The Mystery of the Suwannee Cooter Range Gap

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mtratcliffe
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The Mystery of the Suwannee Cooter Range Gap

Post by mtratcliffe »

There is a gap in the range of the Suwannee Cooter that has puzzled me ever since I heard a local herpetologist, George Heinrich, give a presentation on them last fall. He recently published a manuscript about the Suwannee Cooter in the Journal of North American Herpetology. You can read it here (it's a short read):

http://www.cnah.org/pdf/88320.pdf

The Suwannee Cooter is found only in Florida, in river systems that drain to the northeastern Gulf Coast. Their range is primarily centered on the "Big Bend" of Florida, from the Ochlockonee River (westernmost extent) east and south along the coast to the Weeki Wachee River. However, there is a disjunct population located in the Alafia River some 79 km overland from the Weeki Wachee River. The Alafia River is located on the eastern side of the Hillsborough Bay, which is the eastern half of the Tampa Bay we are all familiar with. As you can see in the map below, if you follow the Weeki Wachee south along the coast, you pass the Pithlachascotee and Anclote Rivers, both of which are small and have only a few miles of non-tidal freshwater. The Suwannee Cooter's presence in these rivers is currently unverified. Continue south down the coast, and you'll reach the opening to Tampa Bay. Follow its southern shore and the next rivers you'll find are the Manatee River and Little Manatee River, neither of which is known to be home to the Suwannee Cooter. Continue following that shoreline, and it bends north, bring you to the Alafia River. Taking the coastal route, that gives us four named rivers between the Weeki Wachee and Alafia that are not known to have Suwannee Cooters living in their watersheds. If the Suwannees reached the Alafia by following the coastline south from the Weeki Wachee River, then why are they not found in those rivers? Did they travel overland?

ImageSuwannee Cooter Range by zeonicweapon, on Flickr

Let's look at the overland route. To get from the Weeki Wachee to the Alafia River, the Suwannee Cooter would traverse right through the watershed of the beautiful Hillsborough River, which drains from the Green Swamp, much like the Withlacoochee River (which is home to Suwannees). I have paddled an 8-mile stretch of the Hillsborough three times, and have also visited a park along the river at least five times, and I have never seen a Suwannee Cooter there. In fact, they are most certainly not found in the Hillsborough watershed at all. There are lots and lots of Peninsula Cooters and Florida Redbellied Cooters there, but not Suwannees, and the latter is easily distinguishable from the former two.

So, that raises the question - how did these turtles get to the Alafia River without being found anywhere else between that river and their main distribution further north? Their presence in the Alafia isn't a recent find - their populations there have been known for decades, so I doubt accidental release is the answer. There were concerns that the Alafia population was wiped out after a devastating sewage spill in the 90s, but they have since rebounded. I have personally seen several along the river, though they were not found in large numbers. I have also seen them on the Weeki Wachee, so I can attest to their presence there.

I've promised George that I would keep an eye out for them in the other rivers of the region. I've paddled the Little Manatee before, and only saw a few Peninsula Cooters. I plan on kayaking the Braden River (tributary of the Manatee River) and possibly the Anclote River in June. I doubt I'll see any Suwannee Cooters on those rivers, but perhaps if I do, I can have my name in a peer reviewed journal someday!

Has anyone ever been on any of the rivers I mentioned? If you ever find yourself on these waters, keep your eyes open for Suwannees! They may yet be lurking in some rarely-explored corners of these bodies of water. I'd also like to hear any theories you all have about the gap in their range. These are fascinating turtles - take a look at some of my photos below if you are unfamiliar with them. Suwannee Cooters have green eyes, grow larger than other Cooter species, have an upside-down chevron marking on the front end of their plastron, and generally have flatter carapaces than the highly-domed Peninsula and Redbellied Cooters. I hope one day we can solve the puzzle surrounding their known range!

ImageDSCN6413 by zeonicweapon, on Flickr

ImageDSCN6400 by zeonicweapon, on Flickr

ImageDSCN6642 by zeonicweapon, on Flickr
Carl D. May
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Re: The Mystery of the Suwannee Cooter Range Gap

Post by Carl D. May »

The first thought that comes to mind with me is the possibility that early Floridians introduced the Suwanee cooters to the Alafia River as a food source.
It is known--or at least highly suspected-- that the South American red-footed tortoise, Chelonoidis carbonaria reached some of islands of the Caribbean by being brought there by Caribe Indians.

Also, I've heard from several folks over the years that the loggerhead musk turtles, Sternotherus minor that are so common in the Rainbow River, are not actually native to that system. From what I've heard (or read somewhere?) they were introduced in the 1940s.
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mtratcliffe
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Re: The Mystery of the Suwannee Cooter Range Gap

Post by mtratcliffe »

Carl D. May wrote:The first thought that comes to mind with me is the possibility that early Floridians introduced the Suwanee cooters to the Alafia River as a food source.
It is known--or at least highly suspected-- that the South American red-footed tortoise, Chelonoidis carbonaria reached some of islands of the Caribbean by being brought there by Caribe Indians.

Also, I've heard from several folks over the years that the loggerhead musk turtles, Sternotherus minor that are so common in the Rainbow River, are not actually native to that system. From what I've heard (or read somewhere?) they were introduced in the 1940s.
Interesting theory, Carl! I know that Suwannee Cooters are better suited for rivers with currents due to the streamlined shape of their carapace. This might be why they are very common in spring-fed rivers, which generally have a noticeable current. Peninsula and Florida Redbellied Cooters have highly-domed carapaces which are better for swimming in lakes and slow-moving bodies of water. The Alafia River has a stronger current than some of the other rivers around here, such as the Hillsborough. Perhaps the first Floridians introduced them in the Alafia due to low populations of FL's other endemic Cooter species there (as a result of the current). I know that Peninsula Cooters can be found in the Alafia, but I've never seen one. The Little Manatee River has a swift current much like the Alafia, and does not have a lot of Peninsula/Redbellied Cooters compared to a river like the Hillsborough. If the theory is correct, they must have skipped introducing them to the Little Manatee for one reason or another.

I'll have to float this idea off of George to see if he's considered it. And I wish I had seen a Loggerhead Musk Turtle when I paddled the Rainbow River back in March. If I go there again, I'll have to bring a snorkel mask and get into the water to explore the world below the surface.
Carl D. May
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Re: The Mystery of the Suwannee Cooter Range Gap

Post by Carl D. May »

Did some further checking...according to Biology and Conservation of Florida Turtles the population of loggerhead musk turtles in the Withlacoochee River system in Marion, Citrus and Sumter Counties was introduced in the 1950s. However this book doesn't mention the population of Sternotherus minor in the Rainbow River being introduced, although I'm sure I've seen this written somewhere.

Regarding Pseudemys concinna, this same source mentions that it is found in the Alafia River but only comments that it is strange that the animal is not found in the Hillsborough River.
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BillMcGighan
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Re: The Mystery of the Suwannee Cooter Range Gap

Post by BillMcGighan »

Nothing new to add here, just more questions, but this is really fascinating.
If you find something new on this from George, please share.



Peninsular reptile range maps always take me to ice age oscillations causing sea level oscillations that affected the geology (and subsequently plants and animals.)
With so many Florida endemic species, you can match significant parts of their ranges to land exposure and inundation with ice age phases.
Example: mole skink range (Plestiodon egregius) to the islands during inundation.


Image




The turtle mystery


The shoreline between then and now let some (sub)species who were best suited expand and adapt, but, your mystery gets more interesting when you look at this aquifer map that includes the Alafia River and the Hillsboro.


Image


This all just adds to the mystery :)

Either way it sounds like a worthwhile project to kayak those other rivers with a herpers eye to see if they are present or not!
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mtratcliffe
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Re: The Mystery of the Suwannee Cooter Range Gap

Post by mtratcliffe »

That map of the aquifer is interesting, as is the one showing the effects the rising/falling seas had on Florida thousands of years ago. Thanks to the aquifer, we are able to enjoy the beauty of Florida's many natural springs. Interestingly enough, the Hillsborough and Alafia Rivers both have a spring or two that feed into them, but I'm not aware of any springs south of Alafia. Nor are there any between the Hillsborough watershed and the Weeki Wachee. That fact matches the the coloration on the aquifer map you provided.
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mtratcliffe
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Re: The Mystery of the Suwannee Cooter Range Gap

Post by mtratcliffe »

To anyone still interested in this topic...

Ireceived some great news today! I ran into George Heinrich at a nearby nature preserve, and he shared something interesting with me. He's been actively paddling the rivers in the region, especially the Alafia, looking for Suwannee Cooters. Like me, he paddled the Braden River recently, but didn't turn up any there. However, he was absolutely beaming when he told me that he found several on the Pithlachascotee River (see map in my first post), which would be an official range extension for the turtle! I haven't yet made it up to that river, but I was planning on it, and I think I'm now obligated to check it out soon. It's only a few miles north of the Anclote River, which I paddled two weekends ago, which also leads me to wonder if there aren't Suwannees in the Anclote as well. This is a great find, and it makes sense that Suwannee Cooters would be found in the Pithlachascotee, as it is not terribly far from the Weeki Wachee River to the north.

He still suspects that Suwannee Cooters may be hiding out in a few other rivers in the region, though it will be difficult to find them. The Anclote and Pithlachascotee Rivers have very few access points along their freshwater portions, meaning they are rarely paddled. It's possible that no one ever thought to go looking for them there, or couldn't be bothered to put in the effort.

George mentioned that he has enough data on the Suwanee population in the Alafia River to start working on a paper, and I'll be sure to share it in the future when it become available.
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Noah M
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Re: The Mystery of the Suwannee Cooter Range Gap

Post by Noah M »

Thanks for the update. That is really neat.

Do you know how far upstream they've been found in the Withlacoochee? There looks to be a spot where that river gets very close to the Hillsborough, also by its headwaters. I don't know what the terrain is like between them - maybe an elevation map could help to understand turtle dispersion, but just from looking at what you have below, seems like the path of least resistance.
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BillMcGighan
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Re: The Mystery of the Suwannee Cooter Range Gap

Post by BillMcGighan »

Good stuff, Matt.
Keep them coming.
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mtratcliffe
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Re: The Mystery of the Suwannee Cooter Range Gap

Post by mtratcliffe »

captainjack0000 wrote:Thanks for the update. That is really neat.

Do you know how far upstream they've been found in the Withlacoochee? There looks to be a spot where that river gets very close to the Hillsborough, also by its headwaters. I don't know what the terrain is like between them - maybe an elevation map could help to understand turtle dispersion, but just from looking at what you have below, seems like the path of least resistance.
That's a great question, and one I wish I had an answer to. Per the Herp Atlas from the FLMNH, the furthest south P. concinna (which they treat Suwannee Cooters as a subspeies of) have been found on the Withlacoochee River is on the portion of the river where it divides Hernando and Sumter Counties. That's a far ways up the river, and I don't see why they wouldn't be found throughout the river and its watershed. Make that another paddle I need to conduct! It'll be hard to verify their existence near the headwaters of the Withlacoochee, as I don't believe there are many access points in the Green Swamp.

As far as the terrain, I believe there's a mixture of uplands, swamp, and pasture between where the Withlacoochee is navigable by canoe and the headwaters of the Hillsborough. They really are only a few miles apart from each other. If Suwannee Cooters have settled in that far up the Withlacoochee, I don't see what would stop them from populating the Hillsborough. Yet, no one has ever turned up one in the latter, unless they live in the far upper reaches that are largely inaccessible to humans.
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