Queen Conch and the Graveyard Hypothesis

By Emma Boling, Sofia Gonzalez, David Marsh, and Emma Pranger, Spring 2025 students ~ Edited by C.E. O’Brien, Associate Professor of Tropical Marine Ecology and Dani Backman, Waterfront Assistant, The School for Field Studies, Center for Marine Resource Studies, South Caicos ~ Special thanks to Fall 2024 Grave Conch-erns research team: Zachary Baskin, Eva Connor, Corrina Schell, and Lauren Bulik, Fall 2024.

Would you want to live with a dead body in your house? Probably not, and Queen conch seem to feel the same. This is the idea behind the “Graveyard Hypothesis”: That conch avoid areas where empty shells from fished conch have piled up.

This belief is grounded in the observations and experience of Caribbean fisherfolk, many of whom go out of their way to dump their empty conch shells away from conch grounds after knocking their catch. Given the importance of Queen conch to the ecosystems and economy of the Turks & Caicos Islands (TCI), we decided to ask the conch themselves how they feel about cadaverous roommates. 

Queen what?

The Queen conch’s eye pokes out from its shell, with the cephalic tentacle underneath.

The Queen conch (Aliger gigas) is a marine snail inhabiting the Caribbean and Western Tropical Atlantic. It can often be found in shallow, sandy areas as well as seagrass meadows. Surprisingly for a snail, the Queen conch can live up to 25 to 30 years and reaches sexual maturity around the 3.5 to 6-year mark.

Queen conch meat is one of the largest exports of South Caicos, with the small-scale fishery supporting 70% of the island’s population by some estimates. It’s also a staple in the Caribbean diet, common in dishes like conch salad, conch fritters, and other delicious meals. Despite the existing fishing regulations, a decline in the Queen conch population throughout surrounding regions has raised concerns that the current rate of harvest is not sustainable. This makes studying the feeding, mating, and migration patterns of Queen conch more important than ever.

When Queen conch are caught by fishers, the meat is removed through a process called “knocking”: First, a hole is drilled or broken in the top of the shell to expose the adductor muscle that keeps the conch inside its shell. Next, the muscle is “jerked” or cut to allow the conch to slide out. Fishers then discard the mostly empty shells, often with little bits of meat still stuck inside, in large piles called “middens.” Conch middens vary widely in size, from a few dozen to hundreds of thousands of shells. Some middens are so large that they are navigational hazards to boaters or even form islands, and some are so old that archaeologists have used them in investigations of past Caribbean inhabitants and cultures. 

In the TCI and surrounding regions, conch fishing traditions extend back many generations. Among local communities, the belief is widely held that these middens, which are effectively “graveyards,” cause conch to flee the vicinity and has guided their resource management historically. This belief reflects the deep cultural knowledge and environmental observations of local people, and this wisdom is critical for modern marine resource management. If the presence of these middens alters conch behavior and causes them to flee the area, this could potentially separate them from key feeding grounds and alter important migration routes, compounding the impacts of fishing if not done strategically.

How do they know? 

In the field experiment the artificial midden is encircled by conch.

How could a snail possibly know that a midden was nearby? For one thing, they have great eyesight. Queen conch have lensed eyes, located at the ends of two long, movable eyestalks, which allow them to distinguish shapes and shadows. This, in theory, could allow them to see and possibly identify middens visually.

Conch also have an incredible sense of smell. Queen conch will use their cephalic tentacles—two short “noses” located on their eyestalks—to sniff out food, mates, and to get a general sense of their environment. This could also allow them to “smell” where other conch have been knocked. Indeed, scientists have found that several other species of marine snail show high sensitivity to the scent released by injured individuals of the same species. This scent is called a “conspecific alarm cue” and is a potential mechanism for the behavior described in the Graveyard Hypothesis: the Queen conch might pick up on the scent of the pieces of meat still sticking to shells in the middens and high-tail it out of there. (Well, as much as a snail can high-tail it.) A recent (2023) study by Elvidge and colleagues at the Cape Eleuthera Institute in the Bahamas partially supports this, finding that some conch move more in response to the presence of conch guts nearby than a sea water control, and that these chemicals cues have a stronger impact on conch behavior than visual ones (i.e. just seeing a midden).

This is a close-up of the experimental conch midden.

Asking the locals

To put the Graveyard Hypothesis to the test, we conducted two experiments, one in the conch’s own habitat, and one in small artificial pools. The field tests took place in the beautiful waters of Shark Alley Lagoon, a protected area next to Long Cay off the southwestern coast of South Caicos. There, we created our very own middens, made of three different materials: Either rocks, old knocked shells, or fresh knocked shells. We used rocks as our control, as they don’t look or smell like knocked shells, and we predicted the live conch would not react to them. The old knocked shells were used to test if the conch could visually identify conch shells in a midden, and the fresh knocked shells were used to test for the effects of a combination of visual and scent cues, as the meat clinging to these shells would emit a conspecific alarm cue. We predicted that the conch would move from both types of shells but travel farther from the fresh-knocked midden since scent cues presumably travel farther than visual cues.

The mock middens we created were made up of 20 rocks or shells, stacked on each other in a pile around a cinder block with a buoy attached (to aid in relocating it more easily). Once the midden was erected, 30 numbered plastic stakes were placed in a circle one meter from the midden, and the hunt for live conch commenced. Our team randomly collected 30 conch from the vicinity, which we measured, temporarily tagged, and placed in a circle around the midden, matching the tag number to the stake number. With the last conch placed, we left them alone for an hour and a half and then returned to measure the distance each conch had traveled. Finally, we removed the number tags and returned the conch to the seafloor, making sure that there was no air trapped inside the shell and placing them aperture (opening) down so that they would not have to flip themselves. We repeated this process for 15 trials, and at the end of our experiment, we had data from 450 conch. And boy, it’s surprising how far they move!

On dry land, a different experiment was run. We temporarily collected 12 juvenile conch from the wild and placed 4 individuals into 3 rectangular pools, each with one of 3 “cues”: plain seawater, barracuda guts, and Queen conch guts (collected from local fisherfolk). The sea water acted as a negative control, and we expected the conch to have no reaction to it. On the other hand, the barracuda guts, an unrelated fish, acted as a positive control—it definitely emits a scent, but not one conch should associate with danger. Lastly, Queen conch guts provided the conspecific alarm cue we wanted to test, and we expected the conch to move more frequently and further with this cue compared to the others. The conch were evenly spaced around the cue, and a GoPro was suspended above the pools to record their behavior for 60 minutes. Afterwards, they were taken back to where they had been collected and released, again making sure to remove air from their shells and place them aperture down. 

Analysis of our data found that there was a significant difference in conch movement by cue type, with the conch moving the most in the presence of the dead conch cue. In other words, it seemed like they were trying to get away from a dead roommate in the house! These results support the Graveyard Hypothesis, suggesting that the conch in these trials recognized the conch smell and moved away from it in the pool. Confusingly however, this means that the findings of the two experiments did not match up—despite the clear response in the lab trial, we found no significant difference in the distances traveled by the conch in the field experiment. But if conch recognize and avoid the smell of conch meat in a small pool, why wouldn’t they flee out in the wild? 

Well, there are a couple of reasons this could be. Like we mentioned, the middens we made for our field trials consisted of 20 shells (or rocks), as we were limited by the size and weight of the objects we could transport to and from the site. Any fisher can tell you that real middens are made of a lot more than 20 shells; they’ll contain at least several dozen, if not thousands of shells. Because of this, it’s plausible that more shells will create a stronger smell. Our middens, try as they might, just may not have been big enough, and therefore smelly enough, to send the conch for the hills. 

Another reason may be the timescale. Now, snails have their strengths, but they’re not known for their speed. While there were some pretty impressive distances traveled by a few individuals (just over 23 meters in one case), the conch may have just needed more time to show significant differences in their distances traveled in response to the three different cue types. 

Finally, Queen conch are ectotherms, meaning that the external environment controls their internal body temperature. The average water temperature of Shark Alley Lagoon dropped about one degree over the course of our trials. This may not seem like much, but a shift like this can strongly affect ectotherms. These cooler temperatures may have caused the conch to “chill out,” causing an overall decrease in movement, which would affect our experimental results. 

Slow and steady wins the race

The “Conch-erors” research team tags and measures conch using an old windsurfing board as a floating “lab bench,” with Long Cay in the background.

To recap: while the field experiment did not detect a clear effect of middens, this may have been due to confounding circumstances. The lab experiment did suggest that live conch can detect and respond to conch alarm cues—the proposed mechanism underlying the Graveyard Hypothesis. These laboratory findings provide compelling support for the plausibility of the hypothesis, and it remains a promising area for further investigation. We recommend that future studies take into consideration the midden sizes and longer timescales to better simulate the natural environment of the Queen conch. This could be through constructing larger middens and measuring distance traveled over a greater period of time, or even using established middens in the wild.

Another important topic for future study is determining where middens would be the least ecologically damaging. If conch do flee from areas with middens in them, they could be forced out of feeding or mating grounds, or they may have to navigate around them during migrations. Therefore, areas of little importance to conch should be identified and designated for shell disposal. On the flip side, with the rate of coral bleaching and degradation increasing, conch middens have the potential to provide refuge for some reef organisms (particularly damselfishes, wrasses, and brittlestars), potentially partially compensating for lost coral habitat. If so, determining the best locations for these middens, along with ideal size, stabilization time, and distance from existing reefs, would be important topics for future study.

The results of our research showcase the importance of listening to fisherfolk, as well as incorporating traditional practices into local, regional, and national fisheries management. Protecting Queen conch is essential not only for preserving marine biodiversity but also for sustaining the cultural identity and economic well-being of the Turks & Caicos Islands. As a cornerstone of local cuisine, tradition, and livelihoods, conch must be managed responsibly to reverse their decline. Safeguarding these iconic animals today ensures they remain a vibrant part of the ecosystem—and the island community—for generations to come.

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