Annual Wetland Drydown Produces Massive Concentration of Fish

Staff record video of nonnative catfish stranded in gator wallow

The annual drydown of freshwater wetlands typically strands small fish in isolated deepwater ponds and results in a feeding frenzy - wading birds reap the benefits of an easy meal during a critical time in their nesting season. Last week, staff at Audubon’s Corkscrew Swamp Sanctuary recorded video of a rare, unusually large concentration of fish (primarily the nonnative walking catfish, Clarias batrachus) trapped in a ditch along the edge of the Sanctuary. Instead of wading birds, the beneficiaries of this buffet were alligators, turtles, and hundreds of Black Vultures.

As the dry season comes to a close, alligators act as ecosystem engineers, wallowing in the muck to dig “alligator holes.” These deeper pools are often the last places of refuge for millions of fish and a veritable dry season buffet for fish-eating snakes, turtles, raccoons, otters, alligators, and other scavengers. Sometimes, a gator hole provides just enough water for these fish to survive until wet season resumes, but that was not the case with the gator hole captured in this video.

Nonnative walking catfish stranded in gator wallow

“I’ve certainly never seen that number of Walking Catfish in one spot,” said Shawn Clem, Ph.D., Director of Research for the Sanctuary. “We currently have no control methods for non-native fish, and seeing a sight like this where they appear to be the only fish surviving in this dry season depression really demonstrates the challenge of managing these highly-adapted invaders in our ecosystem,” she added.

Even though walking catfish can breathe air and move across nearly-dry stretches of land, these fish were stranded in one of the last drying holes in the area and perished.

“The stench was horrible,” said Senior Resource Manager Allyson Webb, who filmed the scene.

Smell typically comes with the territory of most jobs in the field of biology, but the odor at this unusual scene was putrid, as it combined the sheer mass of writhing fish exposed to the air, rotting flesh, muck being turned up by the wallowing gators, and excrement from both alligators and vultures.

Audubon’s Corkscrew Swamp Sanctuary, recognized in 2019 as a Wetland of Distinction by the Society of Wetland Scientists, has been an Audubon-protected nature site for more than 100 years. It protects more than 13,000 acres, including the world’s largest remaining, old-growth bald cypress forest. At least 100,000 visitors annually explore the Sanctuary’s 2.25 miles of boardwalk through ancient forest and marsh habitat. The Sanctuary remains closed to visitors until further notice. Only essential activities are continuing at Corkscrew, and staff is following CDC guidance and social distancing practices.

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