If you dive in shallow water on the right side of the Salaya house reef, or on such famous Dauin dive spots like “Secret Corner” or “Ceres”, you will see some odd creatures sticking out of the sand: Long and thin, with a tiny head, and always in groups of tens to hundreds of animals. Are these worms? No, these are garden eels, fishes which don’t swim, but spend almost all of their lifes partially buried in the sand. If a diver or big fish comes too close, they completely disappear under the sand for a short while. Here is video of a group of garden eels at “Secret Corner”. The odd jerking movements are not a funny eel party-dance, but their feeding movements when they gulp up plankton:
Hans and his Garden Eel
The garden eels belong to the family of the family Congridae, the conger and garden eels, and are hence a distinct group of fishes from the well-known moray eels and freshwater eels. We have several species of garden eels in Dauin; One which I hold especially dearly is the spotted garden eel, with the scientific name Heteroconger hassi. It is named after my countryman, the late great diving pioneer Hans Hass. This is Hans:
And this is Hans’ garden eel:
Since garden eels don’t swim, they really don’t need regular fins anymore. But if you are digging yourself into the sand all your life, you will need a … shovel! And it seems that evolution has transformed the regular fish tail into a shovel-like organ in these fishes.
Natalie De Schepper and colleagues report in a study published in the Journal of Morphology that “The [garden eel] caudal skeleton is highly reduced and fortified, forming a firm, pointed burrowing tool.” Many of the muscles normally responsible for fine control of the tail of a fish are missing in garden eels. Look at this image, from De Schepper’s article, of the bones in a spotted garden eel’s tail (fish facing to the left; one muscle shown, in red). It does not look much like your usual fish tail anymore, does it?
Garden Eel Spawning
You might wonder, how do these fishes even mate when they are dug into the sand all of their lifes? Good question! Garden eel spawning has only been observed a few times, in large tanks in public aquaria. Even during spawning, the garden eels never completely left their sand tubes, though their bodies came out much further than usual. This limits the mate choice to eels burrowing in close proximity, in the same colony. Check out this really cool drawing of a mating sequence of splendid garden eels, from a research paper by Tomohiro Kakizaki and colleagues (published in Marine and Freshwater Behaviour and Physiology). M1, M2 and M3 are 3 male eels, and F is a female eel.
Garden eel photography
Lastly, how do you photograph and film garden eels? It’s very hard! These animals are extremely shy and very quickly retract into their sand tubes when you as a diver approach them. With other marine animals I have found that a very calm approach, and careful exhalation through my nose (generating smaller, less noisy bubbles escaping through my mask) help me to avoid spooking them. Not so with garden eels! Even if I swim towards them very carefully, they disappear underground before I am within photo-distance.
I found two ways around this dilemma:
– It seems that on overcast days, the eels’ small eyes don’t get enough light for them to see well, and on such days I have managed to approach them closely.
– another option, for video, is to put your camera in the sand in front of the garden eels, press record, and then retreat. The eels will eventually re-emerge from their burrows, and your unmanned camera will film the action. Just stay back a few meters and enjoy the dancing before retrieving your camera – that’s how I got the video above.
Happy diving! If you have any questions about garden eels or other Dauin underwater critters, please contact me at firstname.lastname@example.org