What the science says on whether we need to change the way we eat crustaceans.

by Brian Dunning

Filed under General Science

Skeptoid Podcast #607

January 23, 2018

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Among those issues that sharply divide certain groups is the question of whether crabs and lobsters feel pain. We tear crabs apart while they're alive and throw lobsters into boiling cauldrons — barbaric actions, unless, of course, those animals lack the physiological ability to feel pain and suffering, as many people believe. For some, this live preparation of crustaceans is a way of life. For others, humanely rendering the animals dead or insensitive first is a moral imperative. Today we're going to look at what the research has shown, and see if we can find a science-based answer to the question of whether crustaceans should be humanely killed before cooking.

Our subjects today are crustaceans, primarily the decapod crustaceans, the ten-footed ones including lobsters, crabs, shrimp, crawfish, and prawns. As shrimp are often frozen, most of the controversy surrounds the lobsters and crabs. They are usually killed for food preparation by either being boiled alive or physically torn apart while alive. Both methods, were they to happen to a person or a dog, even a chicken — would be unthinkable to a reasonable person. So why do we do it to crustaceans? Because conventional wisdom, stretching back far into prescientific days, tells us that crustaceans do not feel pain — or more to the point, that they do not suffer from that pain.

The difference between pain and suffering is an important one. Pain is a physical response, and suffering is an emotional response. Pain without suffering — like having a deep tissue massage or something we choose like getting a tattoo — we don't mind. Suffering is what is so abhorrent, whether or not it is accompanied by physical pain. Science fiction offers us at least one familiar analog for the conventional model of a crustacean, a robot called the Terminator:

JOHN: Does it hurt when you get shot?

TERMINATOR: I sense injuries. The data could be called pain.

But the Terminator doesn't suffer when he detects pain. He even gives the thumbs-up when he disappears into the vat of molten steel. Crustaceans are traditionally believed to be just like the Terminator. This is to do with their nervous systems, which truly is radically different from mammals. Instead of centralized brains, crustaceans have multiple ganglia (clusters of nerves), variously distributed around their anatomy, each very simple and responsible for some local function. Crustaceans do have nociceptors — nerve receptors that sense pain — which trigger reflexive actions, like pulling back or fleeing. But without a brain in charge of analyzing these signals, a crustacean's experience of being harmed is a mystery to researchers.

Do we simply say stop eating all animals just in case? The reality is that's not an option. That would be as useless as saying we should wish all cancers into rainbows. It's not going to happen. People are going to continue eating crabs and lobsters in huge numbers no matter what anyone says. Foolishly unrealistic solutions are not what's needed here; if our goal is to allow crustaceans to be eaten without suffering, then we need a science-based solution that will either prove no suffering takes place with the current methods, or that will provide a way to prepare them that is free of suffering.

This question came to the forefront, as it periodically does, in January 2018 when newspapers reported that Switzerland had banned the live boiling of lobsters. Most often cited was a 2015 paper by Elwood and Adams published in Biology Letters which detailed their study of stress hormones in crabs subjected to shocks. Shocked crabs moved around more vigorously than unshocked crabs, and among shocked and unshocked crabs that displayed the same amount of movement, the shocked ones had elevated stress levels — measured by sampling haemolymph lactate and several other factors. Elwood and Adams concluded that although the study did not prove that the crabs were experiencing pain, the physiological responses did fulfill the criteria for pain established for other animals.

But some of the newspaper headlines said things like "Switzerland Bans the Boiling of Lobsters, Despite Scientific Evidence that They Don't Feel Pain". And these articles always referenced a single article, also published in Biology Letters, titled "Stress is not pain: Comment on Elwood and Adams (2015)". Although a very brief piece, it was co-authored by thirteen biologists representing marine institutions all around the world. Contrary to the newspapers' characterization, this article did not claim that crustaceans don't feel pain. All it said was that Elwood and Adams' study did not prove that the crabs were in pain. However, Elwood and Adams had said that same thing in their original paper. It was an odd response; it was almost as if the thirteen had not read the Elwood and Adams study. But it was enough for the newspapers to claim science proves crustaceans don't feel pain.

So the stress hormones have not proven to be an answer for us. Therefore, scientists moved down the list to see how else we might be able to judge a crustacean's pain or suffering, and decided to study their behavior. Could we devise a non-ambiguous test to see if they would actively change their behavior to avoid painful stimuli?

In 2013, a pair of biologists at Queen's University in Belfast published a study where they created an indoor pool, brightly lit, but with two dark shelters in it. They took 90 European shore crabs and ran this test with them, one at a time. One shelter, selected at random each time, would be the "shock shelter" — the crab would get a mild 10V shock every five seconds for as long as they remained inside. Once they left the shock shelter, 91% of them would go only to the other shelter from then on. Despite the researcher's attempt to make the shocks mild enough not to do any damage, ten of the crabs autotomized (dropped off) the leg to which the electrode was attached. The results were clear that crabs learned which shelter gave them a shock, and then avoided it. An earlier study showed that hermit crabs that had received a shock while inside one shell were more likely to choose a different shell when offered a choice, and would continue to do so for up to one full day. Crabs who hadn't received a shock were more likely to move right back into their familiar shell.

What did these studies tell us? The experimenters noted:

The findings are consistent with respect to criteria for pain that are accepted for vertebrates.

But they stopped short there, saying:

Perhaps such motivational changes and learning can arise without any unpleasant experience...

Research has also looked at another indicator for pain: the presence of endogenous opioids, which are the natural painkillers the body produces when it gets injured. Obviously, if some creature cannot feel pain, it has no need for natural painkillers. It turns out that crustaceans do indeed have functional endogenous opioid systems. A number of studies have proven that when traumatized, these opioids are released into the tissues. In most countries, crustaceans are not subject to ethical limitations in research, due to the belief that they don't feel pain. Yet in one representative study in 2005, researchers stressed American lobsters by either cutting their legs off (or "pereiopod-ablation" as they called it) or by injecting them with an irritant. Stressed lobsters increased their natural morphine levels by almost 50%, which took some five days to return to normal.

While some researchers conclude that these responses fulfill all the criteria for pain, others argue that it's not necessarily so. They could be simple biological responses to stress, or they could be triggered by other causes, such as simply moving around. The rationalization that many scientists are making is that these responses are all autonomic and reflexive; there is no pain signal going to a brain where it is processed and interpreted as a painful experience.

Where all the empirical research has brought us is to a dead end. Nearly all researchers agree it's proven that crustaceans are stressed by a violent demise. Somewhat fewer agree that the stress is accompanied by pain, and fewer still have concluded that the pain constitutes suffering. Only the staunchest outliers assert that the crustaceans can take it to the farthest end of the spectrum and have any meaningful understanding of their painful death, a perspective that is supported by no data at all. We move from questions of pure objective measurement into more subjective and philosophical interpretations. From what we know now — and indeed, from all we may ever be able to know — it is clear that no lines can be drawn that all the researchers are going to agree with. Is the pain and/or suffering that crustaceans undergo in a violent demise substantial enough that we should change the way we kill them? The fact is we do not have proven data; and even if we did, people will have varying opinions on the attendant ethics.

There is another factor which some seafood enthusiasts may wish to consider that has nothing to do with ethics, and that's flavor. Some anecdotal reports are that the meat of a crustacean that was killed before cooking tastes better than one that was boiled alive. I repeat, these are anecdotes, not data and not proof, and of course "taste" is a subjective and personal thing anyway. But this is in the ballpark of plausibility. We do know for a fact that stress hormones and endogenous opioids build up in the muscles when a live crustacean is subjected to boiling alive, which changes the chemistry of the meat. Some also point to muscle contraction and that it affects the way the meat cooks. Again, this is not proven research, but it is something that impacts some people's decision of whether to kill before cooking.

This leads us to the next question: can we humanely kill crustaceans, even if we want to?

This is a question we do have the answer to. Fortunately it is very easy to humanely kill crustaceans before cooking, and many animal rights groups have web pages giving instructions. They can be killed in less than a second with an electric shock, but so far, commercially available devices for that purpose are absurdly overpriced. They can be humanely killed by chilling in the freezer (just don't let the meat actually freeze) though this is obviously pretty slow. Crabs can be killed by what's called spiking, which is a quick thrust of a knife into two nerve centers; lobsters can be killed by splitting, which is a single knife slice through multiple nerve centers. Instructions for all these methods can be easily found online.

Considering that spiking and splitting are fast, easy for anyone to do, and free, there is no compelling reason for a thoughtful person not to do them before throwing the lobster into the pot or tearing the crab limb from limb. Maybe they are not necessary; we can't definitively say. But if there's even a small chance that taking those few extra seconds spares an animal some painful experience, even though it's one we can't quantify, it is worthy of the consideration of every responsible seafood lover.

This episode is dedicated to the memory of author David Foster Wallace, 1962-2008.



By Brian Dunning

Follow @BrianDunning