Thursday, April 15, 2010

Lord Geekington In The Field: Giant Snappers

From Hell's heart, I photograph thee!

I've had big turtles on the mind after writing posts about Mega-Turtles and editing an article on a speculative giant snapping turtle; the last thing I expected was to casually stumble across a giant individual. Whilst surveying the damage caused by the recent Hundred Year Flood, I impulsively explored the coastline of a ~100 acre (40 hectare) pond. I had previously seen painted, red-eared slider, and wood turtles in the locale, so I admit that I was expecting to see turtles of some sort. Heading back, I noticed that what I initially assumed to be a large rock was covered in scutes. I actually said "Holy shit!" out loud for the first and only time that I can recall. Having plenty experience seeing car tires in the water, I estimated the length of the shell to be about 2 feet (60 cm) long. The size and flatness of the shell, coupled with Narragansett Bay only being a mile away, made we wonder if this was a sea turtle that had gotten very lost. However no flippers were visible and as I got closer (about 5-6 feet away at the closest) I realized that I was staring at an alarmingly large snapping turtle. Only having a cell phone at the time, here is the only photo I could manage before the turtle disappeared:


This Cryptozoology-caliber photograph is clearly too prone to pareidolia to be of any analytical value. The next day I came back with a DSLR in a desperate gambit to get a clearer photograph, and somehow succeeded:




Sort of. The turtle caught me off guard by being on the different side of a small peninsula and once again it managed to disappear before I could photograph it further. While still blurry (as auto-focus doesn't work well on submerged objects) there's no doubt the object in question is a snapping turtle. I wasn't sure if I saw subtle keels in the photo, so that coupled with the outrageous size made me wonder about species identification. Common Snapping Turtles (Chelydra serpentina) are native to my region, have keels that effectively disappear with age, and have a maximum SCL (strait carapace length) of 49.4 cm (1'7") (Ernst and Lovich 2009). Since the turtle I observed appeared to be around (or exceeding) the record size, I wondered if the prospect of running into an accidentally introduced species would be more likely. Alligator Snapping Turtles (Macrochelys temminckii) can reach an SCL of 80 cm (2'7" - typically 40-50 cm or 1'3" to 1'7"), but have prominent keels on the carapace, and only occupies river systems flowing into the Gulf of Mexico (Ernst and Lovich 2009). I noticed that some specimens have keels that are surprisingly subtle, so I can't discount them based on that trait.

I set out once again with a friend in tow - partially to ensure that I was not insane - to try and figure out the size and identification of the turtle once and for all.


TJ's photograph. The bright red/orange coloration seems rather odd - is it indicative of a disease or is it within the range of variation?


My photograph of the head. Red/orange coloration is also present. The turtle must be a sight to behold out of the water... if it ever leaves the water.

I revisited the area after the water levels went down...


Photo-montage of an ISO/IEC 7810 ID-1 card (8.56 x 5.4 cm or 3.37" x 2.13") in relation to the turtle's head. 


These photos unambiguously show a Common Snapping Turtle (Chelydra serpentina) and the landmarks support the notion of considerable size. Using an 8.5 cm figure for my outdated Blood Bank card yields a head length of 14.5 cm (5.7") and width of 13.5 cm (5.3") - but I also shaved off 0.5 cm "just in case" to get lower bounds of 13.5 cm (5.3") and 12.5 cm (4.9"). Herrel and O'Reilly (2006) have a table of measurement data from 11 Chelydra individuals and I assumed that minimum and maximum measurements correspond to singular individuals. Using those figures I estimate the carapace to be 44-47 cm (1'5"-1'6.5") using the head length and 47-51 cm (1'6.5"-1'8") using width. The head length/carapace length proportions in Herrel and O'Reilly (2006) are about 1:2.5 (minimum - 2.7 cm/6.7 cm), 1:3.0 (average - 6.5 cm/19.7 cm), 1:3.25 (maximum - 11.8 cm/38.6 cm) - so the given carapace length estimates may be a bit low. The head width/carapace length proportions are about 1:3.5 (minimum - 1.9 cm/6.7 cm), 1:3.8 (average - 5.1/19.7), 1:3.8 (maximum - 10 cm/38.6 cm) - so the given estimate is probably reasonable. Scaling up from the 38.6 cm/16.65 kg maximum in Herrel and O'Reilly gives estimated masses of 25 kg (55 pounds - 44 cm SCL), 30 kg (66 pounds - 47 cm SCL), and 38 kg (83 pounds - 51 cm SCL).

Clearly there is no substitute for actually measuring the turtle! Such a feat would be nigh-impossible to do safely as the turtle appeared rather suspicious of humans and even their food (chicken and ham... my intended lunch), it was right next to a tunnel in which it could casually escape, the water was close to waist-deep right off the bank, lots of branches were in the way, oh, and the turtle looked like it could swallow and severely mangle my hand. I must note that you should NEVER NEVER NEVER pick up a snapping turtle by its tail as it can cause severe injury - I cannot emphasize that enough - NOBODY gets it right. Well actually TJ knew better, but that appears to be a rare exception. Chelydra.org illustrates how you should pick up a turtle, unsurprisingly none of these methods look plausible for an animal close to the size of the Alligator Snapper in their photograph. Curious as I am about the turtle, it is not worth risking the life and well-being of a potentially decades-old animal just to find out how large it is.

While my friend and I were walking back from photographing the snapping turtle (waiting for it to re-emerge), unbelievably, we saw a second individual which appeared to be almost the same size about 50 m (160 feet) away. It lacked the conspicuous orange coloration and dwarfed a painted turtle right next to it (which looked plausibly bite-sized). I am certainly curious as to how many large turtles are living in the pond. If there is a potential way of getting the vital stats of the turtles and to be involved in some sort of official program, I certainly wouldn't mind spending a summer tracking them down...


Oh, and I'm just getting started with snapping turtle posts.


References:

Ernst, C. H., and Lovich, J. E. (2009). Turtles of the United States and Canada. John Hopkins University Press: Baltimore, Maryland.

Herrel, A. and O'Reilly, J. (2006). Ontogenetic Scaling of Bite Force in Lizards and Turtles. Physiological and Biochemical Zoology 79(1), 31–42. DOI: 10.1086/498193

2 comments:

Chelydra said...

It depends on habitat as well as the individual, but common snappers of both sexes will regularly leave the water to travel between different wetlands in their territories, presumably in search of food, mates or a deep place to overwinter. They're also easy to find hauled out basking at this time of year in southern Michigan - they're almost catlike, draped over a log with legs dangling, half asleep in the sun.

They can be strikingly orange when stained with tannins.

Also, my internet handle is merely a coincidence.

"the Dude" said...

Cameron, why not bring some chicken scraps to bait it out of the water?