Thursday, March 26, 2009

Seduced by a Siren

For the past several weeks, I’ve cheerfully placed my jacket and sweatshirt in the back of my closet several times, confident that the periodic warm spells had finally signified the last gasp of winter. After each of these gleeful episodes, I’ve had to grudgingly retrieve them the next morning after I opened my front door and was predictably greeted by the cold, crisp air. But now, surely, this is the real deal.

When I stick my head out of the window, I can no longer hear upland chorus frogs calling for mates. This winter-breeding amphibian, whose call sounds like a finger running down a plastic comb, is usually the first species to start singing each year, and the first to stop. Instead, last night I heard grey tree frogs and southern toads trilling in the pond near my home. It’s a good time of year.

Undergraduates at Auburn University sometimes conduct independent research projects for credit and for experience. Since my lab is known for studying interesting critters, there are often individuals working with us and looking for help with their projects, particularly when it gets warm and the amphibians and reptiles start to move around. Last week I received an e-mail from a student looking for help catching one of the most elusive animals in the south, the greater siren.

Sirens are a group of salamanders that don’t subscribe to the typical amphibian way of life, instead of laying their eggs in the water and waiting on land until the next breeding season, sirens simply never leave the water at all. They obtain oxygen through the large, feathery gills that emanate from their neck.

Over time, sirens have lost their hindlimbs and are left with only greatly reduced forelimbs, rendering them incapable of meaningful terrestrial movement. It’s no matter to these eel-like creatures as they patrol the watery depths, legs would only slow them down. We know very little about these secretive animals, they spend the majority of their lives in the muck lining the bottom of swamps, ponds, and similar bodies of water. We do know, however, that they are ruthless and effective predators. Sirens can reach lengths of three feet long and at that size there are few other animals in the water that aren’t potential prey.

The Auburn undergraduate was interested in shedding some light on the ecology of this little known organism. By capturing some and bringing them temporarily back to the lab, he hoped to make observations on how efficient they are at absorbing oxygen. The first step (and what I feel is the most fun part) was finding and catching the sirens.

On Friday afternoon we gathered on campus to collect our gear, into the van went numerous nets, crayfish traps, and a large seine. Crayfish traps, although designed for edible crawdads, are effective at capturing a large number of different animals. They have a simple design: plastic-coated wire mesh is molded into a rough pyramid shape; at the base, there are three funnels leading inside. Aquatic animals crawling around the bottom of the pond may find their way through the funnel and become trapped. The seine is even simpler, a ten foot rectangular net with weights on the bottom is stretched between two wooden poles; one person grabs each pole and drags the net (weighted side down) through the water. Animals get swept up in the net as it is brought through the water. After a sweep, the net is brought to land and the contents examined.


The van loaded, we headed down to Henry County, Alabama to search a pond that was the site of a siren study many years ago. On the drive down I envisioned wading through a vast expanse of marshy wilderness, parting reeds as I strolled through the water exploring the pristine swamp. Imagine my surprise as the van pulled to the side of the road alongside a farm pond surrounded by acres of grassland closely cropped by a multitude of cow mouths. This is it? I thought to myself as I surveyed the pond, similar to so many dotting the agricultural landscape of south Georgia and Alabama.

Carefully avoiding any cow patties, I gave the pond a preliminary examination. I noticed there were some tupelo trees along the shore and a few small patches of aquatic vegetation. I decided I would focus on these areas and any other form of structure I could find. I thought that in a relatively uniform pond such as this, any animals would be concentrated there.

In the fading light, we set out our crayfish traps. We’d check them when our evening was over. I grabbed a steel framed dip net and began to work the shoreline, thrusting the net into the water and working it along the bottom for several feet before hoisting it into the air. It didn’t take long before my arms began to tire from lifting the various leaves, sticks and assorted muck that I captured. After each sweep I eagerly and optimistically peered into the depths of my net, half expecting to see a squirming siren within my grasp.

I began having trouble with my headlamp, it seemed to blink out whenever I tried to see what I had captured, making for a frustrating exercise. It’s unfortunate that we weren’t there to catch aquatic beetles and other insect larvae, we could’ve made it an early night due to my great success. Any amphibians, however, effectively evaded me. I was considerably discouraged by the time I heard some excited yelling coming from the bank several hundred yards away.

Curious, I slowly made my way back to our starting point. By the time I had arrived, there was nobody in sight, however, there lay a large red cooler on the bank. The lid was weighted down by a bucket full of water. I couldn’t resist removing the bucket and peering inside the cooler. There, with gills billowing through a couple inches of water, lay a two foot long siren. Thick as a vacuum hose, the amphibian looked relaxed as I excitedly peered at him.

It turned out to be the only one captured that night, he had been nabbed during a sweep of the seine, likely as he hid within a leaf pack. Despite the traps, the seine, the nets, and six enthusiastic searchers, our success was limited. But the confirmed presence of just one siren indicates that there were probably dozens, if not hundreds more within the pond.

Sirens are rarely seen and hard to capture. We know little about the species, but you should consider how many of these huge, unique salamanders live within your neighborhood pond, marsh or lake. You may be surprised.

4 comments:

nina at Nature Remains. said...

You've got a great premise for a blog and the potential for some cool reads here! --will definitely be back. Thanks for visiting.

David Steen said...

Thanks for your interest. I hope to meet that potential!

Tom said...

Hey David,

Great post, and as always a pleasure to read.
I studied Sirens in a zoology class last semester. Sadly, the specimens I was able to observe had been preserved in a gallon jar most likely before I was born. I would really like to see one in a cooler at pond's edge. How cool is that?

Thanks for sharing your experience.

Tom
Environmental biology major (Junior)
Fort Lewis College, Durango Colorado

David Steen said...

Thanks Tom.

I'm familiar with the type of specimens you describe and they just don't do justice to a living, breathing siren. Another reason to visit the Southeast.

Dave