How to catch a moray eel… and keep all of your fingers!

Posted on May 18, 2012 by

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7 Diving amongst coral

Author: Kelton McMahon

Why on earth (or the ocean in this case) would anyone want to catch a moray eel?  The Giant Moray Eel, as its name so cleverly suggests, is not exactly inconspicuous. They can reach almost 10’ long and weigh nearly 80 pounds.  And with a set of teeth like these, they can do some serious damage. To make matters worse, moray eels have a second set of jaws in their throat called pharyngeal jaws that also have teeth. I would not recommend googling “moray eel bite,” as the pictures are rather gruesome… ok, now that you’re back from googling “moray eel bite,” I’ll let you know what rational I came up with for wrestling with these beasts on a recent dive trip to the Red Sea.

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A giant moray eel (Gymnothorax javanicus) caught at Canyon Reef near Al Lith, Saudi Arabia in the Red Sea. Photo: Li Ling Hamady

A little background: I’m a post-doctoral fellow in marine science.  It’s basically those awkward teenage years between being a wide eyed, impressionable graduate student and a responsible,  adult faculty member. I get to develop my own research, but they don’t quite trust me with molding the minds of the youth just yet.  My research interests in the broad sense revolve around understanding movement and trophic ecology of marine animals.  Basically, I want to figure out where animals live at different parts of their lives and what they eat, so we can better design conservation efforts, like marine protected areas, to promote healthy ecosystems and sustainable fisheries.  At least, that’s how I justify the years and years… and years in graduate school avoiding a real job. Most people think that I just picked a job that would let me travel all over the world, diving on beautiful tropical reefs.  Yeah ok, that might be part of it.

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Diving on Saut Reef, near Al Lith, Saudi Arabia in the Red Sea. Photo: Michael Berumen

Anyways, I’m currently trying to understand how coral reefs are so productive and diverse, despite being in such nutrient poor water.  The land equivalent is like finding a rainforest in the middle of the desert.  It’s quite perplexing, and has been a head scratcher for far longer than I’ve been around. Here’s an impressive (at least to me) fact: coral reefs occupy < 1% of the surface area of the world oceans, yet they hold 25% of all marine fish species. One plausible explanation is that coral reefs are very, very efficient at pulling all of the nutrients out from the surrounding water.  Alternative, they could be really good at recycling what energy they already have, over and over, so they don’t need to import a lot of new food. I’m developing tools, well chemical tools, to tease apart these two possibilities.  The first step is to collect tissue samples from a wide variety of coral reef animals that occupy different feeding guilds.  That is to say, we want animals that feed on everything from plants at the base of the food web (herbivores) to other fishes at the top of the food web (piscivores), and everything in between. In this way, we can reconstruct a very complex food web of who’s eating whom, and identify the crucial sources of energy and nutrients at the base of the food web support the commercially targeted animals at the top of the food web.

This is where our adventure with the moray eels kicks off.  Giant moray eels are big time predators and would make an excellent choice for one of the apex predators in our study.  The problem is, as excellent apex predators, they’re generally kings of the coral reef world, they don’t fear anyone (expect maybe sharks), and they can really pack a wallop.  So, of course this was the apex predator I had to have in my study.  The next step was to figure out how we were going to get a small muscle sample from not one but 25 moray eels over the course of a 6 day dive trip in the Red Sea.  It’s not as though they were going to offer up said sample on a silver platter.

Our first idea was to use a biopsy probe underwater.  Basically, we have a 6 foot long pole (long enough to stay far away from that devastating moray smile), with a large elastic loop at one end and a sharp hollow biopsy probe at the other. With the elastic loop hooked over your hand, you slide your hand up the pole to “charge” the band, and point in the direction you want to biopsy. Release the pole and wham, you’ve biopsied what ever is in front of you, be it your foot, a wall of coral, or if you’re lucky, a moray eel.  We’ve been doing this for quite a while on whale sharks and manta rays, so our confidence was pretty high. After swimming around looking for morays for what seemed like ages, we finally found our first target poking it’s head out of a coral wall, gaping those teeth than all of a sudden look a lot bigger than I had recalled. Now we only get one shot at this before the eel either makes a mad dash back into its hole, or leaps out to attack us like the Killer Rabbit of Caerbannog from Monty Python.  Ready, set, fire… and nothing. No sample and the eel was gone.  Well, maybe we’ll have better luck with the next one.  Spoiler alert: we didn’t.  We went 0 for 3 that day.  Morays have very thick skin, and a lot of mucus that appeared to be a pretty effective shield against our biopsy probe.  Couple that with the challenges of finding eels in the first place and we quickly concluded that a new plan of attack was in order, no pun intended.

Rather than searching out eels and trying to tackle them on their own turf, we decided to let the eels come to us.  We did this with the help of some large wire fish traps, and a few parrotfish that sacrificed themselves for the sake of science.  The fish traps look like half a sphere with a funnel on one side pointing inwards.  It’s easy for the eel to get in, but hard to get back out. We strategically placed these traps on the bottom at a variety of locations around the reef and let them do the work for us.  We came back an hour or two later, and sure enough, many of the traps had eels in them!  Sweet, we’ve got a trap full of large, angry eels. Ok, now what? We decided to haul the traps back to the boat in the hopes of shifting the odds of winning this wrestling match in our favor.  With the trap resting on the back deck and my advisor standing off to the side already drawing up the accident report, we opened the trap.  I used a large catch bag in one hand and a hook in the other to do my best Steve Irwin impression.  Once secured in the bag, we pinned the eel to the deck to sample it.  It took four large men, ok three large men and me, to hold the eel down, while I took a scalpel and excised a small chunk of muscle.  Who would have thought that a 6’ and 30 pounds of pure muscle would be so damn strong!?! It was so strong, in fact, that we couldn’t always hold him down.  On more than one occasion, the eel out wrestled us and escaped the catch bag and our grasp.  Everyone scattered, and one prominent marine scientist that will remain nameless may have shrieked and leapt onto a bench, as the eel slid around the back deck of the boat gnashing its teeth.  After I wrangled the eel back into the catch bag, we were able to finish the job and get the small muscle sample that had been surprisingly elusive. We scooped the eel up, and released him back to the reef to resume his position as top dog.  In just a short time, that wound will heal and he’ll have a badass story to tell all of his buddies.  Now just 24 more eels to go, haha. We certainly got better at it as we went along.  And much to the relief of our mothers, everyone came back with all of their fingers and toes intact.  With samples in hand, we wrapped up our trip and I headed back to Woods Hole to add this piece to the puzzle of how coral reefs support so many amazing creatures in the desert.

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Back in the lab at Woods Hole Oceanographic Institution, conducting stable isotope analyses on moray eel samples collected in the Red Sea.