Taking a Bite Out of the Crawfish Population

About a month ago I decided to watch our local great blue heron more carefully. The heron can been seen daily stalking across the water, sometimes belly deep, step by calculated step. Every few minutes the heron splashes its head down into the water after some unseen (by me) prey beneath the surface. I wanted to see just what he was catching and eating out there in our little wetland.

Ever since I began to see red swamp crawfish in the waters of the wetland, more than eight years ago, I also noticed changes occurring both above and below the water of the ecosystem. There is virtually no submergent vegetation where there once was abundant plant life. Most emergent vegetation is also gone. See more here: crawfish, Crawfish Among Us part I, Crawfish Among Us part II.

Over the years I’ve tallied 13 species of frogs and toads in and around the wetlands. Across the seasons, I now see fewer species and far fewer numbers of individuals of the species observed. Bullfrog tadpoles, and adults, which were once ubiquitous are now difficult to find.

We’ve traditionally had only one species of fish (golden shiner) swimming our wetlands’ waters. At one time there were large numbers of them. I haven’t see a shiner in over six months, perhaps longer.

It’s with these thoughts in mind that I wanted to see what our heron was catching. The heron often comes up empty. But when it does snag something, it’s a crawfish. I’ve not witnessed the bird catch anything but small crawfish in over a month (since I’ve been making note of such things).

Stabbing at prey.
Great blue heron with red swamp crawfish.

I feel confident in saying that the heron is content catching and eating crawfish. It wouldn’t be here in our wetland if it wasn’t doing well in that endeavor. The fact is, great blue herons will eat whatever they can catch from aquatic insects, fish, eels, tadpoles and frogs, mice and rats, snakes and other reptiles, and even small birds. Whatever makes itself available to the heron is what the heron eats. As long as the bird can get the object past its bill and down its throat, it’s fair game.

I would go as far to say that fish and amphibians top the menu for any respectable great blue heron (have a look at this: gbh & bullfrog). I just haven’t seen our heron catch either of those items recently. And, as mentioned above, I haven’t seen a living golden shiner within recent memory. I’ve seen very few bullfrogs over the past spring, summer and fall seasons.

What’s going on with the wetlands? I like to blame all ills associated with our wetlands on crawfish, red swamp crawfish (Procambarus clarkii). They’re not native to our area and their destructive effect on ecosystems is well known. This quote from the Invasive Species Specialist Group’s (ISSG) web site says a lot.

“Its introduction may cause dramatic changes in native plant and animal communities…alter water quality and sediment characteristics…and reduce populations of invertebrates, mollusks, and amphibians through predation and competition.”

There may, however, be other factors at work, but I think the crawfish have played a major roll it what’s happening to the aquatic wildlife in our wetland.

Whether our heron knows it or not, it’s hard at work helping to rid the wetlands of what may be the main agent of change in our little wetland. Eat ’em up, great blue!

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