Thursday, February 16, 2006

Still more Chelydran awesomeness

The second promised snapping turtle post, transcribed from an e-mail exchange on Feb. 12, and filled with bizarre feeding behaviors, including ichthyological mucophagy. Enjoy.

I have some more snapping turtles stories to share with you.

Like box turtles and kinosternids, snappers have musk glands around the edges of their carapaces. Normally the musk they emit is a thin, clear oil that smells pretty much like dead turtle. Since the turtle is usually wet, the oil isn't visibly noticeable. Suddenly the turtle just smells like it's dead. But Julian Hilliard and I once caught an old snapper that hadn't been molested in a long time. We surmised that that was so because when I picked it up, the stuff that came out of the musk glands looked like orange toothpaste, and smelled like a landfill full of dirty diapers and sweaty jock straps.

On the gluttony of snappers. When my little Chelydra, Maverick, was about 5 inches in carapace length, I would go to the OU duck pond and catch mosquitofish (Poecilia) to feed him. In the winter the mosquitofish were so desperate for organic sustenance that I could hock a loogie into the pond and within thirty seconds there would be hundreds of fish fighting to eat my snot. I just dipped them up with an ordinary aquarium net, one of the square green ones. I once got 67 fish in a single pass, and just over 300 in six passes. They're invasive and they're pushing out native minnows, so I never felt bad about doing it. I'd take 'em home and dump 'em in the tank and Maverick would go to town. He'd come up below them as they schooled near the surface and get half a dozen at a time, even as small as he was. Even when his carapace was only 5-6 inches, he would easily eat 60-70 mosquitofish on the first day. He'd eat until his stomach was full and then start stuffing them into his esophagus. When the epic murder glut was over, he'd sit on the bottom with all four limbs, tail, and neck maximally extended; I suppose there was simply no more room in his shell for anything besides stomach. You could tell when he'd pack his esophagus full because when he turned his head to the side the back 2/3 of his neck would be held stiff by his distended esophagus. It was a disgusting spectacle, and one that I enjoyed orchestrating and watching.

After the initial bloodbath, Mav would sit on the bottom for 4-5 days and digest. After that he'd pick off the rest of the fish at a rate of 10-20 per day. The dieoff was exponential, not linear; as the number of fish got small, it was easier for them to evade him, and I'm convinced that some of them got smarter. When I couldn't get mosquitofish, I'd give him feeder goldfish 30 or 60 at a time (they were 10c apiece at the time). There would always be one or two survivors that he would never catch, no matter how long I left them in...until the next time I added fish. The survivors seemed to get stupid again when they were back in a school, and they'd get nailed, and there would be a new survivor at the end of it all.

I also witnessed some pretty interesting feeding behaviors from Mav. If you've never seen a snapper in action, their underwater strike is pretty cool. They thrust their heads forward so fast that your eye can't really track it; the head just disappears in one place and reappears in another. At the same time, they use their hyoid apparatus to balloon up the pharynx, which draws in vast amounts of water. Between the strike and pharyngeal suction, Mav could really grab the fish. Sometimes he would be right behind a fish on the bottom of the tank, and the fish would simply disappear. I'm just guessing here, but I'd say the entire strike could take less than a tenth of a second. Sometimes he would do one slow enough that you could see what was actually happening. Those took about a quarter of a second, and it really felt like watching slow motion if you were used to watching him eat. He only used the slow strikes when he was really full and lazy, or to snap up the leftover bits after some serious predator theater.

One behavior I never saw referenced in the literature: Mav would open his jaws fractionally, tilt his head to put one side of his mouth next to the bottom, and use the hyoid balloon technique to vacuum up uneaten bits of fish food.

For a turtle, Mav was pretty darn smart. When I first got the big tank (44 gallons), Julian and I would go seine the local creeks and split the catch (Jules had a caiman at the time). I had all kinds of stuff in my tank: bullhead catfish, several varieties of sunfish and crappie, even a little smallmouth bass. As Mav got bigger, they all disappeared, one by one (this was before the giant Poecilia dumps). The last of the big fish to go was one of the bullheads. At 9 inches long, it was about the same mass as Mav, and it was canny. No matter what hour or angle Mav chose for his approach, no matter how slowly he sidled up, the bullhead would always jet at the last minute. But after about 3 months of pursuit, Mav finally got him. I had a big log angled across the tank so he had something to hang on when he was resting near the surface. He learned how to dangle upside down from the log, hanging on with his hind legs, and strike straight down at the bullhead's back. On the first attempt he put a neat triangular notch in the bullhead's dorsal fin, but on the second try he got the epaxial muscle, and that was the end of it. Once he had his jaws in something he'd retract his neck to pull the prey to him (or to pull himself to the prey, depending on who was stronger). Once the prey was up close, he could use his forefoot claws to rip it to shreds. It wasn't always fast, and it was rarely pretty, but it sure was effective.

I had a 300 gallon/hour filter on the tank, by the way. It would have been massive overkill if I'd just had fish. With Mav, I think it was just what I needed.

I know Mav was a male because when I picked him up he would hiss, snap, and (incongruously) stick out his penis. It was purple and about 2 inches long and just over a quarter of an inch wide. That's when his carapace was about 6 inches. I let him go shortly thereafter. He was just getting too big. Normally it takes a hatchling snapper 6 or 7 years to get that big, but Mav did it in two. Of course, he was warm all year long and had all the food he could handle...

More on the indestructibility of snappers. One evening I was driving to Julian's place for a barbeque and I saw a big snapper smashed on the road near the OU duck pond. It was off on the shoulder, but I could see red flesh in the middle of its shell, so I knew it was toast. When I got to Julian's, we decided to go back and see if we could get the head.

Whew. The next part isn't pretty. The snapper was a monster. I measured the carapace: 15 inches. It had been run over on its right side, and that half of the carapace was caved in. I could see the lungs, liver, and intestines exposed through the hole in the shell. It gets worse. The turtle had been hit in the middle of the road, and managed to drag itself more than 15 feet from the center median to the shoulder; the path was marked with blood and fluid. And here's the worst bit: when we got there, the turtle had its head up and was looking around. It was not just waving it's head in some kind of stupor. It was alert. That that hideously wounded animal was still alive was the most sickening thing I'd seen in my life to that point (and may still be).

Well, we had to put it out of its misery. I don't know how long that poor animal had been there since the collision, but we were going to give it a swift, merciful death. Trouble is, killing a snapper is no easy task. First we tried to crush its neck with an axe handle. No luck. Keep in mind, this was two guys, fresh back from hucking 100-lb bags of matrix around in the field, and we couldn't break the turtle's neck. Unfortunately, we were just working with what we had on us, and the axe handle in the bed of Julian's truck didn't have a head on it. Then we tried to saw through its neck with the saw on my Swiss Army knife. That saw is no joke. I had used it for cutting holes in sheetrock and trimming the edges of plaster jackets. It was sharp as hell, but I could not get through the skin on that snapper's neck. It was like trying to saw through, I don't know, a Kevlar boot, maybe. I couldn't even draw blood. In the end, Julian drove back to his house and got a hatchet, and we chopped the turtle's head off. The severed head continued to move its eyes and snap at us for five minutes, I shit you not. (We pithed it after a few minutes.) Julian still has the skull. It's four inches across at the widest point.

I got my own snapper skull later that summer, and learned a little more about the toughness of snapper skin. I was cleaning out a warehouse at OU and found a trash bag with a mummified snapper in it. I guess someone had found a dead one and collected it, and then just forgotten about it. Bugs must have gotten to it at some point, because the flesh and guts were mostly gone. It was mainly mummified skin and shell. I decided to clean it up using bacterial maceration. I put the crispy critter in a 5 gallon bucket, filled it with water, covered it with 2 boards and a cinder block to keep the opossums and raccoons out, and let it sit on my back porch in the 100+ F Oklahoma heat for two weeks. At the end of that time I had a bucket of thin turtle soup with greasy but otherwise clean bones at the bottom. Unfortunately the shell fell apart--snapper shells are solid enough in life, but take off the soft tissue and they go to pieces, just like trionychids. I degreased the bones and still have most of them, although I gave the skull away (but not before I'd gotten a better one). One cool discovery was that the spikes on the tail consist of bony cores under a keratin sheath. Most of the spikes were floating in connective tissue, but the most proximal one had gotten so large that it had contacted the neural spine of the adjacent caudal vertebra and fused to it. I could probably take some pictures for you if you're interested...

Oh, on the ruggedness of snapper skin. I forgot to mention that after the two weeks of maceration, the bones were clean and the shell had fallen apart, but the skin was still more or less intact. I fished it out and it could be torn, but it would not fall apart on its own. That's after a certain amount of decomposition, several years of dessication, and two weeks of maceration in 100+ temperatures. So the lesson is that snapper skin may look and feel soft, but it is nearly impenetrable.

Finally, I kept a Platysternon (Southeast Asian Big-Headed Turtle) for most of the past three years. I think the most recent phylogenetic analyses posit Platysternon as an aberrant batagurid or batagurid ally. That makes sense to me. The similarities to the chelydrids are entirely superficial. Platysternon has a flat, unserrated shell, a short neck, a fairly flat plastron, skin without the numerous spikes, fringes, and tubercles of chelydrids, and a prehensile, spikeless tail. I'd read about the tail prehensility, and about Platysternon supposedly vocalizing. It's all true. My turtle, Carl Hungus, had remarkable ability to control the tail and to exert force through it. Put him in a five-gallon bucket and he'd prop himself up on his tail alone, and keep pushing with progressively more distal segments, until he could hook a forelimb over the edge and pull himself out. That's a turtle with a seven-inch carapace. Platysternon's head is shaped very differently from Chelydra's, and the top of the head is covered with a single large, rigid scale, very unlike the soft leathery skin on the heads of snappers.

Oh, the vocalizing. Sorry, I'm pooped and frankly even I'm getting sick of writing about turtles. Yeah, Platysternon vocalizes, both in and out of the water. Out of water it comes out as a scream. I've heard tortoises wheeze, but Carl's screams could be mistaken for a baby's. Once when I was giving him a checkup he screamed and Vicki came out of the bedroom to see if it was London. In the water, Carl would growl. It sounded like someone sliding furniture across a wood floor. It was just an incredible amount of noise to come out of an animal that is basically the size of a really big sandwich.

There you go. If you're really nice, maybe someday I'll write about my experiences keeping box and musk turtles.


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