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Helping to Sustain a Way of Life in the Bahamas

Big or small, we love them all!

By Catherine | 15 July 2011 | No Comments
Published in Exuma Cays Expedition 2011, Uncategorized

Over the past few weeks we’ve seen lots of queen conch. We’ve spent what amounts to days and days in the water and covered miles (or kilometers) of seabed in search of these animals. Each day the crew from the dive boat and the crew from the tow boat compare notes. Where did you go? How many did you see? How big? Any mating? Eggs? How old were they?

After listening to these daily reports and seeing hundreds of conch myself, I am amazed by the variety of shell sizes and shapes within the species, Strombus gigas. This variety is likely due to a combination of genetics, the kind of the habitat the conch is living in, and the age of the animal. In a previous post I briefly talked about the differences between juveniles, rollers, and adults (a little more on that soon), but for this post I am really talking about the adults.

A thin-lipped, "young adult" queen conch shell at Warderick Wells. photo by C. Booker

Measuring the flared lip of an older adult conch shell. photo by M. Peyton

Here in Warderick Wells the dive crew is finding a lot of older conchs in the deeper waters we are exploring. Most of the old conchs we find have shells that are very rounded and have long since lost the beautiful pale pink on the outside of their shells. They are extremely heavy because of the layers and layers of calcium carbonate shell the animal has built up over the years. The younger conchs the towing crew finds generally have a much more delicate appearance because their shell has not been worn down over time and the beautiful hues of pinks still stand out. So, age does obviously make a difference in the appearance of the conch.

A conch covered in algae. photo by C. Booker

All animals are shaped by their environment, and the queen conch is no different. The appearance of a conch shell is very influenced by the biological environment it lives in. Fishermen know that a conch’s shell tends to take on certain characteristics of its habitat and are not fooled by this “disguise”. Our towing team has had a great time trying to spot conchs disguised by lots of algae growing on their shell that resemble little “Chia pets”, or “rasta conchs” (depending on who you ask).  These guys blend into their habitat really well! Towards the end of a conch’s life the thick shell has almost certainly become a little ecosystem itself.  We’ve seen many different species of algae, some corals, and boring worms in the oldest shells.

Another reason for such great variety in the conchs we have seen may have to do with their genetic “flexibility”, or what scientists call phenotypic plasticity. Most immobile (or less mobile) animals can change the way their genes are expressed based on the habitat they live in. Scientists think that depending on the habitat (the physical environment and the food that is available), a conch’s shell might actually form differently in size and even in shape. After all, the better adapted they are, the more likely they are to survive!

An adult "samba" conch shell (on the left) and an adult "broad-lipped" conch shell (on the right).

We have also been finding a lot of a small variety of conch we call “sambas”. They are like miniature versions of the big broad-lipped queen conch that usually represents the species. The samba adults are still recognized by the flared lip, but it is not as big and beautiful. We do not know what exactly causes these conchs to grow smaller (type of food, availability of food, water quality, genetics?), but scientific investigations have indicated they may be genetically different than the normal sized queen conch.

In the end, we don’t mind what they look like; they all get counted as queen conch. However, from what we have heard, fishermen do care what a conch looks like. The small samba conchs are harder to get out of the shell and the meat is tougher, so they are often skipped over. The really old conchs may be passed up too for the same reason. The large conchs with the broad shell lips are tastier and you get more return ($) for your effort. Is this preference by fishermen (what scientists call selective fishing pressure) having an affect on the overall fishery? If only the sambas are left to reproduce, is that what we can expect to see more of in the future? From what we saw in the Berry Islands and Andros, this could be happening already.

Thanks for checking in…

Catherine

 

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conch eggs

Conchs lay hundreds of thousands of tiny eggs in a sandy egg mass. The larvae emerge after 5 days and drift on currents for up to a month before settling to the bottom of the ocean.

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