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Some interesting trends are appearing in the local Nerodia populations of a small area in central Oklahoma.

I live in a residential area with a nearby 160-acre urban wilderness area. It features a small lake. I've been monitoring snake populations in this area for the last five years. Some readers may remember what I posted last fall regarding the diminishing populations of the two prominent Nerodia species: rhombifer (Diamondback) and erythrogaster (Plainbelly/Blotched). Both were common several years ago, but their numbers have diminished to the point where both were virtually nonexistant for most of last year. The mystery is that populations of other snakes in the area have shown no such decline.

I may have found an answer. Recent visits to a retention pond near our subdivision, and immediately adjacent to the wilderness area, shows that the Nerodias there are thriving. I caught a massive female rhombifer yesterday that was a new personal record at 56 inches (7 short of the published record, and she had a stub tail; probably gravid, as she was as big around as my forearm). Meanwhile, the wilderness lake has shown an apparent increase in populations of large fish - most likely carp but possibly catfish. They're several feet long, and make a huge commotion in the water when they're disturbed from their apparent spawning nests a few feet offshore. Only two Nerodias have been seen near the lake this year - a far cry from the numbers seen only a few years ago.

So while it can't be confirmed yet, it appears that either carp or catfish have proliferated in the wilderness lake, and have upset the local balance of nature by preying on the local water snakes. I note also that the only other aquatic snake in the area, Graham's Crayfish snake, now seems to have disappeared from the area as well.
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MichaelB

Thats a nice study site, and interesting findings. As with most studies it will be important to control for variables though. Are the big fish eating snakes, or eating the small fish the snakes feed on, for example. Or are they muddy-ing the water that makes it harder for the small fish to be caught, etc.

Is it a well "managed" lake
Some Natural Resource departments "manage" lakes and other wild areas to the specific benefit of game species, often to the detriment of other species. I've seen marshes with an abundant herpetofauna almost wiped out by the treatment of an oxygen reducing chemical that kills all aquatic creatures. They do this in order to wipe the slate clean before introducing "game" fish to please the fishermen.

Its sounds like an interesting area to learn from!

Joe

>>Are the big fish eating snakes, or eating the small fish the snakes feed on, for example.

That's waht I was thinking...

>> Or are they muddy-ing the water that makes it harder for the small fish to be caught, etc.

My very limited experience with my captive nerodia leads me to beleive that they hunt mostly by feel when under water, or maybe mine are just blind?

The lake really isn't managed at all. The area is designated as a wilderness area, which means it's off limits to camping, swimming, boating, hunting, etc; only catch-and-release fishing is allowed. With hiking/jogging trails and whatnot, it's just a nice little getaway place for nature lovers. The OK Dept. of Wildlife Conservation may stock the lake for recreational fishing purposes, but I even doubt that. I'll look into it, though. In fact, they might even help with further research into the matter.

I'll let you know if there are any new developments.
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MichaelB