Written by Jimmy Elliott, Greencrab.org Science Communications Advisor

My name is James (Jimmy) Elliott and I am currently a scientist at New England Biolabs in Ipswich, MA. During my education, before I was involved with the biotech industry, I worked for several years on many aspects of green crab biology and ecology. Much of the green crab related work I did was during my time employed at the Cat Cove Marine Laboratory in Salem, MA. Since I have moved on from my time in marine biology, a lack of resources has forced me to continue as an amateur researcher from home (and man do I miss it). After being a member of greencrab.org for many years, I hope this is the first of many posts where I regularly share scientific articles from the past, present and future in order to summarize the most up to date literature relevant to the message at greencrab.org. I feel a one-way conversation is pointless in science, so I encourage a dialogue in the comment section below. Please don’t be afraid to ask questions and share your experience, especially if it contradicts the information I am presenting!

There is something inherently fascinating about green crabs. They are so persistent and really amazing in the way that they spread to new places so quickly. They are easy to identify and they lend themselves very well as a model system for those getting interested in marine science. Even a slightly motivated enthusiast can quickly feel like an expert with so much secondary and primary literature available on green crabs. But as with anything, the more you learn, the more you realize you don't know! It can be overwhelming trying to decide which direction to take to solve such a multifaceted problem. Obviously, we are in the “eat the enemy” camp, but still, there are questions about how to most efficiently trap these green beasts:

Where do I find green crabs?
What bait do I use to catch green crabs?
Where could I catch the biggest green crabs?
When do I trap for green crabs?

and so on...

Well, the funny thing is that there is often a huge dichotomy between the answers that scientists give, and the answers the practitioners give. Scientists are limited by experimental design and statistical power, which is largely driven by sample size. There are many more limitations to scientists, but obviously we can’t ignore the results from adequately controlled experiments. There is still a lot to learn from these studies.

The first question I want to address is “What bait do I use to catch green crabs?”

I have talked with many people at conferences, greencrab.org “meet and greets”, and just people I encounter in my life that feel they need to entertain my perfectly normal obsession with crustaceans. This is a common question. More than one person has told me anecdotally that old KFC chicken bones work best as bait (yes I have tried it, and yes I caught green crabs).

But what makes good bait? Well, green crabs are able to smell just like everything else, but they just do it in a weirder way (see here). Olfaction (smelling) for green crabs works by flicking their antennae, trapping fluid in the spaces between hairs during the rapid downward stroke, and holding the water sample during the slower return stroke. Among other things, green crabs like eating fat. It seems a worthy hypothesis to guess that the more fatty the bait, the wider the perimeter is for green crabs to pick up the scent in the water. And while green crabs have a reputation for being indiscriminate pigs, they still have to like what they smell.

A few studies have directly targeted this question. The first to my knowledge was one that I was actually involved from 2014 - 2016. For this study, we used the same trap to hold all the different types of bait (because that's a whole other variable). For each of the five bait trials we did in total, traps were baited with different baits placed in hanging bait bags and allowed to soak for up to 24 hours, after which time crabs were removed, traps were re-baited, rearranged along the dock to eliminate possible differences due to trap location, and then allowed to soak for an additional comparable time. We tried multiple trapping sites as well, just to make sure we weren’t dealing with the picky eaters at the first site.

Due to the availability of certain baits (because I am not independently wealthy), some of the five different baits compared were used more often than others, ranging from five times for herring, halibut, swordfish, and salmon to three times for tilapia, and twice for sardines.

In short, we found that herring is the best bait based on Catch per Unit Effort (CPUE), where effort is measured in how much time the trap was soaking. We also tested crushed soft-shell clams because they are a preferred natural prey item for green crabs, but they actually didn’t catch more than herring, presumably because it was eaten so quickly and was no longer effective as bait. Interesting find.

So is the answer to “what bait do I use to catch green crabs?” = herring. Well based on our results, it certainly works well. But is it the best?

A more recent study targeted the same type of question. In Newfoundland, scientists compared both CPUE and mean body size of green crabs caught in Fukui traps baited with herring, short-fin squid, blue mussels, and Atlantic cod. They found that squid and cod (not herring) produced substantially higher catch rates, and also caught larger-bodied crabs, whereas we didn’t notice any difference between the sizes of crabs caught with different baits.

One of the attributes that make green crabs such an excellent invader is they are generalist predators, but in two different studies, it seems that bait choice greatly influences the catch, and sometimes even the size of the crabs caught! A bit of reality though, people are going bait that is 1) effective 2) convenient 3) cheap. That is because this is a business in the end, and the more I spend on bait, the less I make on the catch.

What do you think about different types of bait? Without giving away all your secrets, have you experienced a difference in catch using different baits? Is it location dependent? Share your thoughts below!

The Best Green Crab Bait?

Green Crabs in the Great Marsh

Shuck at Home