The shore crab aquarium – a perspective shift.

Revised August 2021. 

I wrote this blogpost a couple of years ago, after a summer when I revisited a childhood paradise, Hallands Väderö, an island on the west coast of Sweden.

As a child, I used to catch small shore crabs there, and get a terrible sunburn. I’d spend six hours crouching on the shoreline, with my back to the unrelenting Scandinavian sun.

No sunscreen.

No protective tan. Just very pale, sun-sensitive skin that I’ve inherited from my freckled red-headed father. Those were the days, when nobody knew about melanoma, and having a deep tan was the height of fashion.

Side note: Over the years, I’ve learned to avoid sunburn (I no longer harbor any illusions of achieving a nice tan, wear sensible long-sleeve clothes, avoid direct summer sunlight between 11 and 15, and wear sun screen lotion if I can’t avoid it).

But I’ve maintained that passion for catching shore crabs, or green crabs as you might know them by – they go by the latin name of Carcinus maenas. And that summer, I had my kids along, and they’d inherited my fascination with these little critters.

In case you’re wondering: this blog post is not going to be a nostalgic walk down memory lane. Rather, it’s going to be about discovering that the lane you’re walking on is no longer a place where you want to be.

I’ll also encourage you to look at the lanes that you’re walking on. The habits you learned as a child, and that you’re still holding on to – but maybe it’s time to let go of.

And, in case you’re not in the mood for philosophy, this post also gives some pointers about what to consider when preparing an enclosure for an animal, regardless of which species we’re talking about.

OK, let’s get back to those crabs.

How to catch shore crabs

If you’re unfamiliar with manual shore crab fishing, there are basically two techniques to catch them:

  • You lure them with bait. Stick a piece of something edible to a string, submerge it so they can access it, and when they climb onto the bait, you carefully and slowly pull them out of the water. They often jump or fall off at some point, but typically eagerly climb back on (the “climb back on” is important information, as will be discussed later).
  • You remove their shelter. Carefully lift a number of small rocks until you happen to expose a hiding baby crab. Grab the tiny critter before it sprints for cover or burrows in the sand, and hope you don’t get pinched.

I’ll return to some ethical reflections about those techniques later.

Most people go for the luring method, it’s safer (especially if you’re using a net once they’re out of the water), and the fishing is done in deeper waters so the crabs are bigger. The shelter-removal method only works in less than knee-deep water (deeper than that it’s difficult to see the tiny crabs since they tend to be a lot smaller).

The lure method. The crab has climbed onto the shrimp, been lifted out of the water and is about to be dropped into the bucket, typically containing sea water and nothing else.

Once the crab is caught, most people keep them in a bucket of sea water while the fishing session lasts, and then let them back out again. They’re too small to eat, anyway.

I’ve caught more crabs than I can remember. And without much thought, I’ve put them in buckets for an hour or two, sometimes piling them up in droves.

Let’s take a moment to reflect on that. In my cultural upbringing, piling shore crabs in buckets for up to a few hours, is the norm.

It’s a habit that’s ingrained in us, passed down through the generations.

“Everybody” does it.

Is there a problem with this?

Why piling crabs in buckets of sea water now bothers me.

For me, it didn’t use to be problematic.

I didn’t cause them any intentional suffering, I changed their water to keep it fresh, I often fed them in the bucket, I let them out after a while.

It didn’t use to bother me.

But this time, I had a different experience.

This time, I’ve spent the last year blogging and teaching online classes about animal behaviour management and animal welfare. Often with an ethical twist.

I’ve questioned the use of dog collars, whether dogs aren’t perhaps weaned too early, and whether hyperflexion in horses should be considered abuse. I’ve argued that we should assume that animals have emotions, if only because that makes the world a better place.

So, I’ve been rationally reasoning about topics related to animal wellbeing.

And yet I’ve always piled live crabs in a bucket of seawater without much thought to their welfare.

Actually, I carried on the legacy and have taught my kids to pile live crabs in a bucket of seawater.

… can they suffer? Tiny shore crabs (caught with the shelter-removal technique)  in a container holding sea water.

So what, you might think.

They’re just crabs.


It’s not like they’re dogs or horses.

Here’s the thing. With mammals and birds, we humans tend to get emotionally involved. We care.

But with regards to shore crabs, we typically don’t get the same emotional sensation of connectedness and engagement as we do with mammals or birds – there’s no limbic resonance. We might find it fascinating to watch them scuttle about, but most people don’t care, on that fundamental emotional level. Some do, for sure, but most people do not.

Not the way I cared about Lodde the harbor seal whom I had just met moments before this film was shot.

Playing with the harbor seal Lodde at Odense Zoo, Denmark. This playful interaction involved a powerful emotional connection, at least on my part, due in part to limbic resonance. Note that Lodde initiates the movements, and I follow: giving control to animals often leads to higher engagement.

So, apparently, on an emotional level, shore crab’s potential suffering, or whether they’re having a bad day, hasn’t concerned me much. But this time, I couldn’t bring myself to piling them in the bucket.

There was a new, nagging concern there. A rational concern, not an emotional one – I simply don’t get that limbic connection to those tiny critters.

The interesting question isn’t really whether I should develop an emotional connection with crabs. Jeremy Bentham said, sometime in the 1800ds, that the relevant ethical question is not whether animals can reason or talk, but whether they can suffer.

To reinterpret that with regards to shore crabs: the relevant question isn’t whether we care, it’s whether they can suffer.

On the island, when my rational mind started making objections to crab-piling, I wasn’t aware of the latest research. But it turns out that as recently as in 2005, whether crabs and their relatives could suffer was unclear to scientists. In later years, the evidence suggests that they can. Apparently, shore crabs show avoidance learning, and they choose to expose themselves to aversive stimuli to access valuable resources – but they won’t do it to get access to resources of less value. They have a suitable nervous system for pain awareness, including opioid receptors, and respond to analgesics and local anesthetics.

So, while at the island, I didn’t know about the recent scientific findings, but I had a major mind shift about how to go about crab fishing. Specifically, about how they’re kept in the bucket (or in this case, the container that we’d brought our lunch in).

The container may hold sea water, but it’s pretty far removed from their natural habitat.

So I decided to offer them a better option.

I decided I wanted to show my kids a better option. After all, learning to empathize will shore crabs (where there’s no limbic resonance) will probably make them more caring with other animals – and other people (where there is). And thinking rationally about animal wellbeing, in addition to emotionally, is another useful exercise, for kids and adults alike.

The shore crab aquarium.

So, how do you go about creating a suitable habitat, for any animal? I talk about some key features of a good habitat, or enclosure, in my senior lecturer’s exam lecture, which you’ll find free access to here, but the principles are the same, regardless of the animal species.

Step 1: added a wad of sea weed. There are three crabs in this image, by the way.

I have no idea whether shore crabs experience the subjective emotion of fear in the same way that we do, but they show the characteristic freezing and fleeing behaviour that we associate with fear in mammals. An important part of habitat creation is to make sure that there are opportunities for the animals to perform behaviours to reduce, or avoid, fearful responses:

  • Shelter
  • Several escape routes
  • Access to vertical space
  • Step 2: included some rocks and empty sea shells. There are two crabs in this image.

Not all animals have the same preferences, so here’s another important design feature you may want to keep in mind, whether you’re furnishing for cats or crabs:

  • Multiple options

Likely, you’ll find that some of the crabs climb the sea weed, some take refuge under the sea shell, and some hide under rocks. The opportunity to choose is crucial in promoting animal welfare.

Finally, adding some sand allows them to burrow. In this group of four, only one of the crabs chose that option.

Step 3: added some sand, and one of the crabs started burrowing.

As an ethologist, I typically have three priorities when it comes to aspects of the physical habitat that impact animals’ welfare:

  • Their social environment
  • Foraging opportunities / time budgets
  • Opportunities for anti-predatory behaviour

Among mammals, different species form different types of social groups. Some are solitary, others form pairs, or groups containing one or more males. Knowing natural group structure is very important in predicting which group constellations are going to get along in captivity.

How about shore crabs? From what I can tell, they don’t form social clusters, unlike the clustering seen in hermit crabs. I sometimes see many crabs in a small area, but I interpret most social behaviour as aggressive or competitive. In this group of four, there was no fighting, but I’d expect that to occur above some threshold density.

So, from the social perspective, I’d avoid adding too many crabs to the aquarium, and I’d be careful about adding food. Studies have shown that they fight more if food is present. Here’s the dilemma, though: feeding may on the one hand potentially be beneficial since it might serve as a type of counter conditioning procedure: being caught by humans and put in a small container predicts great things . On the other hand, it may exacerbate the aversiveness of the holding area if it leads to aggression over defendable resources. Feeding in several locations would probably diminish the risk of aggressive behaviour, though.

This particular shore crab aquarium was short-lived, about half an hour, so thinking about time budgets (that the relative frequency of behaviours shown match what animals would do in the wild), or foraging opportunities, was not a big issue. That’s a huge concern for animals kept in human care on a permanent basis, though.


That day at the island Hallands Väderö, I had the uncomfortable realization that I didn’t like how I’d been handling crabs all my life. Since then, and it’s now been several years, I actually haven’t caught any; much of the allure was lost when I started thinking more about how the capture-and-holding process might impact the animal’s wellbeing. My thoughts are that the lure method gives the animal an element of choice and control which is lacking in the shelter-removal method, for instance. The fact that they typically eagerly climb back onto the bait (normally even in the bucket) suggests that there’s no avoidance learning going on.

The take home message isn’t what you might think it is.

In case you’re thinking that the main take-home message from this blog post is about how to accommodate shore crabs while teaching your kids about animal wellbeing: it’s not.

It’s about how our cultural upbringing blinds us to ethical problems. A type of cognitive bias. It’s about how if everyone else is doing something, we don’t question it. It’s about how we engage emotionally in some types of animals (typically furry ones with big eyes and floppy ears) and not others, and it’s about the usefulness of sometimes trying to be rational in order to reassess what you’re doing to animals that you don’t relate emotionally to.

This time, I took a look at my crab-fishing behaviour, and I didn’t like it. So I changed it. And I taught my kids an important lesson of empathy and rational thinking, too.

Have you ever done the same, breaking with norms you grew up with, and changing how you interact with other animals?

I bet you have. I think we’re all treating animals differently now than we did 10 years ago.

And here’s the difficult question:

What will you do differently 10 years from now? What are you doing now that you won’t like, and change, in the future?

Do me a favour, will you? Don’t wait ten years.

I know it’s uncomfortable and hard, but change today. The animals that cross your path now, and in the future, will thank you for it.


I typically don’t discuss shore crabs but ponies, poodles, pigs, parrots and people. One step towards changing your behaviour and relationship with animals is understanding more about emotional states in animals and how they impact their personality, brain development, social skills and stress sensitivity. If you’re ready to take that step, you may want to check out my course about animal emotions. Enrollment is only open for a brief time every year, and if you sign up below I’ll make sure you won’t miss the announcements and free trainings.

29 Replies to “The shore crab aquarium – a perspective shift.”

  1. Last year when I visited my brother and his family, my youngest niece caught a Roly poly bug, the kind that roll up in a ball to protect themselves. She put it on a plate under a clear plastic. It bugged me, I knew it wasn’t getting air and told her it would suffocate. She argued and my brother looked at me like I was crazy. It’s just a bug. But I persisted. Finally she put the plate/cup and bug outside, in the midday sun… and ran off to play. I snuck out and let the but free. After all that I have learned, I just couldn’t stand to watch the poor thing fry to death. I’ve also had a paper wasp issue, where they get into my apartment, I think through the fireplace. But the males don’t sting and they’ve never acted aggressively, so I get them onto a piece of paper or something and take them outside.

  2. I have experienced this more times than I can count within the past 4 years. My way of keeping animals has been twisted, turned, tied up in knots and released again so many tiles that it’s hard to keep track of the old – mostly because there’s so much new coming in. And there is certainly a lot of those things that has been part of my cultural upbringing. We have to power to change our acts, so we’ll only be decieving ourselves by waiting. Thanks for this wonderful blog❤️

  3. I wonder when we will be able to stretch that view to plants. I’ve been doing spiritual work for decades now and made an important “step” that changed my cognitive abilities from “normal” to heightened and I could “hear” trees scream that had been cut down and lying alongside a road.
    Everybody has experienced that a cut tree, a cut branch, a cut flower will not die immediately. Put in water, they will live on for days, maybe even weeks. A cut tree might even try to keep growing branches. So, they are not dead and they still respond to environmental stimuli. How much discomfort might they experience?

    1. That is a disconcerting thought, for sure! Have you read The Hidden Life of Trees? Very thought-provoking.

  4. We were having a leisurely dinner with a group, and the subject of Disney animated features came up. One of the ladies, a mom with a 6 year old daughter, commented on watching Dumbo with her daugter, a movie her mom had watched with her when she was a child. She was appalled at several parts of the film that had casual prejudices, racial, gender, class, that that have become unacceptable in todays climate.

    I think your crab analogy is really a metaphor, on a micro level, for how the culture has shifted, on a macro level, over the last generation, from blinding accepting the questionable attitudes of prior attitudes of prior generations. Your post, and the protestations of activists creating a fuss in the media, are the kinds of forces that move culture in a positive direction.

    1. Thanks Henry. Interesting, I don’t think I’ve seen Dumbo, but I can relate.

      Over the summer we introduced our kids to James Bond movies – and I was appalled at how he came on to some of the women in certain of the older movies. Completely non-consensual, a sexual predator. I felt I needed to talk to my kids about consent (they’re 12 and 16), and they said “moooooom, we knooooooooow” so luckily to them that behaviour was completely unacceptable. But at the time I’m sure it just looked macho.

  5. Thanks so much for this post. I have had three live-changing experiences in my life-time. The first was becoming a vegetarian after watching a documentary on how the cows, pigs, and other animals that we consume are treated. I was horrified by the abject cruelty and the suffering those poor animals must endure. Not only physical, but emotional suffering too. Then I saw a documentary on the dairy industry. Once again, I was simply horrified by the abject suffering and cruelty to the mother cows AND their calves. And remember, cows are mammals. They don’t produce milk unless they have given birth to a calf. Calves are unwanted products of the dairy industry and are “disposed of” in the most heinous manners (and “cheap”) available. Soon after, I saw a video of workers in the egg industry laughing gleefully to see how could make baby chicks suffer the most before killing them (by sending through a food grinder–alive). I was horrified at that. Now I’m a vegan and will remain so for the rest of my life. I simply could never bring myself to eat meat, dairy products, or eggs again–ever. I will NEVER do anything to intentionally harm an animal–I don’t care if it’s a mammal, a bird, a fish, or a crustacean. And I will try to be as cognizant as I can about how my actions may unintentionally harm animals–like using products that are tested on animals. Just won’t do it. I hope others will have similar “awakenings”. It wasn’t easy, but I am much more comfortable with myself now, knowing that I do everything within my power to cause no harm.

  6. I hope that 10 years from now, most people will be vegetarians and we can greatly reduce the suffering of animals raised for food.

  7. Spiders. My thought process about spiders has changed as I have matured. I noticed this while visiting my kids and grandkids this past weekend. As we were unloading my grandson’s birthday presents out of my van my daughter saw a spider. Her reaction was to kill it. I told her that the spider wasn’t hurting anything and that it was welcome to live in my van. When I was her age I had the same reaction. Spider..kill it. As I have matured I have realized that a fear of spiders is not a rational response and that spiders are beneficial in my life. They eat other bugs that I prefer not to have in my van, or my house. The only spider that I will purposely kill is the brown recluse. And if we let the other spiders live, they like to kill the brown recluse also. Which makes them very useful.

    1. My dad once wrote a poem about a mosquito that he offered up his arm to… I think we grow our tolerance of such critters as we age too..!

  8. Karolina,
    Thank you for this. I’ve changed so many things about how I engage with animals. Dog training is the big, obvious change, but my thoughts about how we treat all animals, as well as plants and our Earth, have shifted dramatically. Things that just didn’t feel right to me as a young child have expanded into a sensitivity that is often painful when I watch how others deal with animals. Is there a way to ethically print this article to share with others who maybe don’t yet recognize the discomfort they are unwittingly inflicting on animals?

  9. Whilst on holiday with my 3 young children plus husband on a Greek island in the ‘80’s, my husband thought it was a good idea to teach our boys how to fish off the jetty with a line, hook and bait. They had caught a fair few white bait by the time I arrived, kept in a bucket, my reaction was so surprising to me as well as the children – I burst into tears and demanded they put them back immediately. They never forgot their mother’s reaction and never fished again. However, my thoughts are :- without fish that is a huge percentage of my diet gone. Therefore, do I continue to convince myself that it’s ok to eat fish(knowing that they may have been caught in humanely), or just get on with life.?

    1. I don’t think I can answer your question – I eat meat, but I try to do so conscientiously and sparingly, and I’m more concerned with an animal’s quality of life while he’s alive – though there is a lot to be done to reduce stress and suffering during slaughter, too, for sure.

  10. I used to work with horses on a daily basis for years, and when I was a rookie they all showed me how to “break a horse” or how to treat a horse because it has been done that way “since forever”.
    Although my inner gut was telling me something was wrong here, I trusted the more experienced and more educated (or I thought they are at thr moment). How time has been passing, I started to resist one thing by time. First the whips then the bridles, then I was famous for being crazy and not using whips, I was not allowing my unexperienced students in the riding school to use whips. Sometimes, I was getting bad comments and instructions from the horse riding school’s owners but I said that if tbe rider is not able to make a connection with a horse and “make him move” by moving his body or other signals, it is not mature enough to carry a whip.
    How time has been passing, I fell in Love with one stallion with the “bad manners” who was famous for biting. It took me few months to gain his trust. One day, I realised that Love is to give someone something he needs, so I stopped riding him at all. Then our relationship flourished. Because I was the only one who gave him what HE needed, daily hours on the pasture, opportunity to be what he is – the horse. Still, I still rode other horses. Eventually, I stopped riding at all, because all of the other horses were also suffering from deficiency of natural behavior opportunities and the fact that they were not “my Special One” is not fair to be treated differently, the least I could do for them is not to be additional burden on their back full of wounds.
    This experience motivated me to write a student scientific research paper which I got a reward for, which explains how much the stable housing effects the horses’ welfare.
    Do I have to tell you that almost everyone was mocking on me for being different? For not settling for how I was told it has been done for years?!
    Sometimes, it has been a disaster.
    I putted my sweat, tears and blood in this research paper. And I am trying to educate others.
    I plan a carrier in inspection, Welfare control. I hope it will come in the next few years.

    In the meantime, my Special One is still being used like a machine, I tried to buy him multiple times but they rejected me or asked for an insane amount of money because they knew how much I care.

    I am not losing Hope that maybe, one day, I will be able to see Him through my window, in the big pasture, on the hot summer day, eating lipsticks of carrots and apples in ice.
    To provide him with Friend, Foragr and Freedom.

    Long story short, trust your gut.
    Put yourself in their shoes, whether it’s a seashell or an elephant.
    They all deserve not to suffer.

    I am not riding horses for years, or any other animals.
    I also do not eat them for a decade also I was told it was also “normal”.

    My favourite Latin saying is
    Dum spiro, spero.
    Which means while I breathe, I do hope for.

    So I hope that I will live to see the better days for all of the non-human animals.
    And working on being a part of this change.

    Thank you, Karolina, for this topic.

  11. Back in ’69 I learned that when a turtle, either wild or not human-socialized, struggles to go in a certain direction (e.g., the other side of the road), he/she relaxes in less than a minute if the human holder turns and steps in the direction the turtle is struggling. The turtle realizes the human is following what becomes his or her kinetic signal and uses air canoeing, pushing back feet against the back of the hand, and/or head orienting to “steer” the human to the desired location–an item of curiosity, refrigerator, window, whatever. Our open-ended exploration of turtle cognition began from this practice, which led to trust and the bonding necessary to motivate learning. Rosemary Lombard, Chelonian Connection, Oregon

  12. Years ago it was quite normal to train dogs with all sorts of correction tools. Corrections were in that time, one thought, needed to get a dog in the Garel/under control.
    10 years ago I already found that the training methods do not fit my way, how to deal with animals. Three years ago I started to train from the dog his eyes. The welfare of the dog is more important ultimately than the result of a good listening dog. But what turned out, it takes a little longer, but the dog did exactly the same and listened just as dogs that were brought up with corrections. But… the difference is my dogs are much happier on the streets. They find it nice to come because they do that for me! I realize more and more that training is the best way of educating in a positive way. Even if it’s XXL’s Bullys or pitbulls.

    1. Yes! I think many people have made that transition – crossing over from traditional punishment- based training to training based on positive reinforcement..!

  13. …..when I started working in the aquarium world ..I was there because I WANTED to work with marine mammals….I walked into work…and sure there were lots of seals/ dolphins…but there 1000’s of fish, 100’s of birds, lots of reptiles…and other mammals I didn’t expect – and I was part of the human team responsible for all these lives.
    What I learned quickly…particularly when the animals were “patients”…….that every single one of them was unique…and I realised…I suddenly cared for how they felt too (little sharks, seahorses, turtles, nautilus, octupus, cuttlefish – so many new to me. When I worked to save their lives when they were sick…or tried to work out why they had “problems” behaviourally/ physiologically – and worked with them through their simple and complex journeys with us – I learned also that each animal within each species…was an individual. A gift…I try hard to share – it is not just about “me”…it’s about ensuring there are enough people who know the “magic” – to care – for all beings – not just the “obvious” ones…. Each has a voice – if we listen.

  14. 13 years ago I had only cats. My cats were all well mannered/trained but the only method I knew at that time was negative reinforcement. “No” and spray bottles of water tended to work well with cats. Then I adopted a brother sister pair of kittens. He was content to avoid negative reinforcement and so trained easily. She, however, was one of those personalities that thrived on attention – even negative. She would walk into a room and instantly perform every active she knew would draw “punishment”. After a water spray, she would do the feline equivalent of a laugh and move on to the next thing she knew she was not supposed to do. I knew I had to find anther way since I was not willing to move to harsher punishment. I started to read training books like Karen Pryor. All these years later, I have dogs and train them in competitive obedience, nosework, etc. They are my playmates and I spend a lot of time working with them. That decision to change my direction and do something different than what I grew up with has actually changed my life.

    1. Thanks for sharing your story! I think many share similar experiences, transitioning from traditional training into the positive reinforcement world.

Leave a Reply

Your email address will not be published. Required fields are marked *