market research. Wouldn't it be wonderful if someone did prize their meat, even though there isn't much on a single crab?

Bill ... two Italian scientists (Mauro and Ferruccio) have said that green crabs are good to eat. Many Italians have migrated to the U.S. and Canada. Why export the crabs? It's better to find local Italian chefs and local recipes.

The Japanese market for exported blue-fin tuna threatens to drive the species to extinction globally. Local markets for local species are much less likely to cause global extinctions. Global markets have much more pernicious effects than local markets because the consumer is disconnected from the food source.

Asian carp species are another good example. Asian carp species have invaded the Great Lakes system and are a threat to native biodiversity. Fishing them out is a good idea, and there are hundreds of suitable Asian recipes and millions of Chinese and Thai restaurants in North America that could make good use of these invasives.

Dear Bill, it is not an issue of meat, but flavor. In a globalized world, where new species come with ships and aircraft, the market and the power supply should change and fit. I do not know if it's possible to export this material (here should be an economist, a market expert), but I think it can be a resource. I am convinced that you, in Maine, will control the development and benefit from its quality. Best

Although really is not well defined, biological control is always an interesting alternative. An useful article is attached. The same principal author has several works on that item.

Thank you for this article Arnaldo. The most promising of the solutions presented in this paper appears to be S. Carcini. Its potential impact on native species is a concern, and further testing seems warranted, but its effectiveness as a natural castrator is hopeful.

I do agree with Bill. Lots of research needed in order to check that while this solves a problem is not creating many new ones. Interesting article, no question.

Why not think on the use of this crab as raw material for biotechnology?

Arnaldo, I strongly advise against the use of Sacculina carcini as a biological control method. This parasite is known to parasitize other portunid crabs, this could include commercial species. There are papers since Kuris's account.

In any case even within the natural range of the species this parasite does not control this crab species:

See: Minchin D (1997) The influence of the parasitic cirripede Sacculina carcini on its brachyuran host Carcinus maenas within its home range. In: Proceedings of the first international workshop on the demography, impacts and management of introduced populations of the European crab, Carcinus maenas. Centre for Research on Introduced Marine Pests. Hobart, Tasmania. Technical Report 11, pp 76-80.

I agree with Dan Minchin on this. Others have shown that S. carcini can be pathogenic in other crab species. They may only develop in C. maenas, but they can infect other species and have some pathogenicity.

Fishing for green crabs sounds like a possible answer. One could also explore their use as fertilizer or in pet food products. Small crabs such as Eriocheir sinensis support a thriving aquaculture trade in China, so perhaps C. maenas could be developed for local markets.

Klassen & Locke (2007) a synopsis of the European green crab Carcinus maenas, fisheries and oceans, Canada

There are Some options offered here but using sacculina carcini is not a method that should be used

If the crab is edible for human consumption, don't worry. Its population will be controlled sooner or later. Most of the crustaceans are over exploited and fully utilized. It may be a new 'manna' for this area. The invasive species which is not having any impacts to the local species such as competition for food or shelter, it may not have problem to the new environment. However, in certain cases, it is indeed a problem too!.

In general terms I agree with Thangaraja about 'eat to beat' - however, fishing hasn't proved a solution for invasive exotic crayfish species, in Britain or elsewhere. Because of dominance hierarchies and other behaviour, catching the large ones tends to release growth and maturation in smaller ones, and populations have almost never been eliminated. Instead, their capture tends to encourage fishermen to move such crayfish to new locations, hoping to profit from them a few years later. As a result, catching exotic crayfish is often banned. It's a very complex problem.

As soon as the species becomes valued enough to sell widely the incentive to reduce it to levels where its impacts are negligible is lost. A more likely scenario than"eat to beat", is "farm" to eat.

With widespread species in other systems the invader is usually ignored throughout most of its range with only the most valuable areas (e.g., biodiversity, valued crops) being protected from impacts through intensive and expensive management. I would be in favor of biocontrol if there were a safe means to do it, it appears this isn't the case with the suggested agent above. I am not sure how well this could work with marine arthropods. In terrestrial systems there are species specific parasites and predators of individual arthropod species. Testing for useful and safe biocontrol agents can cost millions of dollars, but marine environments could be distinct. For any given suite of possible biocontrol agents there are many more dead-ends that are discarded for not meeting specificity requirements , compared to successes.

Thinking about another thread topic related to endangered species, one approach might be to spread the rumor among the world's multitude of ignorant people that these particular crabs, if eaten, prolong life and increase sexual prowess. Problem solved.

In Newfoundland, following the first discovery of C. maenas in 2007 we held a workshop to determine likely control methods, although we discussed biological control (including the castrator worm mentioned above) it was considered too dangerous for the native (also commerical) crab species. We have worked on the trapping method and when focused in areas does reduce the number (catch per unit effort) and size and the native rock crab return. We discourage bait use here as the spread to uninvaded areas in NL is a real concern. We are working on compost and fertilizer locally. This summer and fall we will be attempting a 200 day mitigation in some areas to test the removal effort. Our goal is to remove crab larger than 30mm (after that they become reproductive) and less than 3 crabs per trap per day. Our population here is made up of cold tolerant green crab, not the same genetic population as the warmer climate green crab found along the US coast. (see Blakeslee et al 2010, Diversity and Distribution 1-13). They appear to be more aggressive and destructive than the more established less cold toleralate population. I suspect that what you are seeing in Maine is the hybridization of the populations and now the more aggressive traits are showing up there. The recent cold weather has not helped as we are finding them along the coastline under the ice pan.

Some time ago Cynthia I examined the relative catch rates of Carcinus in Irish waters and these ranged from 1863 to12 per 100 pot days effort in summer and the maximum density found by diving in different areas was 1.1 per square metre. I do not know if these as guides to what we found give you some level of comparison with your studies. I have not published this data and would be glad to share an opportunity should you be interested in some comparative information.

I would add to Cynthia's point that in Prince Edward Island, where the green crab has been present since (likely) early 1990's, the populations continue to spread and are fairly aggressive as well (see work by Rossong et al. 2012, Biol Invasions 14:659-669). The idea of using green crabs as bait has not gathered much enthusiasm here, because it doesn't seem as successful as in Nova Scotia and, from the research side, because has the potential of further expanding these populations into un-invaded areas. Time will tell if that becomes an option for fishermen. Incidentally, unlike Newfoundland this last winter seems to have delayed the appearance of large numbers of green crabs, as we have collected very few so far in May and June.

As a Massachusetts recreational clammer, I have just encountered large green crabs toward the end of Cape Cod on the Bay Side. The good news is that they taste good, but even the largest are a lot of picking, and the first idea around here (more for mainland tidal marshes) is to sell them to chefs to make stock. Tautog bait has been mentioned. I have just received a recreational license to really figure them out, but where I encountered the large and aggressive ones a few weeks ago, there were an unusual number of fresh, empty surf clam shells. So I suspect big ones eat large commercial shellfish, although I had a couple of decent clamming tides among them. Blue mussels have gone missing over much of the bay side in the last 15-20 years, but I am not sure what the cause is. Beds of some kinds of sea grass are doing well, but it may not be eelgrass. What is worrisome about green crabs is their adaptability to a variety of temperatures, salinity, and depth. If they go out into deep water, they will be as troublesome as Lionfish in the Caribbean. We need to study their breeding habits, that being the focal point for control, and also to find out how to locate moults, as this is the gourmet item in Europe.